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Estuarine sediment transport and Holocene depositional history, Upper Chesapeake Bay, Maryland

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Estuarine sediment transport and Holocene depositional history, Upper Chesapeake Bay, Maryland

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Content ESTUARINE SEDIMENT TRANSPORT AND HOLOCENE DEPOSITIONAL HISTORY, UPPER CHESAPEAKE BAY, MARYLAND by JOSEPH FRANCIS DONOGHUE A D isse r ta tio n Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P artial F u llf illm e n t o f the Requirements for the Degree DOCTOR OF PHILOSOPHY (G eological Sciences) August 1981 UMI Number: DP28554 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UM T D i s s e r t a t i o n P u b l is h i n g UMI DP28554 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 UNIVERSITY O F SO U T H E R N CALIFORNIA THE GRADUATE SCHOOL. UNIVERSITY PARK LOS A N G ELES. C A LIFO R N IA 9 0 0 0 7 This dissertation, written by Joseph Francis Donoghue under the direction of h.i-.§... Dissertation Com mittee, and approved by all its members, has been presented to and accepted by The Graduate School, in partial fulfillment of requirements of the degree of D O C T O R OF P H IL O S O P H Y Dean D ate y - ± Q ~ M . . " P , G \ €L 'S '! DISSERTATION COMMITTEE Chairman DEDICATION This dissertation is dedicated to my parents. ACKNOWLEDGEMENTS j Thanks are due to the many people who made t h i s work not only p o s sib le but thoroughly enjoyable. Professor D. S. j G orsline, of the Department o f Geological Sciences, U niversity of Southern C a lifo rn ia , guided the research ! from the s t a r t and defined many of the tec h n ica l problems j that were taken up. As an endless source o f id ea s, | j in s ig h t and energy, Dr. Gorsline has i n s t i l l e d an appreci- j j j ation and enthusiasm not only for g e o lo g ic a l research but j ! I also for the s c i e n t i f i c way of l i f e in general. I hope j that t h i s t h e s i s r e f l e c t s some o f the p r o fessio n a l q u a li- | t i e s that he imparts to a l l of h is stu dents. ! ! j J Prof. D. E. Hammond f i r s t introduced me to estuarine research, using the t o t a l immersion technique, at San Francisco Bay. He too has been a continual source of encouragement, and has taught me most o f what I know about geoch em istry. Dr. J. W . Pierce of the Division o f Sed im entology, Smithsonian I n s t i t u t i o n , generously contributed his exper t i s e in Chesapeake Bay m atters, h is time, equipment, tec h - n ic a l help and f i e l d a ss is ta n c e for the Rhode River work plus associated laboratory an aly ses. Through his e f f o r t s a Smithsonian Fellowship was made a v a ila b le and museum funding was obtained, enabling the f u l l extent of the proposed research to be r e a liz e d . Hopefully the r e s u lt s herein include a few things he hasnTt already discovered. M y education as a g e o lo g is t and as a per son has prog ressed due to the in flu en ce of a number of g ift e d tea ch ers. The l a t e Prof. R. 0. Stone, who f i r s t made me think of m yself as a g e o l o g i s t , has had a l a s t in g e f f e c t on me. Profs. R. W . Ridky, R. H. Merriam, B. W . Pipkin, G. J. Bakus, T. L. Ku, R. H. Osborne and the la t e M . Norton have a l l considerably expanded my s c i e n t i f i c h o r i zons . Dr. 0. P. Bricker , of the U. S. Geological Survey, cooperated in the Susquehanna and Chesapeake Bay sample c o l l e c t i o n , and arranged for the use o f a 7-kHz acoustic p r o f ile r on the Rhode River. The b e n e fit o f h is e x p e r i ence on the Chesapeake has been of great value in carrying out t h i s work. J eff Halka, Randy Kerhin and Jim H il l , of the Maryland Department o f Natural Resources, contributed th eir ex p e rtise and a ss is ta n c e in the 7-kHz work and with the upper bay and Susquehanna River sample c o l l e c t i o n . i v Dr. A. P. Eaton, of Johns Hopkins U n iv e r sity ’s Chesapeake Bay I n s t i t u t e , enabled me to c o l l e c t some of the Chesa peake samples using the R/V D. W. P ritch ard . Most of the f i e l d work on the bay was carried out using the f a c i l i t i e s of the Smithsonian’ s Chesapeake Bay Center for Environmental Stu dies. I am g r a te fu l to Dr. J. K. S u lliv a n , D irector, for providing ship time and f i e l d a s s is t a n c e . Dr. D. L. C orrell, A ssociate D ir e c to r , was an e x c e lle n t source o f id ea s, u sefu l data and tec h n ica l help. Periodic abuse of h is Boston Whaler and other equipment ra rely dampened his good nature. D. Higman, also of the Chesapeake Bay Center, provided valuable land-use and m eteorologic data. R. R. Timms and H. H. Brown always teamed together to make the Rhode River and Chesapeake c r u is e s on the R/V Blue Fox anything but d u l l. Neither winter ice f l o e s nor l a t e summer storms could keep them o f f the water. A ssistance in the f i e l d was c h e e r fu lly supplied by Smithsonian employees Frank Dulong, Ray Podany, Randy Burke and Joe Souther, and by my brother Peter Donoghue. Rob Hull, Marc Stanley and Myles W hitfield each spent a summer working in the Sedimentology Laboratory, with much o f th e ir time devoted to helping me in the f i e l d and in v the lab. They were compensated only in beer and luxury vacation c r u is e s on the Chesapeake. Their a ss is ta n c e is much appreciated. Richard Robinson, of the Smithsonian, taught me more about x-ray d i f f r a c t io n than I ever learned in books. Technical advice and a ss is ta n c e were provided by B ill Boykins, Harrison Sheng, Leo Bernard and Rick Herrera. Generous help and su ggestion s in geochemical matters came from Chris F u lle r, Blayne Hartman and Larry M iller. I g r a t e f u lly acknowledge the contribution of gamma- counting f a c i l i t i e s for a l l of the Chesapeake and Susque hanna samples by Dr. C. Olsen of Oak Ridge National Labo ratory. Dr. H. J. Simpson, of Lamont-Doherty Observatory, Columbia U n iversity, also provided advice and arranged for counting time. Radiocarbon dates were supplied by Dr. R. Stuckenrath of the Radiation Biology Laboratory, and by E. C. Spiker of the U. S. G eological Survey. These dates were extremely u sefu l and are appreciated. C. S. Moy and Dr. G. Wong, of the Oceanographic I n s t i t u t e at Old Dominion U n iversity, contributed alpha-counter time for some of the lead-210 samples. vi Dr. F. O ld fie ld , of the U niversity of Liverpool, performed a l l of the magnetic measurements on my core samples and supplied in te r p r e ta tio n s of the r e s u l t s . I thank him for introducing me to a p o t e n t ia lly valuable to o l for the in te r p r e ta tio n of recent geolog ic even ts. Dr. D. J. Stanley, of the Smithsonian, supplied informa tion from his f i l e s on Rhode River fauna and acou stic p r o f i l e s , for which I am g r a te f u l. Advice on computer and s t a t i s t i c a l matters was supplied by Dr. S. Leroy, whose understanding of sediment tex tu ra l nuances extends far beyond mine. Additional help with computer work was provided by Mark Olsen. Dr. T. D. Dickey and Ken McCormick. During the course of t h i s work I have b e n e fitte d from my acquaintance with Andy and Robin Harper, good friend s both. Drs. Tom Nardin, Scott Thornton, Eric Frost and Roy Dokka , as well as Tom Wilson and Tom Hartnett lik ew ise made the experience in te r e s tin g and enjoyable. Eleanor Crow, my a lt e r -e g o and e g o -a lt e r e r , i s respon s i b le for a l l of the fig u r es that look p r o fe s s io n a l. I am resp on sib le for the r e s t of them. To her also goes c r e d it for the fa ct that I remain p r a c t ic a lly sane. I hope that v ii I w i l l be able to recip rocate in the future by helping to make some of her in c r e d ib le p rojects c r e d ib le . The research encompassed in t h i s d i s s e r t a t i o n was made p o ssib le by a Smithsonian Fellowship, with add ition al support from a G eological Society of America research grant, a USC Department o f Geological Sciences ARCO research grant and a USC Sea Grant Internship. v i i i TABLE OF CONTENTS DEDICATION...............................................................................................................i i ACKNOWLEDGEMENTS ....................................................................................... i i i ABSTRACT....................................................................................................................vi Chapter Page I. INTRODUCTION ....................................................................................... 1 Thesis ................................................................................................. 1 Background ....................................................................................... 2 Geology and Physical Setting ............................... 2 E stuaries in the Geologic Record . . . . 2 Chesapeake Bay and the Paleo-Susquehanna R i v e r ..........................................................6 Geology o f the Western Shore, North- Central Chesapeake B a y ................13 Hydrology and Flood History o f the Chesapeake Bay/Susquehanna River B a s i n ...................................................................21 Freshwater Discharge to the Chesapeake . 21 S a l i n i t y ..................................................................27 Flood H i s t o r y ...................................................32 Holocene Sea-Level Rise Chronology . . . . 39 Long-Term Sea Level Rise R a t e s .......... 39 Short-Term Sea-Level Rise Rates . . . . 44 Summary of Sea-Level History .......................... 45 Sedimentologic E ffec ts o f Land Use in the Northern Chesapeake Bay Area . . . . 50 I I . METHODOLOGY................................................................................. 60 Field M e t h o d s ..................................................................60 Bottom Sediment C ollection .................................... 60 7-kHz P ro filin g and Sediment Probe . . . . 68 Fluorescent Sand Tracer .............................................. 69 A nalytical Methods .................................................................. 70 Sedimentology ........................................................................ 70 Percent Water and Percent Combustible . 70 San d-S ilt-C lay ............................................................. 70 Coulter Counter ........................................................ 71 ix X-Radiography ............................................................. 73 A nalysis o f 7-kHz P r o f ile s ............................... 74 D ig i t iz a t io n of H istoric Bathymetric C h a r t s ......................................................................74 UV Photography of Fluorescent Sand C ores.75 Dessicated Core Photography .................. 75 Magnetic Stratigraphy ......................................... 76 M i n e r a l o g y ................................................................................77 Clay Minerals— X-Ray D iffra c tio n . . . . 77 Heavy Mineral I d e n t if ic a t io n .................. 79 Scanning Electron Microscopy and Energy D ispersive X R F ..................................................80 Isotope Geochemistry ................................................... 80 L e a d - 2 1 0 ................................................................................ 80 Cs-137 and Reactor Nuclides............................... 81 C a r b o n - 1 4 ........................................................................... 82 I I I . EXPERIMENTAL RESULTS .................................................................. 83 Sedimentology ............................................................................ 83 Textural Analyses ............................................................. 83 San d-S ilt-C lay ............................................................. 83 Coulter Counter Analyses: Textural P r o f i l e s .................................................................84 Coulter Counter Analyses: Scatter P l o t s . 104 Water and Organic C o n t e n t ................................112 Core D essicatio n : Sand L a m i n a e .................132 Magnetic Stratigraphy .............................................. 139 X-Radiography .................................................................. 146 7-Kiloherz P ro filin g and Sediment Probe . 153 Paleobathymetry ................................................... 153 Volume o f F i l l .....................................................155 Compaction E ffec ts .............................................. 162 Mass o f sediment f i l l ................................ 166 Comparison of H istoric Bathymetric Charts, 1845-1972 ............................................................. 167 Shore E r o s i o n ................................................. 167 Volume Changes and Sediment Accumulation, 1845-1972 . . . . 180 F luorescent Sand Tracer ......................................... 181 M i n e r a l o g y ........................................................................... 188 Clay Minerals--X-Ray D iffra c tio n . . . . 188 Rhode River Estuary Bottom Samples . . 189 Rhode River Estuary Suspended Sediments.196 Rhode River Watershed S o ils and Suspended Sediments .......................... 196 Rhode River Estuarine Shoreline M i n e r a lo g y ............................................ 197 Clay Mineralogy o f Chesapeake Bay S a m p l e s ................................................. 197 Susquehanna River Clays ............................... 199 x Sand Fraction Mineralogy .......................... 204 Heavy M i n e r a l s ...............................................................204 Scanning Electron Microscopy ..................... 206 Energy D ispersive X-Ray Fluorescence . 218 Isotope Geochemistry ........................................................ 219 C a r b o n -1 4 ...................................................................................219 Sedimentation Rates ......................................... 219 Rates of Sea-Level R i s e .....................................223 L e a d - 2 1 0 ...................................................................................229 Sedimentation Rates ......................................... 229 Storm E v e n t s ....................................................................236 Cesium-137 and Reactor-Generated Nuclides 241 Tracers for Susquehanna River Sediments.243 Radionuclide Tracers ......................................... 245 Reactor Releases ................................................... 247 Reactor Nuclides in Sediments of the Lower Susquehanna River and Upper B a y .........................................................................253 Radiocesium in Rhode River Estuary S e d i m e n t s ......................................................... 254 IV. DISCUSSION AND CONCLUSIONS .............................................. 259 Sources o f Sediment to the Rhode River E s t u a r y ..............................................................................259 Shore E r o s i o n .........................................................................260 Watershed Erosion ........................................................ 263 Biogenic Sources ........................................................ 266 Sediment Input from the Chesapeake Bay . 267 Storm D e p o s i t i o n ......................................................... 272 Rates and Volumes o f Sediment Input to the Rhode River E s t u a r y .........................................275 Holocene Sedimentation ......................................... 275 River-to-Estuary Transition ..................... 275 Total Holocene F i l l : 7-kHz Records . . 276 Pre-Settlem ent Radiocarbon Dates . . . 277 H isto ric Sedimentation ......................................... 278 Post-Settlem ent Radiocarbon Dates . . 278 Sedimentation Rates from H istoric C h a r t s ....................................................................278 Lead-210 and Cesium-137 Rates o f F i l l 278 Recent Sediment Budget ......................................... 283 Sedimentation in the Upper Chesapeake Bay and Susquehanna River .............................................. 287 Nuclide Inventory ........................................................ 287 Trap E ffic ie n c y o f R e s e r v o i r s ................................293 Sediment Storage in the Susquehanna and Upper Chesapeake B a y .....................................296 xi V. FATE OF THE ESTUARY.......................................................................... 301 REFERENCES CITED ....................................................................................... 306 Appendix Page A. X-RAY DIFFRACTION D A T A ................................................................317 B. RADIONUCLIDE ACTIVITY IN SUSQUEHANNA RIVER AND CHESAPEAKE BAY SEDIMENT ......................................... 324 LIST OF TABLES Table Page 1. ANNUAL DISCHARGE LEVELS FOR SUSQUEHANNA RIVER AT CONOWINGO, MARYLAND.........................................................................23 2. ANNUAL RAINFALL AND FLOOD HISTORY FOR MARYLAND, 1842-1978 ............................................................................................ 36 3. U. S. POPULATION GROW TH DURING THE COLONIAL ERA . 51 4. SEDIMENTATION IN COLONIAL MARYLAND PORTS FROM COMPARISON OF BATHYMETRIC SURVEYS ............................... 57 5. CORE DESSICATION D A T A ......................................................................133 6. AREA LOSSES FOR ISLANDS, 1845-1972 ................................ 168 7. HISTORIC CHART DATA, RHODE RIVER ESTUARY . . . . 178 8. ESTUARINE SHORELINE LOSSES, 1845-1972 179 9. RELATIVE HEAVY MINERAL ABUNDANCE IN RHODE RIVER CORES....................................................................................................... 207 10. RHODE RIVER ESTUARY RADIOCARBON DATA ............................ 221 11. RELEASE HISTORY FOR SUSQUEHANNA RIVER NUCLEAR POW ER P L A N T S ...................................................................................248 xi i 12. SEDIMENT YIELD RATES AND CURRENT LAND USE PERCENTAGES IN THE RHODE RIVER WATERSHED . . 264 13. SUM M ARY OF SEDIMENTATION RATES FOR THE RHODE RIVER ESTUARY..................................................................................................283 14. RECENT SEDIMENT BUDGET FOR THE RHODE RIVER ESTUARY.................................................................................................. 285 15. CESIUM-134 ACTIVITY RETAINED IN SUSQUEHANNA RIVER RESERVOIRS AND UPPER CHESAPEAKE BAY ..................... 290 16. CESIUM-134 RELEASES FOR SUSQUEHANNA RIVER NUCLEAR PLANTS, DECAY-CORRECTED TO 1/1/80 .......................... 292 17. TRAPPING EFFICIENCY OF LOW ER SUSQUEHANNA RIVER SEDIMENT BASINS ........................................................................ 295 18. SEDIMENT TRAPPED AND LOST BY LOW ER SUSQUEHANNA RIVER D A M S ..................................................................................298 19. RATE OF INFILLING OF SUSQUEHANNA RIVER RESERVOIRS, BASED O N SEDIMENT CS-134 DATA.......................................... 300 LIST OF FIGURES Figure Page 1. Chesapeake Bay region, showing major t r ib u t a r ie s and geographic f e a t u r e s .................................................................7 2. Depth to base of Chesapeake Bay paleo-channel , based on bridge borings. Data from Hack ( 1957)...................................................................................................... 10 3. Geologic c r o s s - s e c t io n at Chesapeake Bay Bridge. Data from Ryan ( 1 95 3)................................................................ 14 4. Geology of the Rhode River Estuary watershed, Maryland.....................................................................................................17 5. Susquehanna River discharge at Conowingo, Maryland, 1929-1966, monthly averages. Data from Boicourt ( 1969).................................................................. 25 x i i i 6. Chesapeake Bay surface s a l i n i t y , spring average. Data from Pritchard ( 1 9 6 8 )............................................... 28 | 7. Chesapeake Bay surface s a l i n i t y , autumn average. Data from Pritchard ( 1968)............................................... 30 l 8. Surface s a l i n i t i e s for Rhode River mouth and nearby Chesapeake Bay. Data from Han (1975). . 33 9. S e a -lev e l curves for the ea st coast o f the United S t a t e s ..........................................................................................................42 10. S e a -lev e l curves for the Chesapeake Bay region, 8,000 years BP to p r e s e n t ......................................................... 47 11. Population maps o f the United S ta te s , 1625-1790. Data from F r iis ( 1940)............................................................. 52 12. Rhode River Estuary sample l o c a t i o n s ...................................... 62 13- Chesapeake Bay clay mineralogy sample l o c a t i o n s . . 64 14. Susquehanna River and upper Chesapeake Bay sample j l o c a t i o n s ...................................................................................................66 I i 15. S a n d - s il t - c l a y percentages for Rhode River core sam ples....................................................................................................... 85 16. Textural parameters for Core 1......................................................88 17. Textural parameters for Core 3-B................................................90 18. Textural parameters for Core 13...................................................92 19. Textural parameters for Core 16................................................... 94 20. Textural parameters for Core 19...................................................96 21. Textural parameters for Core 2 1...................................................98 22. Textural parameters for Core 30.................................................100 2 3 . Textural parameters for Core 3 8 .................................................102 24. Mean diameter versus standard d ev ia tio n for Cores 1, 21 and 3 8..................................................................................... 106 25. Mean diameter versus skewness for Cores 1, 21 and 38 108 x iv 26. Mean diameter versus d e lta for Cores 1, 21 and 38 ...................................................................................... 110 27. Percentages o f water, i g n it io n l o s s , sand, s i l t and clay for Core 1.............................................. 113 28. Percentages o f water, ig n it io n l o s s , sand, s i l t and cla y for Core 3-B......................................... 115 29. Percentages o f water, i g n it io n l o s s , sand, s i l t and clay for Core 13............................................117 30. Percentages o f water, i g n it io n l o s s , sand, s i l t and clay for Core 16......................................... 119 31. Percentages o f water, ig n i t io n l o s s , sand, s i l t and clay for Core 19......................................... 121 32. Percentages o f water, i g n i t io n l o s s , sand, s i l t and clay for Core 21......................................... 123 33. Percentages o f water, ig n i t io n l o s s , sand, s i l t and clay for Core 3 0......................................... 125 34. Percentages o f water, i g n it io n l o s s , sand, s i l t and clay for Core 3 8 .....................i ............................................127 35. Rhode River Estuary bottom fauna.......................130 36. Core d e s s ic a t io n photographs: Rhode River Cores 13, 16 and 19..............................................................135 37. Magnetic s u s c e p t i b i l i t y p r o f i l e s for Rhode River Estuary c o r e s ..............................................................142 38. Magnetic parameters for Rhode River watershed sam ples............................................................................. 144 39. X-Radiographs o f Rhode River Estuary c o r e s. . . 148 40. Acoustic sub-bottom p r o f ilin g t r a n s e c t s , Rhode River E stuary..............................................................157 41. 7 -k ilo h e rz records for c r o s s - s e c t i o n s in Figure 40. Depths in f e e t ...............................................159 42. P re-estuarine Rhode River v a lle y and Chesapeake Bay, c. 7,000 B.P.: reco n stru ctio n from 7-kHz a c o u stic p r o f i l e s ....................................................163 43* 1845 bathymetric ch art, Rhode River Estuary. . . 169 x v 44. 1903 bathymetric chart, Rhode River Estuary. . . 171 45. 1933 bathymetric chart, Rhode River Estuary. . . 173 46. 1972 bathymetric chart, Rhode River Estuary. . . 175 47» Fluorescent sand tracer core lo c a t io n s and r e s u l t s .............................................................................................. 184 48. UV photograph o f flu o r e s c e n t sand co res, taken 10/3/79 and 7 /1 1 /7 9 , follow in g Hurricane David ( 9 / 5 / 7 9 ) ............................................................................................ 186 49. V ertica l v a r ia tio n o f m ontm orillonite and i l l i t e in Rhode River Estuary c o r e s ......................................... 191 50. Areal d is tr ib u t io n o f mean m ontm orillonite and i l l i t e values for clay fr a c tio n o f a l l cores and grabs: Rhode River, Chesapeake Bay and Susquehanna R iver.....................................................................1 94 51. Clay mineralogy o f Rhode River, Chesapeake Bay and Susquehanna River: i l l i t e vs. m o n tm o r illo n ite .................................................................................200 52. Clay mineralogy o f Rhode River, Chesapeake Bay and Susquehanna River: k a o l i n i t e + c h lo r it e vs. m o n tm o r illo n ite .................................................................................202 53* Scanning e lectro n micrographs o f sa n d -size grains from Rhode River Estuary c o r e s .......................................... 211 54. Rhode River Estuary sedimentation r a t e s , based on sediment core radiocarbon d a t a .......................................... 227 55. Lead-210 a c t i v i t y p r o f i l e s for Rhode River Estuary c o r e s . 231 56. Lead-210 sedimentation r a te s and sample l o c a t i o n s ................................................................................................237 57» Radiocesium r e le a s e h is to r y for Three Mile Island and Peach Bottom nuclear power p la n ts. . . . 250 58. Cesium-137 a c t i v i t y p r o f i l e for Rhode River Core 3 8 ........................................................................................................... 257 59. Rhode River sedimentation r a te s versus time. . . 281 xvi ABSTRACT ! The Holocene h is to r y of a portion o f the upper Chesapeake j Bay— the Rhode River E stu a ry --is revealed by a number of sedim entologic and geochemical techn iqu es. S ig n ific a n t changes have occurred in both sediment input r a te s and sediment sources during the time sin ce the r i v e r - t o - e s - tuary t r a n s i t i o n . Acoustic p r o f ilin g of the Eocene basement enables c a lc u la t io n o f the t o t a l volume of sediment deposited in the estuary sin ce f i l l i n g began about 6,800 years before present. Radiocarbon dating of peat and other organic m a teria ls in sediment cores provides a record o f sedimen ta tio n r a te s and sea l e v e l r is e over the past 2,000 years. D ig it iz a t io n o f a s e r i e s of four h i s t o r i c bathymetric charts g iv e s information on r a te s o f f i l l i n g and sh orelin e erosion sin ce 1845. Lead-210 a c t i v i t y p r o f i l e s in cores provide sedimentation r a te s over the past hundred years. In a d d itio n , the p r o f i l e of f a l lo u t cesium-137 in a core from the estuary mouth g iv es the rate of sedimentation sin ce the f a l lo u t maximum in 1963. In a l l o f these methods for quantifying sediment input, an a c c e le r a tin g pace o f f i l l i n g can be seen, from a mid-Holocene rate o f - j about 0.5 mm/yr to the present value of 5-10 mm/yr. i Sources o f sediment also appear to have varied over h i s t o r i c time. Clay mineralogy of core samples in d ic a t e s th at erosion o f the Tertiary sh o re lin e m a teria ls over the past few c e n tu r ie s has c o n s i s t e n t l y been the predominant source o f sediment to the estu a ry . This conclusion i s confirmed by the rapid r e tr e a t of the s h o r e lin e , as deduced from a n a ly sis o f the h i s t o r i c c h a r ts - - a s much as 0.5 meters per year in p la c e s . Further confirm ation is obtained from p r o f i l e s of magnetic s u s c e p t i b i l i t y for the same co res. For some o f the more landward co re s, however, the magnetic parameters in d ic a te that erosion o f watershed s o i l s has in recent years become a more important sediment source than sh o relin e ero sio n . The infrequent major storms o f the Chesapeake region appear to be another important sediment source. D iscer n ib le storm d e p o s its can be seen in the lead-210 records. A d d itio n a lly , a flu o r e sc e n t sand tracer study revealed that a s in g le storm in 1979 contributed 2 cm of new s e d i ment to the estuary within 30 days. xv ii i Tidal c Ur rent trans port" o f Chesapeake Bay “ sediments in through the mouth o f the estuary i s another source of sediment, although not a major one. Lower Susquehanna River nuclear plants r e le a s e reactor n u clid e s in s u f f i c ie n t quantity to act as tra c er s for Chesapeake sediments when adsorbed to clay p a r t i c l e s . The e a s i l y d e te c ta b le presence o f these n u clid e s in an e n tir e s u it e o f upper Chesapeake Bay samples, but not in Rhode River sediments, im plies that the Chesapeake is not a s i g n i f i c a n t source of sediments to the Rhode River Estuary. As tr a c e r s for Susquehanna River sediment entering the upper Chesapeake, the reactor r e le a s e s appear to be an e x c e ll e n t device for quantifying sediment transport r a te s and sources for the f l u v i a l - e s t u a r i n e system. Comparing the integrated a c t i v i t y in the various sediment trapping basins with the known r a te s and times o f reactor r e le a s e s enables the determination of trap e f f i c i e n c i e s , expected l i f e t i m e o f dams, and the percentage con trib u tio n of Susquehanna sediments to the upper Chesapeake Bay. A s i g n i f i c a n t finding r e s u ltin g from the nu clide record is th a t , under normal hydrologic c o n d itio n s , th r e e -fo u r th s of the Susquehanna River sediment entering the Chesapeake remains trapped in the uppermost part o f the bay. x ix Chapter I INTRODUCTION 1 . 1 THESIS Knowledge o f the r a te s and means by which e s t u a r ie s f i l l i s an e s s e n t i a l f i r s t step in understanding how to pre serve and w isely use them. Some s i g n i f i c a n t a t t r i b u t e s o f e s t u a r ie s make wise management a n e c e s s it y : 1) estu a rin e waters are commercially and e s t h e t i c a l l y in v a lu a b le , pro viding abundant f i s h e r i e s and recreatio n o p p o rtu n ities and serving as n u rseries for marine l i f e ; 2) the net area of e s t u a r ie s and wetlands dim inishes y early, due to the pres sures o f development along sh o r e lin e s ; 3) even without the a c c e le r a tio n induced by man, e s t u a r ie s are s h o r t-liv e d g e o lo g ic fea tu re s; 4) estu arin e sediment acts as a trap for many p o t e n t i a l l y harmful substances ( p e s t i c i d e s , her b ic id e s , reactor and f a l lo u t n u c lid e s , heavy m eta ls, PCB’s and other to xic chemicals) from the c u ltiv a te d and indus t r i a l i z e d estuarine watersheds. The purpose o f the work described herein was to exam in e — over both the long and the short term --the rate at 1 "which e s t u a r ie s f i l l , to in v e s t ig a t e the means by which ~ ] i ! sediments are carried into e s t u a r i e s , and to determine the j I source o f i n f i l l i n g sediments. Q uan titative answers to i these questions have always been d i f f i c u l t to ob tain , but i j j use o f a combination o f sedim entologic and geochemical i t o o ls in t h i s work has resu lted in answers that are both r e l i a b l e and c o n s i s t e n t . 1.1.1 Geology and Physical S e ttin g 1.1. 1.1 E stu aries in the Geologic Record It has been said that n either the past nor the future of e s t u a r ie s holds much promise ( R u s s e ll, 1967). Owing th e ir e x is te n c e to tra n sg ressin g p o s t g la c ia l se a s, e s t u a r ie s p e r s i s t only as long as the rate o f r is e o f the sea exceeds the rate o f f i l l i n g by sedim ents. As the sea l e v e l r i s e wanes, e s t u a r ie s ra pidly f i l l and become part o f the c o a sta l p la in . With renewed growth o f ic e caps and a f a l l of sea l e v e l , former estu arin e d e p o s its are subjected to e ro sio n , making th e ir g e o lo g ic record d i f f i c u l t to i n t e r pret . Even during the m o re-or-less steady r i s e over the l a s t 15,000 years, the incursion has been interrupted repeatedly by minor s t i l l s t a n d s and r e v e r s a ls in trend ( Shepard, 1961). 2 Consequently there are few examples o f e s t u a r ie s in the g eo lo g ic record and most o f these are ambiguous. Because modern e s t u a r ie s vary widely in sediment te x tu r e , primary s t r u c t u r e s , degree o f oxidaton, mineralogy and b i o t a - - i n sh ort, a l l o f the c h a r a c t e r i s t i c s used for paleoenviron- mental i n t e r p r e t a tio n - -t h e y can seldom be c o n c lu siv e ly i d e n t i f i e d in the record of the past. I d e n t if i c a t io n o f a c erta in str a tig r a p h ic feature as an estu a rin e d e p o sit i s u su ally done on the b a sis of a dark clay content and a lim ited fauna. In the Coal Measures of Pennsylvania, the Berea Sandstone o f Ohio and the Middle Jurassic and Great Estuarine S eries o f Scotland and England, various workers have found analogs o f modern e stu a r in e environments. A lter n a tiv e in t e r p r e t a tio n s have been made, however, for a l l of these fea tu res (K lein, 1967). In the record of the more recent g e o lo g ic past, e s tu a rine d e p o s its have not yet undergone the e r o siv e e f f e c t s o f m u ltip le t r a n s g r e s s i v e / r e g r e s s i v e c y c l e s , and subse quently are more e a s i l y i d e n t i f i e d . Estuarine d e p o sits have been reported by Swift ( 1980) on the co n tin en ta l s h e l f o f f New Jersey, on the b a sis o f morphology. In a d d itio n , Cronin and others (1981) have reported an e stu a rine fauna in 187,000-year-old V irginia c o a sta l sediments 3 that were la id down during a time when the sea stood two J I meters higher than at p resen t. j j j ! I Another reason for the s c a r c ity of e s t u a r i e s during most o f g e o lo g ic time is the fa c t that th e ir l i f e span is b r i e f r e l a t i v e to other fea tu re s o f the e a r t h ’ s su rface. A ty p ic a l e s tu a r y 's l i f e t i m e is measured in a few thou sands o f years. It begins when a r is in g sea flo o d s the lower reaches o f a r iv e r , causing shoaling at the river mouth, formation o f an e stu a r in e d e lta near the head, and development o f an estu a r in e c ir c u la t io n p attern . Thence forth the e s tu a r y 's e x is t e n c e depends upon the r e l a t i v e sea l e v e l . A slow steady rate o f sea l e v e l r is e prolongs the l i f e o f the estu ary . A f a l l i n g sea hastens the d e str u c tio n o f the estu ary . But the major cause o f the e s tu a r y 's b r i e f l i f e span i s in t e r n a l. Once the dimin ished c ir c u la t i o n pattern i s e sta b lish e d in the r i v e r ' s drowned lower reaches, the estu a r in e basin becomes a trap for sediment from a l l sources (Emery, 1967). Fresh- or brackish-water marshes develop at the head, w hile marine marshes and bars grow near the mouth and around the margins. Meanwhile, the main body of the estuary f i l l s with the products o f stream ero sio n , sh o r e lin e r e t r e a t and biogenic d e p o s itio n . 4 During th e ir short but e ven tfu l l i v e s e s t u a r ie s act as | an e f f e c t i v e trap for sediments tr a v e lin g from the c o n t i - j nental platforms to the ocean b a sin s. Emery (1967) charac- [ te r iz e d e s t u a r ie s as a sedim entological vacuum, a t tr a c tin g c l a s t i c sediment from a l l d i r e c t io n s , including the adja cent s h e l f . The sediment trapping e f f e c t i s ephemeral, however. After f i l l i n g is complete, a l l u v i a l d e p o sits i blanket the former estu ary, and c o n tin e n ta l sediments are once again transported unhindered to the sh elv es and basins o f the ocean. V ir tu a lly a l l o f our knowledge about e s t u a r ie s comes i from examination of examples from the past few thousand years. At the most recent low stand, about 15,000 years ago, the sh o re lin e was near the edge o f the c o n tin e n ta l sh elv e s (D illo n and O ld a le , 1977)* E stuaries were probably rare at that point sin ce the s h e l f v a lle y s seem to have been narrow, deep and few in number (R u ss e ll, 1967) . The rapid rate o f sea l e v e l r is e between 15,000 and 6,000 years ago probably hindered estuary development, sin ce the ty p ic a l "estuarine" sequence would have had l i t t l e time to develop before being overridden by s h e l f d e p o s its (Emery and Uchupi , 1972). But the slowing of 5 t h is rate o f r i s e between" 6,000 years ago and the present has encouraged the growth o f e x te n s iv e estu arin e systems. During t h is b r i e f in te r v a l in g e o lo g ic time when sea l e v e l and clim ate have favored development o f e s t u a r i e s , they have dominated the w orld’ s c o a s t l i n e s . It can be said in fa c t that v i r t u a l l y a l l c o a sta l embayments have been at some time e stu a r in e , sin ce such embayments are topographic lows that f i l l as the r e s u l t o f submergence (G orslin e, 1967)* In the United S ta tes at the present time 80% to 90% of the A tlan tic and Gulf Coasts and 10% to 20% of the P a c ific Coast c o n s i s t o f e s t u a r ie s and lagoons ( Emer y , 1 967) . 1.1.1.2 Chesapeake Bay and the Paleo-Susquehanna River A prime example of the drowning of a r i v e r ’ s lower course and i t s t r i b u t a r ie s is the Chesapeake Bay. With an area 2 o f 6,500 km , i t i s the l a r g e s t estuary in North America (Cronin, 1971)* F ifte en thousand years ago, near the end o f the Wisconsin lo w -sta n d , the mouth o f the Susquehanna River (fig. 1) was far to the south and east o f i t s present p o s itio n at Havre de Grace, Maryland. It flowed an a d d itio n a l 390 km before i t reached i t s base l e v e l near the s h e l f break, p o s sib ly at the head of Norfolk Canyon. 6 Figure 1 Chesapeake Bay region, showing major tributaries and geographic features. Chesapeake GRACE C|»0 CANAL TURBIDITY WASHINGTON AN NAPOLl DELMARVA N ?U L CAPE HENLOPEN W I L M I N G T O N f SBURV p o t o m B A L T I M O R E CHINCOTEAGUE INLET W A S H I N G T O N CHARLES N O R F O L K S * C . B . B R I D G E - T U N N E L ^ CY N NAUTICAL MILES O 13 » 0 *S CAPE HENRY 0 10 20 30 40 Kl L O M E T E R S iToar 76*30" 75* 30' 75*0 a 76*00 8 [ During the Wisconsin and previous low-stands the Susquehanna in c ise d a deep v a l le y into the T ertiary and Cretaceous sedimentary formations o f the Maryland and j V irgin ia c o a s ta l p la in . Sub-bottom p r o f i l e s and borings for bridge c r o ss in g s have revealed that t h i s paleo-chan- n e l — now f i l l e d with sed im en t-- l i e s more than 60 m below present sea l e v e l at the Bay Bridge in the northern se c tio n o f the bay (Schubel and Zabawa, 1972). It might then be assumed that deeper segments o f the Paleo-Susque- hanna's thalweg would be d e te c ta b le further south, but such i s not the c a se . Data from borings for the two bridges c ro ssin g the bay and for some o f the bridges across the mouths o f the major t r i b u t a r i e s are shown in Figure 2. Continuation of the same gradient seen at the Bay Bridge would require a thalweg depth of approximately 105 m at the mouth o f the Bay (Hack, 1957). The la r g e s t channel discovered during the borings for the Chesapeake Bay Bridge Tunnel near the mouth had a depth o f only 51 m. Harrison and others ( 1965) took t h i s to mean that u p l i f t o f more than 50 m had occurred in the lower Chesapeake region during l a t e P le is to c e n e time. A growing body of evidence has le n t support to an a l t e r n a t i v e h y p o th e sis. F ille d paleo-channels with depths at l e a s t as great as that found at the Bay Bridge have been discovered near the mouth o f the Choptank River and Figure 2 Depth to base of Chesapeake Bay paleo-channel , based on bridge borings. Data from Hack ( 1957) • 10 CHE5HPEHKE H O T BRIDGE BORINGS X— DEPTH TO BR5E OF PHLEOCHRNNEL <M> 39* h O 9 11 77* also in the subsurface of the Delmarva Peninsula near S alisb ury, Maryland (Schubel and Zabawa, 1972; Weaver and Hansen, 1966). At Salisbury ( f i g . 1) the channel s t r ik e s e a s t , while at the mouth o f the Choptank i t can be followed on sub-bottom p r o f i l e s for over 75 km in a so u th -s o u th e a ste r ly d i r e c t io n . The hypothesis offered by Schubel and Zabawa (1972) is that the lower Susquehanna followed various courses during the P le is t o c e n e , some of which may have flowed to the sea through the Delmarva Peninsula--and p o ssib ly through Washington Canyon— rather than through Capes Henry and Charles as the Bay does at p resen t. According to Schubel (1971) there is also evidence that the Potomac River carved a course through the Delmarva at some time during the P le is t o c e n e . A d e ta ile d g eo lo g ic c r o s s - s e c t i o n ( f i g . 3) developed by Ryan ( 1953) from the borings carried out prior to the Chesapeake Bay Bridge co n stru ctio n shows evidence that the river occupied many d i f f e r e n t channels at times o f lowered sea l e v e l . The deepest channel shown in t h i s c r o s s - s e c tion i s 59 m below present sea le v e l near the eastern shore. It i s in t e r e s t in g that most o f the f i l l e d P l e i s t o cene channels are steeper and higher on th e ir western s id e . One might sp ecu late that the channel migrated down-dip, which i s s o u th e a s te r ly . There' i s a lso the 12 p o s s i b i l i t y that none of th ese channels i s older than Wisconsin, sin c e radiocarbon evidence from southeastern V irginia r e v e a ls three or four c y c le s of lowered and elevated sea l e v e l sin ce the Sangamon I n t e r g l a c i a l (Caks and Coch, 1963)- The evidence su ggests that channel migration was common for the Paleo-Susquehanna , and a previous o u t l e t through the Delmarva Peninsula i s p o s s i b l e . One in d ir e c t proof that the present bay mouth may not always have marked the bay’ s course to the open sea l i e s in the fa c t that no w e ll-d efin e d s h e l f v a l 1e y -- s im ila r to that o ffsh o r e from the adjacent Delaware B a y has been lo c a te d . Such a v a lle y has been recognized by Swift (1973) and Swift et a l . (1980) as a s e r i e s o f d e p o s itio n a l and e rosion al fea tu re s marking the landward movement o f a r iv e r mouth estuary as sea l e v e l ro se. The data are s t i l l sparse but future seism ic work may e v e n tu a lly explain the shallow thalweg at the present bay mouth. 1 . 1 . 1 . 3 Geology o f the Western Shore, North-Central Chesapeake Bay Situated e n t i r e l y within the c o a sta l plain province o f eastern Maryland, the Rhode River and i t s watershed r e st for the most part upon Paleocene to Miocene shallow marine 13 Figure 3 Geologic c r o s s - s e c t i o n at Chesapeake Bay Bridge. Data from Ryan (1953)* 14 KL H I IJIAW LOCATION PLAN 194 0 ft 193 0 TEST BORINGS f« 8 1 ( O Q K 3 f M A L ) 3AW DY POINI fcwvsm sw - auoeowrit s * * * » aw*™**. N O T E S -4 C < E f * * C ©►e*W| « # fcay M W It b««U « tmtc wmirflny by J.iOrtmtr Co wrf h * * » *« •* » by PRELIMINARY GEOLOGIC SECTION SANDY POINT TO KENT ISLAND FRO M CHESAPEAKE BAY BRIDGE ENGINEERING REPORT J.E. GREINER COMPANY, CONSULTING ENGINEERS 1948 -E X PL A N A T IO N ' I otiwtt wo nuwKCNe•jtw-uator'w vwr soft, oc*« s * t* wo cut U * w ■ I 'v ’ y A m K r i v o f i m M w M a w A t i # * « ■ * m f i i l H i J * b fu l * * - V » W rw tft3 l).< l*'rM M .*> M *< > « MdlllWWU c m ( V f » A « i « T » n t l t l | 5m m t W « W T 3 . n » * i fe fW ttftin it cn sedim ents, with o cca sio n a l outcrops o f m id -P le isto ce n e ter ra c e d e p o s its o f Sangamonian or older age. A b r i e f d e s c r ip tio n o f the l i t h o l o g y i s given here sin ce erosion o f these g e o lo g ic u n its c o n s t i t u t e s the major part o f the e s t u a r y ’ s sediment load. The g e o lo g ic d e s c r ip tio n s that fo llow are taken from Glaser (1976) and Bennion and Brook- hart (1949). The reg ion a l s e t t in g of the Rhode River estuary is shown in Figure 1. S u r f i c ia l geology o f the estuary i s diagrammed in Figure 4. The o l d e s t formation cropping out in the watershed i s the Paleocene/Eocene Aquia (Ta in Fig. 4 ), a w e ll-s o r te d g la u c o n it ic medium-grained sandstone. Glauconite dominates the sand f r a c t io n , but r a re ly exceeds 50 p ercent. Limonite c r u s ts are common. Unweathered color i s dark gray-green or o l i v e green. Faunal and te x tu r a l evidence in d ic a te shallow marine d e p o s itio n and record a r e g r e s s iv e c y c l e . On the shores o f the South and Severn R iv e rs--th e next two e s t u a r ie s north o f the Rhode R iver--th e Aquia forms sp ectacu lar b l u f f s o f up to 25 m. Due to the low ( 0 .2 degrees) so u th e a ste r ly d ip , however, most o f the Aquia is in the subsurface in the Rhode River area. The Aquia is a good low-iron aquifer and is tapped for domestic purposes throughout southern Anne Arundel County. 16 F igure 4 Geology o f the Rhode River Estuary watershed, Mar yland . Gj r l . - r u l . u v G 3 T R —T R U B U T T N N R N U E M P Y The Lower Eocene Marlboro Clay (Tm in F ig. 4) crops out sp a rsely in the watershed and, being a thin d e p o s it, I c o n tr ib u te s l i t t l e to the sediment load. It i s unique, however, in that i t i s a nearly pure cla y and i s worked for brick and pottery a p p lic a tio n s (Kuff, 1976). I ts color i s s i l v e r - g r a y to reddish-brown. Occasional massive s i l t l e n s e s occur. Burrows are common, as are small mollusk s h e l l s . Fauna and sedimentary str u c tu r e s in d ic a te a shallow marine or i n t e r t i d a l environment. The Nanjemoy Formation (Tn in F ig. 4 ) - - a middle Eocene g l a u c o n i t ic sand, s i l t and s i l t y c l a y — covers the major part o f the watershed and most o f the e stu a r in e s h o r e lin e . It i s a f i n e - to medium-grained clayey sand, poorly sorted and containing up to 50% g la u c o n it e . Lenses o f dark-gray s i l t y clay are found interbedded with the sand. Unweath ered co lor o f the sand is dark g reenish -gray to b l u is h - green. Molluscan f o s s i l s are common, c h i e f l y Veneri- c a r d i a , and sands become coarser u p -s e c tio n . L ithology, tex tu re and fauna in d ic a te a marginal s h e l f environment in r e l a t i v e l y shallow water. The middle Miocene Calvert Formation (Tc in Fig. 4) crops out only in the upland areas o f the watershed. Lithology v a r ie s from a fin e -g ra in e d clayey quartz sand to 19 a high ly diatomaceous s i l t . The f o s s i l fauna include Pecten s p . and la rg e ba rn acles. The environment o f depo s i t i o n was probably a r e s t r i c t e d marine b asin . P le is to c e n e ter ra c e d e p o s its ( Qt in Fig. 4) also crop out sp a rsely in the upper watershed. These formations c o n s i s t o f interbedded g la u c o n it ic sand, quartz gravel and s i l t y c la y . They are thought to have been deposited during i n t e r g l a c i a l s by the a n c e stra l Susquehanna. In other areas o f eastern Maryland these d e p o s its contain c l a s t s o f c r y s t a l l i n e rocks from the Piedmont and Blue Ridge Provinces. Occasional peat beds, plant debris and f o s s i l cypress stumps occur. An a l t e r n a t i v e explanation for such d e p o s its has been o ffered by Hoyt ( 1972), who s t a t e s that many o f the s o - c a lle d te r r a c e s o f the A tla n tic Coastal plain are a c tu a lly former barrier island se q u en ce s. Quaternary alluvium (Qal in Fig. 4) covers most o f the flood plain o f Muddy Creek, the main feeder stream o f the Rhode River. All o f the u n its designated Qal on the map in Figure 4 were deposited within the l a s t 10,000 years. 20 1 .1 .2 Hydrology and Flood H istory o f the Chesapeake Bay/Susquehanna River Basin j i 1 .1 .2 .1 Freshwater Discharge to the Chesapeake | Fresh water runs to the Chesapeake o f f a drainage area o f i i 2 i approximately 166,000 km ’ discharged from more than 50 r i v e r s . The g r e a t e s t o f these r iv e r s i s the Susquehanna, which alone i s r esp o n s ib le for more than h a lf o f the fresh water co n trib u tio n to the bay. Throughout the bay, and e s p e c i a l l y in the northern s e c t i o n , hydrologic c o n d itio n s are dominated by the la rge f l u v i a l input. Tidal f l u c t u a tion i s s m a l l - - t y p i c a l l y 0.3 to 0.6 m--and t i d a l currents range from 0 to 3*5 km/hr (McKay, 1976). Pritchard (1952), in h is pioneering work on the s a l i n i t y stru ctu re and general c ir c u la t i o n o f the bay, described the portion o f the Chesapeake north o f the Bay Bridge ( f i g . 1) as e s s e n t i a l l y a huge mud f l a t o f the Susquehanna River. The Susquehanna provides 87% of a l l the fresh water entering t h i s northern h a lf o f the bay. AH o f the other major r iv e r s enter through the bay's western shore. The Potomac c o n tr ib u te s about 18% of the fresh water flow, the James River about 16%, the Rappahan nock 4% and the York 2%. In a ty p ic a l year the t o t a l fresh water volume supplied to the hay by streams is s l i g h t l y greater than the t o t a l volume o f the estu a rin e 'system (P ritch ard , 1952). i j | Streamflow records for the Susquehanna River near i t s mouth at Conowingo, Maryland, are shown in Table 1. Average annual discharge for the 10-year period ending in 10 q 1977 was 3*95 x 10 m . Suspended sediment discharge records are a lso displayed in the ta b le for the seven years for which such data are a v a ila b le at Conowingo. The only major perturbation in the annual hydrograph can be seen in 1972, when the storm of the century, tr o p ic a l storm Agnes, inundated the Susquehanna watershed. Two mejor events are v i s i b l e in the annual suspended sediment records: Agnes and a l e s s e r t r o p ic a l storm, E lo ise in September o f 1975. The data in Table 1 make i t obvious that major storms dominate the sediment discharge into the bay, while exertin g a l e s s s i g n i f i c a n t in flu e n c e h y d r o l o g i c a l l y . The non -lin ea r response o f sediment disch arge to water discharge i s in part r e la te d to the long-term sediment- trapping e f f e c t o f the three la rg e power dams on the lower Susquehanna ( f i g . 1). It appears that flu sh in g o f the dams takes place only during major storms. The s i g n i f i cance o f t h i s e f f e c t w i l l be explored in Chapter 4. 22 TABLE 1 ANNUAL DISCHARGE LEVELS FOR SUSQUEHANNA RIVER AT CONOWINGO, MARYLAND. Year Water Discharge Sediment Discharge ( x 10*^ ) ( x 10^ tonnes ) 1968 2.91 -------- 1969 2.32 0. 32 1970 3.86 -------- 1 971 3.43 1.0(1) 3 3 . 0 k '' 1972 6.01 1973 4.04 1. 2 1974 3.57 0 .8 (2 ) 1 1 . 0 ^ ; 1975 4.77 1976 4.08 1.2 1977 4.49 -------- mean 3.95 ± 0.94 1.2 + 0 . 6 (3) All data from U. S. G eological Survey r eco rd s. 1. Includes t r o p i c a l storm Agnes, 30.0 x 10 tonnes (June 24-30, 1972). 6 2. Includes t r o p ic a l storm E lo is e , 9.9 x 10 tonnes (S ep t. 26-30, 1975). 3. Excluding June 24-30, 1972 and Sept. 26-30, 1975. 23 [ One further point needs to be made in regard to the ] hydrologic behavior o f the Susquehanna River. Like that | o f many ea stern r i v e r s , the Susquehanna’ s discharge under goes la rg e seasonal v a r ia tio n due to snowmelt and r a i n f a l l p a tte r n s. The bulk o f the r i v e r ’ s flow occurs during March and A p ril. B o ic o u r t’ s (1969) data, sketched in Figure 5, d e p ic t average flow by month at Conowingo for the period 1929-1966. The March and April l e v e l s are more than tw ice the long-term average flow o f 985 / s e c . The e f f e c t o f t h i s e r r a t i c discharge i s to concen trate the bulk of the f l u v i a l sediment tran sp ort to the bay within t h i s March-April f r e s h e t . This c h a r a c t e r i s t i c w i l l be examined in more d e t a i l in Chapter 4. Another e f f e c t o f the unusually high disch arge l e v e l s in the spring is to push the head o f t i d e more than 40 km south o f the r iv e r mouth. Thus, the upper third o f the Chesapeake Bay becomes an ex ten sio n o f the Susquehanna River during the sp rin g. The net n on tid al estu a r in e c ir c u la t i o n pattern i s destroyed and flow becomes purely f l u v i a l , th at i s , seaward at a l l depths (B oicou rt, 1969)- 24 Figure 5 I ___ Susquehanna River discharge at Conowingo Maryland, 1929-1966, monthly averages, from Boicourt (1969). Data 25 C D N D W I N G D R V E R R G E D I 5 C H R R G E B Y M G N T H / I 3 2 3 - I 3 G G 3000 2000 1000 0 dRN FEB MRR RPR MRY dLJN dUL RUE 5EP OCT NOV DEC 2 6 ■ " 1 . 1 . 2 . 2 S a l i n i t y Spring and f a l l i s o h a lin e s for Chesapeake surface waters are depicted in Figures 6 and 7. C o r io lis d e f l e c t i o n o f freshwater along the western shore i s r e a d ily apparent. The strong d i l u t i n g e f f e c t o f the Susquehanna spring f r e s h e t i s a lso evid en t in the s a l i n i t y p a tte r n s. There are a number o f tr ib u ta r y embayments on the western shore o f the northern Chesapeake Bay. Such embay ments are defined as small drowned riv er v a l le y s whose fresh water input i s u s u a lly i n s u f f i c i e n t to generate s a l i n i t y g r a d ien ts throughout most o f the estuary (Han, |1975). Their c ir c u la t i o n thus i s c o n tr o lle d to a la rge ex ten t by s a l i n i t y changes in the larger o u tly in g Chesa peake . The Rhode River Estuary i s one o f these embayments. Being r e l a t i v e l y shallow (average depth about 2 m) the Rhode River e x h i b i t s a s a l i n i t y pattern that i s c l o s e l y linked to the surface s a l i n i t i e s o f the nearby p ortio n s o f the Chesapeake. This c o n tro l o f Rhode River c i r c u la t i o n by bay surface water r e s u l t s in r e l a t i v e l y rapid and unpredictable changes in c ir c u la t i o n p a tte r n s, in response to v a r ia t io n s 27 Figure 6: Chesapeake Bay su rface s a l i n i t y , spring average. Data from Pritchard (1968 ). CHESAPEAKE BAY SURFACE S A LIN ITY (% 0) S P R IN G A V E R A G E R H O D E RI VER V 29 Figure 7 Chesapeake Bay su rface s a l i n i t y , autumn average. Data from Pritchard (1968). 30 CHESAPEAKE BAY SURFACE S A L IN IT Y (%«,) A U T U M N A V E R A G E 10' 39' R H O D E RI V E R 38' 23 10' 2 5 >29 76 ' 31 in Susquehanna River discharge to the bay. This e f f e c t i s p a r t ic u la r ly evid en t at times o f major storms. During the 1972 Hurricane Agnes f lo o d s , for example, s i n g l e - l a y e r c ir c u la t i o n p revailed for a number o f weeks over much of the bay north o f the Bay Bridge (F ig . 1). N e v er th e le ss, over the course o f a year the Rhode River undergoes a d i s c e r n i b l e c y c le o f s a l i n i t y , as seen in Figure 8. These fe a tu r e s are: a l a t e s p r in g /e a r ly summer minimum, a f a l l maximum, a regular in crea se from July to October, and v a r ia b le s a l i n i t y throughout the sp rin g. Other fa c to r s a f f e c t in g c ir c u la t i o n and mixing in the Rhode River are wind and fresh water flow. Due to the shallow depth, moderate winds are capable o f t o t a l l y mixing the water column. Freshwater flow from the main feeder stream, Muddy Creek, i s sm all. During w in ter- spring high flow p e r io d s, however, Han(1975) found that s a l i n i t y and exchange r a te s for the upper h a l f o f the estuary depended on river flow. 1 . 1 . 2 . 3 Flood H istory Since sediment disch arge from the Susquehanna i s linked to periods o f high flow and p a r t ic u la r ly to f lo o d s , i t i s worthwhile to examine a longer-term hydrologic record than that a v a ila b le for Conowingo. None o f the 32 Figure 8 Surface s a l i n i t i e s for Rhode nearby Chesapeake Bay. Data River mouth and from Han (1975 ). 33 5U R FR C E 5 R L I N I T Y FDR RHODE RIVER MOUTH FIND NERRBY CHE5RPERKE BRY/> NORTH RND 5D U TH OF RHODE RIVER 1 5 14 13 12 _ 10 Q - q Q. J 8 - 7 c o 6 1 0 5 4 3 2 f l C.B. 5DUTH a----- ° C.B. NORTH * ----- A R.R. NOUTH o------o 0 M onths o f the Y ear 1972 stream -discharge records for the region i s r e l i a b l e for much beyond 50 y ea rs. R a in fa ll records have been kept for Annapolis, Maryland, however, s in c e 1843 and for Baltimore sin c e 1817. Although p r e c i p i t a t io n and sediment discharge are not always c l o s e l y c o r r e la t e d , i t i s u sefu l to examine long-term r a i n f a l l records and incid en ce o f major storms. Major flo o d s ( i . e . , those in v olv in g s i g n i f i c a n t l o s s o f l i f e or property) for the Susquehanna region have been catalogued by Hoyt and Langbein ( 1955). The d ates o f th e se and the most recen t major flo o d s are l i s t e d along with the Baltim ore/Annapolis p r e c i p t i a t io n records in Table 2. The Indians o f the Susquehanna basin held a t r a d i t io n a l b e l i e f that flo o d s occurred every 14 years (Hoyt and Langbein, 1955). The actu al frequency o f major flo o d s in the Susquehanna area, as shown in Table 2, i s about 7 2 years. This fig u r e encompasses the e n t ir e 71,225 km Susquehanna watershed. It might be assumed that a small subwatershed such as the Rhode River Estuary would not experience sedim entologic e f f e c t s from every storm. The recurrence in te r v a l for such events might be as much as double the r egio n al average, as d iscu ssed l a t e r in Section 3 . 1 . 3 . 35 co "O C V j OO C M = f = f CO O < J> LPi C M ^ C O O O L O C M C M O O C O C - =r 0 0 c m c r > m d o iN'-^o^riNC^vOvocMoocoa^ts^- (MOtOCMOO t — c o o ^ ^ r o o c o L O v o c o f - f - c n T — cn co t"- co zr c-- cm co 0 0 cr> 0 0 o o r - o c o z t c o c m c m c ^ v o c o c m co o> o cr> CO CO LO OO C T > O ' C M CO z j- LO O C 1 — CO 0> O ' — CM CO zj" LO MD t>— CO 0> O t— C M CO z j- LO MD D — CO 0> O *— C M CO iMscooocococococooooooooM^a>a>CT\o>chCho>o>oooooooooO'-r-r-r- cococococooococococooococococococoooaocoooooo'vcncr> cncncncncncr> cncna> cncr> LO vO OO OO OO S ~ T 3 cnLncoLnoo^roococooo^r^r^-v-~cMOi>-^rcocr>cr>cocoi>-LnococMLPi'—i >-coi>-m dm d COCOC— IC -C O M D O '— O ^ T O O ' — O O O I C - C — C^CT»C—vOCOCMC^vOOOCT»uDLOCMLPi^t‘ Cr» '-cocois'-'cncooMri[sLncoc?icoo^cocc1 -o=riCivococoO'-o^'-c^'-'-o M CM CO z f L O v O t > - C O C ^ O < — CMCOzT LOvO C— CO O'* O T — CM CO z f L O v O C --a O C r> 0 < — CMCOzf LPivOlC- z r z r z r z r z r L n L 0 L P i L 0 L 0 L 0 L 0 L P i L 0 L 0 v 0 v 0 v 0 v 0 v 0 v 0 v 0 v 0 v 0 '- O t c - t > - c - t > - c - t > - i c - i > - COCOCOOOCOOOCOCOCOCOOOOOCOCOCOOOCOCOCOCOOOCOOOCOOOCOCOOOCOCOOOCOCOCOCOCO Table 2 ( c o n t in u e d ) . Year Rain^ . Major f a l l Flood (cm) Dates Year (3) Rain-r . Major f a l l ' ’ iL) Flood (cm) Dates (3) 1914 1 0 2 .2 1947 79.4 1915 104. 8 1 948 125-9 Mar. 1948 1916 105.3 1949 89. 1 1917 98.2 1950 115.0 1918 87.6 1951 102. 3 1919 1 2 2. 1 1952 132.3 1 920 1 0 7 .0 1953 1 2 1 .6 1 921 81.5 1954 79.0 Oct. 1954 1922 114.2 1955 97.7 Aug. 1955 1923 112.4 1956 9 1 .2 1924 1 2 2 .8 Oct. 1924 1957 8 6. 2 1925 87-7 1958 129. 9 1 926 1 0 2 .0 1959 105. 4 1927 97. 1 1960 100. 9 1 928 123-3 1961 111.7 1 929 110.5 1962 90. 4 1930 53.7 1963 ------- 1931 107. 4 1964 82. 0 1932 129. 4 1965 73.5 1933 125.9 Aug. 1933 1966 1 00. 9 1934 1 1 0 .1 1967 95. 9 1935 1 15.6 J u l. 1935 1968 85.2 1936 108. 3 Mar. 1936 1969 121.3 1937 143.6 1970 9 0.0* 1938 89.4 1 971 142. 9 1939 1 0 0. 8 1972 134.7 Jun. 1972 1940 95.0 1973 116.4* 1941 71.8 1 974 95.9* 1 942 89.6 1975 1 0 9.6* Sep. 1975 1943 73-7 1976 1 1 0.2* 1 944 91.8 1977 94.9 1945 105.6 1978 1 1 0 .8 1 946 62.6 May, J u l . 1946 mean 108. 4 (7 .0+ 6.8 i n t e r v a l ) 1. P r e c ip it a t io n data from Fassig (1932) and 2. R ain fa ll data marked with a s t e r i s k (*) are from Baltimore; o th ers are from Annapolis. 3. From Hoyt and Langbein (1955) and Slaughter (1967)* 37 The g r e a t e s t floo d in g on record in the Susquehanna Basin, a ss o c ia te d with t r o p ic a l storm Agnes, occurred during June 24-30, 1972. This flood brought to Conowingo the la r g e s t instantaneous peak flow ever reported on the 4 3 Susquehana: 3.2 x 10 m / s e c . The previous high was in the 1936 flood: 2.2 x 10^ / s e c (T ice, 1968). During t r o p ic a l storm Agnes the r iv e r basin was deluged with up to 45 cm of r a i n f a l l in a weekTs tim e. The head o f t i d e in the bay was pushed seaward nearly to the Bay Bridge, 80 km from the river mouth--35 km further seaward than ever p r e v io u sly reported (Schubel, 1974). Transport o f f l u v i a l sediment in to the bay a lso reached record l e v e l s as noted above in Table 1. Concentration o f suspended sediments in the riv e r at Conowingo went from the normal l e v e l s o f about 10 mg/1 to over 10,000 mg/1 ( Schubel , 1 974 ) . The long-term sedim entologic e f f e c t s o f t h i s flood pulse have been documented for the upper bay by Hirschberg and Schubel (1979) and w i l l also be d iscu ssed in Chapters 3 and 4. 38 1.1.3 Holocene Sea-Level Rise Chronology 1.1.3*1 Long-Term Sea Level Rise Rates As mentioned e a r l i e r , the development o f e s t u a r i e s i s a d i r e c t r e s u l t o f a r i s i n g sea moving in over the sh e lv e s and flo od in g the mouths o f c o a s ta l p la in r i v e r s . To understand the p r o l i f e r a t i o n o f e s t u a r i e s on Holocene s h o r e lin e s one must r e fer to the sea l e v e l r i s e curve. Such a curve can a lso g iv e an approximate date for the r iv e r - e s t u a r y t r a n s i t i o n for a p a r tic u la r estu a ry, that i s , the point in time when mean high water f i r s t reached the mouth o f the riv e r and began transforming the sedimen t a t io n regime from prim arily e r o s io n a l to prim arily depo- s i t i o n a l . This curve appears in many v e r s io n s , depending upon the c ho ic e o f samples for dating and the lo c a t io n o f the samples. Most o f the d ates are radiocarbon determ inations on r e l i c t o yster beds. Due to p o s td e p o s itio n a l landward tr a n sp o rt, th e se s h e l l d a tes often g iv e depth/age informa tion that i s erroneously shallow (Macintyre, e t a l ., 1978). Sample lo c a t io n i s important because even on such a r e l a t i v e l y s t a b le margin as the U. S. A tla n tic co ast there 39 i s a n o n -e u s ta tic component in the sea l e v e l curve which may vary from place to p la c e. Even in the r e l a t i v e l y small and s t r u c t u r a ll y uniform area between Chesapeake Bay and Long Islan d , a recen t study by D illon and Oldale (1978) using seism ic r e f l e c t i o n methods has revealed d i f f e r e n t i a l downwarping of the c ru st underlying the c o n tin e n ta l s h e l f . The study found that r e f l e c t i n g su rfa c es had been depressed as much as 50 m, with the amount o f warping in c re a sin g northward from an i n f l e c t i o n zone o f f c e n tr a l New Jersey. The authors noted that radiocarbon samples c o l l e c t e d north o f the i n f l e c t i o n zone would need to be d e p th -a d ju ste d . Another study in v o lv in g uranium -series d ates on marine d e p o s its throughout the southern U. S. A tla n tic Coastal Plain drew a sim ila r c o n c lu sio n . Cronin and oth ers (1981) found that e le v a t io n s o f samples from P le is t o c e n e high- stands depended not j u s t on i s o t o p i c age but a lso on l o c a l c r u s ta l movements o f unknown magnitude. The e u s t a t i c curve most commonly used for the eastern United S ta te s i s that o f Milliman and Emery (19 68 ), which i s shown in Figure 9» Based on th e ir new evidence of sample m o b ility and c r u s ta l downwarp, D illon and Oldale (1978) have constructed a r ev ise d e u s t a t i c curve, which i s 40 also p lo tte d in Figure 9. In t h i s new curve the -130 m low-stand o f Milliman and Emery (1968) has been raised to -85 m. In a l a t e r study Oldale and 0 T Hara ( 1980) show the approach to present sea l e v e l over the l a s t 5,000 years as a more gradual r i s e , but t h i s would not s i g n i f i c a n t l y a f f e c t the timing o f the r iv e r - e s t u a r y t r a n s i t i o n for the Rhode River and other parts o f the northern Chesapeake Bay. The D illon and Oldale (1978) curve w i l l be referred to l a t e r in estim atin g the point at which t h i s t r a n s i t i o n occurred . The change in a r iv e r - e s t u a r y sy stem ’ s sedim entation pattern s i s not the only e f f e c t wrought by a r is in g sea - l e v e l upon a c o a s ta l system. A model based on the Bruun Rule for sh o r e lin e erosion has been developed by Rosen (1978) and applied to the lower Chesapeake Bay. Rosen found that a l l o f the long-term shore e r o s io n — which i s a major source o f sediment to the bay— can be accounted for by s e a - l e v e l r i s e . This i s not to say that eu stasy i s the cause o f shore e r o sio n , but rather that a e u s t a t i c r is e enables waves and t i d a l currents to erode at s u c c e s s i v e l y higher l e v e l s on the land. Rosen’ s (1978) study w i l l be d iscu ssed in more d e t a i l in Chapter 4. 41 Figure 9 S e a -le v e l curves for the e a st co a st o f the United S t a t e s . 42 ER5TERN U.5. 5ER LEVEL CURVES r h d d e ~ r 7v e r “ PHLEOCHRNNEL tiHESRPERKE PRLEOCHRNNEL £>ILLDN R N £ > OL[>RLE/ 137B M1LLIMRN R N I> EMERY/ ISEB 0 13 IE 23 2E 3 0 3S HE TH0U5RND5 DF YERR5 B. P. 43 1 .1 .3 - 2 Short-Term Sea-Level Rise Rates The worldwide e u s t a t i c rate i s at present considered to be about 1.2 mm/yr (W alcott, 1975). This r e p re sen ts a l e v e l l in g - o u t o f the p r e c ip ito u s rate o f r i s e over the past 15,000 y ea rs, as seen in Figure 9. In the case o f the Chesapeake Bay r eg io n , however, the t e c t o n i c component o f | j r e l a t i v e s e a - l e v e l r i s e i s at l e a s t as important as the ! e u s t a t i c component. The National Geodetic Survey has constructed l e v e l i n g surveys on an e x te n s iv e net surrounding the bay over a time base o f about 50 years i ; (Hohldal and Morrison, 197*0- The r e s u l t s show a s u b s i dence rate for the northern Chesapeake Bay watershed varying from 2.6 mm/yr at the head o f the bay (Havre de | | Grace) to 2 .0 mm/yr in the Annapolis/Rhode River area. I i i | The sum o f these two components, e u s t a t i c and t e c t o n i c , agree well with the lo n gest-ru n n in g Chesapeake t i d e gauge r ec o rd s— those at Baltimore Harbor. Using an averaging I method to a tten u ate short-term f l u c t u a t i o n s , Hicks (1973) j has computed that mean sea l e v e l at Baltimore has been j r i s i n g at a rate o f 3-3 mm/yr over the period 1929— 1971• It i s noteworthy th at Hicks and Crosby's (1975) average rate o f sea l e v e l r is e for U. S. c o a s t s i s 1.5 mm/yr, implying that the Chesapeake area i s undergoing anomalous [ jsubsidence. Shepard and Wanless (1971) suggest that t h i s j r e l a t i v e l y rapid subsidence i s a r e s u l t o f the area returning to i s o s t a t i c equilibrium a fte r undergoing u p l i f t due to p e r i g l a c i a l bulge during the Wisconsin g l a c i a t i o n . 1 .2 .3 * 3 Summary o f Sea-Level History Summarizing the most complete inform ation a v a i l a b l e , the l o c a l r a te s o f s e a - l e v e l r i s e from the time o f in c ep tio n o f the Chesapeake Bay to the present are as f o llo w s : a) between 17,000 and 5,000 years ago sea l e v e l rose along the A tla n tic co a st from approximately -90 m to -5 m, or about 7 mm/yr (D illo n and O ldale, 1978); b) from 5,000 years ago to nearly the present time the average rate o f r i s e has slowed to about 1 mm/yr (D illo n and O ldale, 1978; Milliman and Emery, 1968); c) sin ce at l e a s t 1929 the rate o f r i s e as measured on the t i d e gauge at Baltimore has been 3*3 mm/yr (H icks, 1973)• Thus the rate o f r i s e o f mean s e a - l e v e l observed during h i s t o r i c time at Baltimore i s more than three tim es the rate th a t has p reva iled for the l a t t e r h a lf o f the Holo cene for the e a st c o a s t . Subsidence i s o b v io u sly at work, as demonstrated by Hohldal and Morrison (1 9 7 4 ), but how long the anomalous subsidence has been in e f f e c t i s d i f f i c u l t to a s s e s s . There are three s tu d ie s which in d ic a te th a t t h i s rapid subsidence i s a r e l a t i v e l y recen t phenom- 45 enon. N ichols (1972), in a comprehensive sediment study i o f the lower Chesapeake, obtained radiocarbon d a tes for basal peats from a number o f l o c a t i o n s near the mouth o f j the Chesapeake, the James estuary and the Rappahannock estu a r y . His r e s u lt a n t s e a - l e v e l curve, shown in Figure I 10, r e v e a ls a rate o f r i s e o f about 1.6 mm/yr from about 11,000 years before present (BP) to about 550 years BP, j although only two samples are in the 0-1300 years BP I range. According to Hohldal and Morrison (1974) the ! i t e c t o n i c subsidence rate in the area where N ichols' ! | samples were c o l l e c t e d is 2.0 mm/yr to 2.4 mm/yr--about ! i the same as that found in the Bal timor e/upper Chesapeake i Bay area. j A second study involved the dating of peat, s h e l l and j wood samples from throughout the Delmarva Peninsula and j i the eastern shore of the bay. The curve, compiled by j Kraft and oth ers ( 1973) and shown in Figure 10, shows lo c a l sea l e v e l r is in g 1.5 mm/yr over the past 3,800 y ea rs, in concordance with N ichols' r e s u l t s . Only two of the samples in the study, however, seem to have been in the 0 -2 ,00 0 years BP range. A f i n a l l o c a l sea l e v e l curve, developed by Newman and Rusnak (1965), was obtained by dating basal peats from the eastern shore o f the V irgin ia s e c t io n of the bay. Their 46 Figure 10: S e a -le v e l curves for the Chesapeake Bay r e g io n , 8,000 years BP to p r e sen t. 47 CHE5RPERKE 5ER LEVEL CURVES 0 2 NEWMRN RND RU5NRK/ 1 BBS H E NICHDL5/ 13 7 2 B KRRFT ET RL./ 1373 0 2 H RHODE RIVER PHLEDCHHNNEL B B 20 0 2 H B B 10 12 TH0U5RNDS OF YERR5 B. P . 48 ; r e s u lt in g curve, a lso p lo tte d in Figure 10, r i s e s at a 1.1 mm/yr rate over the past 4,350 y ea rs, in agreement with the other two s t u d i e s . The youngest sample in that study was 2,550 years BP. It would seem, t h e r e f o r e , that a rate o f r i s e o f about : 1.5 mm/yr for the mid-Holocene would be the b est fig u r e to use in determining when the r iv e r / e s t u a r y t r a n s i t i o n occurred for any p a r tic u la r area o f the northern bay r eg io n . It is important to n o te, however, th at none o f the above s t u d ie s adequately d e p ic ts the rate o f sea l e v e l r i s e over the past 1,000 y e a r s. The portio n s o f the curves in Figure 10 that cover the past 1,000 years are almost e x c l u s i v e l y e x tr a p o la t io n s from older samples. Some o f the Rhode River radiocarbon samples are within that range, and in d ic a te a more rapid rate o f r i s e , in b e t te r agreement with the long-term t i d e reco rd s. An older peat sa m p le --1,948 years old--from the Rhode River yield ed a r i s e r a te that agrees w ell with the i n v e s t i g a t io n s mentioned above. These p oin ts w i l l be d iscu sse d in d e t a i l in the third se c t io n o f Chapter 3* 49 1 .1 .4 Sedim entologic E f f e c t s of Land Use in the Northern Chesapeake Bay Area There i s but one entrance by Sea into t h i s Country, and that i s at the mouth o f a very goodly Bay 18 Or 20 myles b r o a d ... Within i s a country th a t may have the p rero g a tiv e over the most p lea sa n t p la c es knowne, for the la rge and p leasa n t navigab le R ivers, heaven and earth never agreed b e tte r to frame a place for a man's h a b i t a t i o n . . . Here are mountaines, h i l s , p l a i n e s , v a l le y s , r iv e r s and brookes, a l l running most p le a s a n tly in to a f a i r e Bay compassed but for the mouth, with f r u i t f u l and delightsom e land. --from the Generali H is to r ie of V ir g in ia , New England and the Summer I s l e s by Captain John Smith, 1606 (H a ll, 1910, p. 25). | The beginning o f the permanent c o lo n iz a t io n o f America began in 1607 on the lower Chesapeake Bay at Jamestown, V ir g in ia . B r it is h immigrants to the New World began to i jarrive soon a f t e r John Smith's d e s c r ip t io n s o f t h i s "delightsom e land" reached the shores o f England. James town, the f i r s t English se ttle m e n t in America, was founded on the lower Chesapeake in 1607. With t h i s foothold the Europeans quickly moved up the r iv e r v a l l e y s o f the A tla n tic Coastal Plain to the f a l l l i n e and beyond. A s e r i e s o f population maps (F ig . 11) has been constructed by F r i i s (1940) which d r a m a tica lly d e p ic t s the 50 rapid spread o f European c i v i l i z a t i o n westward from the Chesapeake and New England areas. Table 3 d e p ic ts F r i i s 1 data on population growth during t h i s period. TABLE 3 U. S. POPULATION GROW TH DURING THE COLONIAL ERA ( 1 ) Year Population — ' 1700 275, 000 1720 475, 000 1760 1, , 600, 000 1780 2., 800, 000 1790 3 a ,900, 000 1. Data from F r i is (1940). The p a ttern s seen on the map n e a tly d e fin e the s u b -e s- t u a r ie s o f the bay and the paths o f a l l o f the navigable r i v e r s . The importance o f n avigab le r iv e r s as a r t e r i e s o f commerce in c o lo n ia l times i s underscored by the f a c t that i t took the s e t t l e r s more than 100 years to cro ss the f a l l l i n e in a pp reciab le numbers. Early commerce in the Chesapeake Bay region prim arily involved tobacco grown for the European tra d e, sin c e the p r o f i t margin was six times that on any other crop. Since proxim ity to a n avigab le stream f a c i l i t a t e d tran sp ort o f 51 Figure 11 Population maps o f the United S t a t e s , 1625-1790. Data from F r i is ( 19-40) - K U \ \ r ' - f M 1 H j « P P P U L R T I CUN T R E N D S I E 5 23 E E ■ — I "731ZI ! the crop, the r iv e r banks and estuary shores became lin e d with farms and p la n t a tio n s . The r e s u l t s were gradual d e p le tio n o f s o i l n u t r ie n t s , erosion o f t o p s o i l and abnor mally high r a te s o f sediment in flu x into the t r i b u t a r i e s I and the bay i t s e l f . Depleted tobacco land was sometimes i ' converted to corn or wheat , but more commonly was aban- i doned. The e s s e n t i a l l y one-crop a g r ic u lt u r a l economy I qu ick ly led to se r io u s s o i l erosion problems (Brown, 1943). By the m id -eig h teen th century some farms had already been deserted and the land-use pattern had been perma n en tly a l t e r e d . Brown (1943), in h is h is to r y o f the l a t e e ig h te e n th century in the Chesapeake Bay area, described the s o i l d e p le tio n in the fo llo w in g words: 54 The co n tra st formed by the productive f i e l d s and w e ll-k ep t mansions o f the en lig h ten ed or f o r t u nate p la n ter s and the surrounding wooded or waste land and d e r e l i c t h a b it a tio n s i s one o f the g r e a t e s t to be seen anywhere in the Eastern s t a t e s . Abandoned tobacco f i e l d s , sometimes so thoroughly exhausted that even t r e e s w i l l not grow, a s s i s t in the general asp ect o f barren ness . F ir e s , most common in the spring and r e s u lt in g from the n e g lig e n c e o f people who burn brushwood to c le a r land, have completed the d e s o la t io n o f some i n t e r i o r d i s t r i c t s . Man cannot be held accountable for f l o o d s , but the h e ig h ts to which these r iv e r s may r i s e was demonstrated in the dreadful inundation o f 1771 when mountain r a in s f a l l i n g i n c e s s a n t l y from the tw enty-seventh o f May to the eigh th o f June caused the Rappahannock to sw ell tw e n ty -fiv e f e e t higher than during any p r e v io u sly known f lo o d . The rushing to rr en t swept everything before i t . Every warehouse on both s id e s o f the Rappahannock was f u l l o f water and upwards o f four thousand hogsheads o f tobacco were swept to sea. (Brown, 19^3, P* 227). Concurrent with the w astefu l c u l t i v a t i o n methods, Mary land s e t t l e r s cleared and burned the dense hardwood f o r e s t s on a massive s c a le for purposes o f s e c u r i t y , ease o f t r a v e l and development. During the f i r s t two c e n tu r ie s o f European s e tt le m e n t , v i r t u a l l y every tr e e in Maryland was cut down ( W h it e s e ll, 1960). These unwise land use p r a c t ic e s were in c r e a sin g runoff and stream sediment loa d , r e s u l t in g in g reater s e v e r i t y o f flo o d s and premature sh oalin g o f e s t u a r i e s and navigable r iv e r s by sediment. The most n o tic e a b le e f f e c t s in c o lo n ia l times was the f i l l i n g o f n a vig atio n ch an n els. The e a r ly port towns were 55 s it e d as far up the tr ib u ta r y streams as n a v ig a tio n would permit, sin c e t h i s lig h ten ed the task o f moving hogsheads o f tobacco overland (G o ttsch a lk , 1945). With the a c c e l e r ated r a te s o f sediment i n f l u x , however, i t was sometimes l e s s than 50 years before the r iv e r ports shoaled and became i n a c c e s s i b l e to ocean-going s h ip s . Gottschalk (1945) compared navig atio n ch arts from c o lo n ia l times to the modern era for former port towns on the western sid e o f the Chesapeake. He found that most o f the harbors had f i l l e d r a p id ly , due in part to the r eg io n a l a g r ic u lt u r a l p r a c t ic e s and in part to the c le a r in g o f the land to develop the port f a c i l i t i e s . Some o f h is examples from the northwestern shores o f the Chesapeake are shown in Table 4. The sedim entation r a te s in ferred from the data shown in t h i s t a b le range from 20 mm/yr for Joppa Town to over 50 mm/yr for Georgetown and Elk Ridge. These r a te s are high but not s i g n i f i c a n t l y higher than r a te s measured in the p resent day, in clu d in g those which w i l l be presented in Chapter 3 . Despite the f a c t that farming methods and s o i l co n serv ation p r a c t ic e s have undergone su b s t a n t ia l improvement 56 TABLE 4 SEDIMENTATION IN COLONIAL MARYLAND PORTS FROM COMPARISON OF BATHYMETRIC SURVEYS ( 1 ) Port River Survey Depth HON Reduc- (km) tio n J m T Joppa Town Gunpowder Georgetown Potomac Port Tobacco Port Tobacco Upper Marlboro Patuxent Elk Ridge Patapsco 1750-1897 3.0 4 .0 1783-1837 2 .7 - 7 .7 6 32.2 1800-1882 1.8 1.6 1859-1944 2. 1 12.9 1845-1924 4.6 11.2 Data from G ottschalk (1945). (1) Downstream m igration o f head o f n a v ig a tio n , in km. (2) Without dredging. sin c e c o lo n ia l tim es, urban ization has added new items to the sediment budget. In a study o f changing stream s e d i ment loads in the Baltimore-Washington area, Wolman and Schick (1967) found that urban areas undergoing develo p ment produce far more sediment than rural a r ea s— between 2 and 100 tim es more. Roberts and Pierce (1974) found that the str ip p in g o f s o i l and v e g e ta tio n from areas o f d e v e l opment d ecrea ses i n f i l t r a t i o n and r e s u l t s in much higher sediment c o n c e n tr a tio n s in runoff to stream s. Another study by Guy and Ferguson ( 1963) showed that one square 57 urbanized m ile c r e a t e s l e v e l s o f stream sediment th at are e q u iv a len t to that from 100 square m ile s o f rural land. K eller (1962) i n v e s t ig a t e d the e f f e c t s o f con vertin g rural land to urban use in the Potomac Basin. He found a s i x fold in c re a se in suspended sediment disch arg e fo llo w in g u r b a n iz a t io n . Yorke and Davis (19 71 ), a lso in the Potomac Basin, found that the e f f e c t o f converting 15% of a small watershed from rural to suburban r e s i d e n t i a l was to in crea se sediment y ie ld for the e n t i r e watershed by a fa c to r o f fo u r tee n . And in t h e ir survey o f sediment y ie ld throughout the Susquehanna River Basin, W illiams and Reed (1972) working on a la r g e s c a l e , found that sediment y ie ld c o r r e la te d b e tte r with geology than with land use. However, they expressed a b e l i e f th a t sediment y ie ld was in c r e a sin g in the watershed in step with u rb a n iza tio n . In sum, i t i s probably a reasonable estim a te th at the conversion o f wooded land to c u l t i v a t i o n beginning in the e a rly 17th century increased f l u v i a l sediment disch arg e to the Chesapeake about t e n f o l d . This was the con clu sion reached by Wark and K eller ( 1963) in a study o f the e f f e c t s o f d e f o r e s t a t i o n and c u l t i v a t i o n in the Potomac River b a sin . Although a g r ic u lt u r a l s o i l co n serva tion p r a c t i c e s have improved in t h i s century, t h i s d ecrease in the stream sediment burden has been more than o f f s e t by urban ization and i t s r e s u l t a n t high sediment r u n o ff. 58 If one were to choose a date marking the t r a n s i t i o n from the long-term low sediment y i e l d s o f a fo re ste d watershed to the much higher sediment y ie ld o f a c u l t i vated watershed, th at time would be about 1720. This was the point when, according to F r i i s (1940) , the shores o f the bay and i t s t r i b u t a r i e s became e s s e n t i a l l y f i l l e d with s e ttle m e n ts (F ig . 11) and the population sta r te d to push westward beyond the r iv e r v a l l e y s and estuary sh o re s. From that time onward the sed im en tolog ic aging process o f the Chesapeake has a c ce le r a te d immensely, as w i l l be seen in Chapter 4. 59 Chapter II METHODOLOGY 2.1 FIELD METHODS i 2 .1 .1 Bottom Sediment C o lle c t io n | Sediment samples were c o l l e c t e d from the Rhode River j Estuary, Chesapeake Bay and Susquehanna River during the | |period July, 1977, to February, 1980. Sample l o c a t i o n s |fo r the Rhode River are shown in Figure 12, for the Chesa- ! I ! ! ! peake Bay in Figure 13, and for the Susquehanna River in j Figure 14. All o f the Rhode River samples were obtained using a I s p e c ia lly - d e s ig n e d p is to n -c o r in g d ev ice operated by a d i v e r . The p iston was secured by a s t e e l cable to a winch and d a v it on the Smithsonian I n s t i t u t i o n research boat R/V Blue Fox. The CAB core l i n e r , without a barrel and without catcher was guided in to the bottom at low v e l o c i t y by the diver to about a two-meter depth in the sedim ents. The p isto n was then fix ed in the l in e r and the e n t ir e coring apparatus winched up. Overlying water in the core 60 ; was nearly always c l e a r , and the topmost o x id ize d layer was present in a l l c a s e s . It was f e l t t h a t , for nearly a l l o f the cores c o l l e c t e d , the amount o f d istu rb an ce was minimal and the in t e r f a c e was r e tr ie v e d i n t a c t . ! ! The middle Chesapeake Bay samples were c o l l e c t e d using j Q i a 2500 cmJ grab sampler from the R/V Blue Fox. If the j | sample appeared to have washed during ascen t to the j i su r fa c e , i t was discarded and another was c o l l e c t e d . The ! | upper Chesapeake Bay samples lab eled "CB" (F ig . 13) were i | obtained in February, 1980, using a grab sampler from the j ! Johns Hopkins U n iv e r sity v e s s e l R/V EK W \ P r it c h a r d . All j other upper Chesapeake Bay samples were c o l l e c t e d with a j grab sampler and g r a v it y corer mounted on a Mar yland j G eological Survey Boston Whaler. All o f the Susquehanna River samples were r e t r ie v e d using the g r a v it y corer or grab sampler on the whaler. j Core samples were retain ed in the CAB core l i n e r s and grabs were sealed in Whirl-Pak bags. All samples were j placed in cold storage at 6 degrees C beginning on the day o f c o l l e c t i o n in order to minimize d e s s ic a t i o n and b a c t e r i a l growth. 61 Figure 12: Rhode River Estuary sample l o c a t i o n s . RHODE RIVER CORE SAMPLE LOCA TIO N S 1 0 0 0 0 > I I I I .1 1 0 0 0 ' 2 0 0 0 # sooo* J __________ I ARSH CR. • R R -M WEST RIVER 76 C 32 * 2'/t" CORES * 8 / 7 8 O 1)4* CO RES- 8 /7 8 • 1)4“ C O R E S - 7 / 7 7 ■ OTHER CORES 76° 31' I Figure 13 Chesapeake Bay cla y mineralogy sample l o c a t i o n s . 5UM J^EHRNNR _ R V ^ y CONOWINGO DAM PA MD H D G -5C C.B. BRIDGE 35-1AX-A RHODE > R I V E R /i^ W R -2A X -A — ; BP-AX CHE5RPERKE BRY CLRY MINERRLDEY 5RMPLE LDCRT1DN5 65 Figure 14: Susquehanna River and upper Chesapeake Bay sample l o c a t i o n s . 66 5U5QUEHRNNR RIVER RND UPPER CHE5RPERKE BRY 5RMPLE LDCRTIDN5 H A R R I S B U R G SR-1 THREE MILE ISLAND REACTORS - C O R E T M I - 2 A C O R E T M I - 1 A Y O R K H A V E N D A M G -1 S R - 2 - G - 2 - S R - 5 ' S R - 5 A S R - 4 SUSQUEHANNA RIVER r S R - 6 S A F E H A R B O R D A M C O R E S H - 2 - 1 ——^ C O R E , S H —2 - 2 — C O R E S H - 2 A S R - 7 + H O L T W O O D D A M \ rG _ 3 ^ S R - 8 A \ w / - SR -8B , X ? A / - G - 6 C ORE H - 3 PEACH BOTTOM REACTORS ^ G - 5 - G - 9 , G - 1 0 G - 1 2 - S R - 8 G - 4 P A MD g-7 r G - 8 J G - H CO RE C - 4 C O N O W I N G O D A M G - 1 3 V r G - l 5 G - 1 4 G-17 i CORE SF‘ 3 0 20 G - 2 4 kilom eters G - 2 0 • G - 2 3 S R - 9 ( G - 2 1 G - 2 2 ^ G - 2 7 G - 2 5 CORE E BALTIMORE CORE 3 8 — a. *- — 5R R B5 < 5 / 7 9 > • — ERRB5 < 9 / 7 9 > o — CQRE5 < S / 7 9 > 67 2 , 1 . 2 7-kHz P r o f i li n g and Sediment Probe Acoustic subbottom p r o f i l e s o f the Rhode River were recorded on four o c c a sio n s in July and November o f 1979. Dr. 0. P. Bricker o f the Maryland Department o f Natural Resources gen erou sly provided a Raytheon RTT-100A Survey System with 7-kHz and 200-kHz tra n sd u c er s. The PTR-106A tr a n s c e iv e r had a maximum output power o f 2 k i l o w a t t s , with a reported depth accuracy o f 0.5 p e r ce n t. No measu rable error in the depth or sediment th ic k n e ss readings was found when checked with a sediment probe. Locations at each turning point in the t r a n s e c t s ( f i g . 40) were determined by taking t h e o d o l i t e bearings on two or more o f a system o f th ree dozen survey markers th a t had been planted on the shores o f the estuary for t h i s o p e r a tio n . The two s e t s o f a c o u s tic t r a n s e c t s were separated by four months to see i f the diminished methane production in the sediments during the winter months would enhance the q u a lit y o f the r e c o r d s. No d i f f e r e n c e was n o tic e d , however. Maximum p en etra tion o f the a c o u s tic pulse was 14-15 m in both July and November. 68 A s t a i n l e s s s t e e l sediment probe, c o n s i s t i n g o f four 3-meter s e c t i o n s and four 1 . 5-meter s e c t i o n s with a pointed sampling t i p , was designed and constructed in order to make actu al measurements o f the th ic k n e ss o f r ecen t sediment above the T ertia ry sandstone bedrock. The probe was used at a number o f l o c a t i o n s throughout the estuary as a check on the accuracy of the a c o u stic p r o f i l e r . 2.1.3 F lu o r e s c e n t Sand Tracer Approximately 30 kg o f medium to coarse sand was dyed with rhodamine or anthracene dye, using methods developed by Pipkin and Stone ( 1972). Packets o f the dyed sand were spread over one-square-m eter patches o f the e stu a r y , using SCUBA, on various o c c a sio n s between 1978 and 1980. The experiment reported in Chapter 3 involved the spreading of dyed sand in e a rly September, 1979, j u s t prior to Hurri- cane David, and coring through the sand l a y e r - - a l s o by SCUBA— one month l a t e r . For some o f the sand patches another core was obtained nine months l a t e r . 69 2 .2 ANALYTICAL METHODS 2 .2 .1 Sedimentology 2 . 2 . 1 . 1 Percent Water and Percent Combustible All o f the Rhode River Estuary samples were subsampled by sco rin g the len g th o f the p l a s t i c l i n e r with a t a b le saw, and then c a r e f u l l y com pleting the cu ts with a sharp k n ife blade to avoid smearing. Half o f the core was saved in ja r s and the remainder used for a n a l y s i s . To determine the percent water and percent com bustible m a t e r ia l, one s p l i t was placed in c r u c i b l e s , immediately weighed and dried to con stan t weight in a 90 degree C oven. After a second weighing the com bustible f r a c tio n was removed by heating in a furnace at 550 degrees C for two hours. The sample was then re-weighed to determine the percentage o f com bustible m a t e r ia l. 2 . 2 . 1 . 2 S a n d -S iIt-C lay Another s p l i t - - a b o u t 8 g— was placed in d i s t i l l e d water, d isp ersed by hand and shaken. After s e t t l i n g 24 hours the s p l i t was w e t-siev e d through a 62-micrometer s i e v e . The f r a c t io n remaining on the sie v e was oven-dried at 90 degrees C and then weighed to determine percent sand. The sand was reta in ed for e le c t r o n and l i g h t microscopy and 70 for heavy mineral a n a l y s i s . The f r a c tio n passing the s ie v e was a lso dried and weighed and reported as percent f i n e s . This portion was kept for lead -210 a n a l y s i s . 2 . 2 . 1 . 3 Coulter Counter Samples for Coulter Counter a n a l y s is were ex tracted from the l e s s - t h a n 62 micrometer f r a c t io n in the fo llo w in g manner. Before the f i n e s were d r ie d , the volume o f the suspension was brought up to 300 ml and s t ir r e d r a p id ly . A p i p e t t e was immersed immediately and a 2 ml sample ex tr a cte d and placed in a v i a l . A c o r r e c tio n was made for the amount th at was removed. The 2 ml sample was further d ilu t e d with about 20 ml o f d i s t i l l e d water. O r ig in a lly , the samples were in j e c t e d at t h i s point with 30% hydrogen peroxide s o lu tio n and b o iled g e n t ly on a hot p la te o ver night to remove organic m ateria l before C o u lte r-c o u n tin g , thus enabling the comparison o f the mineral f r a c t i o n s a lo n e . This procedure was found not to make any s i g n i f i cant d i f f e r e n c e in the sample tex tu r e and thus was d is c o n tinued for the remaining samples. The suspended samples were analyzed on the Coulter Counter immediately or placed in a r e f r i g e r a t o r and run within two days. The f i r s t few s e t s o f samples were run on the counter with and without d is p e r s a n t , but chemical 71 d is p e r sio n was found not to be n ecessa ry for three r ea so n s. F i r s t , the io n ic c o n cen tra tio n within the Coulter Counter e l e c t r o l y t e , Isoton I I , was very c lo s e to that found in the Rhode River area o f the Bay. Thus, c la y f l o c c u l a t i o n e f f e c t s caused by changing the con cen tra tion o f the suspending medium did not occur. Second, a l l o f the samples were s t i r r e d throughout the counting procedure at a speed that was high enough to break up any i n c i p i e n t f l o e s . Third, the co n c en tr a tio n o f p a r t i c l e s in the s o l u tio n was kept extrem ely low to avoid c lo g g in g the Coulter apertu re. This had the added e f f e c t o f minimizing the chance o f c o l l i s i o n s between p a r t i c l e s and further d ecreasin g f l o c c u l a t i o n . All samples were run through both the 140-micrometer and 30-micrometer apertu res o f the counter, r e s u l t in g in two d i s t r i b u t i o n s o f percent t o t a l volume. One d i s t r i b u tio n covered the range from 56 micrometers to 2 .8 microme t e r s , and the other ranged from 12 micrometers to 0.6 m icrometers. Each d i s t r i b u t i o n r e s u lte d from a count o f at l e a s t 200,000 p a r t i c l e s . In order to combine the two d i s t r i b u t i o n s a program was w ritten to compare the overlap area, adju st the percentages and re-norm alize the combined d i s t r i b u t i o n . 72 Another program was then w ritten to perform s t a t i s t i c a l a n a ly ses o f the combined d i s t r i b u t i o n , to convert the micrometer diam eters to phi s i z e and to p lo t the percent t o t a l volume versus phi s i z e as a bar graph on the Calcomp P l o t t e r . The s t a t i s t i c a l parameters generated by the Coulter Counter program were then in s e r te d in a SIMPLOT program developed by Dr. S. Leroy, and various combina t i o n s o f the t e x t u r a l data were p lo tte d on the Calcomp P lo tte r to pick out s u b t le t e x t u r a l changes in both the v e r t i c a l and h o r iz o n ta l dim ensions. 2 . 2 . 1 . 4 X-Radiography Within a few days o f c o l l e c t i o n each o f the Rhode River c o res was x-radiographed using an i n d u s t r i a l x-ray u n it that had been modified to accomodate long cores i n t a c t . Industrex AA film was u t i l i z e d for i t s r e l a t i v e l y high speed and high c o n t r a s t . Since extruding and slabbing d is tu r b s core samples, the c o res were x-radiographed in the l i n e r . In order to avoid the edge d i s t o r t i o n blu rrin g caused by having the x-ray flu x pass through a non-uniform t h ic k n e ss o f sedim ent, an aluminum x-ray f i l t e r was designed and b u i l t . This f i l t e r , m odified from the o r i g i n a l design in Baker and Friedman (1 9 6 9 ), was a slab o f aluminum m illed to f i t the o u t s id e curvature o f the core l i n e r s . The r e s u l t s were 73 x-radiographs that were c o n sid era b ly b e t te r than without a f i l t e r , although not q u ite as sharp as the r e s u l t s produced by sla b b in g . 2 . 2 . 1 . 5 A n alysis o f 7-kHz P r o f i l e s All o f the records from the four f u l l days o f a c o u s tic p r o f i l i n g were p lo tte d on a la r g e mylar sh eet o v e rla y in g a bathymetric chart o f the e stu a r y . Depths to bedrock were read o f f the p r o f i l e s at regular i n t e r v a l s and tr a n sfe rr ed by hand to the mylar s h e e t . The r e s u l t was a p a le o -b a th y - m etric c h a r t. The buried P le is t o c e n e channels were then o u tlin e d and te r r a c e s were d e l in e a t e d . Volumes o f f i l l for the estuary and i t s variou s tr ib u ta r y arms were c a lc u la te d by assuming a regular grad ien t between tr a n s e c t p r o f i l e s and a lso assuming a V-shaped c r o s s - s e c t i o n for a l l ch a n n els. 2 . 2 . 1 . 6 D i g i t i z a t i o n o f H is to r ic Bathymetric Charts The changes in the e s t u a r y ’ s volume and su rface area over time were q u a n tifie d by an a n a ly s is o f the 1845, 1903, 1933 and 1972 bathymetric c h a r ts . The ch arts were photo g r a p h ic a lly reduced to the same s c a l e . Each chart was then contoured by hand at t h r e e - f o o t i n t e r v a l s . A M ini-Digi-Pad d i g i t i z e r was then used to compute the area w ithin each contour on each o f the four c h a r t s . By i n t e g ra tin g the areas over the depth i n t e r v a l s , volumes 74 r r e s u l t e d , the sum o f which gave t o t a l water volumes for i ■ the four periods in the e s t u a r y ’ s r ec en t h i s t o r y . The area l o s s for each o f the is la n d s was a lso d e t e r - j ! mined by the d i g i t i z a t i o n p r o c e ss. The change in area for i the estuary as a whole was converted to a net s h o r e lin e | volume l o s s by examining the U.S.G.S. topographic quadran g l e s for the area and reading the s h o r e lin e height at 100 m i n t e r v a l s . The approximately 300 p o in ts that r e su lte d were averaged and t h i s average h eigh t was m u ltip lie d by i the amount o f area l o s t to shore erosio n over tim e, in order to obtain the sh o r e lin e volume l o s s . 2 . 2 . 1 . 7 UV Photography o f F lu orescen t Sand Cores The samples cored through the f l u o r e s c e n t sand tracer areas were c a r e f u l l y s p l i t len gth w ise and photographed before d ry in g . Photos were obtained using Ektachrome d a y lig h t f ilm , a 40-Y f i l t e r and sh ort-w avelen gth u l t r a v i o l e t 1 i g h t . 2 . 2 . 1 . 8 D essicated Core Photography Three o f the cores from the c e n tr a l s e c t io n o f the estuary were s p l i t len g th w ise and allowed to dry u n t i l laminar cracks began to appear. The f u l l len g th o f th ese cores was then photographed to obtain a record o f the t o t a l 75 number o f sand lam in ae--th ought to r ep re sen t storm even ts — in the c o r e s . 2 . 2 . 1 . 9 Magnetic Stratigrap hy Most o f the Rhode River Estuary cores were analyzed for magnetic s u s c e p t i b i l i t y (X) and s a tu r a tio n isotherm al remanent magnetism (SIRM). All o f the a n a ly ses were carried out by Dr. F. O ld fie ld o f the U n iv e r sity o f L iver p o o l. The r a t i o n a le for th ese measurements i s d iscu sse d in O ld fie ld et a l . (1 9 7 9). S u s c e p t i b i l i t y i s the r a t io o f the m agnetization o f a sample to the i n t e n s i t y o f the magnetic f i e l d in which i t i s p la ced . It i s o fte n p roportional to the volume or c o n cen tra tio n o f ferrom agnetic o x id e s in a sample. S u s c e p t i b i l i t y was measured on a whole-core b a s is at the Smithsonian I n s t i t u t i o n Sedimentology Laboratory and on in d iv id u a l sample s p l i t s in L iverp ool. SIRM i s the m agnetization which remains a f t e r a sample has reached the sa tu r a tio n poin t w hile being exposed to an in c r e a sin g magnetic f i e l d at room tem perature. The SIRM/X r a t i o can o fte n be used to d is c r im in a te among d i f f e r e n t sources o f d e t r i t a l m a t e r ia ls . 76 2 . 2 . 2 Mineralogy 2 . 2 . 2 . 1 Clay M inerals--X-Ray D if f r a c t io n Subsamples for x-ray d i f f r a c t i o n were taken from each core in t e r v a l that was sampled for t e x t u r e . Approximately ; 2 grams o f sample was crushed and d isp ersed in a g l a s s jar ! | with about 200 ml o f d i s t i l l e d water c o n ta in in g 0.3% I sodium hexametaphosphate. The samples were e it h e r allowed to s e t t l e overn igh t or c en tr ifu g e d at 2000 rpm for 20 [ minutes and then decanted to remove d is s o lv e d s a l t s . This procedure was repeated and the sample was then resuspended in d i s t i l l e d water with d is p e r sa n t and allowed to s e t t l e o v e r n ig h t. I f no evidence o f f l o c c u l a t i o n appeared o v e r n ig h t, the sample was then resuspended and 1 ml o f the | f r a c t i o n fin e r than 2 micrometers was removed by p i p e t t e ia t a predetermined depth and tim e. Two pre-weighed one- inch square g l a s s s l i d e s were prepared with 1 ml o f the suspension on each. The s l i d e s were allowed to a ir -d r y and were weighed again to determine the amount o f sample l i jon the s l i d e . Sample weights were g e n e r a lly kept as c lo s e to 4 mg as p o s s i b l e . Experiments carried out at the Smithsonian Sedimentology Laboratory have shown th at t h i s i s n ecessa ry in order to prevent la r g e erro rs in the d i f f r a c t i o n process due to the masking of f a s t e r - s e t t l i n g i i 77 c la y s by s l o w e r - s e t t l i n g c la y s on the s l i d e mount (D. Robinson, personal communication). Each s l i d e was scanned on a Norelco Recording D i f f r a c tometer using fin e focus Cu Ka r a d ia tio n (wavelength 1.5418 A) at a p o t e n t i a l o f 35 KV and a current o f 15 MA. ‘ The f i r s t scan was from 2 degrees 29 to 35 degrees 29 at a scanning speed o f one degree per minute. A slow scan was a lso ca rried out on each sample, as suggested by Biscaye (1 9 64 ), at one-quarter degree per minute, from 24 degrees ! 29 to 26 degrees 29 in order to obtain b e tte r d e f i n i t i o n o f the overlapping k a o l i n i t e and c h l o r i t e peaks at 25 ;degrees 29. I The s l i d e was then g ly c o la t e d in a vacuum oven at low i jpressure for two hours at 60 degrees C. G ly co la tio n expands the m ontm orillon ite l a t t i c e , s h i f t i n g the 5 .2 jdegree 29 peak and making i t more e a s i l y d i s c e r n a b le . The I I vacuum oven was used in order to take advantage o f the low vapor pressure o f the e th y len e g l y c o l , as describ ed by Brunton (1 9 55 ). The g ly c o la t e d sample was run, g e n e r a lly w ithin two hours o f g l y c o l a t i o n , at one degree per minute between 2 degrees 29 and 10 degrees 29. 78 For each x-ray scan the area under s e l e c t e d peaks was measured using a Hewlett-Packard d i g i t i z e r and a HP 9820A computer. The peaks d i g i t i z e d on the untreated scan were the 1 0 .2A i l l i t e , the 7*1A k a o l i n i t e + c h l o r i t e and the 4.26A qu artz. The slow scan separated the 3 • 6A k a o l i n i t e and 3 • 5A c h l o r i t e peaks, which were then d i g i t i z e d . On the g ly c o la t e d scan the 7.1A k a o l i n i t e + c h l o r i t e , the 17A m o n tm orillon ite and 1 0 . 2A i l l i t e were measured. Any change in areas between the untreated and g ly c o la t e d scans was corrected by comparing the i l l i t e peaks. No weighting f a c t o r s were used, due to problems in v o lv in g inter-com par- ison among the variou s weighting schemes, as demonstrated by Pierce and S ie g e l (1 9 6 9 ). A background spectrum obtained by i r r a d i a t in g a blank g l a s s s l i d e was su btracted from each o f the above sc a n s. The peak areas were reported as r e l a t i v e p ercentages o f t o t a l d i f f r a c t e d i n t e n s i t y . 2 . 2 . 2 . 2 Heavy Mineral I d e n t i f i c a t i o n The sand f r a c t io n from a number o f the Rhode River core samples was allowed to s e t t l e through bromoform to sepa rate the heavy m inerals from the l i g h t o n e s. The heavy f r a c t io n was then run through a magnetic separator to further r e f i n e the se p a r a tio n s and a lso to q u a n tify the amount o f m a g n e tite . Each o f the s u s c e p t i b i l i t y groups 79 ! from the magnetic sep ara tion process was examined under a petrographic microscope and i d e n t i f i e d using p o la rized l i g h t . Two hundred to three hundred gra in s were i d e n t i fie d and counted in each sample. R esults were reported as percentages o f a l l gra in s counted. 2 . 2 . 2 . 3 Scanning Electron Microscopy and Energy D isp e r siv e XRF j The sand f r a c tio n o f a l l core sample s p l i t s was examined under a d i s s e c t i n g microscope in order to s e l e c t any unusual g r a in s or te x t u r e s th at might aid in determ ining provenance. A s e t o f the more unusual g r a in s was photo graphed under a scanning e le c tr o n m icroscope. Samples o f j i n t e r e s t from that group were then analyzed in an energy- i jd is p e r s iv e x-ray f lu o r e s c e n c e unit to determine the elem ental makeup for a few o f the unique m inerals and also I for some o f the more common m in e ra ls. i ! [ 2 .2 .3 Isoto p e Geochemistry 2 . 2 . 3 . 1 Lead-210 [Four cores were sampled for le a d -2 1 0 . S p l i t s o f approxi mately 2 g were taken from s e l e c t e d i n t e r v a l s in the c o r e s . Leaching and p la tin g o f the samples was carried I jout in accordance with methods developed in the U n iv e r sity i I i 80 | o f Southern C a lifo r n ia Geochemistry Laboratory (D. Hammond and C. F u lle r , personal communication). Each sample was leached with concentrated hyd rochloric and n i t r i c acid at 80 degrees C for 5 hours, during which time a polonium-208 ; spike o f known a c t i v i t y was added as an in te r n a l standard. After further d i s s o l u t i o n s in HC1 , the lead was plated onto a s i l v e r p la n c h e t t e . The p la n c h e tte was counted on : an alpha spectrom eter for 6 to 48 hours, depending on the a c t i v i t y . The areas under the Po-208 and Po-210 peaks were in te g r a te d and compared in order to determine the Pb-210 a c t i v i t y in the sample. i ! i | 2 . 2 . 3 - 2 Cs - 137 and Reactor Nuclides Samples from the Rhode River, Chesapeake Bay and Susque hanna River were prepared for gamma-counting by f r e e z e - |drying and canning in 100 cm^ aluminum cans. Counting was carried out at the U n iv e r sity o f Southern C a lifo r n ia and Lamont Geophysical Observatory by means o f l i t h iu m - d r if t e d germanium d e t e c t o r s and m ultichannel a n a ly z e r s. Counting time varied from 8 to 24 hours and c a li b r a t io n was based i on a National Bureau o f Standards environmental r a d io a c t i v i t y standard (#4 35 0). 81 [ 2 . 2 . 3 . 3 Carbon-14 j I All carbon-14 a n a ly se s were performed by Dr. R. Stucken- ; rath o f the Smithsonian Radiation Biology Laboratory, with j the ex ception o f Core LP. This core was analyzed by E. I j i Spiker o f the U. S. G eological Survey Radiocarbon Labora- ; tory in R eston, V ir g in ia . The radiocarbon a n a ly ses were carried out on organic muds, except in the c a ses where the sample was nearly pure peat. Samples were b o ile d in 2% NaOH to remove humic contam inants, and were then leached in 2N HC1 to remove ca rb on a tes. Ages were reported in terms o f years before present (BP), where present i s taken to be 1950. 82 Chapter II I EXPERIMENTAL RESULTS I ; 13.1 SEDIMENTOLOGY ! j i j ' 3-1.1 Textural Analyses i | 3 .1 . 1 . 1 S a n d -S ilt-C la y | I A s e t o f cores from head to mouth down the a x is o f the j J j |Rhode River estuary was s e le c t e d for t e x t u r a l a n a ly s e s, j | Core l o c a t i o n s are shown in Figure 12. A s a n d - s i l t - c l a y j determ ination was carried out in order to c h a r a c te r iz e the average sediment from d i f f e r e n t parts o f the e stu a r y . The e ig h t c o r e s — two from the head, f i v e from the main body o f j jthe estu ary and one from the mouth— are l i s t e d on Figure j 15, along with a ternary s a n d - s i l t - c l a y diagram. The diagram i s divided in to s e c t i o n s according to the method o f G orsline ( 1960) and a l l o f the s p l i t s from each core are p l o t t e d . It i s e v id en t from t h i s diagram that every sample from the mouth and main s e c t io n o f the estuary f a l l s under the cla y e y s i l t d e s c r ip t o r . Samples from the mouth (Core 38) are s l i g h t l y more s i l t y than those taken further u p -estu a r y . 83 The two cores c o l l e c t e d from the head o f the estuary (Cores 1 and 3-B) demonstrate a wider range o f t e x t u r e , but the m ajority o f the samples from th ese cores f a l l into the s a n d y - c l a y e y - s i l t ca te g o ry . Thus, on the b a s is o f th e ir s a n d - s i l t - c l a y proportions i t would appear that there i s a s i g n i f i c a n t t e x t u r a l d i f f e r e n c e between s e d i ments from the head o f the estuary and those c o l l e c t e d | further downstream. i 3 - 1 . 1 .2 Coulter Counter Analyses: Textural P r o f i l e s j In order to determine i f t h i s t e x t u r a l d i f f e r e n c e seen in | | the s a n d - s i l t - c l a y diagram is due to a d i f f e r e n c e in s e d i ment source a r ea s, a Coulter Counter a n a ly s is o f the fin e f r a c t io n ( l e s s than 62 micrometers) of each sample was ca rried o u t. This was n ecessa ry because o f the lo c a t io n o f the two anomalously coarse c o r e s , 1 and 3-B (Fig. 12). These co res were taken w ithin the narrow mouth o f Muddy Creek, the l a r g e s t stream tr ib u ta r y to the e stu a r y . On e it h e r bank at t h i s point are b l u f f s up to 6 meters high c o n s i s t i n g e n t i r e l y o f the sandy Upper Eocene Nanjemoy Formation. The frequent slumps from th ese b l u f f s would r e s u l t in a l o c a l c o n cen tra tio n o f sand, s in c e the t i d a l currents are not competent to tra n sp o rt sand but are able to winnow out the f i n e s . 84 Figure 15 S a n d - s i l t - c l a y percentages for Rhode River core samples. 85 ! j 1 0 0 % CLAY S Y M B O L C O R E N O . SA N D Y SILTY CLAY S IL TY CLAYEY S A N D S A N O Y C LA Y EY SILT S A N D S A N D Y SILT SILTY S A N D 100% SAND Consequently, i t was decided that a more meaningful t e x t u r a l comparison could be made among the fin e fr a c - t i o n - - t h o s e m a te r ia ls that are carried to the estuary f lo o r by t i d a l c u r r e n ts. Textural parameters obtained with the Coulter Counter are shown in Figures 16 through 23. | It can r e a d ily be seen that when the f in e fr a c t io n i s j examined ind ep en dently, the core from the estuary mouth, i 38, i s n o t ic e a b ly coarser than the o t h e r s . The average o f the mean phi v a lu e s for the upper estu ary cores ranges ; from 7*22 to 7*70, w hile the average o f the mean phi v a lu e s in Core 38 i s 6.98. When the sand f r a c t io n i s removed, Cores 1 and 3-B from the head o f the estuary are ; not n o t ic e a b ly d i f f e r e n t from those in the main body o f the e stu a r y . Core 38 may be more a f fe c t e d than the ; in n e r -e s tu a r y c o r e s by t i d a l tra n sp o rt o f Chesapeake Bay sediments in to the e stu a r y . | Another b i t o f inform ation th at can be e x tra cted from such data i s the presence o f storm d e p o s i t s . A combina tio n o f coarser grain s i z e (lower phi v a lu e s) and poorer so r tin g (higher s o r tin g v a lu es) at a c e r ta in l e v e l in a core may be the sig n a tu re o f a storm d e p o sit at th a t l e v e l . This combination occurs in Core 1 (Fig. 16) at | 5-11 cm and 130-140 cm, in Core 3-B (Fig. 17) at 5-11 cm 87 Figure 16: Textural parameters for Core 1 88 D E P T H I N C P R E < C M > Figure 17* Textural parameters for Core 3-B. 90 I J in in 3 a • n n k ? ID 2 : 9 • Z H h E 3 J > E P T H A I N c o r e : < CM > ta ta in ta ta i ta i ta ta VO — m j: m m m — -j hj m ta m la j : in m ta — m kj L d ta in ta — m *x hj In' in i 1 1 1 in in 3 A • m n 0 ID r • 2 \ l \ m Figure 18: Textural parameters for Core 13. CDRE 13 v ibb MEFIN — 5 . D . 5KEW. M E^N 5 .D . 5KEW. 7 . 0 B.0 I .HS 0.2 0.2 0 .H 0.0 93 Figure 19: Textural parameters for Core 16. 94 in in 2 n • n □ 3 3 zf • • z P E P T H 1 N C P R E < CM > H 1 - m is H K IS ts H 1 ------1 - IS cs H 1 - -I-----1 - I ts I ts V O Ln • • n m in — hj In h ts — ts X In ' m ts — m ki * U i is m ts — C D X * h J in' m in a n i i i i in n zi I □ Figure 20: Textural parameters for Core 19. 96 I j L. ... I O E P T H I N C O R E < C M > A Figure 21: Textural parameters for Core 21. 98 . I j O E T R T H I N C O R E < CM > ' V / vo vo Figure 22: Textural parameters for Core 30. 100 CDRE 30 / S ' . MERN 5.D. SKEW. M E ^ N 1 g . ' s 1 i ! b 1 V — H 7 . 5 -H -— i - B . 0 ~ b ! T 5 . D . 1 . 6 5 1 . 5 5 1 . H 5 1 . 3 5 1 . 2 5 S K E W . - 0 .H - 0 . 2 0 . 0 0 . 2 0 .H 101 A Z V v lit I t □ V 100. I I- D . U G 1 5 0 .. <> Figure 2 3 - Textural parameters for Core 38. 102 in m 3 7* • mi m c? ar r • z + -i- a P E P T H I N CDRET < CM > IS s m is is i ts i ts — m x m m M l — hJ M l BJ m E s a — # ♦ • f l ts x m M l ts — m k j L i kf m is — to !r L i ini m V ? in i 7S • n □ n u m o u > and 120-160 cm, in Core 13 (fig * 18) at 15-27 cm, in Core 16 ( f i g . 19) at 15-27 cm, in Core 19 ( f i g 20) at 2-7 cm., in Core 30 ( f i g . 22) at 38-50 cm, and in Core 38 ( f i g . 23) at 4-6 cm and 9-11 cm. The uppermost zones o f coarse te x tu r e and poor s o r tin g may be a remnant o f Tropical Storm Agnes in 1972. Although s c a t t e r w ithin the p r o f i l e s makes t h i s storm lay er in d ic a to r l e s s than t o t a l l y c o n c lu s i v e , a combination o f t e x t u r a l and other parameters w i l l enable the e stim a tio n o f storm e f f e c t s on sedim entation in Chapter 4. 3.1.1*3 Coulter Counter Analyses: S c a tter P lo ts By p l o t t i n g d i f f e r e n t combinations o f the t e x t u r a l moments r e s u l t i n g from Coulter Counter a n a ly s e s , d i s t i n c t d i f f e r ences between cores begin to appear. Taking three r ep re s e n t a t i v e c o r e s — Core 1 from the head, Core 21 from mid estu a r y , and Core 38 from the m o u th --it becomes obvious th a t Core 38 i s t e x t u r a l l y d i s t i n c t from the o t h e r s . Figures 24, 25 and 26 are p l o t s o f mean grain s i z e (in phi u n its ) versus standard d e v i a t io n , skewness and d e l t a , r e s p e c t i v e l y . Standard d e v ia tio n i s a measure o f the degree o f s o r tin g w ithin a sample. Figure 24 i n d i c a t e s th a t the sediments at the mouth o f the estu ary are s l i g h t l y more p o o r ly -so r te d than those from u p -estu a r y . 104 The so r tin g in a l l c a se s i s poor, however , owing to the low-energy environment o f d e p o s i t i o n . Skewness i s p lo tte d versus mean diameter in Figure 25. Samples from Core 38 at the estuary mouth are predominantly fin e -sk e w e d , that i s , the frequency curve i s asymmetric with a t a i l toward the f in e end. Samples from up-estuary are more nearly symmetrical or c o a rse -sk ew ed . Figure 26 shows the r e l a t i o n between mean diameter and d e l t a . Delta i s d efined as: 2K - 3( Sk2 ) - 6 K + where K i s k u r t o s is and Sk i s the r a t i o between the s o r tin g in the c e n tr a l portion o f the up -estuary are s l i g h t l y mor peaked d i s t r i b u t i o n s ) than tho 3 skewness. K urtosis measures in the t a i l s and the s o r tin g d i s t r i b u t i o n . Samples from e le p t o k u r t ic ( e x c e s s i v e l y se from the mouth. 105 Figure 24: Mean diameter versus standard d e v ia tio n for Cores 1 , 21 and 38. 106 MEAN DIRMETER V5 . STD. DEV I FIT I PN o = c o r e i < h e r d o f e s t u r r y > = CORE 21 < M 1D-E5TURRY > - + - = CORE 3B < MOUTH OF E5TURRY > CD T C D HETHD V ' 0 A < o CD ' " V J r T T -J-T-r T ~ r Oltc Lu MOUTH CD i = 20 1 , 40 SC SFRND. DEV. 107 Figure 2 5 : Mean diameter versus skewness for Cores 1, 21 and 38. 108 MERN \>IRMETER V 5 . 5KEWNE55 O = CORE I < HERD OF E5TURRY > = CORE 21 < M ID -E5TU R R Y > r CORE 3 0 < MOUTH OF EETURRY > n o C O o c r > r- o r\i i_> c g cr^c o o LG G HERD MOUTH - 1.01 -0 .6 0 SKEWNESS - 0.20 C. 20 0 . 60 109 Figure 26: Mean diameter versus d e lt a for Cores 1, 21 and 38. 1 10 MERN DIRMETER VS. DELTR C D = CORE I < HERD OF ESTURRY) = CORE 21 < M ID-E5TURRY > - 4 - = CORE 3B < MOUTH OF ESTURRY) MOUTH 1 1 1 3.1.2 Water and Organic Content P r o f i l e s o f percent water and percent i g n i t i o n l o s s are drawn for the e ig h t co res in Figures 27 through 3^» Percentages o f sand, s i l t and c la y are a lso p lo tte d alon g sid e th e se p r o f i l e s . In g e n e r a l, percent water and percent c la y seem to fo llo w the same trend , but th e re are some n otab le e x c e p t io n s , e s p e c i a l l y in the uppermost parts o f the c o r e s . This could be due to p a r t i a l drying o f the core tops a f t e r c o l l e c t i o n . Water conten t and percent l o s s on i g n i t i o n do not n o tic e a b ly dim inish with depth. This may imply th a t there i s no w e ll- d e f in e d mixing zone. Indeed, there i s no mixing zone evid en t in the lead -2 10 a c t i v i t y p r o f i l e s which are shown in a l a t e r s e c t io n o f t h i s ch ap ter. C erta in ly there i s l i t t l e mechanical m ixing, s in c e the estu ary i s m eso tid al and w e ll- p r o t e c t e d from most wave and wind d i r e c t i o n s . B ioturbation may be p r e se n t, but an i n v e s t i g a t i o n by D. J. Stan ley (Smithsonian I n s t i t u t i o n f i l e s ) im p lie s th a t i t i s not a major f a c t o r . S ta n le y 's r e s u l t s , reproduced in Figure 35, show th at bottom fauna— - e s p e c i a l l y burrowing worms— are sparse throughout the estu a ry and nearly n o n - e x is t e n t in the upper r ea c h e s. 112 Figure 27: Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 1. 113 C D R E — 5HND — CLHY 0 T 2 0 H 0 E 0 PERCENT 5 FIND PERCENT CLRY 114 PERCENT WHTER PERCENT L 0 5 5 □N IGNITION Figure 28: Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 3-B. 115 CORE 3-B i v u m □ v i h Q . U 5FIND CLRY 0T 100 " 10 \ \ PERCENT WPTER PERCENT LOGS □N IGNITION H I 1 ----1 ----1 h — 2 0 H 0 E 0 PERCENT 5 FIND PERCENT CLPY 116 Figure 29: Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 13* 117 D E P T H I N CDRE < C M > C O R E 1 3 ■ 5R N E > ■CLRY 0T 1 0 0 - H — I — I — I — I — I — I — h- H 0 5 0 E 0 10 PERCENT WRTER PERCENT L 0 5 5 2 0 H 0 E 0 PERCENT 5RND DN IGNITION PERCENT CLRY 118 Figure 30 Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 16. 119 CDRE IE 0T 20 H0 60 PERCENT 5 FIND PERCENT CLRY __________________ 12J2. PERCENT WRTER PERCENT L D 55 □N IENIT1DN Figure 31 Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 19. 121 CDRE 13 0T A 5 0 - H — I — I— I — I— I — I — I- M 0 £0 E0 IB PERCENT WRTER □N IENITIDN 5RND CLRY 20 H0 E0 PERCENT 5RND PERCENT CLRY 122 Figure 32: Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 21. BAND CLRY 0T 2 0 H 0 E 0 PERCENT 5RND PERCENT CLRY _______________ 124 PERCENT WATER PERCENT L 0 5 5 □N IENIT ION Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 30. C U R E 3 0 -5R N D -CLRY 0T 1 0 0 - 70 H a B 0 PERCENT SRND PERCENT CLRY 126 3 G 3 12 PERCENT LOSS □N IGNITION PERCENT WRTER Figure 34: Percentages o f water, i g n i t i o n l o s s , sand, s i l t and c la y for Core 38. 127 C U R E 3 B 5RND CLRY 0T A 5 0 - 100- ■ \—i—i—i—i—i—i—h- H 0 5 0 5 0 7 0 PERCENT WRTER 2 0 H 0 6 0 PERCENT SRND PERCENT CLRY 128 PERCENT L 0 5 5 DN ISNITIDN In g eneral there i s l i t t l e d i f f e r e n c e in water conten t and i g n i t i o n l o s s between th e se cores and co re s c o l l e c t e d from the northern Chesapeake Bay by Hirschberg and Schubel (1 9 7 9 ), or cores taken from the southern Chesapeake ( B ig g s, 1963; Harrison et a l . , 1964). The portion o f the i g n i t i o n l o s s th a t i s due to organic carbon may be estim ated from F o lg e r ’ s ( 1972) com p ilation o f Che sapeake sediment da ta. Reported organic carbon v alu es increased from 0 . 3% at the mouth to 2.7% at the 1 atitu d e o f the Rhode River, to 4.9% near the head . Folger a ttr ib u t e d the higher v a lu e s near the head o f the bay to the presence o f upper Susquehanna River coal in the bottom sediment t h e r e . 129 igure 35: Rhode River Estuary bottom fauna. RHODE RIVER BENTHIC FRUNR 2000 3000 F T sniTH JO N iA rJ P I E R $ 1 n p t f* e q b b c r v c p ] RMPH1 POOS 3 PPLYCHRETES r 3 OTHER WORMS < ? 0 1 SOPODS ~ n S i SETS RNEMDNE5 3 OTHER RNI MRUS 3 CRRBS.*,,,,i > ^ — *\ 3-1.3 Core D e s s i c a t i o n : Sand Laminae Three cores from the main s e c t io n o f the e s t u a r y — Cores 13,16 and 19— were s p l i t len g th w ise and h a l f o f each core was a i r - d r i e d . This was done to t e s t the h y p o th e sis th at sand lam inae— i n d ic a t o r s o f storm d e p o s its --w o u ld be p r e f e r e n t i a l areas for d e s s i c a t i o n cracks to occu r. This would be expected because sand g r a in s are l e s s c o h e siv e than c la y s and sand la y e r s would thus be more l i k e l y to y ie ld to the t e n s i o n a l s t r e s s o f d e s s i c a t i o n than would c la y l a y e r s . D eposits o f sand are obvious in only a few p la c e s in the percent sand p r o f i l e s (F igures 27 to 3^) . This may in part be due to the f a c t th a t sand la y e r s are r e l a t i v e l y th in and as a r e s u l t the m ajority are not d e te c te d at the sampling in t e r v a l used. Some o f the l a y e r s were d e t e c t e d , as can be seen from a comparison o f the p r o f i l e s in Figures 27 to 3^ with the photographs o f the d e s s ic a t e d cores in Figure 36. The inform ation in Table 5 i n d ic a t e s th a t the number of laminae seen in each o f the th ree cores i s r ea so n a b le . Table 2 showed a recurrence i n t e r v a l o f approximately 7 years for major storms in the Susquehanna area. Since the 132 Susquehanna watershed drains 71,225 sq .km ., i t can be assumed th a t not a l l o f the storms recorded in the Susque hanna area have a se d im e n to lo g ic e f f e c t on the Rhode River Estuary. It would be reason ab le to assume th a t h a l f o f the storm s--app roxim ately one every 14 y e a rs--m ig h t a f f e c t the estu a ry in a s i g n i f i c a n t way. Assuming a sedim enta tio n ra te between 10 and 15 mm/yr (se e S ection 3 -3 - 2 .1 of t h i s c h a p t e r ) , Table 5 dem onstrates th at the number o f laminae in each core i s a reason able approximation o f the number o f storms during the period represented by the len g th o f the co re . TABLE 5 CORE DESSICATION DATA Core No. 13 16 19 O riginal len g th (cm) 142 161 172 Number o f complete laminae 12 17 20 Predicted number o f la m in a e ^ ^ 10-20 12-23 12- 1. Assuming 14-year storm i n t e r v a l and 5-10 mm/yr sedim entation r a t e . 133 Storms thus seem to have some e f f e c t on the Rhode River sediment lo a d . The sand laminae probably r e s u l t from storm ero sio n o f the sandy s h o r e l i n e s , concurrent with an in c r e a se in f l u v i a l sediment input to the e s tu a r y . The lam inae, however, do not appear to be very t h i c k , as w i l l be noted in the s e c t io n on x-radiography below. 134 Figure 36: Core d e s s i c a t i o n photographs: Rhode River Cores 13 5 16 and 1 9 CORE R R - 1 6 CORE RR-19 -OS- CORE RR-1 3 C O R E RR-1 6 CORE RR-19 CORE RR-19 CORE RR-1 6 - 1 5 0 - 3.1.4 Magnetic S tra tig ra p h y Most o f the Rhode River co re s shown in Figure 12 and some o f the Susquehanna River co res in Figure 14 were analyzed for magnetic s u s c e p t i b i l i t y . Dr. F. O ld fie ld o f the U n iv e r sity o f Liverpool performed a l l o f the magnetic s u s c e p t i b i l i t y and remanent magnetism measurements d is c u sse d below. D e t a ils on measurement tec h n iq u es are given in Chapter 2. Magnetic s u s c e p t i b i l i t y p r o f i l e s for 18 cores w ithin the Rhode River estu a r y are shown in Figure 37. Two char a c t e r i s t i c s o f th e se curves are important: the magnitude o f the s u s c e p t i b i l i t i e s and the p o s it io n o f the s u s c e p t i b i l i t y peaks. For most co re s there i s a d ecrease in s u s c e p t i b i l i t y down c o re . The magnitude o f the s u s c e p t i b i l i t y in the upper p arts o f the co re s i s s im ila r to that seen in watershed s o i l samples and in the suspended s e d i ments carried in the streams o f the catchment area. Some o f th e se s o i l and stream su sp en sate samples are d ep icted in Figure 38. Also p lo tte d in t h i s fig u r e are s u s c e p t i b i l i t i e s for su b s tr a te m a t e r ia ls o f the w a tersh ed --th e sandy T ertia ry bedrock--which are g e n e r a lly lower in magnetic mineral co n ten t and thus lower in s a t u r a tio n isotherm al remanent magnetism. 139 Based on the s u s c e p t i b i l i t y l e v e l s i t would appear that the more r ec en t sedim ents in the upper estuary (for example, Cores 1, 3-B, 13 and 16) are derived from watershed s o i l s with t h e i r high proportion o f secondary fe r r im a g n e tic o x id e s . Older sedim ents, in th e-lo w er parts o f th e se c o r e s , seem to have a d i f f e r e n t sou rce, probably the low -iron bedrock. The bedrock weathering m a t e r ia ls can r e s u l t e it h e r from shore e ro sio n w ithin the e stu a r y or I d i s s e c t i o n o f the watershed. Sim ilar r e s u l t s in other s t u d i e s (Bloemendal et a l . , 1979; Thompson e t al . , 1975) in d ic a t e th a t th e se down-core s u s c e p t i b i l i t y v a r i a t i o n s are not the r e s u l t o f in. s i t u o x id a t io n - r e d u c t io n e f f e c t s on the ferru g in o u s m inerals in the sedim ents. The s u s c e p t i b i l i t y p r o f i l e s o f co res from the main body o f the estu a r y (for example, Cores 19 and 20) appear to be the r e s u l t of a d i f f e r e n t sediment regime than those nearer the head. Figures 27 through 34 show the t e x t u r a l p r o f i l e s for e ig h t o f the cores whose s u s c e p t i b i l i t i e s are p lo tte d on Figure 37. The s u s c e p t i b i l i t y peaks g e n e r a lly c o in c id e with c la y peaks for upper estuary cores (Cores 1, 3-B, 13 and 16), implying th a t s o i l - d e r i v e d c la y s are the lo cu s for the magnetic m inerals in th e se c o r e s . 140 On the other nand, for cores from the lower h a l f o f the estu ary (Cores 19, 21 and p o s s ib ly 38) the s u s c e p t i b i l i t y peaks g e n e r a lly c o in c id e with sand and s i l t peaks. Most o f the magnetic m inerals in th ese cores are in the s i l t - sand f r a c t i o n , implying that bedrock weathering (shore e r o s i o n ) , rather th a t s o i l e r o s io n , i s the major c o n t r i b utor o f sediment to the lower h a l f o f the e stu a r y . Another l i n e o f evidence p o in ts to a bedrock source for the sediments in the lower h a l f o f the e s tu a r y . Measure ment o f s a tu r a tio n isotherm al remanent magnetism and s u s c e p t i b i l i t y has been carried out for s i n g l e samples on some o f the c o r e s . P lots o f th e se measurements (not shown) g e n e r a lly f a l l in the lower l e f t quadrant o f Figure 38. This i s true o f the e n t i r e len g th o f Core 5A, p o s s ib ly a l l o f Core 38, and the portion o f Core 3B-1 below 112 cm. In summary, a study o f the magnetic parameters i n d i c a te s th at bottom sediments in the main body and lower h a l f o f the estu ary d e r iv e from bedrock e r o s io n . S ed i ments in the area o f the head o r i g i n a l l y had a s im ila r sou rce, but beginning at some point in the r ec en t past s o i l erosion products have come to predominate in the bottom sediments th e r e . 141 Figure 37 : Magnetic s u s c e p t i b i l i t y p r o f i l e s for Rhode River Estuary c o r e s . 142 MRBNET(C BUBCEF'T I B I L I TV C D H E I B - B f f l S E i i 3 -fl CORE 13 CORE l-B SB SB SB SB SB SB IBB ISB ISB ISB ISB ISB ISB ISB - 16A ■16 B flgs 1 3 S B OW E i-w SP R E 3-P IBB 5B SB SB SB IBB ISB ISB ISB ISB 3A, 3 - B AA CORE 2 - g Q3RE 26 SB -2 C -A SB SB 2C ISB ISB ISB 5 a SB SB IBB ISB ISB ISB SB " C O R E S - 8 78 ” C O R E S - 8 78 ISB WES T RIVER ■ OTHER CORES 143 Figure 38: Magnetic parameters for Rhode River watershed sa m p le s . 5RTURRTIDN I5DTHERMRL REMRNENT M R E . /\ T C D 0 ^ 'i 300T V O B0 0 ■ 7 0 0 - E 0 0 ■ 3 0 0 • H00 3 0 0 ■ 2 0 0 100 0 0 RHODE RiVER WRTER5HED 5ED i MENT 5RMPLE5— MRENETIC PRRRMETER5 5YMRDL5 5 D IL -D E R I VED U=PR5TURE 5TREHM SEDIMENT GsCORNFIELD 5TRERM SEDIMENT M=MUDDY CR. 5TREHM SEDIMENT BEDRDCK-DERIVED F=FURE5T 5TRERM SEDIMENT X=PH5TURE 5UB5TRRTE 5RMPLE5 3 10 13 2 0 2 3 3 0 S P E C IF IC S U S C E P T IB IL IT Y 145 3 . 1 . 5 X-Radiography All o f the Rhode River cores were x-radiographed w ithin a few days o f c o l l e c t i o n . Typical examples are shown in Figure 39. Most o f the co re s were found to absorb x - r a d i - atio n uniform ly along t h e i r e n t i r e len g th ( e . g . , Cores 18, 27 and 3 0 ). S h e lls and s h e l l fragm ents, u s u a lly not in growth p o s i t i o n , occur at random ( e . g . , Cores 16A-1, 16A-2, and 2 0 ) . In some co re s sand l e n s e s - - p o s s i b l y due to storm s--and laminae can be seen ( e . g . , Cores 2A, 2C, 16A-1, 19 and 3 8). It would appear that i f la m in a tio n s are p r e se n t, they are th in and do not presen t enough o f a d e n s ity c o n tr a s t to be rev ealed by x -ra y . The homogeneous character i s f a i r l y t y p i c a l o f upper Chesapeake Bay sedim ents. X -radi- ographs o f cores taken by Hirschberg and Schubel (1979) c lo s e r to the head o f the bay were f e a t u r e l e s s , save for a l i g h t e r la yer near the to p , which they a t tr ib u t e d to Trop i c a l Storm Agnes of 1972. It was o r i g i n a l l y hoped that x-rad iograp hs o f the Rhode River co re s might r e v e a l storm l a m in a e - - p a r t i c u la r l y major storms l i k e Agnes— that would be c o r r e l a t a b l e between c o r e s . Such i s not the c a s e . There seem to be no s t r u c tu r a l s i m i l a r i t i e s between one core and another. The same r e s u l t was obtained in a second study by Schubel and Hirschberg (1 9 7 8), a lso on Chesapeake Bay core samples. Pairs o f cores taken from the same place at the same time e x h ib ite d no c o r r e l a t a b l e s t r u c t u r e s that were e v id en t to the eye or x -r a y s . D espite the homogeneity, the x-radiographs would i n d i cate a minimum o f b i o t u r b a t i o n . No worm tubes can be seen in any o f the x-rad iographs nor on the su rfa ce o f the c o r e s , and s h e l l s o f burrowing m ollusks appear only o c ca s i o n a l l y in the x-ray r e c o r d s. No worm tubes nor mollusks in growth p o s i t i o n were found in any o f the fre sh cores when sampled. A b e tt e r exp lan a tion for the homogeneity, rather than b io tu rb a tio n , i s the low-energy environment, supplying a f a i r l y c o n s ta n t-te x tu r e d low -organ ic clay ey s i l t to the bottom throughout the year. 147 Figure 39: X-Radiographs o f Rhode River Estuary Cores. 148 ' V AUG'7 8 RHODE R. STN 2 7 J r - U D R H D D E R I VETR CORET X — RRO I D E R R P H 5 0 CM STN 2 0 STN 1 9 M O CM AUG'7 8 RHODE R STN 19 EXP 85 ui o RHDOEZ R I VER C D R E X - R R O I D E R R P H 5 151 3 . 1 . 6 7 -K iloh erz P r o f i l i n g and Sediment Probe A coustic sub-bottom p r o f i l e s were obtained by running t r a n s e c t s throughout the e stu a ry and in the area adjacent to the mouth. P r o f i li n g d a tes were June 22, 1979, July 3-6, 1979, and November 19-20, 1979. In a d d it io n , an e a r l i e r s e t o f 7-kHz t r a n s e c t s o f the estu a ry was run on April 24, 1974, by Dr. D. J. Stanley and Dr. H. D. Palmer. The e a r l i e r s e t was made a v a i la b l e for the p resen t study and i s combined with the 1979 data in the d is c u s s io n b elow . 3 . 1 . 6 . 1 Paleobathymetry Track l i n e s for a l l o f the a c o u s tic surveys are drawn in Figure 40. Many o f the l i n e s were re-run a number o f tim es at d i f f e r e n t s e t t i n g s o f g a in , s e n s i t i v i t y and chart speed, in order to minimize the d i f f i c u l t i e s involved in o b ta in in g high q u a lit y r etu r n s through m ethane-rich s e d i ments in the r e l a t i v e l y sh a llo w water o f the e s tu a r y . A sediment probe was used as a spot check on the accuracy o f the depth recorded by the a c o u s t ic p r o f i l e r . P r o f i l e s for the la b e le d c r o s s - s e c t i o n s o f Figure 40 are shown in Figure 41. The records revea l deep channels i n c is e d in the sandy T ertia ry bedrock o f the e s tu a r y . At the estu ary mouth th e se channels are about 13 m below 153 p resen t sea l e v e l , or approximately 10 m below the present estu ary f l o o r . Throughout most o f the main s e c t io n o f the e stu a ry the paleo -ch an n el depth i s 10-12 m below p resen t sea l e v e l ( F ig . 41, c r o s s - s e c t i o n s W-V and N-P). In some t r a n s e c t s t e r r a c e s can be seen at -2 m to -3 m (F ig . 41, c r o s s - s e c t i o n s F-G and C-H). In the upland areas o f the northern and western parts o f the e stu a r y , p aleo-ch an n el depth d im in ish es to about 4 m below presen t sea l e v e l . Figure 42 i s a sk etch map r ec o n str u c ted from a l l o f the 7-kHz p r o f i l e t r a n s e c t s in Figure 40. The map shows, with a v e r t i c a l ex ag geration o f about 50x, the Rhode River as i t probably appeared about 7,000 years BP. As might be e x p ected , the r e l i e f was g r ea ter and the drainage more complex during the f l u v i a l ( l a t e Wisconsin) phase than e x i s t s in the e s t u a r in e phase today. The Rhode River had many more t r ib u t a r y stream s, some as high as f i f t h - o r d e r . As an example, between Sand Point and Locust Point on the southwest po rtion o f the estu a r y ( F ig . 42) the sub bottom p r o f i l e s rev e a l an i n t r i c a t e network o f small branching stream s. The only topographic evid en ce o f th ese streams today i s a s e r i e s o f sm a ll, almost i n d i s t i n g u i shable notches in the th r ee -m e te r -h ig h e r o s io n a l scarp that borders the estu a ry between the two p o in t s . 154 The a c o u s tic data a lso provide evid en ce th at two of the is la n d s were part o f a s i n g l e r id g e , th a t the th ird isla n d was once a much la r g e r topographic high, and that the watershed was being more a c t i v e l y d i s s e c t e d than i t i s at p r e se n t. The r a is in g o f the r i v e r ' s base l e v e l during the l a t t e r h a l f o f the Holocene marine tr a n s g r e s s io n has ar re sted fu rth er development o f the r i v e r ' s drainage system and has co m p letely f i l l e d the channels o f a l l but the l a r g e s t stream s. 3 . 1 . 6 . 2 Volume o f F i l l Due to the un usually high d e n s ity o f 7-kHz t r a c k s , the volume o f e s t u a r in e sediment f i l l i n g th e se p a le o -ch a n n els can be computed with high accuracy. The t r a n s e c t s ( f i g . 40) provided the depth at the middle o f each c r o s s - s e c t i o n , plus the width o f the p aleo-ch an n el . To compute volumes only two assumptions were r e q u i r e d : a V-shaped c r o s s - s e c t i o n for the channels and a co n sta n t gra d ien t from one c r o s s - s e c t i o n to the n e x t. The f i r s t assumption i s reason a b le s in c e the area was o b v io u sly in a youthful sta g e o f stream development immediately p rior to f i l l i n g . The second assumption i s j u s t i f i a b l e for the same reason, and a ls o because the underlying bedrock through which the streams were eroding had a n ea rly co n sta n t l i t h o l o g y , dip and r e s i s t a n c e to e r o s io n . Since the 7 kHz u n it produces no usable records in depths l e s s than 1 m, i t was further 155 assumed th a t the unsurveyed shallow p o r tio n s o f the estu a r y were covered with a blanket o f sediment whose t h ic k n e s s decreased uniform ly with d is ta n c e from a c h a n n e l. Volumes o f f i l l were computed for the e n t i r e Rhode River west o f a l i n e between Dutchman Point and Cheston Point ( f i g . 12). This volume included Cadle Creek, Sellman Creek and the Mouth o f Muddy Creek. Volumes were as f o llo w s : Sediment f i l l in p a le o -ch a n n els F i l l on banks and t e r r a c e s Total sediment f i l l , Rhode River Estuary 1.126 x 107 m3 0.485 x 107 m3 1.611 x 107 m3 156 Figure 40: A coustic sub-bottom p r o f i l i n g t r a n s e c t s , Rhode River Estuary. 157 1/2 RHODE RIVER I O O O I O G O KHZ TRRN5 ECT 5 158 Figure 41: 7 - k ilo h e r z records for c r o s s - s e c t i o n s in Figure 40. Depths in f e e t . 159 K Z & x m sn ss i & r m m m TTT 3 . 1 . 6 . 3 Compaction E f f e c t s To convert th e se volumes to t o t a l mass o f sedim ent, i compaction must be taken in to account. Some dewatering must take place under a burden o f as much as 13 m o f j f in e - g r a in e d sedim ent, but the magnitude o f t h i s water l o s s i s p r o b le m a tic a l. The water c o n ten t p r o f i l e s ( F ig s . 27 to 34) extend two m eters in to the sedim ents and show only minor changes in water conten t with depth. Average for a l l samples from a l l cores i s approxim ately 58% water, on a wet weight b a s i s . The reason for the absence o f any d is c e r n a b le dewa t e r in g in the upper two m eters o f sediment i s undoubtedly the rapid sedim entation r a t e , to be d is c u s s e d l a t e r in t h i s c h a p ter. In Santa Barbara Basin, C a l i f o r n ia , the mean sedim entation ra te i s n early an order o f magnitude l e s s . Emery and R ittenberg (1952) produced a g e n e r a liz e d curve o f water con ten t versu s depth with data from a 526 cm Santa Barbara Basin c o re , plus w e l l - l o g data down to 1,500 m in the Los Angeles Basin. I n te r p o la t in g from t h e ir d a ta, and taking the d i f f e r e n c e in sedim entation r a t e s in to account, one would expect approxim ately a 48% water co n ten t at the bottom o f the t h i c k e s t la y e r s o f channel f i l l in the e s t u a r y — 13 meters down. 162 Figure 42: P r e -e stu a r in e Rhode River v a l l e y and Chesapeake Bay, c . 7»000 B .P .: r e c o n s tr u c tio n from 7-kHz a c o u s t ic p r o f i l e s . 163 j ■ ■ * i t i p " iJ ■ m { i V |K \m I . c \ m % a / m , > ' « V>. k j i - - . / r ' ; ■ O • ■ ^ . * . s i y ^ : \ >— r x L .& m ’ > • \ f y ' S''-"''*' N U r " " [, p -V | S u siju th iin 'ia Hiver Sjrste*n I % » M '• - • \ : ■ ■ ;• 7 / 0 0 0 5 .F . PHE-ESTUHR I NE R H C 30ET R I VCR VALLEY RNO CHESAPEAKE BAY— RECQNSTRUCTEP F “ROM V— KM2: PROF I LES . HPOERN SHPREL 1 N E T SHOWN BY DHSHE5 . VERT i CRL SCALE EXABBERATED . J>EPTH O F * PPLEOCHRNNEL RT MOUTH I H M BELPW PRESENT MSL * S N5ET SKETCH SHOWS SUSQUEHANNA R I VER RN£> PROTD-CHESRPERKE SHY SYSTEM . HRROW I Ni> I CATES LOCPTIPN O F * RHP1>E RIVER. 164 Given the geometry o f the estu ary filT ^ Tess~~tTian h a l f o f the t o t a l volume o f the sedim ents are deep enough to be s i g n i f i c a n t l y a f f e c t e d by compaction. As noted above, 0.485 x 10^ or 30%, o f the sediment i s on shallow banks and t e r a c e s and th e r e fo r e uncompacted. Assuming a t r ia n g u la r c r o s s - s e c t i o n , another n ea rly 30% o f the volume o f a f i l l e d channel 13 m deep would be in the upper uncom pacted 2 m eters. This r e p r e se n ts 30% of the 70% of the e stu a r y f i l l that i s in ch a n n els, or 21% of the t o t a l f i l l . Thus, at l e a s t 51% of the t o t a l f i l l i s not su b je c t to any compaction at a l l . This i s a minimum e s t im a t e , s in c e not a l l o f the f i l l in channels i s in 13 m deep c h a n n e l s . Making the s im p lif y in g assumption, however, th a t 49% of the estu a r y i s 2 m or more below the su rfa ce o f tr ia n g u la r channels 13 m deep, the weighted average percent water for t h i s f r a c t i o n o f the f i l l , based on Emery and R itte n b e r g 's ( 1952) d ata, i s 55%. For the mass computation, then 51% o f the f i l l i s assumed to contain 58% water by w eight, and the remaining 49% i s assumed to co ntain 55%. The f i n a l weighted average for a l l sediments i s 56.5% water by w e i g h t . 165 3 . 1 . 6 . 4 Mass o f sediment f i l l Average grain d e n s ity o f Rhode River Estuary sedim ents i s taken to be 2.7 g/cm . This v a lu e , with l i t t l e v a r i a t i o n , was reported by Harrison e t a l . (1965) for a la r g e number o f Chesapeake Bay bottom sediment sam ples. Assuming an average s a l i n i t y o f 10 parts per thousand for the pore water, the d e n s it y o f t h i s water i s 1.009 g/cm3 . I f water r e p r e s e n ts 56.5% of the wet weight o f the estu ary f i l l and sediment i s 43.5%, then the t o t a l mass o f sediment f i l l i n g the estu a r y i s found by: % S x V Mass (sedim ent) = % W % S + ___ Dw Ds where V = Total volume o f f i l l % S = Weight percent sedim ent, wet % W = Weight percent water Ds = Sediment d e n s ity Dw = Water d e n s ity Thus, the t o t a l mass o f sediment f i l l i n g the e stu a r y i s 0.435 x 1.611 x 107 m3 0.565 + 0.435 177X39 g7"cm3 2.70 g/cm3 9.72 x 109 kg 166 In other words, a mass o f sediment equal to about 9*72 x 10^ has been d e p o site d in the estuary s in c e the t r a n s g r e ss in g p o s t g l a c i a l sea r a ised the r i v e r ’ s base l e v e l and dim inished the a b i l i t y o f the Rhode River to export s e d i ment through the mouth. This q u a n tity w i l l be used in the next and l a t e r s e c t i o n s to examine the change in sediment r a t e s over time and to e stim a te how much o f the sediment e n ter in g the e stu ary i s r eta in e d th e r e . 3 . 1 . 7 Comparison o f H is t o r ic Bathymetric Charts, 1845-1972 The National Ocean Survey and i t s p r e d e ce sso r s have carried out bathym etric surveys o f the Rhode River e stu ary on four o c c a sio n s: 1845, 1903, 1933 and 1972. The r e s u l t i n g ch arts are shown in Figures 43 to 46. By reducing a l l o f the ch a r ts to the same s c a le and d i g i t i z i n g the area w ithin each bathymetric contour, i t i s p o s s i b l e to compute volumes and su rface areas for the estu a ry at the time o f each survey and to determine the e x te n t o f shore e ro sio n over the 127-year p erio d . 3 . 1 . 7 . 1 Shore Erosion Much o f the s h o r e lin e l o s s has occurred on the southwest shore o f the e stu a r y , as seen in F igures 43 to 46 The c l i f f s between Cheston Point and Sand Point have receded 167 TABLE 6 AREA LOSSES FOR ISLANDS, 1845-1972 18450Area ( m2 ) 1972 Area ( m2 ) 1845-1972 Loss(m ) % Loss 1845-1972 Big Island 55,443 52,555 2,888 5 .2 F lat Island 11,331 5,376 5,955 52. 6 High Island 6,091 2,609 3,482 57.2 as much as 60 m. Slumping o f the 3-m eter-h igh c l i f f s has created a wide shoal at t h e ir base. Cheston Point i t s e l f has r e tr e a te d by 50 m. Dutchman P o in t, on the n o r th e a st s id e o f the estu a r y mouth, has accreted s l i g h t l y to the westward, and a la r g e shoal has developed southwest o f i t . Locust Point has receded about 40 m on i t s north s i d e . (A ll geographic l o c a t i o n s are shown in Figure 12). The is la n d s have su ffer ed severe l o s s e s , p a r t i c u l a r l y F lat Island and High Isla n d , whose so u th e a st s h o r e l in e s have r e tr e a te d at l e a s t 50 m. Big Is la n d , the b e s t - p r o te c te d from so u th e a st wind and waves, has l o s t the l e a s t area. The areas in Table 6, taken from the 1845 and 1972 c h a r ts , show th a t the three is la n d s have l o s t substance in rough proportion to t h e ir d is ta n c e from the mouth. 168 Figure 43: 1845 bathymetric c h a r t, Rhode River Estuary. * 4 iV Jlg U ---- v O \ o to v> v e X k'* u t o a*t)- D- / » X * ^ X t X • ^ to v \ V J VO \\ v i T _ v ^ ' fl> v A \1 v o RHODE RIVER 1.70 I Figure 44: 1903 bathymetric c h a r t, Rhode River Estuary. 171 * •ft to • f t ¥ , m 3 4 2 * * !***& * * . 4 t V o / i - r t '2 / « i r t R IVER 1303 Figure 45: 1933 bathymetric c h a r t, Rhode River Estuary 173 «U>. <3ii A W /v * Tar*»\ L*llfc Octih CARR WHF 7i « ! ! « . - . * a 0 0 8 0 8^8 « 3 ? i 3 8 9 Sj5 3 / y K > . . ,* 3 » a * . v d r i f t , , ? * £ . «A , . j K f O ^ v w Jm ^ * V • * f '/Ti ' * 9 • * 'y<W i *£& £»»» • * \ f «- r t d y V & i A ' i ««»'•» « » j j i .TNv' A ' * * * • » • » »s» " » » u!* i ’ 9 ’ 9 " • * V » ’ L 'i A l a »’• » 59 93 . « • » » * • • » 9 • » • 9 » » » » » 7 » » I & I SS» 9 W W » » « {« J' ' , . . . . . . , . . . . . . . , , 9 i V j i 9 « . » r i . T . i 8 I I ? i {% '* ■ * * 3*0 0 0 0 8 • «0 • 0 B H 9BB91 - ** «000 • • CONTEER WHF * , , , 9 sl»»« s , ;,9 < \ &r rV i \ \ v iSWi • „ . N ab I *V r» Vlayo FU i rw t C wa • n m % * 3. • • » •• 7 3 * < * s '. 1 * * • B • # * i **. A ’ r' ‘ A. /'A-J'fl f v f . r . v * j ' ■ i *»*« • * « " •* * 1 , 1 •** * * 0 - * ft • • •. * \ vv«: * > / ,w X “i I * * 7 * » * * * *1 /; ‘ t«3 s i i . »r* „ * * M I J S , »»*■. * fc * i 4 i * * * I ^ \ V a J ? ' V * ’ d^v s 9 * * * J » » 0 “ * 1 * \ \C X k > H -r-_ ; . a * 4’ ‘ 5 > » ' » n ; \ . ,. J \ y s ‘ » J — o< ! 1 'I t '1’ 1 t i 1 < ’ 31* • * » ^ *v ^ r ' i==< * ‘ * i 1 i < ’ • '“JL ‘ s *-fc 1 1 i 6 1 * > ; i » I ! - • — \ f i \ \ \ I ; I t Li \j lid1 ’; ; ; , 7 ‘ > 1 a — » I * L V . ' r * w * « " l • ~ i J 3 Um t ' 3 ’ i . 1 v » i i ?; 3 : > * * ’ • • t / i 3 \ i“ * s ’ i • t « — * R!VER !933 Figure 46: 1972 bathymetric c h a r t, Rhode River Estuary. i 175 s * . \ . ' ■ ; i >. RHODE RIVER I 3 7 2 RHODE RIVER 1 76 Table 7 shows the e x te n t o f the changes in the e s t u a r y ’ s su rfa ce area and volume during the period . Surface area has in crea sed by 5-9%, due p rim a rily to shore e r o s io n . The mass o f sediment eroded from the s h o r e lin e i s computed as f o l l o w s . The area o f the m a ter ia l eroded i s obtained by taking the d i f f e r e n c e between the e s tu a r in e su rface area in 1972 and that in 1845. (Sin ce most o f the e s t u a r y ’ s s h o r e lin e i s an e r o s io n a l scarp and th e r e fo r e n ea rly v e r t i c a l , a c o r r e c tio n for change in area due to sea l e v e l r i s e i s not n e c e s s a r y ) . To convert t h i s area to a volume, the average s h o r e lin e h e ig h t was found by reading the e le v a t io n at 100-meter i n t e r v a l s along the s h o r e lin e on the 1:24,000 USGS to p o graphic maps o f the e s tu a r y . The n ea rly 300 read in gs were averaged. The r e s u l t a n t volume was converted to mass by assuming a bulk d e n s i ty o f 2.5 g/cmJ for the s h o r e lin e m a t e r i a ls . This was the value measured by Biggs (1970) for a sim ila r p r o je c t in the northern Chesapeake Bay. A range o f bulk d e n s i t i e s between 1.65 and 2.50 g/cm^ i s reported for p o o r ly -so r te d sandstones by C h ilin g aria n and Wolf (1 9 7 5 ). Thus, use o f B ig g s ’ value may produce a mass l o s s th a t i s s l i g h t l y h ig h . The r e s u l t s are shown in Table 8. 177 TABLE 7 HISTORIC CHART DATA, RHODE RIVER ESTUARY Chart Year 1845 1903 1933 1972 % Change Surface Area ( m i ll i o n sq. m.) 4.58 4.74 4.90 4.85 +5.9 Actual Water Volume ( m i ll i o n cu. m.) 10.88 11.96 10.61 9.84 - 9 . 6 Sea Level Rise Since 1845 (mm) 0 .0 191.4 290.4 419.1 Volume Reduction for Sea Level Rise Since 1845 ( m illio n cu. m.) 0 .0 0.907 1.423 2.033 Adjusted Net Volume ( m i ll i o n cu. m.) 10.88 11.05 9-19 7.81 - 2 8 .2 Mean Chart Depth (m) 2 .4 2 .5 2 .2 2 .0 - 2 0 .0 Mean Depth a f t e r Adjustment for Sea Level Rise (m) 2 .4 2 .3 1.9 1.6 - 3 3 .0 178 TABLE 8 ESTUARINE SHORELINE LOSSES, 1845-1972 Sh orelin e Area Loss, 1845-1972 2.70 X 105 m2 Sh orelin e Length, 1972 (estu a r y shore plus is la n d s ) 2 8 .0 km Average R ecession Rate 7 .6 cm/yr Average Sh o relin e Height 1 .35 m S h o relin e Volume Loss 3. 64 X 1 o5 m3 S h o relin e Bulk Density 2.50 g/cm J Total Sh orelin e Mass Loss 9. 10 X 108 kg Annual Mass Loss, 1845-1972 7.16 X 106 kg/yr Annual Mass Loss/m o f Sh orelin e 2. 56 X 102 kg/yr/m The f i n a l fig u r e in Table 8 agrees with th a t obtained in an i n v e s t i g a t i o n by Singewald and Slaughter (1 9 4 9 ). In th a t study the 1845 and 1933 bathym etric ch a r ts were compared . Only about o n e -th ir d o f the Rhode R iv e r f s s h o r e lin e was exarnined--the portion n e a r e st the mouth, and th e r e fo r e most s u s c e p t i b l e to e r o s i o n . Their r e s u l t s , then, are biased toward the high s id e and g iv e an e ro sio n o rate o f 5.98 x 10 kg/yr/m , about 2 .3 tim es the ra te given in Table 8 179 ______ _ The e r o sio n ra te given by Singewald and Slaughter (19^9) for Anne Arundel County s h o r e l in e s as a whole i s 2 8.55 x 10 kg/yr/m , or 3.3 tim es the r a te given above. This se r v e s to point up the f a c t th a t d e s p it e the immense l o s s o f s h o r e lin e and e x te n s iv e i n f i l l i n g over the 127-year perio d , the Rhode River i s com paratively w e l l - p rotected and i s l o s i n g s h o r e lin e at a slower rate than other l o c a l e s t u a r i e s . The Chesapeake Bay-wide average e ro sio n r a te given by the same authors i s 1.20 x 10 kg/yr/m , or 4 .6 tim es the r a te determined in the present s t u d y . 3 . 1 . 7 . 2 Volume Changes and Sediment Accumulation, 1845-1972 As seen in Table 7» the a ctu a l water volume o f the estu a ry has dim inished by nearly 10% in 127 y e a r s, t h i s d e s p it e a l o c a l 3 .3 mm/yr rate o f sea l e v e l r i s e . When the in c re a se in volume th at i s due to sea l e v e l r i s e i s deducted, the net volume l o s s due to sediment i n f i l l i n g sin c e 1845 i s found to be over 28%. At th a t ra te o f f i l l i n g , i f sea l e v e l were suddenly to become s t a b l e , the estu a ry would f i l l co m p letely in l e s s than 350 y e a r s. Referring again to Table 7, the amount o f sediment added to the estu a r y f lo o r can be determined and an e s t i mate made o f the accumulation r a t e . The bathym etric 180 charts ( F ig s . 43 to 46) show s i g n i f i c a n t sh o a lin g o f about 1 m in the e n t i r e Muddy Creek mouth area. The estu a ry as a whole has shoaled by an average o f 0.4 m. Subtracting out the e f f e c t o f the 3*3 mm/yr sea l e v e l r i s e , t h i s quan t i t y doubles to j u s t over 0 .8 m o f sh o a lin g in 127 y e a rs. Sediment accumulation in the estu ary during t h i s period i s computed as f o llo w s : Volume o f Sediment Added, 1845-1972 3*07 x 10° m3 Mass o f Sediment Added (assuming 56.5% water, by weight) 1.88 x 10^ kg Annual Sediment Mass Input, 1845-1972 1.48 x 10^ kg/yr Sedim entation Rate (based on 1972 area) 4.98 mm/yr This l a s t value assumes a uniform sedim entation ra te over the e n t i r e su rfa ce o f the e stu a r y , which i s undoubtedly not the c a s e . Rates probably vary l o c a l l y by about a f a c to r o f th ree or more, as w i l l be d is c u sse d in the s e c t io n d e s c r ib in g lead -2 10 p r o f i l e s l a t e r in t h i s c h a p t e r . 3.1.8 F lu o re sc en t Sand Tracer Coarse sand dyed with rhodamine or anthracene f lu o r e s c e n t dye was spread, using SCUBA, in a number o f o n e-sq u a re- meter patches throughout the estu a r y on the morning o f 181 September 5 , 1979. This was j u s t a few hours prior to the on set o f T ropical Storm David. The storm brought heavy r a i n f a l l to the northern Bay area and high t u r b i d i t y to the Rhode River Estuary. A rain gauge w ithin the Rhode River watershed recorded 10.8 cm o f p r e c i p i t a t i o n for September 5 . The day a f t e r the storm a dense sediment plume was observed moving out o f the mouth o f Muddy Creek in to the upper e s tu a r y . Six o f the sand patches were cored by SCUBA on October 3, 1979. Three o f the cores were lo c a te d in the lower h a l f o f the estu a r y and show a la y er o f n ew ly -d ep osited sediment ranging in th ic k n e s s from 1.8 to 2.8 cm, which accumulated over the one-month period (fig. 47). Three o f the c o re s were near the head o f the e s tu a r y . One d isp la y ed a t h ic k n e s s o f 2.4 cm o f new sedim ent. In the other two the dyed sand was mixed to as much as 3-9 cm. The mixing was probably accomplished by high flood current v e l o c i t i e s , s in c e both o f the mixed cores were taken from shallow ( 0.3 m) water in a c o n s t r i c t i o n near the mouth o f Muddy Creek. In a l l o f the co re s the la yer above the f l u o r e s c e n t sand i s thought to be predominantly new s e d i ment, s in c e the p r o te c tio n that the estu a r y enjoys from waves and wind tends to minimize resu sp en sion o f bottom m a t e r i a l s . 182 Some o f the sand patches were again cored nine months l a t e r , on July 11, 1980, to determine how much a d d it io n a l sedim entation had occurred during t h i s sto r m -fre e i n t e r v a l . Four o f the October, 1979, co re s and two o f the July, 1980, cores are shown photographed in u l t r a v i o l e t l i g h t in Figure 48. The October core from Bear Neck Creek, BN-1 , has a zone o f tr a c e r sand down to 17.0 cm. The zone has the shape o f a clam burrow, which may e x p la in i t s o r i g i n . No measurable change in sediment t h ic k n e s s above the sand la yer i s o b serv ab le between October and J u l y . 183 Figure 47: F lu o rescen t sand tra c er core l o c a t i o n s and r e s u l t s . 184 1/2 RHODE RIVER DEPCSITION DUE to Hurricane David, 9 /6 / 7 9 - 1 0 / 3 / / 9 , BASED ON FLUORESCENT _ $4NP BAR K ER BEES. IO O O 3 0 0 0 F T . IOOO ] LORE PH-1: NEW DEPOSITION 1 , 9 CM Core J : m ix e d LAYER 0 . 0 - 3 , 9 CM Core CC-1: new DEPOSITION / Core M: m ix e d LAYER 0 . 0 - 1 . 0 CM DEPOSITION C M Corf P ? - 5 : DEPOSITION CM 185 r Figure 48: UV photograph o f f lu o r e s c e n t sand c o r e s , taken 10/3/79 and 7 /1 1 /7 9 , fo llo w in g Hurricane David ( 9 / 5 / 7 9 ) . 186 FLUDRE5CENT 5RNO TRRCER CDRE5 c o r e : c p r e C O R E S CC-I C O R E S SN-I M C — I U ~ 1 I I / 7 S 7 / S 0 ! I / V S 7 / 0 0 1 I / V S { I / V S < :M - ----------------- 0 0 " ■ J 3 .2 MINERALOGY 3 .2 .1 Clay M in erals— X-Ray D i f f r a c t io n Cores and grab samples for x-ray d iffr a c to m e tr y were c o l l e c t e d from the Rhode River Estuary, the northern Ches apeake Bay and the lower Susquehanna River. Sampling methods, a n a l y t i c a l procedures and mineral i d e n t i f i c a t i o n methods are d escrib ed in Chapter 2. All numerical data for in d iv id u a l m inerals are given in terms o f percent d i f f r a c t e d i n t e n s i t y — that i s , the percent o f the t o t a l scanned peak area rep resen ted by the c h a r a c t e r i s t i c peak for a given m in era l. This method fo llo w s the su g g e s tio n o f Pierce (1974) th a t r e l a t i v e d i f f r a c t e d i n t e n s i t y adequately r e f l e c t s tren d s without r e s o r t in g to one o f the dozens o f a r b itr a r y schemes for w eighting the areas o f d i f f e r e n t peaks in the d if f r a c t o g r a m . The numerical data given in t h i s s e c t io n r ep r e se n t the unfactored area under the peaks and can be compared with published data by m u ltip ly in g by the d e sir ed f a c t o r . Sample l o c a t i o n s are shown for Rhode River samples in Figure 12, for Chesapeake Bay samples in Figure 13 and for Susquehanna River samples in Figure 14. 188 3 * 2 .1 .1 Rhode River Estuary Bottom Samples All o f the core samples analyzed for te x tu r e in Section 1.1 of t h i s chapter were a ls o su bjected to x-ray d i f f r a c - tometry o f the l e s s - t h a n 2 micrometer f r a c t i o n . Montmo- r i l l o n i t e , i l l i t e , quarts and k a o l i n i t e + c h l o r i t e were the only m inerals d e te c te d in the core samples in grea ter than tra c e amounts. Appendix A l i s t s the d i f f r a c t e d i n t e n s i t i e s for a l l samples. Of t h i s s u i t e o f m in e r a ls, m o n tm o rillo n ite and i l l i t e convey the most in form a tion . Quartz does not c o n s t i t u t e more than 1% of the t o t a l | d i f f r a c t e d i n t e n s i t y in any sample. K a o lin ite + c h l o r i t e always t o t a l 11% or l e s s and e x h i b i t l i t t l e v a r ia t io n e it h e r a r e a l l y or with depth. For e ig h t o f the cores lo c a te d on Figure 12 a p r o f i l e o f m o n tm o rillo n ite and i l l i t e v a r ia t i o n with depth i s shown in Figure 49. In a l l o f the Rhode River Estuary ; samples m ontm orilIonite c o n s i s t e n t l y accounts for 75-90% of the t o t a l d i f f r a c t e d i n t e n s i t y , w h ile i l l i t e remains w ithin the 0-15% range. Both m in e r a ls, however, fo llo w a I d e f i n i t e trend down the e stu a r y as well as a l e s s w e l l - d e fined v a r ia t io n with depth. In a l l but one c o re , #30, i l l i t e in c r e a s e s and m o n tm o rillo n ite d e c r e a se s downcore . This v a r ia t io n may in d ic a t e a s l i g h t p ro p o rtio n a l change 1 in the components o f the e s t u a r y 1s sediment budget over 189 tim e, the i m p l ic a t io n s o f which w i l l be taken up in Chapter 4. The down-estuary change i s more pronounced. The mean percentage o f d i f f r a c t e d i n t e n s i t y for m ontm orilIonite d e c r e a se s from 88.4% in Core 1 at the head o f the estu a r y to 81.6% in Core 38 at the mouth. I l l i t e d e c r e a se s down- e stu a ry from 3-5% in Core 1 to 9.4% in Core 38. These v a r i a t i o n s are p lo t t e d on the l e f t h a l f o f Figure 50. 190 Figure 49 V e r t ic a l v a r ia t io n o f m o n tm o rillo n ite and i l l i t e in Rhode River Estuary c o r e s . 191 MDNTMDR I LLDN I TE < — > + I LL I TE < — PERCENTRGE5 IN RHODE RIVER CDRE5 CORE 100 \ m MONT B0 MONT 0 0 es CORE 13 CORE IE £ 0 100 100 MONT 0 0 M O ML3NTMDR 1 LLDN I TE < — > + ILLITE < — PERCENTREE5 IN RHDDE RIVER CDRE5 CORE 13 CORE 21 \ m MONT B0 MONT B0 3 0 BE 3 0 CORE 3 0 CORE 3B 100 3 0 MONT B0 3 0 193 MONT B0 IL L . E BE Figure 50: Areal d i s t r i b u t i o n o f mean m o n tm o r illo n ite and i l l i t e v a lu e s for c la y f r a c t i o n o f a l l cores and grabs: Rhode River, Chesapeake Bay and Susquehanna R iv e r . 194 RHODE R . /CHEERPERKE CLRY MINERRLS 5PL NOS 3 0 - • 30 -• 2 rA H 70 2 o E0 3 | 5 0 n r n H 0 2 n 3 0 - 2 0 - a /V 2 2 2 2 2 2 2 2 2 2 0 0 3 22 222 22 2 22P 12 I — Id----------hi Id U lh J ! 2 tn | rcnuitD—s m o—x ? u m lAririrArAfA mmmmmm whJhj— m tn x su ih j | s U i v L l MONT . MONT . ** 22 * ■ 23 " 2H u r \ *■ 20 n H " I 3 " I 2 a * * H n v£> L n 3 H < WEST > £ > I 5TRNCE 2 0 20 H0 30 30 I 00 FROM RHODE R I VSR E5TURRY 1 20 I H0 1 30 < NORTH > MOUTH < KM > 3 * 2 .1 .2 Rhode River Estuary Suspended Sediments Data on suspended sediment m ineralogy for the estu a r y are a v a i l a b l e in Hearn (1 9 8 0 ). Although Hearn's study ! involved the s i l t f r a c t i o n as w ell as the c l a y s , the same down-estuary tren d s are d is c e r n a b le in the m o n tm orillon ite and i l l i t e p e r c e n ta g e s . M ontm orillonite percentage i s | i j g r e a t e s t near the head or upper h a l f o f the e stu a r y , w hile i j i l l i t e in c r e a s e s in percentage from head to mouth. Hearn I i | (1980) found th at bottom grab samples follow ed a s im ila r j : trend and a t tr ib u t e d the d i s t r i b u t i o n to a mixing of i l l i t e - r i c h Chesapeake Bay water and m o n t m o r illo n it e - r ic h ! j Rhode River water. j | 3 * 2 .1.3 Rhode River Watershed S o i l s and Suspended Sediments j Information on the c la y mineralogy o f the s o i l s and stream j ! ! | suspended sedim ents o f the Rhode River watershed was | compiled by Podany (1 9 8 0 ). He found th at s o i l m ineralogy ; changed l i t t l e with depth in the p r o f i l e . Watershed [ su sp en sate m ineralogy, w hile varying with season and flow r a t e , n e v e r t h e l e s s was always s i g n i f i c a n t l y d i f f e r e n t in m ineralogy from the e s t u a r in e bottom sediments or sh o re l i n e samples as presented in t h i s paper. Podany's (1980) i c la y m ineralogy d ata , converted to percent d i f f r a c t e d j i i n t e n s i t y , are included and la b e le d in F igures 51 and 5 2 . ! 3 . 2 . 1 . 4 Rhode River Estuarine S h orelin e Mineralogy As mentioned in Chapter 1, the Upper Eocene Nanjemoy Formation com prises the major part o f the e s t u a r y ’ s sh ore l i n e — v i r t u a l l y a l l o f the southern, western and northern i boundary o f the Rhode River ( f i g . 4 ). A sample o f the Nanjemoy taken from a fr e sh ly -e x p o s e d outcrop in the bank jbetween Sand Point and Locust Point was su b jected to x-ray a n a l y s i s . This sample i s included in Appendix A and i s p lo t t e d in Figures 50 to 52. It can e a s i l y be seen th at the estu a r y s h o r e lin e r ep re - j | s e n ts an extreme in the sample p o p u la tio n . The percent | d i f f r a c t e d i n t e n s i t y o f m o n tm o rillo n ite for t h i s sample i s j i j ! 91%, w hile i l l i t e r e p r e s e n ts only 3%• As reported p r e v i- i o u sly in t h i s c h a p te r, the estu a r y s h o r e lin e i s reced in g j at a rapid r a t e - - 7 « 6 cm/yr on the average, and l o c a l l y by ; as much as 50 m in 127 y e a r s. The s h o r e lin e then, which seems to be a major item in the sediment budget, p o s s e s s e s ! c la y m in erals th a t appear in uniquely i d e n t i f i a b l e proper- j i t i o n s . I | 3 . 2 . 1 . 5 Clay Mineralogy o f Chesapeake Bay Samples The Rhode River c l a y s , and e s p e c i a l l y those from the s h o r e l i n e , d i f f e r s i g n i f i c a n t l y from bottom samples taken from the Chesapeake Bay i t s e l f . The d i f f e r e n c e becomes | more and more obvious as one t r a v e l s the 95 km north j i 197 I ' towards the source o f more than h a l f o f the northern b a y ’ s s e d im e n t--th e Susquehanna River. Sample l o c a t i o n s are shown in Figure 13. Appendix A !l i s t s the x-ray d i f f r a c t i o n data for the l e s s - t h a n 2 micrometer f r a c t i o n . Moving outward from the mouth o f the Rhode River, the f i r s t th ree samples (WR-2AX, 35-1AX and ! i BP-AX) are at approxim ately the same l a t i t u d e as and p r o g r e s s i v e l y more d i s t a n t from the mouth. All three e x h i b i t d i f f r a c t e d i n t e n s i t i e s th a t are lower for montmo- r i l l o n i t e and higher for i l l i t e than any o f the Rhode River cores ex cep t for Core 38 at the mouth ( f i g . 5 0 ). These th ree samples are in turn higher in m ontm orillo- f ! n i t e and lower in i l l i t e than the e n t i r e s e t o f samples going up the a x is o f the bay towards Havre de Grace : (sample numbers CB-25, CB-24, CB-20, CB-16, CB-12, CB-6 and CB-1). All o f the samples are q u a n tif ie d in F igures 50 and 51. The r e l a t i o n s h i p between m o n tm o r illo n ite and k a o l i n i t e + c h l o r i t e , p lo t t e d in Figure 52, a ls o se rv e s to emphasize the d i f f e r e n c e between Rhode River Estuary s e d i ments and those from e it h e r the Rhode River watershed or the Chesapeake Bay. 198 3.2.1.6 Susquehanna River Clays The Susquehanna River samples from Figure 14 th a t were analyzed for c la y m ineralogy were numbers SR-1 , SR-3, SR-4 and SR-3. The e f f e c t o f the varying l i t h o l o g y along the course o f the Susquehanna i s r e f l e c t e d in the g r e a te r s c a t t e r among the Susquehanna samples in Figures 51 and | 52. N e v e r th e le s s , i t i s obvious from th e se two f ig u r e s ! and Figure 50 th a t the Susquehanna River c la y s are minera- l o g i c a l l y s im ila r to Chesapeake Bay c la y s but s i g n i f i c a n t ly d i f f e r e n t from Rhode River c l a y s . This i s not a su r p r is in g r e s u l t , s in c e the e s t im a t e s o f the percentage ! o f Susquehanna sediment th a t i s permanently trapped north I o f the Bay Bridge range as high as 90% (B ig g s, 1970). Figure 51 Clay m ineralogy o f Rhode River, Chesapeake Bay and Susquehanna River: i l l i t e v s . m o n tm o r illo n ite . 200 MDNTIiDR I LLDN I TE V5 . ILLITE 3 0 •• B 0 " y \ r - 7 0 Z a j J E0 t r □ r j: s b z □ z H0 H V 0- 3 0 20 • 10- RHODE RIVER 5H 0RELINE RHODE RIVER CORES U . L . X . T . R . C . 5 . NEHRBY CHESHPERKE BRY UPPER CHESRPERKE RND 5U5HUEHRNNR R RHODE RIVER WATERSHED .UPPER RHODE RIVER CORE 5RMPLE5 .LOWER RHODE RIVER CORE 5RMPLE5 . RHDDE RIVER SHORELINE MRTERIRL .RHODE RIVER WRTER5HED 5TRERM SEDIMENT .NERRBY CHESRPERKE BRY SEDIMENTS .UPPER CHESRPERKE BRY SEDIMENTS . 5U5QUEHRNNR RIVER SEDIMENTS IB 2 0 3 0 P C T . ILLITE HB EB 201 Figure 52: Clay m ineralogy o f Rhode River, Chesapeake Bay and Susquehanna River: k a o l i n i t e + c h l o r i t e v s . m o n t m o r illo n it e . 202 j MONTMORILLONITE V 5 . KROL. + CHLOR 00 •• 3 0 B0 t U h - 7 0 Z □ J J E0 K □ * 5 0 Z □ I H0 h V II 3 0 20 • 0 RHODE RIVER SHORELINE RHODE RIVER CORES NERRBY CHESRPERKE BRY UPPER CHESRPERKE RND SUSHUEHRNNR R . t c j s RHODE RIVER WRTER5HED U . L . X . T . R . C . 5 . UPPER RHODE RIVER CORE 5RMPLE5 LOWER RHODE RIVER CORE 5RMPLE5 RHODE RIVER SHORELINE MRTERIRL RHODE RIVER WRTER5HED 5TRERM SEDIMENT NERRBY CHESRPERKE BRY SEDIMENTS UPPER CHESRPERKE BRY SEDIMENTS SUSHUEHRNNR RIVER SEDIMENTS 0 2 0 3 0 H0 P C T . KROLINITE + CHLORITE £0 203 3*2.2 Sand F raction Mineralogy All o f the Rhode River bottom samples were w e t-sie v e d into f r a c t i o n s g r e a te r than and l e s s than 62 m icrom eters. The coarse f r a c t io n for s e l e c t e d samples was analyzed in three ways to find out i f the sand had any unique c h a r a c t e r i s t i c s th a t might corroborate some o f the other l i n e s o f evid en ce as to sediment s o u r c e - - n o t a b le the magnetic j s u s c e p t i b i l i t y and the c la y m ineralogy. The th ree a n a l- i i | y ses were: a heavy m ineral d e te r m in a tio n --u s in g a p o la r - j iz in g m icroscope and magnetic s e p a r a t o r - - o f samples from the to p , middle and bottom o f Cores 2B, 3B-1and 5A (se e Figure 12 for l o c a t i o n s ) ; scanning e le c t r o n m icroscopy I (SEM) of samples from Cores 1, 19 and 38; and energy | d i s p e r s i v e x -ra y f lu o r e s c e n c e o f some o f the SEM sam ples. i 3 . 2 . 2 . 1 Heavy M inerals | Sand samples were taken from the top (0-15 cm), middle j (30-60 cm) and bottom (100-130 cm) of the th ree c o r e s . i Between 200 and 300 g r a in s were i d e n t i f i e d in each o f the nine sam ples. The p e r ce n ta g es r ep r e se n t the com position j o f the 200-300 g r a in s th a t were counted for each sample. ! | As such, they have l i t t l e q u a n t i t a t i v e s i g n i f i c a n c e , and j r e f l e c t on ly g eneral trends in m ineralogy. Percentages ) for each m ineral are given in Table 9. The l i n e la b e le d 204 'O th e r s’ in c lu d e s a l l o f the opaque m in erals (other than m agnetite and i l m e n i t e , which were i s o l a t e d by magnetic s e p a r a t o r ) , rock fragm ents, m in erals appearing only in tr a c e amounts (such as p y r i t e ) , and u n i d e n t i f i a b l e m i n e r a l s . The heavy m ineral s u i t e i s dominated by g l a u c o n i t e , a hydrous potassium iron s i l i c a t e . Although not always reported as a heavy m in era l, i t s d e n s it y - - e n h a n c e d , perhaps, in the e s t u a r in e environment by i r o n - r i c h c o a t- - ings and i n f i l l i n g s - - w a s g r ea t enough to keep i t from ! f l o a t i n g during the heavy l iq u i d s e p a r a tio n . I t s abun- ; dance in the sedim ents r e f l e c t s i t s abundance in a l l o f j I the T e rtia ry rocks th a t outcrop in the watershed and s h o r e lin e o f the e s t u a r y . G lauconite i s a major c o n s t i t uent o f the Eocene Nanjemoy Formation ( f i g . 4) and o f the i underlying Paleocene-Eocene Aquia Formation. Both o f the ■ form ations are sometimes r efe r r e d to in the l i t e r a t u r e as ! i ! greensands due to t h e i r high g la u c o n it e c o n te n t. j j j i I Other heavy m in erals appearing in g r e a te r than tra ce ; amounts are m a g n e tite , ilm e n it e and z ir c o n . The m agnetite ! (Fe^ 0^ ) and ilm e n it e (Fe Ti 0^ ) are both high in I s u s c e p t i b i l i t y and may in part be r e s p o n s ib le for the I j shape o f the s u s c e p t i b i l i t y curves in S e c tio n 3*1*4, e sp e-j j c i a l l y Core 2B ( f i g . 3 7). As mentioned p r e v io u s ly ,! 205 - I however, the magnetic s u s c e p t i b i l i t y o f the sediments seems to be c o n t r o lle d p rim a rily by m inerals in the fin e f r a c t i o n . All o f the heavy m in era ls l i s t e d in Table 9 were a ls o i d e n t i f i e d by Drobnyk (1965) in a study o f the Maryland I Eocene , although he found p r o p o r tio n a te ly more leucoxene j ! :and p y r i t e . Many o f the zircon g r a in s , as w ell as some o f the g arn ets and to u r m a lin es, were eu h ed ra l, which i s co n sid ered to be an i n d ic a t o r o f an immature sediment i j d e p o s it , with a low degree o f w eathering. I i I [ t i | 3.2.2.2 Scanning E lectron Microscopy j The co arse f r a c t io n was r e ta in e d for a l l samples from the j j e ig h t co re s that were w e t-sie v e d for t e x t u r a l a n a l y s i s , j These sand samples were i n d i v i d u a l l y examined under a ! ; i d i s s e c t i n g m icroscope to i s o l a t e any unusual g r a in s or t e x t u r e s th a t might provide provenance in fo rm a tio n . Some o f the more unique p a r t i c l e s were then observed and photo- j i ! jgraphed with a scanning e le c t r o n microscope (SEM). j j In most c a s e s the s o f t green g la u c o n it e g r a in s , o fte n with a lim o n ite c o a t i n g , comprised more than h a l f o f the j sand p o p u la tio n . Some o f th e se greensand g r a in s were j I ; s e l e c t e d for SEM a n a l y s i s . j j I 206 TABLE 9 RELATIVE HEAVY MINERAL ABUNDANCE IN RHODE RIVER CORES Core 2B Core 3B-1 Core 5A upper mid lower upper mid lower upper mid lower G lauconite 5 7.6 26. 1 42. 7 20. 8 24. 9 22. 8 35.8 2 6.8 64. 7 M agnetite 0 .0 2 .4 9.0 4 .8 2 .4 21 . 0 5 .0 11.0 3 .8 Ilm en ite 0 .0 0 .4 14.6 3 .2 3 .3 25. 3 3. 1 12. 1 1.9 Zircon 1.8 11.1 4 .3 8 .0 14.8 4 .3 10.6 13.6 13.5 Epidote 0 .5 2 .0 1.3 0.5 0 .0 2.5 2 .8 2 .5 1 . 4 Garnet 2 .3 2 .0 2 .2 4 .0 1.9 1 . 2 2 .2 1.5 0 .0 Tourmaline 1 . 2 0 .8 1.7 2 .4 2 .4 1 . 2 4.7 5 .0 1.9 Chlor i t o id 0 .5 7 .5 2.6 5 .6 4.8 8.6 5 .3 4 .5 1.9 Leucoxene 1.2 4 .3 1.7 3 .2 1 . 4 0. 6 0 .3 0 .5 0 .0 Others 34.9 43. 4 19.9 47.5 42. 7 12.5 30.2. 22. 5 10.9 Figure 53, Photographs A and B, show two t y p i c a l exam p le s o f g l a u c o n i t e . The former i s an uncoated s i n g l e g r a in , w h ile the l a t t e r i s a mass o f sm aller fragments ! encru sted with l im o n it e . The te x tu r e in both c a s e s i s s i m i l a r . In n e it h e r o f th ese sam ples, nor in any other g la u c o n it e grain was found the ”accord ion-1 i k e ” te x tu r e d escrib ed by Drobnyk (1965) for the Maryland Eocene g l a u c o n i t e s . Photo C, a ls o g l a u c o n i t e , was the only one th a t even resembled t h i s d e s c r i p t i o n . S k e le t a l p a r t i c l e s were a ls o sought in the coarse f r a c tio n sin c e the s i z e o f the b io g e n ic c o n t r ib u t io n - - a lt h o u g h jthought to be sm all--w as u n c e r ta in . Very few p a r t i c l e s jwere found th a t appeared to be b i o g e n i c . Two o f th e se are I shown in Photographs D and E o f Figure 53- Photograph D I seems to be a sponge s p i c u le and E appears to be a s k e l - ! e t a l fragm ent. Quartz g r a in s were a ls o commonly observed , though not i n e a r ly as o fte n as g l a u c o n i t e . Typical te x tu r e o f such j ! g r a in s i s shown in Photograph F. Most o f the quartz : observed was smoothly p o lish e d and o b v io u sly reworked. j i I P y rite was found in many o f the samples, though i t s j J abundance was much l e s s than 1%. The most common h ab it | found was framboidal , as seen in Photographs G and H o f ! Figure 53. This unusual s t r u c t u r e , once thought to be b io g e n ic (Love, 1957), has been produced a b i o t i c a l l y in the la b o r a to ry by Berner (1 9 6 9 ). That framboids are an j e a r ly d ia g e n e t ic product o f s u l f a t e red u ctio n by anaerobic b a c te r ia has now been w ell e s t a b lis h e d (Love 1967; Berner, 1970). P yrite framboids were found in a s im ila r r ec en t study o f Long Island Sound s a l t marsh sedim ents (McCaf f r e y , 1979). In the Rhode River co re s the framboidal p y r ite g r a in s were t y p i c a l l y seen at some depth in the c o r e s , rath er than near the su r f a c e , underscoring the a u th ig e n ic o r i g i n . Both o f the examples in the photo graphs were found below 140 cm in Core 1. As mentioned in the previous s e c t i o n , m agnetite i s a major c o n s t i t u e n t o f the heavy m in era ls in the sand f r a c - j t io n . In many samples a few g r a in s could be r e a d il y id e n t i f i e d as m agnetite due to t h e ir black c o lo r and o p a c it y . One o f th e se g r a in s appears in Photograph I. The primary impetus for the SEM work was to observe the te x tu r e o f any g r a in s th a t in any way resembled c o a l. Coal i s a major c o n s t i t u e n t o f Susquehanna River s e d i ments, sin c e the r iv e r d r a in s part o f the e x t e n s iv e a n t h r a c it e f i e l d s o f n o r th e a ste rn P ennsylvan ia. D e t r i t a l c o a l , in f a c t , i s mined from the f l u v i a l sedim ents o f the i lower Susquehanna River bed for power plan t use (Levin and Smith, 1954). It was a ls o found in abundance in the sand f r a c t i o n o f a l l o f the samples c o l l e c t e d north o f the Bay i Bridge for the current p r o je c t ( f i g . 13 )• Since no coal occu rs in the A t la n t ic Coastal P la in , on which the Rhode 209 River watershed l i e s , the only n atu ra l source for coa l in I Rhode River sedim ents would be f l u v i a l and t i d a l current I tra n sp o rt through the Susquehanna River/Chesapeake Bay jsystem . Ryan (1953) d e s c r ib e s d e t r i t a l co al in northern ' Chesapeake Bay sedim ents as having the p r o p e r tie s o f a n t h r a c it e : j e t - b l a c k c o lo r , high l u s t e r and conchoidal i f r a c t u r e . P a r t i c l e s th a t were s in g le d out under the d i s s e c t i n g microscope as p o s s i b l e co a l are shown in Photo graphs J, K and L o f Figure 53. Photograph J appears to be c e l l u l a r , but Photographs K and L may be fragments o f a n t h r a c it e . 2 1 0 Figure 53 Scanning e le c t r o n micrographs o f s a n d - s iz e g r a in s from Rhode River Estuary c o r e s . 21 1 5CFINN I NE ELECTRON M i CRDERHPH5 H <R> ELRUCDNITE ELRUCDNITE 21 3 5CRNN I NE ELECTRON M I CRDERHPH5 <C> ELRUCDN!TE <350X> <O > 5KELETRL < !50X> 5C R N N 1NE ELECTRON MICROERRPH5 £ < E > 5 K E L E T R L < 2 3 X > < F > QURRTZ < 7 5 X > SCHNN i NE ELECTRON M I CRDERRPH5 - <G> P Y R iT E < H > P Y R IT E < 2 I t2X > V J l SCHNNINE ELECTRON MICRDERHPH5 r o O N MRBNET i TE < J > CDHL 5CHNN i NE ELECTRDN M ! CRDGRHPH5 ro ~ < K > CDHL < H £ > < L > CDHL < H D X > 3 - 2 . 2 . 3 Energy D isp e r siv e X-Ray F lu orescen ce Energy d i s p e r s i v e XRF o f some o f the SEM samples provided elem en tal a n a ly s e s for t y p i c a l s a n d -s iz e p a r t i c l e s . For th ree g la u c o n it e p a r t i c l e s , in c lu d in g the sample in Photo graph B o f Figure 53 , the mean co m p o sitio n , c a l c u l a t e d as the oxide , w as: S i 0 2 5 8.3 + 0.8% FeO 21 .3 + 1.8% A l2 0^ 7.9 + 2.2% K2 0 7-2 + 0.3% MgO 4 .7 + 0.3% C a 0 0 . 5 + 0 . 0 % For the m agnetite p a r t i c l e shown in Photograph I o f Figure 53 the a n a l y s i s was: FeO ai2 o3 95.0% 2 . 8 % 218 3 .3 ISOTOPE GEOCHEMISTRY 3-3-1 Carbon-14 3 - 3- 1 - 1 Sedim entation Rates Five o f the estu a r y co re s plus a core from the marsh behind Locust Point (Core LP) were radiocarbon-dated . The r e s u l t i n g d a te s provide a u s e fu l comparison between pre- and p o s t - s e t t l e m e n t sedim entation r a t e s , and agree r e a so n ably w ell with sedim entation r a t e s obtained by other I 1 methods . ! I The d a te s are shown in Table 10. Core l o c a t i o n s and j i j sed im en ta tio n r a t e s can be examined in Figure 54. Due to j a s c a r c i t y o f organic carbon, only one c o r e -t o p sample was j i j found to be d a t a b le , in Core 16A. The radiocarbon age o f i I | t h i s sample was determined to be 620 + 180 years b efo re ! I ~ ! ( i j p resen t (BP) where the c o n v e n tio n a l 1950 A.D. i s taken to , be 0 years BP. j i I ! i ! i | | The anomalously old date i s due to the presence o f j i i i | carbon th a t i s d e p le ted in C-14, p o s s i b l y as a r e s u l t o f ! j i ! the presence o f l o c a l carbonate source rocks th a t are l o w ; J in C-14, o r , more r e c e n t l y , as a r e s u l t o f the l a r g e - s c a l e | i combustion o f f o s s i l f u e l s th a t began with the I n d u s t r ia l i R ev olu tio n . There i s a gen era l curve developed by Michael and Ralph (1970) to c o r r e c t radiocarbon d a te s over the past 6000 years for se cu la r v a r i a t i o n s in the amount o f C-14 in the atmosphere. This c o r r e c t io n , plus an a d d it io n a l 28 years to bring the radiocarbon d a te s from 1950 to the 1978 counting d a te , i s shown in column 4 of Table 10. However, the magnitude o f the se cu la r c o r r e c t io n fa c to r for the range o f d a te s presented here i s only about 50 y e a r s. Thus, the date for the top o f Core 16A remains s i g n i f i c a n t l y o ld er than modern. A s im ila r s i t u a t i o n in a Long Island Sound ra d io - i carbon p r o f i l e was ex p la in ed by Benoit e t al . ( 1979) as j the r e s u l t o f long-term input o f s o i l - d e r i v e d f o s s i l carbon to the e s t u a r y . i It i s p o s s i b l e th a t the u n u su ally la r g e amount o f 1 I ■ f o s s i l carbon seen in the top o f Core 16A i s a l o c a l or i r e g io n a l phenomenon and i s p resen t in a l l o f the c o r e s . Column 5 o f Table 10 examines t h i s p o s s i b i l i t y , reducing j j the c o rr ec ted radiocarbon d a te s by 620 y e a r s. The ! r e s u l t i n g sed im en tation r a t e s , taken over the dated i n t e r - i v a ls and ta b u la ted in column 6, f a l l in to two groups | i d i f f e r i n g by about a fa c to r o f sev en . In a l l c a s e s the j i upper sample in the core e x h i b i t s the f a s t e r r a t e . | TABLE 10 RHODE RIVER ESTUARY RADIOCARBON DATA Core Level ( cm) C-14 Age ( y e a r s , * . B . P . ) U ; Cor- r0C~(2) t ion Correct-*-- ^ ed Ag e Sed im entation Rates (mm/yr) (Pre- and Post S ettlem en t) 1A 100-120 380 + 140 +78 ------ 1 B o c n i o 0 0 770 + 115 +28 178 + 27 4.77 + 1.19 - 0 .8 7 Post 150-162 1475 + 90 -22 833 + 50 1 .08 + 0.33 - 0 .2 6 Pre 2B 108-120 970 + 55 -22 328 + 20 3.48 + 0. 42 - 0 . 38 Post 170-182 2490 + 70 +78 1948 0 0 in + l 0.38 + 0.10 - 0 . 08 Pre 16A 0-10 120-136 620 955 + I+I 180 85 0 0 C V I 0 0 0 0 + 1 313 0 0 0 0 1 1 + 1 1 3-93 + 0.84 -0 .4 1 Post 16B 130-140 880 + 105 +28 288 ± 34 4. 69 + 0, 82 - 0 . 65 Po st 160-169 1585 + 125 -22 943 ± 0.44 i + o o ro 0 0 - 0 Pre LP 0 0 l 810 + 50 + 28 218 ± 13 3.62 0 0 00 o o + i Post mean 4.11 +0.75 - 0 ,5 5 Po st 0.63 Pre 1. BP=Before P resen t, where present=1950 A.D. 2. C orrection for se c u la r v a r ia t i o n in atmospheric radiocarbon l e v e l s (Michael and Ralph, 1970), plus a d d itio n o f 28 years to convert years Before Present (BP) to counting date (1 9 7 8 ). 3. Assumes th a t top o f core r e p r e s e n ts 620 BP, as in top o f Core 16A. 221 There are two other ways o f i n t e r p r e t in g the C-14 d a t e s , both o f which produce l e s s c r e d i b l e r e s u l t s than the method above. The f i r s t a l t e r n a t i v e would be to compute sed im en ta tion r a t e s only over dated i n t e r v a l s in the four co re s where two d a te s were o b ta in e d . This compu t a t i o n produces r a t e s o f about 3-7 mm/yr for Core 16A and about 0.4 mm/yr for Core 6B. These two cores were taken at the same l o c a t i o n on the same day and should not e x h i b i t such a la r g e d i f f e r e n c e in sedim entation r a t e . The second a l t e r n a t i v e i s to assume th a t the top o f each core i s zero years BP. This method r e s u l t s in r a te s th a t vary from 2 .8 + 0 .8 mm/yr for Core 1A to 0 .7 + 0 .0 mm/yr for the bottom o f Core 2B, with a mean for a l l samples o f 1.3 + 0 .6 mm/yr. Using t h i s method, the upper sample from Core 2B r e p r e s e n ts a r a te o f 1.2 + 0.1 mm/yr, which i s more than e ig h t tim es l e s s than the Pb-210 rate i for the same region o f the same c o r e , as w i l l be noted in the next s e c t i o n . A lso, using t h i s assum ption, the two | p e a t - c o n t a in in g c o r e s — 2B and LP— e x h i b i t r e c e n t s e a - l e v e l r i s e r a t e s o f 1.5 and 0 .8 mm/yr, r e s p e c t i v e l y . The two | v a lu e s are n e ith e r i n t e r n a l l y c o n s i s t e n t nor in agreement | with the 3-3 mm/yr s e a - l e v e l r i s e ra te for the mid-Chesa- | peake a r e a . 222 The f a c t th a t the sed im en tatio n r a t e s for the samples in Table 10 f a l l in to two d i s t i n c t groups im p lie s a change in sedim entation regime in the rec en t p a s t . All o f the r a t e s la b e le d "Post" ( P o s t - s e t t le m e n t ) in column 6 occur a f t e r the beginning o f European c o lo n iz a t io n o f the bay s h o r e s . These f i v e r a t e s , averaging 4.11 mm/yr, are mark edly higher than the th ree r a t e s la b e le d "Pre" ( P r e - s e t - j t l e m e n t ) , which r ep r e se n t much e a r l i e r d a te s and average ! 0.63 mm/yr. This h y p o t h e s is , th a t the upper samples r ep r e se n t p o s t - s e t t l e m e n t r a t e s o f sediment i n f l u x , and the lower [ samples r e p re sen t an e a r l i e r time o f slower f i l l i n g , w i l l be t e s t e d in Chapter 4 by comparing the two average r a t e s given in Table 10 with sediment in f lu x r a t e s obtained by other means. ! j 3*3*1-2 Rates o f Sea-Level Rise j It i s worth notin g th a t the sample from Core LP and the | upper sample from Core 2B are both p e a t, and presumably j were c l o s e to mean high water (MHW ) when d e p o s it e d . At p resen t the l o c a t i o n where Core LP was c o l l e c t e d i s 20 cm | above mean high water. The presen t water depth at the Core 2B l o c a t i o n i s 30 cm at M HW . Thus the age o f the I I i 223 peat sample from Core LP (with c o r r e c t io n s to 1978) is 810-620+28=218, and i t i s p r e s e n t ly at 8 2 .5 -2 0 = 6 2 .5 cm below MSL. Kaye and Barghoorn (1964) have found th a t such |d e p o s i t s develop at or near mean high water. I f t h i s i s jthe c a s e , then sea l e v e l 218 years ago stood at 62.5 cm. iThis r e p r e s e n ts a rate o f r i s e o f about 2 .7 mm/yr. i Likew ise, for the upper peat sample in Core 2B, the age (with c o r r e c t io n s ) i s 970-620+28-50=328 y e a r s . The depth i s 1 14 + 30=144 cm. This i s a r a te o f r i s e o f about 4.4 mm/yr. I n t e r e s t i n g l y , both o f th e se sea l e v e l r i s e r a t e s , 2.7 mm/yr and 4 .4 mm/yr, agree reason ably w e ll with the rate for t h i s area o f the C h esapeake--3.3 mm/yr--as determined by g e o d e tic surveys (Holdahl and Morrison, 1974) and long-term t i d e records (H icks, 1973)* I f compaction has occurred in the Core 2B peat bed due to loading by the j o v e r ly in g 108 cm o f mud, the agreement becomes even c l o s e r . Another l i n e o f proof for the assumption th a t a c o r r e c tio n f a c to r i s needed for the C-14 d a te s i s provided by Roberts (1 9 7 9 ). In th at study o f the s o i l s o f the Rhode River w a te rsh e d , a o n e -m e te r -th ic k peat bed was uncovered 224 at a depth in the s o i l o f 95 crn below p r e sen t sea l e v e l . A radiocarbon date o f 890 + 70 years BP was obtained for the p e a t. Depending on the l o c a t i o n o f the sample w ithin the p e a t, t h i s would in d ic a t e a sea l e v e l r i s e r a te o f 1.0 to 2.1 mm/yr, s i g n i f i c a n t l y lower than the p r e s e n t l y - a c cepted 3-3 mm/yr r a t e . However, when the same -620 year c o r r e c t io n i s made as for the e stu a ry sam ples, the sea l e v e l r i s e rate i s 3-2 to 6 .5 mm/yr, again dependent on the l o c a t i o n o f the dated sample. ' The rapid ra te o f sea l e v e l r i s e obtained from th ese | Rhode River peats seems to apply only to the past 1,000 | years or so. The lower peat sample in Core 2B, with a co r r e c te d age o f 1,948 + 58 y e a r s, y i e l d s a submergence j j r a te o f about 1.06 mm/yr. This slower r a te i s in r e l a - i i t i v e l y good agreement with r a t e s derived from e a r l y - to !mid-Holocene age (1 1,00 0 to 1,300 YBP) peats o f the Chesa peake r e g io n , as d e sc rib ed in Chapter 1 (N ic h o ls , 1972; Newman and Rusnak, 1965; Kraft et a l . ,1973)* | It would appear, th en , th a t a s e a - l e v e l r i s e r a te o f j approxim ately 1.5 mm/yr i s app rop riate for the Chesapeake Bay for the e a r l y - to m id-H olocene. The r a te over the past 1,000 y e a r s, however, seems to be s i g n i f i c a n t l y f a s t - | e r --p e rh a p s as much as 3-3 mm/yr. Both o f th e se r a t e s 225 w i l l be taken in to c o n s id e r a tio n in d evelop in g the sedim entation h i s t o r y o f the Rhode River Estuary in Chapter 4. 226 Figure 54 Rhode River Estuary sed im en tation r a t e s , based on sediment core radiocarbon d a ta. 227 RHODE RIVER CARBON-14 SEDIMENTATION RATES ( m m / y r ) 2 0 0 0 3 0 0 0 1000 c 1 i l . i .l . X P O S T - S E T T L E M E N T RA TE P R E - S E T T L E M E N T RATE * 2 / . ' CORES- 8 / 7 8 O I V C O R E S -8 /7 8 • I V C O R E S - 7 /7 7 ■ OTHER CORES WEST RIVER 228 3-3-2 Lead-210 3 - 3 - 2 .1 Sedim entation Rates Sedim entation r a t e s during more r ec en t tim e, such as the past c en tu ry , must be examined with a t o o l th a t provides g r ea ter r e s o l u t i o n than carbon-14. As a r e s u l t , lea d -2 1 0 | lanalyses were ca rr ie d out on four c o r e s . A c t i v i t y p r o f i l e s are shown in Figure 55- A supported Pb-210 a c t i v i t y l e v e l o f 0.8 dpm/g was assumed. This i s an javerage o f the Ra-226 background l e v e l s determined by Goldberg et a l . ( 1978) and Hirschberg and Schubel ( 1979), i for c o re s from the same area o f the Chesapeake. Sedimen t a t i o n r a t e s were c a lc u la t e d from the slo p e o f a r e g r e s sion l i n e for each o f the four c o r e s . P oints f e l t to |represent storm ev en ts were excluded from the r e g r e s s i o n , i |as w i l l be explain ed in the f o llo w in g s e c t i o n . Rates and |sample l o c a t i o n s are shown in Figure 56. ! The sed im en tation r a t e s in Figure 56 vary by a fa c to r o f t h r e e . Yet a l l o f them are s i g n i f i c a n t l y higher than the ’’p r e - s e t t l e m e n t ” carbon-14 sed im en ta tion r a t e s reported in the previous s e c t i o n (Table 10) for deeper samples. The mean r a te for the four c o re s shown in Figure 229 56 i s 10.3 + 4 .2 mm/yr— more than six tim es higher than the 1.59 mm/yr r a te for the lower s e c t i o n s o f the C-14 c o r e s . The true mean sedim entation ra te for the e stu a r y as a ! whole may in f a c t be lower than 10.3 mm/yr. The l o c a t i o n s o f the four dated cores may favor the areas o f i i jh ig h er -th a n -a v e ra g e se d im e n ta tio n . Core 2B, for i n s t a n c e , jis in the area at the mouth o f Muddy Creek th a t has shown jthe g r e a t e s t amount o f sh o a lin g over the past c e n tu r y . , I This f a c t was revea led in the study q u a n tify in g the 1845 jand 1972 bathym etric c h a r t s , d e sc rib ed e a r l i e r in t h i s ^chapter. Core 3-B-1 i s a ls o w ithin range o f the f a l l o u t o f Muddy 'Creek sedim ents and may as a r e s u l t r e p r e se n t a g r e a te r jthan average r a te o f sediment in p u t. Core 5A, due to i t s | jproximity to the 3-meter c l i f f s at the west s id e o f the J jestuary mouth, probably e x h i b i t s a higher sed im en tation j irate than would a core fa r th e r out in to the body o f the e s t u a r y . 230 Figure 55: Lead-210 a c t i v i t y p r o f i l e s for Rhode River Estuary c o r e s . 231 ' DEPTH I N C O R E <CM> CERE 2 - B L E R D -2 I □ RCT I V I TY □ • to 20 30 HO SO ED 70 BO SO too I to 120 120 1H Q M ERN SEDIMENTATION RRTE FRO M SLOPE OF REERE55iQN LINE----- 10.0 MM/YR 4 - ■4 " 4 - 4- <STORM . DEPOSIT) 4 h o U ) N > 0 .2 0 .4 O.E 0 .8 i.O 2 .0 3 .0 H.O UNSUPPORTED L E R D -2 I P RCT t V I TV < DPM/ERRM > 5.0 C O R E 3 - B - I L E R D - 2 I □ R C T I V i T Y p ID 20 30 H O ✓ s SO 2 ^ G D Q ? 70 Q ^ B O 2 — 30 X £,oo u £>U0 120 1 3 0 I H O M S R N 5E D IM E N T R T IO N R R T E F R O M SLO PE O F R E G R ESS 1 O N LINE---- IS.S M M /Y R <S T O R M DEPOSIT) 4- N5 O J O J 0.2 O .H O .B 0.0 (.0 2.0 3.0 H .O S .O UNSUPPORTED L-ErRD — 2 I □ RCT 1 V 1 TV < DPM/BRRM > m DEPTH I N C D R E <CM> C D R E S - R L E R D - 2 ! □ R C T I V i T Y □ ID HI 30 H O £0 E D 70 B O 90 100 ! 10 120 130 (H Q M E R N SED IM ENTA TIO N R A T E F R O M SLO PE O F REG RESSIO N LINE----- 10.H M M /Y R 4- 4~ 0 .2 Q.H O.E 0 .9 1.0 U N S U P P O R T E D L E R D - 2 1 P R C T 1V ( TV 2.0 3.0 H.O < D P M / E R R M > £.0 CDRE 3 0 L E R D - Z 1 □ RCT I V I TV <S T O R M DEPOSIT) 10 ■ 20 • 30 * M E R N SEDIM ENTRTIO N R R T E P R O M SLOPE O F REG RESSIO N LINE---- S.2 M M /Y R H O ^ SO v w SO 130 i IH O 0 .2 O.H O.G Q.B 1.0 2 .0 3 .0 U N S U P P O R T E D L E R D - 2 I D R C T 1 V I T V < D P M / E R R M > H.O S.O Core 30, in the cen te r o f the e stu a r y i s probably the i most t y p i c a l o f the fo u r . The r a te computed for that c o r e , 5 .2 mm/yr, w i l l be u s e d - - in a d d itio n to the mean ra te for the four c o r e s — in d ev elo p in g the sh ort-term ! sediment budget for the e s t u a r y . D espite the v a r ia t i o n among the dated c o r e s , i t can be said with some assurance th a t sed im en tation over the past century has been s i g n i f i - | c a n tly more rapid than the long-term average for the l a t e I H olocen e. ! i 3 . 3 - 2 . 2 Storm Events ! As mentioned above, a few o f the sample p o in ts were jexcluded from the sed im en tation ra te r e g r e s s io n a n a l y s i s . j Figure 55 shows the excluded p o i n t s . The r a t i o n a l e for j 'ig n o rin g th ese samples in c a l c u l a t i n g the Pb-210 sedimen- j t a t io n r a t e s i s th a t they a l l occur at or c l o s e to depths jthat mark the expected p o s i t i o n o f a major storm l a y e r . Storm sedim ents should be d e p le ted in Pb-210 because they srepresent sedim ents eroded r a p id ly from the watershed or jstream banks and d e p o site d q u ick ly in the estu a ry by flo o d j w a te rs. The rapid d e p o s itio n l i m i t s sediment scavenging o f Pb-210 in the water column. 236 Figure 56: Lead-210 sed im en tation r a t e s and sample l o c a t i o n s . 237 RHODE RIVER LEAD- 210 SEDIMENTATION RATES ( m m / y r ) 2000 1 0 0 0 ” 1000 l__l_ ***SH * 2'/*' CORES - 8 / 7 8 O 1 CORES - 8 /7 8 • CORES - 7 /7 7 ■ OTHER CORES WEST RIVER Two major storm s, each with a g r e a te r than 100 year j recurrence i n t e r v a l , have struck the lower Susquehanna basin during t h i s c e n tu r y - - T r o p ic a l Storm Agnes in 1972 . and an e a r l i e r storm in 1936. Core 2B p o s s e s s e s two o u t ly in g p o i n t s . Given the f a c t th a t the core was c o l l e c t e d in 1977 and the c a lc u la t e d sed im en ta tio n ra te i s ; 10.0 mm/yr, the 1972 storm d e p o s it should be at 5 cm and the 1936 layer should be at 41 cm. The 1936 la y er d e f i - i n i t e l y seems to be p r e s e n t. The 1972 la y er was not i sampled, but the la y e r im m ediately beneath i t , at 10-15 j cm, was, and was found to be d e p le ted in Pb-210. I f t h i s j | la y e r i s in f a c t due to Agnes, i t may mean th a t the storm j I d e p o s it was mixed down or i s u n u su ally t h i c k . Although | the c o n c lu sio n i s somewhat ten uou s, i t was decided th a t j storm sedim entation i s the b e st o f the many p o s s i b l e j e x p la n a tio n s for t h i s o u t ly in g p o in t. The r e g r e s s io n l i n e j p ^ j (r = 0 .9 4 ) i s for the six remaining p o i n t s . | For Core 3-B-1 th e re are two excluded sam ples. This core r e p r e s e n ts the h ig h e s t sed im en tation r a te o f the four co re s a n aly zed , which may be due to i t s l o c a t i o n at the poin t where the Muddy Creek mouth widens d r a s t i c a l l y and debouches in to the e stu a r y p r o p e r . As such, the Agnes lay er might be expected to be t h i c k . At the c a lc u la t e d j average sedim entation r a te o f 15.5 mm/yr, Agnes d e p o s i t s should be encountered beginning at 8 cm. The sample 239 n e a r est t h i s depth, in the 10-15 cm i n t e r v a l , i s low in r a d io g e n ic lead and thus may r e p r e s e n t the lower part o f Agnes storm d e p o s i t . The other o u t ly in g p oin t may be a remnant o f the flood o f August, 1955 (Table 2 ), s in c e i t i s lo c a te d at the ex a ct l e v e l where 1955 should be. Another p o s s i b i l i t y i s th a t a l l three o f the o u tly in g p o in ts are part o f the Agnes l a y e r . This would make the i storm d e p o s it more than 20 cm t h i c k , however, which seems 2 ' u n l i k e l y . Thus the r e g r e s s io n l i n e (r = 0 .8 8 ) in c lu d e s a l l but the two p o in ts mentioned. j Core 30 e x h i b i t s a s i n g l e p o in t th a t i s l e a d - d e p l e t e d . I j | Given a 5 .2 mm/yr sed im en tation r a t e , the 1972 storm i I ! ‘d e p o s it should l i e 2.6 cm below the s u r f a c e . The o u tly in g j j I jpoint r e p r e s e n ts the 0-2 cm i n t e r v a l , and could r ep r e se n t > the 1972 la y er i f a small amount o f the su rface sediment j was l o s t during the coring o p e r a tio n . The r e g r e s s io n l i n e j 2 ^ (r = 0 .8 4 ) in c lu d e s the remaining s ix p o i n t s . , i L a s t ly , Core 5A a ls o has one p o in t , in the 10-15 cm i n t e r v a l , whose Pb-210 a c t i v i t y i s somewhat low. Given | I jthe c a lc u la t e d sed im en tation r a t e , however, t h i s i n t e r v a l j r e p r e s e n ts the m id -1 9 6 0 's, a period o f no major storm ^ a ctiv ity (Table 2 ) . T h erefore, t h i s p o in t was included in j jthe r e g r e s s i o n . A more complete d i s c u s s i o n o f the s e d i - m en tologic e f f e c t s o f major storms w i l l be taken up in Chapter 4. Lead-210 data from other i n v e s t i g a t i o n s in the northern bay area r e v e a l s im ila r d e p le ted i n t e r v a l s in the Pb-210 p r o f i l e s . Goldberg et a l . (1978) reported low lead a c t i v i t i e s for samples from the 0-3 cm i n t e r v a l o f t h e i r Core ! XIV, c o l l e c t e d 7 km north o f the Rhode River Estuary a month a f t e r T ropical Storm Agnes in 1972. Hirschberg and Schubel (1979) found two th ic k l a y e r s with d e p le ted Pb-210 j in a core taken from the bay, 18 km south o f the Susque- j hanna River mouth, in 1976. The l a y e r s , a t t r i b u t e d by the authors to the 1972 and 1936 storm s, were both homogeneous to x -ra y s and were 16 cm th ic k and 36 cm t h i c k , j r e s p e c t i v e l y . I f th e se i n t e r p r e t a t i o n s o f storm la y e r s j are c o r r e c t , they would in d ic a t e th a t t h ic k n e s s o f major : i storm d e p o s i t s d e c r e a s e s with d is ta n c e from the Susque- ; hanna. This s u b je c t w i l l be pursued fu rth er in Chapter 4. i 3-3*3 Cesium-137 and Reactor-Generated N u clides | ■ ' ■ ■■■■' ' - " - ■ ■ ■ - — — —— - — ■ — ■ — - ................ i In a d d itio n to the e stu a r y watershed and the s h o r e l i n e s o f j the e stu a r y i t s e l f , i t was r e a l i z e d th a t th ere i s another i p o t e n t i a l l y la r g e c o n tr ib u to r to the Rhode River Estuary |se d im e n ts, and to the upper Chesapeake Bay sedim ents in | |g e n e r a l . This source i s the f l u v i a l sediment c a r r ie d in to ! the Chesapeake by the la r g e r t r i b u t a r i e s , and prim arily by the Susquehanna River. As noted in Chapter I, the Susquehanna provides 87% of a l l the fre sh water e n te r in g the northern h a l f o f the bay. The r iv e r a ls o pro vid es an average o f 1.2 m i ll i o n tonnes i o f sediment to the bay ann ually (Table 1). This i s by far the major source o f f l u v i a l sediment to the upper bay. i |Other t r i b u t a r i e s c o n t r ib u t e only an i n s i g n i f i c a n t amount in comparison ( B ig g s , 1970). i j Consequently, i t was f e l t th a t the b e st way to d e t e r mine the f l u v i a l input to the s u b - e s t u a r i e s o f the ; j ] northern bay— such as the Rhode River Estuary--would be to ! |sample the sedim ents down the lower Susquehanna River and j l : the a x is o f the northern Chesapeake. The o b j e c t i v e o f ! j j jth is sampling program was to determine i f any c h a r a c t e r i s - ' ' t i c s o f Susquehanna River sedim ents were s u f f i c i e n t l y ' i ! junique to be i d e n t i f i a b l e many k ilo m e te r s south o f the | r iv e r m outh--in the case o f the Rhode River, the d is ta n c e jfrom the mouth o f the Susquehanna being 76 km. i 3 - 3 - 3- 1 Tracers for Susquehanna River Sediments P o s s ib le ca n d id a tes th at were considered for use as unique t r a c e r s o f Susquehanna River sedim ents in the bay included t e x t u r a l parameters, c o a l , tr a c e m e ta ls , c la y m in e r a ls , and sedim ent-borne r a d io n u c l i d e s . Textural parameters were r e j e c t e d because the v a r ie t y o f source areas for Susquehanna River sed im en ts, plus the d is t a n c e o f t r a n s port between the r iv e r mouth and the Rhode River Estuary would so homogenize and a l t e r any unique t e x t u r a l t r a i t s I as to make them unusable. I Coal was thought to be a good p o s s i b i l i t y , s in c e the | I a n t h r a c it e basin o f n o r th e a ste r n Pennsylvania i s the s o l e j i : I . source o f d e t r i t a l coal to the bay . A n th racite mining j began in 1830 and mine t a i l i n g s were r o u t i n e ly washed in to j the t r i b u t a r i e s o f the Susquehanna River up u n t i l the J i I e a r ly 1 9 5 0 's. Coal was found in abundance in a l l o f the j ! I Susquehanna sediment samples c o l l e c t e d for t h i s stu d y . It | has a ls o been found by oth er i n v e s t i g a t o r s in samples as ! far south as the Patapsco River region o f the bay, near j Baltim ore (Ryan, 1953)* However, the l i t e r a t u r e r e v e a ls j no ev id en ce o f co a l being found in e s t u a r in e sediment o f j j the lower s e c t i o n o f the northern bay. Examination o f the i Rhode River sedim ents by l i g h t and e le c t r o n m icroscopes ; ; produced only a few g r a in s th a t had c o a l - l i k e c h a r a c t e r i s - j 243 t i c s . Some o f th e se are shown in Figure 53» The r a r i t y o f such g r a in s in the sedim ents caused co al to be r e j e c t e d as a tr a c e r . Trace m eta ls were su ggested as p o s s i b l e t r a c e r s for Susquehanna River sediment by Eaton e t a l . ( 1 9 8 0 ). Using i | sedim ent-borne Fe and Ti , which are r e l a t i v e l y c o n serv a- I t i v e , and Zn, which i s r e l a t i v e l y m o b ile, they were able to d e t e c t the presence o f Susquehanna sedim ents as far i I south in the bay as the Potomac River mouth ( f i g . 1). ! ■ This method, however, r e s u l t s in a la r g e d iscrep a n cy j j between d i f f e r e n t i n v e s t i g a t o r s ' e s t im a te s o f the j percentage c o n t r ib u tio n o f shore e r o sio n to the suspen- j i | s a t e s o f the upper bay. Eaton e t a l . (1980) concluded on the b a s i s o f tr a c e metal r a t i o s th a t shore e r o sio n i s only a n e g l i g i b l e f r a c t i o n o f the suspended sedim ent, and that i I j f l u v i a l sedim ents from the Susquehanna are an important I ! c o n tr ib u to r as far south as the Potomac River mouth ( f i g . i 1). B iggs(1970) c a l c u l a t e d , based on sediment sampling j and shore e r o sio n m o n ito rin g , th a t the s h o r e l in e s 1 c o n t r ib u t e 30-50% of the upper Chesapeake Bay suspended sedim ent. Further, he sta te d th at only n e g l i g i b l e j amounts — l e s s than 10%--~of the Susquehanna sedim ents are j ; i [carried more than 50 km from the mouth. A lso, p a r t i c u l a t e ! i ! i i Fe c o n c e n tr a t io n s in Rhode River su sp e n sa te s f o llo w no [ d is c e r n ib le pattern (J. W . P ie r c e , personal | 244 ! communication), and would not be comparable with Susque hanna/Chesapeake sam ples. Thus, tr a c e m eta ls were r e j e c t e d as p o s s i b l e t r a c e r s . Clay m ineralogy o f a l l Susquehanna, Chesapeake and Rhode River samples was analyzed and the r e s u l t s were d e sc rib ed e a r l i e r in t h i s c h a p te r . The Susquehanna River c la y m ineral s u i t e i s h ig h ly i l l i t i c , w hile the Rhode River Estuary c la y s are h ig h ly m o n t m o r i l l o n i t i c . This in i t s e l f i s a unique p rop erty . However, the f a c t th a t th ere I are at l e a s t four major c o n t r ib u t o r s to the t o t a l Rhode River c la y m ineral s u i t e — water shed e r o s io n , Rhode River ; e s t u a r in e s h o r e lin e e r o s io n , Chesapeake Bay s h o r e lin e e r o s io n and Susquehanna River f l u v i a l se d im e n t--c o m p li- c a t e s the use o f c la y m ineralogy for tr a c e r purposes. i 3*3*3«2 R adionuclide Tracers I The l a s t c a n d id a te , sedim ent-borne r a d io n u c lid e a c t i v i t y , was s e l e c t e d for two rea so n s: i t i s e a s i l y d e t e c t a b l e and has a s i n g l e so u rce. E a r lie r i n v e s t i g a t i o n s in v o lv in g the James River Estuary (C u tsh a ll and N ic h o ls, 1979; C u tsh all et a l . , 1981), the Hudson Estuary (Simpson e t a l . , 1976; Olsen e t a l ., 1978) and the Columbia Estuary (G ross, 1972) have s u c c e s s f u l l y u t i l i z e d p a r tic le -b o u n d r a d io n u c lid e s as t r a c e r s for sediment tr a n sp o r t and d e p o s i t i o n . 245 \ All o f the r a d io n u c lid e s examined in t h i s study are produced e x c l u s i v e l y by power r e a c t o r s , with the e x c e p tio n o f Cs-137, which i s a ls o a f a l l o u t product. On the northern Chesapeake and i t s t r i b u t a r i e s th ere are th ree nuclear power f a c i l i t i e s . Two o f th e se --T h r e e Mile Island and Peach Bottom — are on the banks o f the lower Susque hanna. The t h i r d - - C a l v e r t C l i f f s - - i s s it u a t e d on the | western shore o f the Chesapeake, n ea rly 150 km south o f j the mouth o f the Susquehanna and 74 km down-estuary from | the Rhode River. I t s i n f lu e n c e on sedim ents e n te r in g the Rhode River i s n e g l i g i b l e . ! ] ; The Susquehanna River nuclear p l a n t s , however, are | ! | lo c a te d only 15 km (Peach Bottom) and 90 km (Three Mile i Islan d ) upstream from the head o f the Chesapeake Bay. | jL o ca tio n s o f the p la n ts and the dams on the lower Susque- i hanna are shown in Figure 14. This proxim ity and the la r g e sediment input from the Susquehanna River to the bay i | g iv e Susquehanna sedim ents a c h a r a c t e r i s t i c r a d io n u c lid e j s i g n a t u r e , enabling t h e i r d e t e c t i o n even in g r e a t l y d i l u t e d q u a n t i t i e s in the northern bay r e g io n . 246 [ 3«3«3*3 Reactor R elea ses In order to c o n s t r u c t a n u c lid e budget for the system , i t i s n e c essa ry to know the t o t a l q u a n tity o f r a d io n u c lid e s th a t has been r e le a s e d to Susquehanna waters from the two r e a c to r s i t e s during t h e ir o p eratin g l i f e . To t h i s end, o p e r a t o r s ’ r e l e a s e r e p o r ts were obtained from the Nuclear Regulatory Commission for both Peach Bottom and Three M i l e : Island for the years 1974 to May, 1979, coverin g the ; e n t i r e period o f o p e r a tio n up to the sampling d a t e s . j i i In order for a r e a c to r n u c lid e to be u s e fu l as a t r a c e r , i t must be r e l a t i v e l y abundant in the r e l e a s e s , ! must have at l e a s t a moderate h a l f - l i f e , and must be j i ! j capable o f being r e a d ily adsorbed by the sed im en ts. The | n u c lid e s th a t f u l f i l l e d t h i s c r i t e r i a - - p l u s t r i t i u m , which ; does not f u l f i l l the th ir d requirem ent— are l i s t e d in i i Table 11 along with t h e i r h a l f - l i v e s and r e l e a s e t o t a l s . ! ' I The t a b l e shows th a t the r e a c to r n e a r e s t the head of’| ! the bay— Peach B otto m --co n trib u ted 83-9% of the released; a c t i v i t y o f the ten n u c lid e s l i s t e d . Tritium accounted for 89% o f the t o t a l in Table 11. The remaining 31 c u r ie s o f r a d i o a c t i v i t y were p rim a rily c o n trib u te d by cesium andj ; i c o b a lt n u c l i d e s , r e p r e se n tin g f i s s i o n products and reactor! : t I c o rr o sio n products . TABLE 11 RELEASE HISTORY FOR SUSQUEHANNA RIVER NUCLEAR POW ER PLANTS N uclide H a lf-L ife ( days) Peach Bottom R elea ses ( c u r ie s ) Three Mile I. Release s ( c u r ie s ) Total Release s ( c u r i e s ) A g-110 252 0.161 0.0734 0.235 Co-58 71 0. 106 0. 687 0.793 Co -6 0 1 924 0. 386 0.0446 0. 431 Cs-134 752 6.33 0.216 6.55 Cs-137 11019 3.77 0. 296 4. 07 H-3 4506 212. 41.7 2 5 3 .7 . Mn-54 312 0.121 0.0432 0. 164 Sr -90 10585 0.00338 0.00035 0 . 0037: Zn-65 244 1 .73 0.000462 1 .73 Zr-95 64 0.0371 0.00164 0.0387 S u b total 225. 43. 1 268. 1 Percent o f Subtotal 83.9% 16.1% All Other N uclides 16.8 Total R elea ses ( c u r i e s ) 284. 9 Data from U. S. Nuclear Regulatory Commission r e p o r ts and o p e r a to r s' r e l e a s e r e p o r t s , 1974 to May, 1979. T otals not d e c a y -c o r r e c te d . Based on the inform ation in Table 11 i t was f e l t th a t Cs-137 and Cs-134 had been r e le a s e d in la r g e enough amounts to be d e t e c t a b l e in sedim ents w e ll down the a x is j 248 o f the Chesapeake. The q u a r te r ly r e l e a s e h i s t o r y for th ese two n u c lid e s i s shown in Figure 57- The most d i s t i n c t i v e fe a tu r e o f t h i s f ig u r e i s the la r g e s i n g l e j r e l e a s e o f n e a r ly 2 .6 Curies o f Cs-134 from the Peach I i | Bottom f a c i l i t y during the fourth quarter o f 1978. In ! i a l l , Peach Bottom accounted for approxim ately 97% of the j Cs-134 r e l e a s e s and 93% o f the Cs-137 r e l e a s e s to the | r i v e r . Thus, n e a r ly a l l o f the Cs-134 to be found in the Susquehanna and Chesapeake sedim ents was produced at a j s i n g l e s i t e , and n ea rly 40% of i t was r e le a s e d in the j fourth quarter o f 1978. j Figure 5 7 : Radiocesium r e l e a s e h i s t o r y for Three Mile Island and Peach Bottom nuclear power p l a n t s . 250 < M ILLI CUR IE 5 > M hi U E l R H El El El 9 9 9 9 9-9 TM 1 .00 . 0 0 TM .017 i m m TM I TM 1 . 9 0 2 TM I TM I . HS 1 TM 1 TM 1 TM I TM I TM I TM I TM I TM 1 TM I I 9 9 TM 1 TM 1 I S f TM I I 0H 0 C 5- I 37 L _ I QLI I C > RELER5E5/ I /7 S -5 /7 9 5U5BUEHRNNR RIVER NUCLERR PLRNT5 in ui a: B i 0 0 0 P I a R h I Q a u h I J B h R I D I Q p i R R I d P I R - I j a J I Q I D - — I D P I I d R R R - B r a h h I d r B B — a si R P I R h - I D S R h P I I R r r i P I h I P I id - p i i R B S I J o i a a R I I d S a a P I h R h a p i T I F I a I d I h - T I D " h R * * R P I ~ a I II Z B £ I B £ 0 Z 0 I D z a I 0 z a z a i a i a i a z a £ a z a z a I o h O L b I L b I L b 1 b a . b 0 . b i b O L h a . b B . b n b I L b a . b I L b I L b 0 . b a . b I L T M I I 2 3 H I S T S Q T R - I 2 3 H 1 3 7 9 I S T B 3 . 3 . 3 - 4 Reactor N u clides in Sediments o f the Lower Susquehanna River and Upper Bay i | The sedimentary products r e s u l t i n g from ero sio n o f the Susquehanna watershed do not f o llo w a simple path to the I Chesapeake. Between the Three Mile Island nuclear power plan t and the head o f the bay --a d is t a n c e o f 91 km--there i are four dams ( f i g . 14). The lower t h r e e - - S a f e Harbor , i Holtwood and Conowingo— are power dams. The uppermost dam, at York Haven, i s a low s tr u c tu r e used for d iv e r t i n g water through the York Haven Generating S t a t i o n , a small h y d r o e le c t r ic plant. River sed im en ts, plus the adsorbed r a d io n u c lid e s are p r e s e n t ly being trapped behind a l l four | dams, in amounts th a t w i l l be computed in Chapter 4. In I an average year about 1.2 m i ll i o n tonnes o f sediment I pass through the system in to the upper bay, as shown in i i Table 1 . Samples for gamma-counting were c o l l e c t e d in the r e s e r voir behind each dam, below and above each o f the two i |n u clear p la n ts ( f i g . 14), throughout the upper bay ( f i g . I I | 13), and at the mouth o f the Rhode River Estuary ( f i g . ! l 2 ) . The g r e a t e s t d e n s i t y o f samples was at the Peach i Bottom Plant and the Conowingo R eservoir immediately below i t , as w ell as in the extreme upper p o rtion o f the bay jwithin 20 km o f the r iv e r mouth. 253 The four dams and the e s t u a r in e d e l t a area at the head o f the bay c o n s t i t u t e f i v e sediment b a s i n s . In order to determine the areal d i s t r i b u t i o n o f n u c lid e s and s e d i ments, a number o f grabs were c o l l e c t e d in each b a s in . To c a l c u l a t e the t h ic k n e s s o f the sed iment la y e r c o n ta in in g the r e a c to r n u c l i d e s , a core was a ls o c o l l e c t e d in each b a s in . Appendix B and Olsen e t al . (1981) g iv e the r e s u l t s from gamma-counting a l l o f the sam ples, in c lu d in g the Rhode River mouth sample, Core 38. I n te g r a tio n o f the sample a c t i v i t i e s over the area and t h ic k n e s s o f the sediment r e s e r v o i r s e n a b le s the c a l c u l a t io n o f a n u c lid e in v e n to r y , and, by i n f e r e n c e , a sediment in v e n to r y . This w i l l be done in the fo llo w in g ch a p ter. 3-3 -3 «5 Radiocesium in Rhode River Estuary Sediments Gamma-counting o f the Rhode River mouth core revealed no Cs-134. The a c t i v i t i e s d e te c te d for Cs-137 were a t t r i b u t a b l e e n t i r e l y to f a l l o u t from atomic weapons t e s t i n g . The absence o f any r e a c to r n u c l i d e s , p a r t i c u l a r l y Cs-134, might be taken as i n d i r e c t proof th a t Susquehanna s e d i ments have l i t t l e in f lu e n c e on the sed im en tation regime o f the m id -r eg io n s o f the bay. Another p o s s i b i l i t y i s th a t sediment tr a n sp o r t down the bay i s a slow p r o c e s s , and th a t the r e a c to r n u c lid e - b e a r in g se d im en t--h av in g e x is t e d 254 only s in c e about 1974--has not yet reached the middle Chesapeake. These p o in t s w i l l be examined in d e t a i l in I the next c h a p te r. Since i t i s a t t r i b u t a b l e e n t i r e l y to f a l l o u t , the , Cs-137 p r o f i l e in Core 38 can be used as an i n d ic a t o r o f i the average sed im en tatio n ra te over the past few d eca d es. F a llo u t Cs-137 reached a peak in 1963 and d e c lin e d r a p id ly fo llo w in g the sig n in g o f the nuclear t e s t - b a n t r e a t y in th a t year ( U. S. Department o f Energy, 1980). The Cs-137 p r o f i l e for Core 38 i s shown in Figure 58. The d i s t i n c t i v e peak at 8-10 cm probably r e p r e s e n ts the! [ ! | f a l l o u t maximum. S im ilar p r o f i l e s have been found in' ! | j James River c o re s by C u tsh a ll and N ichols ( 1 9 7 9 ), CutshallJ | e t a l . ( 1 9 8 1 ) and Moy ( 1 9 8 0 ), r e s u l t i n g in im plied sedimen t a t i o n r a t e s ranging between 4 mm/yr and 19 cm/yr . In I Core 38, which was c o l l e c t e d in October, 1978, placingj 1963 at 8-10 cm r e s u l t s in an average sed im en ta tion rate! o f 6.0 + 0 .7 mm/yr. The f a c t th a t the peak i s so d i s t i n c - j t i v e im p lie s th a t mixing o f the sedim ents does not occurj on a la r g e s c a l e . The presence o f d e t e c t a b l e radiocesiumj down to about 3^ cm, however, must be due to one o f th ree j mechanisms: d i f f u s i o n , mixing or a change in sedim enta- i j tio n r a t e . D iffu s io n over the 24-year period 1954-1978, assuming a c o n s e r v a t iv e value o f 100 for the so r p tio n c o n sta n t (K), can account for only about 2 .8 cm downward tra n sp o rt o f ! cesium in the sedim ent. An e x t e n s i v e mixing zone appears u n l i k e l y , given the sharpness o f the peak at 9 cm depth. i S m a ll-s c a le mixing i s p o s s i b l e , with a mixing zone o f | I { about 4 cm or l e s s . But even the combination o f d i f f u s i o n i i i I ; and s m a l l - s c a l e mixing s t i l l r e q u ir e s th a t the sedim enta- I j tio n ra te vary by a fa c to r o f about th r ee between top and j bottom o f the c o r e . | I | ; ; j This v a r ia t i o n in r a te in Core 38 i s probably an j | extreme for a l l o f the samples c o l l e c t e d . This core was ! taken in the most open area o f the e s t u a r y , in the middle lof the mouth ( f i g . 12), exposed to the storm surges and t i d a l c u r re n ts o f the Chesapeake. The i m p lic a t io n s o f th e se r a t e s o f sediment accumulation w i l l be taken up in Chapter 4. Figure 58: Cesium-137 a c t i v i t y p r o f i l e for Rhode River Core 38. 257 CE5 I LIM- i 37 RCTIV1TY RHOt>E RIVER CORE 3B i S E 3 FHLLDLIT PERK H0 < NOTE— RLL RCTIVITIE5 DECRY-CORRECTED TO COLLECTION DRTE/- B / ! H / 7 B > 2.0 CE51UM-I37 RCTIVITY <DPM/S> 258 Chapter IV DISCUSSION AND CONCLUSIONS 4.1 SOURCES OF SEDIMENT TO THE RHODE RIVER ESTUARY Sediments e n te r in g the Rhode River Estuary are derived from a v a r i e t y o f s o u r c e s . They come from the e s t u a r in e s h o r e l i n e , from the watershed, from the o u t ly in g Chesa peake Bay and from primary p ro d u ction . Determining the p r o p o r tio n a l c o n tr ib u tio n from each source i s a complex ta sk because most i d e n t i f y i n g c h a r a c t e r i s t i c s - - s u c h as te x tu r e — vary only s l i g h t l y between so u r c e s , and a lso because the c o n t r i b u t i o n s vary over tim e. It i s f a i r l y obvious th a t the p ro p o rtio n s have f lu c t u a t e d s i g n i f i c a n t l y over the Holocene, but i t i s a ls o probable th a t th ere are much sh o r te r -p e r io d v a r i a t i o n s as w e l l . For example, suspended sediment m ineralogy has been found to f l u c t u a t e , both for the e stu a r y and for the watershed stream s, in response to season a l change, hydrology and weather c o n d i t i o n s (Hearn, 1980; Podany, 1980). There a r e , n e v e r t h e l e s s , some c o n c lu s io n s th a t can be drawn concerning the o r ig i n o f the sedim ents th a t have 259 been f i l l i n g in the Rhode River v a l l e y s in c e mid-Holocene tim e. The m ineralogy, h i s t o r i c bathymetry, t e x t u r e and magnetic str a t ig r a p h y d escrib ed in the previou s chapter provide the keys. 4 .1 .1 Shore Erosion M i n e r a l o g i c a l l y , the Rhode River Estuary bottom sedim ents | have been shown to p o s s e s s a c la y m ineral s u i t e q u ite ! d i f f e r e n t from Chesapeake Bay and Susquehanna River s e d i - I j ments, and a ls o s i g n i f i c a n t l y d i f f e r e n t from Rhode River | watershed sedim ents ( f i g s . 50, 51 and 5 2 ). The e stu a r y sedim ents are m i n e r a l o g ic a l ly very s i m i l a r - - w i t h s l i g h t l y l e s s m o n tm o r illo n ite and s l i g h t l y more i l l i t e - - t o the I 1 Eocene banks o f the e s t u a r y . The immediate c o n c lu sio n i s th a t shore e r o sio n i s a major source o f sediment to the e s t u a r y . i | Some c orro b ora tion i s provided by the h i s t o r i c ch a r t! i data (Tables 7 and 8 ) , which showed th at the estu a ry i s | d i g e s t i n g i t s s h o r e l i n e s at an average r e c e s s io n r a te o f 8i j cm/yr , and as r a p id ly as 50 m over 127 years in p l a c e s . | This p ro d ig io u s q u a n tity o f eroded shore m a ter ia l can | account for n ea rly h a l f o f the sediment d e liv e r e d to the j ; i estu ary over the past 127 y e a r s, as w i l l be shown below. Textural s t a t i s t i c s ( f i g s . 16 to 23) the e stu a r y bottom sedim ents in d ic a t e th a t the mouth sedim ents are d i s t i n c t from those in the remainder o f the e s t u a r y . G en erally, the te x tu r e o f the f r a c t io n sm aller than 62 m icrometers becomes f in e r u p -estu a r y , which may mean th a t the in f lu e n c e o f the Chesapeake on Rhode River sedim ents j d im in ish e s with d is ta n c e inland from the mouth. There i s | a ls o v i s i b l e in most o f th e se p r o f i l e s a s l i g h t f i n in g | downcore. This change i s a ls o d e t e c t a b l e in the mean phi | versu s skewness p l o t ( f i g . 2 5 ). The v a r ia t io n i s not i I 1 g r ea t enough to serve as proof o f a source change over tim e, however. The same type o f s m a l l - s c a le change i s i seen in the c la y m ineral p r o f i l e s ( f i g . 49) in some o f the c o r e s , but the v a r ia t i o n i s a ls o small and i n c o n c l u s i v e . j ! i j Magnetic c h a r a c t e r i s t i c s , on the other hand, do e x h i b i t | I i : I | s i g n i f i c a n t downcore v a r i a t i o n . Figure 38 shows t h a t the I : magnetic "signature" o f bedrock-derived sedim ents i s a I i r e l a t i v e l y low Satu ra tion Isotherm al Remanent Magnetism j (SIRM) and low s u s c e p t i b i l i t y . Sediments derived prima- j r i l y from s o i l e r o s io n , however, e x h i b i t high SIRM and higher s u s c e p t i b i l i t y . Examining the core s u s c e p t i b i l i t y p r o f i l e s , there i s a d i s t i n c t change in both s u s c e p t i b i l i t y (shown in Figure 37) and SIRM at mid-depth in many I c o r e s , p a r t i c u l a r l y in the uppermost part o f the e s t u a r y . I f The magnetic c h a r a c t e r i s t i c s o f the sedim ents change from : "b ed rock-typ e” to " s o il- t y p e " up -co re. This change occu rs at 74 cm in Core 1B, at 80 cm in Core 1A, at 112 cm in Core 3-B, and at 60 cm in Core 3A. Referring to the Pb-210 sed im en tatio n r a te n e a r e st each o f th e se co re s ( f i g . 5 6 ), the change appears to occur about 74 years ago in Core 1-B, about 80 years ago in Core j 1-A, about 72 years ago in Core 3-B, and about 39 years ago in Core 3-A. What t h i s changeover im p lie s i s t h a t , at j 1 some time in the r e c e n t p a s t, so i l - d e r i v e d - - r a t h e r than b e d r o c k -d e r iv e d --se d im e n ts came to be predominant in the I uppermost part o f the e s tu a r y , where th e se co re s are j j l o c a t e d . C onversely, Core 5A, c l o s e r to the mouth, 1 d i s p l a y s "bedrock-type" sediment c h a r a c t e r i s t i c s along i t s e n t i r e p r o f i l e , which may imply th a t shore e r o sio n has always predominated in the main body o f the e s t u a r y . ; i Thus the m ineralogy, magnetic str a tig r a p h y and h i s t o r i c i chart data p oin t to shore e r o sio n as the major source o f j sedim ents to the e s t u a r y . The magnitude o f the s h o r e lin e ! c o n tr ib u tio n w i l l be d is c u s s e d below. 4.1.2 Watershed E rosion The net input o f f l u v i a l sediment from the Rhode River watershed streams to the estu a r y can be obtained using data from the Smithsonian I n s t i t u t i o n watershed m onitoring s t a t i o n s . These s t a t i o n s are V-notch wiers th a t sample sudpended sediment and water d isch a rg e on many o f the j streams t r ib u t a r y to the e s t u a r y . With a l l o f the j s t a t i o n s o p e r a tin g , over 60% o f the t o t a l watershed area | j d ischarged through the w ie r s . Knowing y ie ld r a t e s for d i f f e r e n t lan d -u se c a t e g o r i e s , and knowing the percent o f j j the t o t a l watershed in each c a te g o r y , t o t a l y i e l d s for each ca te g o ry can be computed. Wier data for 1974 were used in c a l c u l a t i n g the t o t a l y i e l d s . P r e c i p i t a t i o n in th a t year (P ie r c e and Dulong, 1977) was somewhat below normal th at year, and so the net y ie ld is probably s l i g h t l y low. The y ie ld d a ta, taken from C o r n e ll(1971)> C o rrell et al . ( 1975) and Pierce and Dulong (1 9 7 7 ), are shown in Table 12. The n e g a tiv e y ie ld r a te for marsh and swamp areas i n d i c a t e s th a t such areas are a sediment sink rath er than a so u rce. Total annual sediment y i e l d from the watershed to the estu a r y i s 0.56 x fl 10 kg. It should be noted th a t t h i s fig u r e a p p l ie s to normal stream flow c o n d i t i o n s . The sediment input to the e stu a r y during storms i s included in a sep arate ca teg o ry o f the sediment budget. 263 TABLE 12 SEDIMENT YIELD RATES AND CURRENT LAND USE PERCENTAGES IN THE RHODE RIVER WATERSHED Land Use, - v Category Area in Percent o f Category Total Area (h a ) 1974 S e d i ment Yield Rate ( kg/ha/da) Annual v Sediment ; Y ield a (kg x 10 Crops 615 18.9 0. 38 8.53 Marsh, Swamps and Open Water 18 0.5 - 7 . 4 - 4 .8 6 F o rest and Old F ie ld s 1882 57.7 0.16 11.0 G rasslands 379 11.6 0.21 2. 90 R e s id e n t ia l , Developed 366 11.2 219 38.74 T o ta ls 3260 100.0 56.31 1. Data from 2. Data from Dulong C o rrell (1 9 7 1 ). C o rrell et al . ( 1975), and Pierce (1 9 7 7 ). Does not in c lu d e storm s. and Most o f th e se sedim ents en ter the e stu a r y from the Muddy Creek watershed at the head o f the Rhode River ( f i g . 12). The Muddy Creek watershed com prises 73% o f the Rhode 264 River watershed. Thus, most o f the f l u v i a l sedim ents i en ter the e stu a r y in i t s upper s e c t i o n . According to Han ( 1975), the r e s id e n c e time o f water in t h i s s e c t i o n i s approxim ately 17 days. I f the f l u v i a l suspended sediment averages 4 micrometers in d iam eter, the Stokes s e t t l i n g time for an average p a r t i c l e to s e t t l e through the 2-meter ! average depth o f the e stu a r y would be 1.8 days. Consid- I ' ering the low -energy environment o f the estu a r y and the small t i d a l range ( 0 .3 m) , v i r t u a l l y a l l sediment p a r t i c l e s e n te r in g from streams might reason ably be expected to ; i end up on the f lo o r o f the e s t u a r y . If t h i s i s the c a s e , then the 0.56 x 10^ kg annual j ■ input from the streams would, i f spread even ly over the j estu a r y f l o o r , form a la yer 0 .2 m m th ic k ( t h i s assumes a j ! S j 56.5% water c o n ten t in the bottom sedim ents, as b e f o r e , j ! Comparing t h i s annual ra te with the Pb-210 sed im en ta tion j ra te o f 5 .2 mm/yr for the m id -estu ary Core 30, t h i s f l u v i a l input r e p r e s e n t s only about 4% of the t o t a l s e d i - ; ment d e p o site d in the e stu a ry a n n u a lly . Given th a t 1974; i had l e s s than normal r a i n f a l l , the average f l u v i a l c o n t r ib u t io n might p o s s i b l y be as much as h a l f again as ! g r e a t , or 6%. The watershed streams n e v e r t h e l e s s supply! j l i t t l e o f the e s t u a r y ’ s annual sediment load under normal I | d isch a rg e c o n d i t i o n s . 265 4.1.3 B io g e n ic S ou rces Other than e r o sio n o f the e s t u a r in e s h o r e lin e and ru n o ff from the watershed, th ere are two other p o t e n t i a l sou rces o f sediment under normal h y d ro lo g ic c o n d it io n s : b io g e n ic production w ithin the e stu a r y and a d v e c tiv e tr a n sp o r t o f Chesapeake Bay sedim ents through the estu a r y mouth. Quan t i t a t i v e d e ter m in a tio n s o f th e se two inp uts are d i f f i c u l t to o b ta in , in v o lv in g long-term sampling o f suspended s e d i ment throughout the e s tu a r y . This would be n e c essa ry because suspended sediment l e v e l s w ithin the e stu a r y vary ! w idely with l o c a t i o n , t i d e s t a g e , d isch a rg e and sea so n . I ! Reference to other s t u d i e s , however, and an examination o f the r ea c to r n u c lid e data e n a b le s e s t im a t e s to be made for the c o n t r ib u t io n from each o f th e se so u r c e s . j j The f r a c t i o n o f the Rhode River bottom sedim ents th a t i r e s u l t s from b io g e n ic sou rces i s assumed to be the same as ! th a t found in the o u t ly in g Chesapeake Bay. Biggs (1970) i i found th a t n o n - s k e l e t a l organic m a te r ia l accounted for 22% o f the t o t a l mass o f suspended sediment in the m id -r eg io n s o f the Chesapeake. Most o f t h i s m a ter ia l became decom posed or was o th erw ise l o s t before d e p o s i t i o n , making the organic c o n t r ib u t io n to the bottom sedim ents only about 3%. 266 Combustion o f a l l o f the Rhode River Estuary bottom samples at 550 degrees C r e s u lt e d in weight l o s s e s a v e r aging about 9% (F igures 27 to 3 4 ). Some o f t h i s l o s s r e p r e s e n ts organic m a te r ia l from watershed s o i l ero sio n ■ plus i n t e r l a y e r water in hydrated c l a y s . It would be a reason ab le e stim a te th a t the organic input to the Rhode River sedim ents from b io g e n ic sou rces w ithin the estu ary i i s only about 6% or l e s s . j j 4 . 1 . 4 Sediment Input from the Chesapeake Bay i The portion o f the Rhode River bottom sedim ents th a t | e n te r s the e stu a r y from the Chesapeake Bay can be app roxi- i mated by use o f c la y m ineralogy and r e a c to r n u c lid e d ata. The c la y m ineralogy o f the Chesapeake Bay samples th a t were d escrib ed in the previous chapter i s s i g n i f i c a n t l y | d i f f e r e n t from th a t o f the Rhode River sed im en ts. F igures I | 50 to 52 show th a t i l l i t e i s a minor c o n s t i t u e n t in a l l j I Rhode River sam ples, w h ile m o n tm o r illo n ite i s the dominant c la y m in era l. In the Chesapeake Bay samples i l l i t e becomes far more prominent, w h ile the m o n tm o rillo n ite percentage i s reduced by n e a r ly h a l f . Hathaway (1971) c o l l e c t e d a s e t o f fo u rteen bottom samples down the len g th o f the Chesapeake and, based on v i s u a l o b se r v a tio n o f the d i f f r a c t i o n p a t t e r n s , reported i I i 267 sim ila r r e s u l t s : m o n tm o r illo n ite was a minor c o n s t i t u e n t in a l l samples from head to mouth, w hile i l l i t e was c o n s i s t e n t l y the predominant c la y m in era l. Although, as mentioned in Chapter 3, i t i s d i f f i c u l t to draw q u a n t i t a t i v e c o n c lu s io n s from x-ray d i f f r a c t i o n d a ta , the obvious d i f f e r e n c e s between the Rhode River c la y i ; m ineral s u i t e and th a t o f the Chesapeake enable c e r ta in i n f e r e n c e s to be made. It would appear th a t the input o f Chesapeake Bay sedim ents to the Rhode River Estuary i s | s i g n i f i c a n t l y l e s s than h a l f o f the t o t a l input from a l l i i s o u r c e s . To improve the p r e c is io n o f t h i s e s t i m a t e , the gamma decay a c t i v i t y o f Core 38 can be put to use. Core 38, at the c en te r o f the estu a r y mouth, was sampled at regu lar i n t e r v a l s . Each sample was then su b jected to low -back- graund gamma spectrom etry in a search for r e a c t o r - g e n e r ated n u c l i d e s . Other than n a t u r a lly - o c c u r r in g p o ta s- sium-40, the only n u c lid e d e te c te d was cesium -137. The Cs-137 p r o f i l e , shown in Figure 58, i s a t t r i b u t a b l e e n t i r e l y to f a l l o u t . The complete counting r e s u l t s are shown in Appendix B. 268 As noted in the s e c t io n o f Chapter 3 d e a lin g with r e a c to r r e l e a s e s to the Susquehanna River, Cesium-134 has ! been r e le a s e d to the r iv e r in e a s i l y t r a c e a b le q u a n t i t i e s . Simple c a l c u l a t i o n s can provide an e s tim a te o f how sm all the Chesapeake Bay sediment input would have to be in order for Cs-134 to be in d e c t a b le in Core 38. For th e se j c a l c u l a t i o n s the year o f i n t e r e s t i s 1977. That year had I the l a r g e s t annual Cs-134 r e l e a s e (1 .3 4 c u r ie s ) prior to the August, 1978, sampling d a te , as seen in Figure 57 and Table 11. Two assum ptions are made: a l l o f the cesium i s assumed to be adsorbed on sedim ents, and the trap e f f i c i e n c y o f the dam immediately below the Peach Bottom p la n t, Conow- ingo, i s taken to be 13%. In other words, 87% o f the sediment load i s assumed to pass through Conowingo Dam and i j out in to the upper bay ( f i g . 14). | Making a decay c o r r e c tio n to the December, 1980, counting d a te , the a c t i v i t y p assing to the upper bay in 1977 i s 0.446 c u r ie s (d e c a y -c o r r e c te d ) tim es 0 .8 7 , or 0.388 c u r i e s . The Susquehanna sediment d isch a rg e i s taken q to be the average from Table 1: 1.2 x 10 kg. S p e c i f ic a c t i v i t y , th en , i s : 0.388 c i / 1.2 x 109 kg x 2 .2 x 1012 dpm/ci 269 | =0. 71 dpm/g E stim ates o f the percentage o f sediment e n te r in g the uppermost part o f the bay th a t i s due to Susquehanna River d is c h a r g e range from 83% to 97% (B ig g s, 1970; S c h u b e l, j 1972). The only other s i g n i f i c a n t c o n tr ib u tio n i s from j i i ! shore e r o s io n . Using 90% as an average c o n t r ib u t io n from I the Susquehanna, the s p e c i f i c a c t i v i t y o f Cs-134 in the j uppermost reg ion o f the Chesapeake then becomes: ! ! j 0.71 dpm/g x 0 .9 0 = 0.64 dpm/g i j E stim ates o f the percentage o f the sedim ents e n te r in g t h i s uppermost reg io n o f the bay th a t pass through without j being trapped range from about 4% to about 30% (Schubel j and B ig gs, 1969; B ig g s, 1970; Eaton, 1980). It i s assumed here th a t 25% p a sse s through. The b a s is for t h i s f ig u r e w i l l be d is c u sse d in the next s e c t i o n . Susquehanna River sediment would comprise 90% o f t h i s amount, or 22%. According to Biggs' (1970) budget for t o t a l se sto n j I - in p u ts to the upper bay (0-45 km from the head) and middle | j bay (45-150 km from the head) r e g io n s , t h i s 22% would 270 rep resen t about 32% o f a l l sediment e n te r in g the middle bay. (For r e f e r e n c e , the Rhode River i s in the middle bay r e g io n , 76 km from the mouth; see Figure 13) • Thus, the s p e c i f i c a c t i v i t y o f Cs-134 in the middle bay i s d ilu t e d to : | 0.64 dpm/g x 0 .3 2 = 0 .2 0 dpm/g I f the d e t e c t i o n l i m i t for the gamma sp ectrom eter i s taken to be 0.04 dpm/g, then the minimum percentage o f Chesa- | peake Bay sediment th a t would have to be p resen t in Core j 38 to be d e te c te d would be: I | l j j | 0.04 dpm/g / 0.20 dpm/g x 100 = 20% j i In other words, i f the Chesapeake Bay had supp lied 20% j or more o f the sedim ents in the Core 38 area, Cs-134 should have been d e t e c t a b l e in the c o r e . Based on the above assum ptions, th en , the Chesapeake Bay c o n tr ib u t io n i s l e s s than 20%. P o t e n tia l err o rs in the assumptions could e it h e r s l i g h t l y d ecrease or s l i g h t l y in c r e a se t h i s p ercen ta g e. Since the Rhode River Estuary i s in the northern part o f the middle bay r e g io n , the Susquehanna sedim ents and t h e ir a s s o c ia t e d r a d io n u c lid e s are probably l e s s d ilu t e d than the average for the middle bay. This would have the e f f e c t o f r a is in g the s p e c i f i c a c t i v i t y and lowering the maximum Chesapeake c o n t r ib u tio n to Rhode River sedim ents I below 20%. Conversely, i f a sm aller percentage o f Susque hanna River f l u v i a l sediment p a sse s through the upper bay than assumed here (25%), the percentage would in c r e a s e . On the whole, i t would appear that 20% i s a rea so n ab le upper l i m i t for the portion o f the Rhode River sediment j budget th a t i s f i l l e d by the Chesapeake Bay. 4. 1 .4 .1 Storm D ep ositio n The f r a c t i o n o f the t o t a l e s t u a r in e sediment load th a t i s d e liv e r e d by major storms i s another item in the budget | th a t i s d i f f i c u l t to q u a n tif y . Although the sedim ento- l o g i c e f f e c t o f a s i n g l e storm might be measured, the in c id e n c e o f major storms i s r e l a t i v e l y low. As a r e s u l t , t h e i r long-term average c o n t r ib u t io n i s d i f f i c u l t to e s t i mate. Table 2 l i s t s a l l o f the major f lo o d s for the Susquehanna area from 1842 to 1978. Average i n t e r v a l between f lo o d s for t h i s period i s 7 years for the Susque hanna region as a whole, and c e r t a i n l y l o n g e r - - p o s s i b l y | tw ice as l o n g - - f o r in d iv id u a l w atersheds, such as the Rhode R iv e r . 272 The storms and t h e i r a s s o c ia t e d flo o d s do seem to have ■ a measurable e f f e c t on e s t u a r in e se d im e n ta tio n . The number o f sand laminae seen in th ree d e s s ic a t e d co re s ( f i g . 36) matches up reason ably w e ll with the number o f i storms expected during the period rep resen ted by the c o re s (Table 5 ) . ! A h in t o f the magnitude o f t h i s e f f e c t can be seen in , the Pb-210 p r o f i l e s ( f i g . 55) for four Rhode River c o r e s . | Three o f the c o re s have le a d - d e p le t e d zones at the approx- ! imate l e v e l where 1972— T ropical Storm Agnes- -s h o u ld be. ! j The t h ic k n e s s o f the storm d e p o s i t s i s d i f f i c u l t to gauge j I | at the sampling i n t e r v a l th a t was used, although i t seems j probable th a t the Agnes la y er in Core 3-B-1 has a t h i c k - j ! ; ness o f 2 cm or more. Hirschberg and Schubel ( 1979) I I reported a t h ic k n e s s o f 16 cm for the Agnes la y er in a j ! | | Pb-210 core from the hig h -sed im entation area at the head i o f the bay. A q u a n t i t a t i v e e stim a te for the e f f e c t o f a s i n g l e storm i s provided by the f l u o r e s c e n t sand tr a c e r e x p e r i ment ( f i g s . 47 and 4 8 ), which d e lin e a t e d the la y er o f sediment d e p o site d by Tropical Storm David over the period September 5 -6, 1979- The t h ic k n e s s o f the sediment la y e r \ d e p o site d during the month th a t included the storm varied 273 from 1.8 cm to 2 .8 cm in four c o r e s . In two other cores the f lu o r e s c e n t sand was mixed to 1.0 cm and 3-9 cm. The average t h ic k n e s s o f the storm la y er observed was j u s t over 2 cm. This storm brought 10.8 cm o f p r e c i p i t a t i o n in a s i n g l e day. Although d e t a i l e d records are not a v a i l a b l e for in d iv id u a l storm s, monthly t o t a l s for major storm months in d ic a t e th a t the September, 1979, storm was t y p i c a l . For some o f the storms l i s t e d in Table 2 the monthly p r e c i p i t a t i o n t o t a l s for Annapolis, Maryland, were: 16.5 cm (September, 1975, H urricaine E l o i s e ) , 14.1 cm (June, 1972, Tropical Storm Agnes) , 30.5 cm (August, 1955), 13*1 cm (May, 1946), 1 1 . 3 cm (March, 1936), and 2 9.6 cm (August, 1933). Although the data are sp a r se , i t would seem th at Trop i c a l Storm David was not an unusual storm and th a t 2 cm i s probably not an unusual t h ic k n e s s for a storm d e p o s it in the e s t u a r y . I f i t i s assumed th a t a major storm such as David recurs approxim ately every 14 y e a r s, as suggested in Chapter 3, then storms can account for 1.4 m m o f sedimen t a t i o n per year (2 cm per 14 y e a r s ) . This amount w i l l be used to e stim a te the c o n tr ib u tio n o f storms to the e s t u a rine sediment budget in the next s e c t i o n . 274 4 .2 RATES AND VOLUMES OF SEDIMENT INPUT TO THE RHODE RIVER ESTUARY 4 .2 .1 Holocene Sedim entation 4 . 2 . 1 . 1 R iv e r -to -E stu a r y T r a n sitio n Being one o f the more n o r th e r ly t r i b u t a r i e s , the Rhode River was s t i l l f l u v i a l during most o f the f i r s t h a l f o f the Chesapeake Bay's l i f e t i m e . The buried thalweg at the mouth o f the Chesapeake i s -51 m below p resen t sea l e v e l , as shown in Figure 2 and d escrib ed in Chapter 1 . R efer ring to the sea l e v e l curves in Figure 9, the r i s i n g Holo cene sea reached t h i s e l e v a t i o n between 9,600 years BP (Milliman and Emery, 1968) and 10,900 years BP (D illo n and O ldale, 1978). The older date i s probably more r e l i a b l e , sin c e i t in c lu d e s c o r r e c t io n s for "mobile" s h e l l samples and for c r u s t a l downwarping. Thus, the mouth o f the bay was e s t u a r in e by 10,900 years BP and was probably in the t i d a l r iv e r sta g e for a cen tu ry or two prior to t h a t . For the Rhode River the bottom o f the f i l l e d p a le o - channel at the mouth l i e s - 1 4 .1 m below presen t mean sea l e v e l ( f i g . 4 2 ). The sea had r is e n to t h i s poin t by about 6,800 y ears BP (Milliman and Emery, 1968; D illo n and O ldale, 1978), with the t i d a l r iv e r phase beginning a century or two e a r l i e r . 275 4 . 2 . 1 . 2 Total Holocene F i l l : 7-kHz Records Knowing th a t the Rhode River v a l l e y has been f i l l i n g with e s t u a r in e sediments for 6,800 years and a ls o knowing the geometry o f the v a l l e y from a n a l y s is o f the a c o u s t ic p r o f i l e s , i t i s p o s s i b l e to c a l c u l a t e the long-term Holo cene sedim entation r a te for the e s tu a r y . The t o t a l volume o f sediment f i l l i n g the e stu a r y , c a lc u la t e d from the 7-kHz data d escrib ed in S ection 3 - 1 . 6 . 2 , i s 1.61 x 107 cubic m eters. Taking d e n s i t i e s and compaction e f f e c t s in to account, t h i s volume was converted in Sectio n 3 * 1 .6 .4 to a mass o f 9-72 x 10^ kg. The lo n g term Holocene sediment accumulation r a te for the Rhode River Estuary, th en , i s : 1.61 x 107 m3 / 6,800 yr = 2.37 x 103 m3/yr or , 9.72 x 10^ kg / 6,800 yr = 1.43 x 10^ kg/yr M ultip lyin g the modern e s tu a r in e su rfa c e area taken from the 1972 bathym etric chart (Table 7 ) - - 4 . 8 5 x 106 — by the 3*3 mm/yr l o c a l sea l e v e l r i s e r a t e , the present annual in c r e a se in volume o f the e stu a r y due to sea l e v e l r i s e i s : 276 4.85 x 10^ m2 x 3-3 mm/yr = 1.60 x 10^ m^/yr This volume in c re a se overpowers the long-term rate o f f i l l i n g by a fa c to r o f n ea rly sev en . Thus, before the in c r e a se in the f i l l i n g rate began during h i s t o r i c tim e, the e stu a r y was in c r e a s i n g - - r a t h e r than d im in i s h in g - - in volume. Even using the slower ra te o f sea l e v e l r i s e obtained from the peat sample in the lower part o f Core 2B (Table 10)--abou t 1.06 mm/yr--the r a te o f in c r e a se in estu a r y volume would s t i l l be more than tw ice the lo n g term ra te o f f i l l i n g . The above r a t e s are shown in Table 13- 4 . 2 . 1 . 3 P re -S e ttle m en t Radiocarbon Dates P r e -s e ttle m e n t sed im en tation r a t e s were obtained from the o lder radiocarbon sam ples. The sample d a te s encompass the period from about 800 to about 1900 years ago, and r e s u l t in a mean sedim entation ra te o f 0.63 mm/yr. This r e p r e s e n ts a r a te o f sediment volume in c r e a se o f 3-06 x 10^ m3/yr. This ra te o f sediment in f lu x i s slower than the ra te o f in c r e a se in e s t u a r in e volume due to sea l e v e l r i s e - - a t e it h e r the 3*3 mm/yr r a te or the e a r l i e r 1.0 mm/yr r a t e . At the p r e - s e t t le m e n t r a te o f f i l l i n g , th en , the e stu a r y was e i t h e r near se d im e n to lo g ic eq u ilib riu m or was in c r e a s in g in volume each year. These data are a lso included in Table 13. 277 4.2.2 H i s t o r i c S e d im e n ta tio n 4 . 2 . 2 . 1 P o st-S e ttle m e n t Radiocarbon Dates The most r ec en t samples in Table 10— those datin g from roughly the past 300 y e a r s - - y i e l d a mean sedim entation ra te o f 4.11 mm/yr. This ra te o f i n f i l l i n g would r e s u l t 4 3 in a sediment volume input o f 1.99 x 10 m / y r . At t h i s r a t e , sed im en ta tio n would overtake the 3-3 mm/yr sea l e v e l r i s e and c om p letely f i l l the estu a r y in l e s s than 2500 y e a r s. These r a t e s appear in Table 13- 4 . 2 . 2 . 2 Sedim entation Rates from H is t o r ic Charts In Section 3 - 1 - T an examination o f the 1845-1972 changes in the bathymetry o f the estu a r y enabled the c a l c u l a t i o n o f sediment volume input and sedim entation r a t e s over the 127-year p e r io d . The mean annual sediment volume added was 2.41 x 10^ m3 / y r . At t h i s r a te o f f i l l i n g , the 3-3 mm/yr sea l e v e l r i s e would be n u l l i f i e d and the estu a ry f i l l e d in 1200 y e a r s . These f i g u r e s appear in Table 13. 4 . 2 . 2 . 3 Lead-210 and Cesium-137 Rates o f F i l l As shown in Figure 18, four co re s from the Rhode River Estuary y ie ld e d Pb-210 sed im en tation r a t e s ranging from 5 .2 mm/yr to 15.5 mm/yr, for a mean r a te o f 10.3 + 4 .2 mm/yr. At 10.3 mm/yr the sediment f i l l on the estu ary f lo o r grows at a r a te o f 5 .0 x 10^ m3 / y r . This extrem ely 278 rapid r a te o f f i l l i n g would convert the e stu a r y to a f i l l e d marsh in l e s s than 300 y e a r s , as shown in Table 13- As mentioned in Chapter 3, i t was f e l t th a t th ree o f the four co res analyzed for Pb-210 may have been obtained from areas where sedim entation r a t e s were higher than normal. The fourth r a t e , 5 .2 mm/yr for Core 30, i s probably the most r e p r e s e n t a t iv e o f sedim entation r a t e s in the main body o f the e stu a r y . A 5 .2 mm/yr sedim entation r a te r e s u l t s in an accumulation r a te o f 2.52 x 10^ m3 / y r . This input r a te would f i l l the e stu a r y in l e s s than 1100 year s . The Cs-137 p r o f i l e from Core 38 at the e stu a r y mouth ( f i g . 58) gave a sedim entation r a te o f 6.0 mm/yr. This r a te i s more in l i n e with th a t o f Core 30. The annual volume input based on Core 38 i s 2.91 x 10^ / y r , which would f i l l the estu a r y in about 750 y e a r s. Core 30, at 5 .2 mm/yr, r e p r e s e n ts a reason able average for the recen t r a te o f sedim entation in the e s t u a r y . It f a l l s between the high Pb-210 r a te s from the sediment trapping area at the head o f the estu a ry and the lower C-14 r a t e s , which are averages over a longer period o f tim e. In c a l c u l a t i n g the sediment budget for the e s tu a r y , 279 then, 5 .2 mm/yr w i l l be used as the average annual sediment input for r ec en t tim e. Table 13 summarizes the r a t e s o f sediment input derived by each o f the above methods. Figure 59 g r a p h ic a lly d e p i c t s the e f f e c t s o f both c o lo n iz a t io n and submergence on sedim entation r a t e s . The sea l e v e l r i s e ra te for the Chesapeake region over most o f the e a r ly e s t u a r in e h is t o r y o f the Rhode River was about 1.5 mm/yr ( f i g . 10). This r a te i s corroborated by the lower peat sample in Core 2B, as noted e a r l i e r ( t a b l e 10). The two upper peat samples, however, in Cores 2B and LP, as w ell as th a t o f Roberts (1979) g iv e more rapid r a te s o f r i s e over h i s t o r i c tim e, more c l o s e l y in l i n e with the 3»3 mm/yr rate th at i s p r e s e n t ly measurable in the region (S e c tio n 1 . 2 . 3 * 2 ) . The net e f f e c t o f European c o lo n iz a t io n and increased submergence ra te can be seen in Figure 59 as a g r e a te r then te n f o ld in c re a se in sedim entation r a t e . The fig u r e i l l u s t r a t e s the reason a b le correspondence between the sedim entation r a t e s obtained in the presen t work and the sea l e v e l r i s e ra te . 280 Figure 59: Rhode River se d im e n ta tio n r a t e s versus tim e. 281 RHODE R IV E R 5EDI MENTRTI ON RRTE5 V 5 . TIME G • S O U R C E S F O R S E D I M E N T A T I O N R R T E S R 7 - K H Z R E C O R D S B C - IH D R T E 5 £ \D\ C D C - 1 H D A T E S H I S T O R I C B A T H Y M E T R I C C H A R T S E P B - 2 1 0 \ 0 F C S - 1 3 7 M © / N a t : S E AL E V E L R I S E R R T E S O B T A I N E D > - N 2 C 0 \ F R O M R H O D E R I V E R P E R T S A M P L E S 1 C O R E 2 - B / L O H E R 1 9 H 0 B .P . 2:3 2 c o r e L P 2 1 0 B .P . V 0 \ 3 < R O B E R T S / I 0 7 S > 2 7 0 B .P . U J H C O R E 2 - B / U P P E R 3 2 0 B .P . H * □ : o : 2 1 0 R I V E R - E S T L f f l R Y E U R O P E A N T R A N S I T I O N C O L O N I Z A T I O N - - - - - - - - - - - - -® S 0 O O I 9 E 3 1 0 7 0 1 B H S I B 0 7 R .D . R .D . R .D . A .D . B .P . 1 a N 5 • 1 fin i pan 1 ooao 0 0 N 3 YERRS BEFORE I 3 7 0 R . O . < L.PG SCALE> TABLE 13 SUMMARY OF SEDIMENTATION RATES FOR THE RHODE RIVER ESTUARY Method Period Sedim entation Rate Years U n til 1 F i l l e d mm/yr x 106 kg/yr x 103 c u . m per yr 7-kHz 6800 BP-present 0. 48 1 . 43 2.37 C-14 (pre) 1948 BP-1650 AD 0. 63 1.88 3. 06 -------- C-14 (post) 1650 AD-present 4.11 12.2 19.9 2491 H is t o r ic Charts 1845 AD-present 4. 98 14.8 24. 1 1200 Cs -137 1963 AD-present 6. 0 17.9 29. 1 751 Pb-210 (Core 30) 1870 AD-present 5 .2 15.5 25. 2 1067 Pb-210 (four core avg) 1870 AD-present 10.3 30.7 50.0 289 1. H y p o t h e t i c a l , assuming a l o c a l sea l e v e l r i s e r a te o f 3-3 mm/yr, and keeping su rfa ce area co n sta n t at 1972 value (4 .8 5 m illio n s q . m e te r s ). 4 . 2 . 3 Recent Sediment Budget Gathering a l l o f the inform ation on sediment in p u ts to the estu a ry and r a te s o f se d im e n ta tio n , i t i s p o s s i b l e to c o n s tr u c t a sediment budget for the Rhode River Estuary. The r e s u l t i s shown in Table 14. There are fewer unknowns and somewhat l e s s u n c e r ta in ty in t h i s budget than in most such a ttem p ts, s in c e the estu ary i s sm aller and more c o n t r o l l a b l e than la r g e r system s. 283 Each o f the item s in the t a b le has been d iscu sse d p r e v io u s ly . The e x te n t o f shore e r o sio n i s measurable by observing changes in h i s t o r i c c h a r t s . If i t i s assumed th a t a l l o f the eroded m a ter ia l i s r eta in e d w ithin the boundaries o f the e stu a r y , then t h i s must be the major input during modern times--46% i f the annual volume. Biogenic p rodu ction , as derived from combustion o f the core samples and from B ig g s 1 study (1 9 7 0 ), i s probably a maximum figure--6% or l e s s . The c o n tr ib u tio n from the o u t ly in g Chesapeake Bay, deduced from the radiocesium data, i s a ls o a maximum--20% or l e s s . The input fig u r e for watershed streams in v o lv e s some u n c e r ta in ty , s in c e the wier data cover n e ith e r the e n t i r e watershed nor an e n t i r e year. Thus, e x tr a p o la t io n s had to be made. The 6% fig u r e i s probably reason ab le for normal ( i . e . , non-storm) hydrologic c o n d i t i o n s . The l a s t item , based upon o b ser v a tio n o f a s i n g l e storm, in v o lv e s the l a r g e s t u n c e r ta in t y . The f a c t th a t the t o t a l comes to 105% im p lie s th a t th a t the storm c o n tr ib u tio n i s probably c l o s e r to 22% than to 27%. The e x c e ss i s due to resu sp en sion o f p r e v io u s ly - d e p o s it e d bottom m ateria l and to shore ero sio n during storm s. The bulk o f the storm d e p o s it i s f e l t to be sedim ents th a t are 284 TABLE 14 RECENT SEDIMENT BUDGET FOR THE RHODE RIVER ESTUARY Components Method o f Depo- % o f Measurement s i t i o n Total ( mm/yr) Shore Erosion H is t o r ic c h a r ts 2.40 46 Primary Combustion; and Production Biggs (1970) < 6 Chesapeake Bay Radiocesium <20 Watershed Streams Wier sampling 0 .2 6 Storms^^ ^ F lu o rescen t t r a cer ; rain f a l l record s 1.4 27 ^ ' Component Total 105 Measured Total Pb-210 rate 5 .2 100 (2) Assuming an average 2-cm d e p o s it per storm, with a 14-year in t e r v a l between major storms. Component t o t a l exceeds 100% because storm input in c lu d e s part o f other components (shore e r o sion and resu sp en sio n o f bottom s e d i m e n t s ) . new to the e stu a r y , c a rr ie d in from the stream v a l l e y s by flo o d w a te r s . There i s some o b s e r v a tio n a l evidence for t h i s . As mentioned p r e v io u s ly , the Tropical Storm David flood d isch arg e from Muddy Creek was observed as a h ig h ly 285 sedim ent-laden plume carrying f l u v i a l sedim ents r a p id ly from the watershed to the e stu a r y . O r ig in a lly t h i s f l u v i a l m a teria l was eroded from the su rface o f the watershed, but there i s evid en ce th at i t s immediate source i s the banks and channels o f the l o c a l stream s, where i t i s stored between major f l o o d s . Other s t u d i e s have reached such a c o n c lu s io n . Costa (1975) found th at most (52%) of the volume o f m a teria l eroded from Piedmont h i l l s lo p e s and floo d p la in s can be found stored as colluvium in watershed stream banks and chan n e l s . Trimble ( 1975) estim ated that 96% of the s o i l eroded from the Savannah River watershed has not yet been discharged through the mouth. And in a portion o f the Rhode River watershed Roberts (1979) found th a t 91% o f the m a ter ia l eroded over the past 4,000 years was r eta in e d in lowlands and stream v a l l e y s . On the b a s is o f wier data, Pierce (1980) concluded that the eroded m a teria l from Rhode River upland areas moves in to the estu a ry in a s e r i e s o f s t e p s over a time span o f many decades, t r a n s ported during the in fr eq u e n t la r g e storms. In sum, i t i s f e l t th a t the sediment budget presented in Table 14 i s a reason able one, a c c u r a te ly portraying the r e l a t i v e c o n t r ib u t io n s o f shore e r o sio n and storm even ts to the t o t a l sediment input for the e s t u a r y . The e f f e c t 286 that th e se various agents o f sedim entation and e ro sio n have on the fa te o f e s t u a r i e s w i l l be taken up in Chapter 5. 4 .3 SEDIMENTATION IN THE UPPER CHESAPEAKE BAY AND SUSQUEHANNA RIVER 4 .3 •1 Nuclide Inventory From the rea c to r r e l e a s e data presented in Table 11, i t appears th a t r e l e a s e s from the Peach Bottom r e a c to r s account for about 97% of the t o t a l Cs-134 input to the r i v e r . It a lso appears th a t the r e l a t i v e l y la r g e r e l e a s e o f n ea rly 2.6 c u r ie s o f Cs-134 from the Peach Bottom s i t e during the fourth quarter o f 1978 ( f i g . 57) w i l l provide an extrem ely u s e f u l tr a c e r for the fa te o f suspended p a r t i c l e s in the lower Susquehanna and upper Chesapeake Bay. Nuclide in v en tory d e t a i l s appear in Olsen e t a l . (1 9 8 1 ). F igures 13 and 14 show the l o c a t i o n o f the Chesapeake and Susquehanna sam ples, r e s p e c t i v e l y . All o f the Susque hanna samples and most o f the upper Chesapeake Bay samples were gamma-counted, with the r e s u l t s ta b u lated in Appendix B. 287 As mentioned in Chapter 3, th ere are four darns on the r iv e r between the Three Mile Island plant and the bay, a d is ta n c e o f 91 km. All o f th e se dams trap sediment to some d eg ree. It has lik e w is e been noted p r e v io u sly th a t the uppermost region o f the Chesapeake, w ithin about 20 km o f the mouth, i s a lso an e f f e c t i v e sediment tra p . Thus there are f i v e trapping b a sin s for sedim ents--and n u c l i d e s - - i n the study a rea. L ocations o f the dams and the two nuclear p la n ts are shown in Figure 14. The r e s u l t s o f the gamma-counting can be used to tra ce the f a t e o f sedim ents in the Susquehanna/Chesapeake system . Cs-134 a c t i v i t i e s in the samples g e n e r a lly d im inish with d is ta n c e from the mouth o f the Susquehanna. As noted in Chapter 3> Core 38 from the Rhode River, 76 km from the head o f the bay, had no d e t e c t a b l e Cs-134. By com piling the inventory o f Cs-134 in each o f the f i v e trapping b a sin s--a n d making the assumption th at v i r t u a l l y a l l o f the Cs-134 e x i s t s in the adsorbed s t a t e on sediment p a r t i c l e s - - i t i s p o s s i b l e to convert a n u c lid e budget in to a sediment budget for the Susquehanna and upper bay. In so doing, areas o f e x t e n s iv e sediment depo s i t i o n can be i d e n t i f i e d . It i s a ls o p o s s ib le to d e t e r mine how much sediment le a v e s the system, being carried in to the main body o f the Chesapeake Bay. And l a s t l y , the 288 rate at which the variou s trapping b a sin s are f i l l i n g can be c a l c u l a t e d . Table 15 shows the d e c a y -c o rr e cte d a c t i v i t y o f Cs-134 p resen t in the sedim ents o f each o f the f i v e trapping b a s in s . This inform ation was obtained by takin g the mean a c t i v i t y o f a l l samples w ithin the basin (column 4 ), m u ltip ly in g t h i s by the depth w ithin the sedim ents to which Cs - 134 i s d e te c te d (column 5 ) , and m u ltip ly in g again by the area o f the basin (column 3)- A f i n a l m u ltip ly in g fa c to r , the dry d e n s ity — — 0 .7 g / c m 3 __g iv e s the in te g r a te d a c t i v i t y for each basin (column 6 ) . Examination o f Table 15 p rovid es some u s e fu l i n s i g h t s in to sediment movement w ithin t h i s f l u v i a l and e s tu a r in e system . F i r s t , the major part o f the Cs-134 p resen t in the sedim ents (2 .4 3 c i) - - a n d by e x t e n s io n , most o f the sediment introduced during the years s in c e the c o n str u c tio n o f the nuclear p l a n t s - - i s trapped w ithin the upper 20 km of the Chesapeake Bay. Another 0.48 c i i s d ep o sited behind the lowermost dam, Conowingo. It can be seen th at the upper three dams contain l i t t l e o f the Cs-134 in v en to r y , but t h i s i s due p rim arily to the f a c t th a t they are trapping Cs-134 from the Three Mile Island s i t e o n ly . They are upriver from the major source o f the n u c lid e , the Peach Bottom p la n t. As mentioned above, the Peach Bottom 289 TABLE 15 CESIUM-134 ACTIVITY RETAINED IN SUSQUEHANNA RIVER RESERVOIRS AND UPPER CHESAPEAKE BAY Reservoir Di stance Down r iv e r from TMI (km) Reser voir Area (km ) Mean Cs-134 A c t i v i t y o f Samples ( . ( p c i / k g ) Mean Depth o f D etec t a b le Act i - v i t y ( cm) Reser v oir I n t e grated A c ti- v i t y (3) ( c i ) (TMI(4) ) 0 .0 York Haven 2 .4 1 77 10 0.0054 Safe Harbor 41.0 1 1 . 04 18 2 0.0028 Hoitwood 5 2.3 4.80 42 10 0.0141 (PB(4) ) 6 2.8 Conowingo 75.5 13.64 338 15 0. 483 Upper Chesa peake Bay 90.9 275.77 126 10 2. 430 (RR(4) ) 166 0 0 0 .0 Total ( f i v e r e s e r v o i r s ) 2.938 Samples c o l l e c t e d 5/79 and 9/79; gamma-counted 1/80. 1. Areas for lower three dams from Williams and Reed ( 1972); upper bay area from Cronin ( 1971)» and in elu d e s upper 20 km o f Chesapeake Bay, plus su b e stu a r i e s , plus Susquehanna River up to Port D ep o sit, Md. 2. P ic o c u r ie s per kilogram . 3. Assumes a dry sample d e n s it y o f 0 .7 g /c u . cm. 4. Three Mile Island Nuclear Plant (TMI), Peach Bottom Nuclear Plant ( PB) and Rhode River Estuary (RR) l o c a t i o n s shown for r e fe r e n c e o n ly . 290 f a c i l i t y i s r e s p o n s ib le for about 97% of the Cs-134 present in the system. In order to determine the percentage o f n u clid e --a n d se d im e n t--th a t i s r eta in e d in each r e s e r v o ir , the opera t o r s ’ q u a rterly l iq u id r e l e a s e r ep o r ts must be compared with the measured a c t i v i t y in the sediment samples. Figure 57 i l l u s t r a t e s the t o t a l Cs-134 r e l e a s e s for the two power plant s i t e s from the date the f i r s t r e a c to r s went c r i t i c a l ( e a r ly 1975) to mid-1979- Table 16 makes a decay c o r r e c t io n for each o f th e se q u a rte rly r e l e a s e s to g iv e the net a c t i v i t y presen t in the system as o f the average counting date for the samples, January, 1980. Comparison o f Tables 15 and 16 i n d i c a t e s th a t about 76% of the Cs-134 r e le a s e d between January, 1975, and May, 1979, was s t i l l w ithin the system as o f May, 1979. Table 17 p r e se n ts a budget sh eet comparing the em p iri c a lly -d e te r m in e d a c i t v i t y presen t in each o f the f i v e r e s e r v o i r s (column 3) with the d e c a y -c o rr e cte d r e le a s e data (column 4 ) . Examination o f t h i s t a b le r e v e a ls that most o f the n u c lid e a c t i v i t y — and by i n f e r e n c e , most o f the s e d im e n t - - is r eta in e d w ithin the system . Of the t o t a l d ec a y -c o rr e cte d a c t i v i t y passing Conowingo Dam, only 26% 291 TABLE 16 CESIUM-134 RELEASES FOR SUSQUEHANNA RIVER NUCLEAR PLANTS, DECAY-CORRECTED TO 1/1/80 Year Peach Bottom Release s ( cur i e s ) Three Mile I. R eleases ( cur i e s ) PB + TMI Total ( cur i e s ) 1975 0.190 E- 03 0.312 E-03 0. 502 E-03 (0.399 E- 04) (0.769 E-04) (0.117 E-03) 1976 0.913 E 00 0. 634 E-02 0.919 E 00 (0.270 E 00) (0.21 0 E -02) (0.272 E 00) 1977 0. 137 E 01 0.579 E-01 0. 143 E 01 (0.608 E 00) (0.265 E-01 ) (0.634 E 00) 1978 0. 286 E 01 0. 144 E 00 0.300 E 01 (0.193 E 01 ) (0.866 E-01 ) (0 .2 02 E 01 ) 1979 (Jan -May) 0.119 E 01 0.750 E-02 0. 120 E 01 (0.942 E 00) (0.586 E-02) (0.948 E 00) TOTALS 0.633 E 01 0.216 E 00 0. 655 E 01 (0.375 E 01 ) (0.121 E 00) (0.387 E 01 ) Upper value i s t o t a l r e le a se d a c t i v i t y for y e a r ; lower value , in parentheses , is r e le a s e d a c t i v i t y , decay- corrected to counting d a te , 1/1 /8 0 • has passed beyond the uppermost 20 km o f the bay. It can be s a id , t h e r e f o r e , th a t the e s tu a r in e d e lt a region at the head o f the Chesapeake has a trapping e f f i c i e n c y o f at l e a s t 74%. 29 2 Whether t h i s 74% trapping e f f i c i e n c y i s a long-term c h a r a c t e r i s t i c o f the upper Chesapeake Bay cannot be determined from th ese o b s e r v a t io n s , sin c e they cover only a fo u r - a n d - a - h a lf year period o f r e l a t i v e l y normal hydro l o g i c c o n d i t i o n s . The only major storm to a f f e c t the upper bay during the o p e r a tio n a l period o f the Susquehanna r e a c to r s was Hurricane Eloi se in September, 1975. This storm h it the watershed before 99% of the present inven tory o f Cs-134 had been r e l e a s e d . As a r e s u l t , i t s e f f e c t s are not i d e n t i f i a b l e in the sediment n u clid e record . 4.3*2 Trap E f f i c i e n c y o f R eservoirs Another r e v e a lin g comparison can be made by looking at the trap e f f i c i e n c i e s o f the three lowermost dams— as computed from the Table 17 data (column 5)--an d the published trap e f f i c i e n c i e s for the same dams (column 6 ) , as reported by the U. S. G eo log ica l Survey (W illiams and Reed, 1972). In th a t rep ort trap e f f i c i e n c i e s were computed using an emporical formula developed by Bruun (1 9 5 3 ). The formula r e l a t e s a r e s e r v o i r ’ s trap e f f i c i e n c y for sediment to i t s c a p a c ity and drainage area. It can be seen th at the comparison i s reasonably good for Conowingo Dam: 12.9% from the samples and r e le a s e d ata , versus 17% from W illiams and Reed (1 9 7 2). For Holtwood Dam the comparison i s a lso rea so n ab le: 12.5% versus 8%. For Safe Harbor Dam, 293 however, th ere i s a la r g e d iscrep an cy : 2.5% based on the p resen t data versu s 30% reported by W illiams and Heed ( 1 9 7 2 ). Either r a d io n u c lid e s , or sedim ents, are being removed by some mechanism, or the low Safe Harbor c a p a c i t y / i n f l o w r a t i o d e c r e a se s the accuracy o f the empir i c a l equation used by W illiams and Reed ( 1972) to c a lc u l a t e the trap e f f i c i e n c y . 2 94 TABLE 17 TRAPPING EFFICIENCY OF LOW ER SUSQUEHANNA RIVER SEDIMENT BASINS Source Reservoir Cs-134 Trapped - ( c i ) 1 Cs- 134 Passed 0 ( c i ) ^ Trapping E f f i c ie n c y Reported Trapping E f f i c i ency TMI 0. 121 York Haven 0.0054 0.116 4.4% Safe Harbor 0.0028 0.113 2.5% 30% Holtwood 0.0141 0. 099 12.5% 8% PB 3.75 Conowingo 0. 483 3.27 12.9% 17% Upper Ches-^ apeake 2. 430 0. 84 74.3% Lower Ches apeake 0.84 1. From Table 15. 2. From Table 16. 3. From W illiams and Reed (1 9 7 2 ). 4. Includes upper 20 km o f bay, from Havre de Grace to S a ssa fr a s River mouth ( f i g . 13). 295 4.3-3 Sediment S to ra g e in th e Susquehanna and Upper Chesapeake Bay Using th e se e s t im a te s for trapping e f f i c i e n c y , and r e f e r ring to the U. S. G eolo gical Survey sediment disch a rge data for the lower Susquehanna River (Table 1), i t i s p o s s i b l e to c a l c u l a t e the amount o f sediment being c o l l e c t e d behind each o f the dams and in the northernmost part o f the Chesapeake Bay. In doing t h i s , the e f f e c t i v e ness o f using r e a c to r - r e le a s e d n u c lid e s as sediment t r a c e r s can be dem onstrated. Sediment d isch a rg e records are a v a i la b l e for H arris burg, P ennsylvania, approxim ately 15 km upriver from Three Mile Is la n d . These records provide a good estim a te for the amount o f sediment e n ter in g the lower reaches o f the Susquehanna. Data from Table 1 for sediment d isch a rg e below the l a s t dam, Conowingo, q u a n tify the r i v e r ' s s e d i ment output to the northern Chesapeake. These data are shown in Table 18. The f i r s t pair o f columns in Table 18 g iv e the lo c a t i o n where the sediment measurements have been carried ou t, plus the r e s e r v o ir trap e f f i c i e n c i e s from Table 17- In columns 3 and 4, f i v e - y e a r averages for sediment disch arg e at Harrisburg and Conowingo are used. The c a lc u la t e d 296 amounts o f sediment r eta in e d behind each dam are based on a comparison o f the known r a d io n u c lid e r e l e a s e s with the measured inventory o f n u c lid e s in the sedim ents o f each trapping b a s in . Using the f i v e - y e a r average q u a n tity o f fl sediment passing Conowingo (0 .9 8 x 10 t o n n e s ) , t h i s value i s found to be about 37% lower than the sediment d isch arg e c a lc u la t e d from the n u c lid e data (1 .5 5 x 10^ t o n n e s ) . In the l a s t two columns th ere i s seen to be good agree ment between the c a lc u la t e d and the measured amounts p assin g Conowingo for 1976, the most r ec en t year with complete record s: 1.14 x 10^ tonnes c a lc u la t e d v s . 0.98 x £ 10 tonnes measured. The co n c lu sio n seems to be th a t the rea c to r n u c l i d e s - - p a r t i c u l a r l y Cs-134— are an a c c u r a te , and p o t e n t i a l l y very powerful t o o l for m onitoring sediment tr a n sp o r t and d e p o s itio n in the Susquehanna and northern Chesapeake Bay. One f i n a l use to which the Suquehanna River n u c lid e data can be put concerns the l i f e t i m e o f the sediment trapping b a s in s . Table 19 takes the annual sediment r e t e n t io n f i g u r e s from column 5 o f Table 18 and d i v i d e s them in to the c a p a c i t i e s for each b a s in . The r e s u l t g i v e s the tim e, in y e a rs, for each o f the b a s in s to f i l l . It can be seen th at none o f the dams i s f i l l i n g r a p id ly . Due to the f a c t that the dams trap n e a r ly h a l f o f the r i v e r ’ s 297 TABLE 18 SEDIMENT TRAPPED AND LOST BY LOW ER SUSQUEHANNA RIVER DAMS fl Loca- Trapping Sediment Trapped or Lost (x 10 tonnes) t io n E f f i - --------------— T - p ' v-----------— ----------------------------- ----- cie n c y 5-Year Avg. 1976 Only Trapped Lost Trapped Lost H arris burg (3) 2.19 2.79 York Haven 4.4% 0.10 2.09 0 .1 2 2.67 Safe Harbor 2.5% 0.05 2.04 0.07 2.60 H olt- wood 12.5% 0.26 1.78 0.33 1.43 Cono wingo 12.9% 0.23 1.55 0.29 1.14 UCB(4) 0.98 0.98 1. Trap e f f i c i e n c i e s taken from Table 17 2. F ive-year averages are for the most r ec en t f i v e years o f normal flow for which a f u l l s e t o f suspended s e d i ment data was a v a i l a b l e : 1966, 1971, 1973, 1974, 1976. The major storm years 1972 ( Agnes) and 1975 ( E l o i s e ) were exclud ed , as were 1967-1970 (low flow or no data) 3. Harrisburg, P a., suspended sediment d isch a rge data taken from U. S. G eo lo gica l Survey r e c o r d s. 4. Upper Chesapeake Bay sediment input from Table 1. 298 sedim ent, the uppermost s e c t i o n o f the Chesapeake Bay i s f i l l i n g more slow ly than sea l e v e l i s r i s i n g . I f the dams fl did not e x i s t and a l l o f the 2.19 x 10 tonnes o f suspended sediment annually p assin g Harrisburg was ca rr ie d to the Chesapeake, the uppermost p ortion o f the bay would f i l l in l e s s than 600 y e a r s . The dams have thus had the e f f e c t o f prolonging the l i f e o f the upper bay. All o f the above c a l c u l a t i o n s have assumed normal h y d ro lo g ic c o n d i t i o n s . During a major storm many y e a r s 1 worth o f sediment d isch a rg e may occur w ithin j u s t a few days, as shown in Table 1. The n u c lid e data does not as yet provide any i n s i g h t in to the e f f e c t o f such e v e n t s , s in c e th ere have not been any major storms w ithin the watershed during the time when most o f the n u c lid e s have been r e le a s e d to the r iv e r - - 1 9 7 6 to the p r e s e n t. The e f f e c t s o f the next major storm, however, w i l l be uniquely d is c e r n a b le by use o f th e se r a d io n u c lid e t r a c e r s . 299 TABLE 19 RATE OF INFILLING OF SUSQUEHANNA RIVER RESERVOIRS, BASED ON SEDIMENT CS-134 DATA Reservoir ( 1 ) Annual D eposition Capa-, p v c i t y 6 3 ( x 1 0 rn ) Years U ntil F il l e d (x 10^ tonnes) (x 106 m3 ) (3) York Haven 0.12 0. 17 10 59 Safe Harbor 0. 07 0. 09 185.0 2312 Holtwood 0.33 0. 48 74. 0 154 Conowingo 0.29 0.41 370.0 902 ucb(4) 0.84 1 . 20 727.9 1. Annual d e p o s itio n r a te s from Table 18, column 5. 2. C a p a c itie s o f Safe Harbor, Holtwood and Conowingo r e s e r v o ir s from Williams and Reed (1 9 7 2 ). Capacity o f Upper Chesapeake Bay from Cronin (1 9 7 1 ), in c lu d e s M LW volume o f upper 20 km o f bay plus major t r i b u t a r i e s plus Susquehanna River up to Port D ep o sit, Md. Capacity o f York Haven r e s e r v o ir e stim a te d . _ 3. Assumes th a t sediment dry d e n s it y i s 0 .7 g/cm . 4. Sediment trapping e f f i c i e n c y o f uppermost 20 km o f Chesapeake Bay i s taken to be 74%. 5. At a sea l e v e l r i s e r a te o f 3.8 mm/yr (Holdahl and Mor r is o n , 1965) water l e v e l in the uppermost Chesapeake Bay r i s e s f a s t e r than r a te o f sediment i n f i l l . 300 Chapter V FATE OF THE ESTUARY What has been presented in the foregoing chapters has been a q u a n t i t a t i v e d e s c r i p t io n o f the impact o f both natu ral and man-induced ev en ts upon the l i f e c y c le o f e s t u a r i e s . The natu ral phenomena consid ered were: the p o s t g l a c i a l r i s e o f sea l e v e l , the e f f e c t o f major storms, and the long-term e f f e c t o f normal e ro sio n o f the watershed. The impact o f man was seen in the rapid in c re a se in sediment d e p o s itio n r a te s fo llo w in g the in f lu x o f European c o l o n i s t s in the 17th Century, and a lso in the e f f e c t th a t the Susquehanna River dams have had on the sedim entation p a tte r n s o f the lower Susquehanna and upper Chesapeake Bay. E stu a r ie s are ephemeral f e a tu r e s at b e s t . Their normal l i f e span i s g e o l o g i c a l l y very b r i e f . By examination o f the depth o f the paleo-Susquehanna1s thalweg ( f i g . 2) and the sea l e v e l r i s e curves ( f i g . 9 ), i t can be observed that the age o f the Chesapeake as an estu a ry i s a l i t t l e l e s s than 11,000 y e a r s. Knowing the p resen t-d ay geometry o f the bay (volume 5 .0 x 1010 m^’ area 6 .5 x 10^ m2 ’ mean- 301 depth 8 .4 m) , and the average ra te o f sea l e v e l r i s e in the region (approxim ately 3*2 mm/yr), and making some c o n s e r v a t iv e assumptions about the o r i g i n a l dim ensions, a long-term ra te o f f i l l can be c a l c u l a t e d . The Holocene r a te o f f i l l i n g for the bay i s about 1.6 x 7 R 10 mJ / y r . At t h i s r a te the in c r e a se in volume due to sea l e v e l r i s e exceeds the l o s s in volume due to i n f i l l i n g . If no other fo r c e s were at work, t h i s c o n d itio n would p e r s i s t i n d e f i n i t e l y , or u n t i l the rapid r i s e o f the sea siackened . In the case o f the Rhode River (Table 13 and Figure 5 9 ), i t was found that the r a te o f i n f i l l i n g had increased by about a fa c to r o f seven from p re -C o lo n ia l to p o st-C o lo - n i a l tim e s, and seemed to have increased even more during the past cen tu ry, to about ten tim es the p re-C o lo n ia l r a t e . If we make the assumption th a t t h i s in c re a se i s true for the bay as a w h o le --th a t the bay i s p r e s e n t ly f i l l i n g at about ten tim es the long-term r a t e - - t h e n the expected period for the bay to remain open water d e c re a ses from i n d e f i n i t e l y long to about 360 y e a r s. Considering th a t the bay i s only about 1 1,000 years o ld , t h i s means th a t the estu a r y has been th r u s t in to 302 se d im e n to lo g ic old age, having already passed through more than 95% o f i t s l i f e s p a n . It i s doubtful whether t h i s process i s r e v e r s i b l e . As d is c u sse d in Chapter 1, the o r i g i n a l cause o f the in creased i n f i l l i n g rate was the unwise c u l t i v a t i o n p r a c t i c e s o f the e a r ly s e t t l e r s , r e s u l t i n g in in te n se ero sio n o f the Chesapeake watershed. But now th a t modern farming p r a c t i c e s are more e f f i c i e n t l y conserving t o p s o i l , i t has been d iscovered th at urbaniza tio n and development cause more s o i l l o s s and higher stream t u r b i d it y l e v e l s than a g r ic u lt u r e ever d id . U nfortunately for the Chesapeake, development o f i t s s h o r e l in e s and watershed are a c c e l e r a t i n g , spurred by population growth. According to a recen t rep o rt on the b a y Ts future (U. S. Army Corps o f Engineers, 1978), the p resen t population o f the region w i l l double to 18 m illio n by the year 2020. Bulk o i l t r a f f i c on the bay w i l l a lso double. R ecreational boating a c t i v i t y w i l l in c re a se f i v e fo ld from the presen t 200,000 b o a ts. Demand for e l e c t r i c i t y w i l l m u ltip ly more than t e n f o l d . And the demand for land for development w i l l double. The n e g a tiv e e f f e c t s o f such unbridled growth can be seen in the record o f the b a y Ts l a r g e s t in d u s tr y , s h e l l f i s h . In 1890 the s h e l l f i s h catch was 141 m illio n 303 pounds. By 1978 i t was down to 60 m illio n pounds (Maryland Dept, o f Natural Resources, 1980). The primary reasons for the d e c lin e are increased sediment loading and increased l e v e l s o f t o x i c s in the water. In j u s t one day 400 m illio n g a l lo n s o f raw and p a r t i a l l y tr e a te d sewage are r e le a s e d in to the bay. Given the i n e v i t a b l i t y o f growth in the bay area over the fo r s e e a b le fu tu r e , proper r e g u la t io n and balance among the d i f f e r e n t f o r c e s th a t compete for the b a y f s reso u rc es becomes e s s e n t i a l . The i n t e r e s t s o f the natu ral en viro n ment, f i s h e r i e s , commerce and r e c r e a t io n must a l l be weighed. Much has been made o f the f a c t th a t many typ es o f b ir d s , f i s h and s h e l l f i s h , and e s p e c i a l l y commercial m ollusk s p e c i e s , a r e dependent on e s t u a r i e s for h a b ita t and spawning grounds. But the important f a c t th a t i s o fte n ignored i s th a t man, not m ollusk, i s the most e s t u a r i n e - dependent o f a l l s p e c i e s . Unwise use o f e s tu a r in e r eso u rc es has i t s g r e a t e s t impact on humans. The b a t t l e to save the b a y 's r e so u r c e s i s far from being l o s t . D espite the rapid pace o f u r b a n iz a tio n , more than h a l f (57%) o f the Chesapeake region i s s t i l l f o r e s t or w etla n d s. An a d d it io n a l th ir d i s in a g r ic u l t u r a l u se. Only about 7% o f the land i s used for r e s i d e n t i a l , commer c i a l or i n d u s t r i a l purposes. D espite the s t r e s s e s o f 304 development, i t s t i l l remains p o s s i b l e to view the bay through Captain John Sm ith’ s eyes as 1 1 . . . a country th a t may have the p r e ro g a tiv e over the most p le a sa n t p la c e s known, for the la r g e and p le a sa n t n av iga b le R ivers, heaven and earth never agreed b e t t e r to frame a p la c e for man's h a b i t a t i o n ." 305 REFERENCES CITED Baker, S. R., and Friedman, G. M., 1969, A n o n -d e s tr u c tiv e core a n a l y s is technique using x -r a y s: Jour. Sed. P etro lo g y , v. 39, p . 1371-1383. Bennion, V. R., and Brookhart, J. 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G ., 1968, The Chesapeake Bay, geology and geography: in Proceedings o f the Governor's Conference on the Chesapeake Bay, Wye I n s t i t u t e , Maryland, Sept. 12-13, 1968. _________________ , and Schick, A. P., 1967, E f fe c t s o f c o n str u c tio n on f l u v i a l sediment in urban and suburban areas o f Maryland: Water Resources Research, v. 3, P- 451-464. Yorke , T. H ., and Davis, W . J ., 1971, E f f e c t s o f urb a n iza tion on sediment tra n sp o rt in Bel Pre Creek Basin, Maryland: U. S. G eological Survey P r o fe ssio n a l Paper 750-B, p. 218-223. 316 Appendix A X-RAY DIFFRACTION DATA 317 Grab No. Core No. I n t e r val (cm) % o f Tot . D iffr a c te d I n t e n s i t y Mont- m o r il- l o n i t e K aol. + C hlor. I l l i t e Quartz B-3 66 25 5 4 B-5 50 18 18 14 B-9 77 4 14 4 B-15 69 20 7 4 B-20 74 10 14 2 B-25 74 11 13 2 B-30 74 12 12 2 B -6 1 63 18 12 7 B-62 59 23 12 6 B-63 47 25 21 7 B-64 50 17 23 10 M-1 58 13 20 9 MC-1 67 11 14 7 MC-3 70 13 13 4 MC-4 57 24 10 9 318 Grab No. Core Inter No. val (cm) % o f Tot. D i f f r a c t e d I n t e n s i t y Mont- K aol. I l l i t e Quartz m o r il- + I o n i t e Chlor. C ornfield S o il s ( C a lv e r t) C ornfield S o il s ( Nanj emoy) F orest S o il s ( P l e i s t .) Pasture S o i l s ( C a lv e r t) Pasture S o il s ( Nanjemoy) 56 54 24 36 35 22 19 32 22 16 18 22 29 37 30 15 18 0-2 2-4 4-6 6-8 8-10 10-12 12-14 14-16 20-24 28-3 2 90 87 88 90 88 88 92 89 90 92 6 9 7 5 8 8 6 8 7 6 2 4 4 4 3 4 1 2 3 2 319 Grab No. Core I n te r - % o f Tot. D iffr a c te d I n t e n s i t y No. val ----------------------------------------------------------- (cm) Mont- K aol. I l l i t e Quartz m o r il- + I o n it e Chlor. 1 44-48 90 6 2 1 60-64 92 5 2 1 84-88 92 6 2 0 108-112 86 7 7 0 132-136 81 11 6 2 140-148 80 11 8 2 3-B 0-2 85 6 8 0 44-48 89 6 5 0 64-68 74 10 15 0 152-156 79 9 12 0 13 0 - 0 .5 90 6 4 0 5 0 -5 0 .5 89 6 5 0 136-136.5 85 7 8 0 16 0 - 0 .5 92 4 4 0 5 0 -5 0 .5 90 5 4 0 153-153.5 86 6 7 0 19 0 - 0 .5 90 5 5 1 5 0 -5 0 .5 86 8 5 1 164-164.5 84 6 10 0 320 Grab No. Core I n t e r - % o f Tot. D iffr a c te d I n t e n s i t y No . 21 v a ± (cm) Mont- m o r il- l o n i t e K aol. + Chlor. I l l i t e Qu a r t z 0-2 87 7 6 0 2-4 87 6 6 0 4-6 85 7 6 1 6-8 87 5 7 0 8-10 88 6 6 0 10-12 87 6 6 1 12-14 85 6 8 1 14-16 85 7 8 0 20-24 87 5 7 0 28-32 87 6 7 0 44-48 86 7 6 1 60-64 83 9 7 1 84-88 85 6 8 0 108-112 85 6 8 0 132-136 87 6 7 0 156-160 86 4 9 0 180-184 82 7 10 1 200-203 81 8 10 0 321 Grab No, Core I n t e r - % o f Tot. D iffr a c te d I n t e n s i t y No. val ----------------------------------------------------------- (cm) Mont- Kaol. I l l i t e Quartz m o r il- + I o n i t e Chlor. 30 2-4 86 6 7 0 55-60 87 6 6 1 125-130 86 7 7 0 38 0-2 79 9 1 1 1 2-4 78 9 13 1 4-6 81 8 10 1 6-8 78 11 11 0 8-10 83 6 10 1 14-16 81 9 9 0 60-64 86 8 5 1 180-184 83 8 8 1 RR-B 91 6 3 0 BP-AX 68 14 16 2 WR-2AX-A 74 14 11 0 35-1AX-A 83 8 8 1 322 Grab No. Core I n t e r - % o f Tot. D i f f r a c t e d I n t e n s i t y NO . vai (cm) Mont- m o r il- l o n i t e K aol. + C hlor. I l l i t e CB-25 56 23 19 CB-24 65 18 15 CB-20 57 14 24 CB-16 62 19 18 CB-12 64 15 22 CB-6 54 17 22 CB-1 38 38 23 HDG-5C 70 14 15 SF-5 TOP 73 17 9 SR-4 67 16 17 SR-3 51 21 27 SR-1 40 24 31 3 2 5 1 0 7 2 1 1 0 0 5 323 Appendix B RADIONUCLIDE ACTIVITY IN SUSQUEHANNA RIVER AND CHESAPEAKE BAY SEDIMENT 324 S p l . No . I n t e r - Gamma A c t iv i t y ( p i c o c u r i e s / k g ) val ----------------------------------------------------------------------------- (cm) Cs-134 Cs-137 Co-60 K-40 ( d ecay-corrected to date o f c o l l e c t i o n ) SR-1 grab 1 1+8 170+9 3+7 7010+240 SR-2 grab 125+11 465+16 165+10 9710+340 SR-3 grab 2+6 280+10 10+10 8370+300 SR-4 grab 16 + 4 175+8 4+7 8480+260 SR-5 grab 105+12 635+22 255+13 15590+520 SR-5A grab 185+16 620+23 170+40 10840+420 SR-6 grab 20+9 765+26 9+16 18720+620 SR-7 grab 67+10 395+15 8 + 12 1544 0+4 9 0 SR-8 grab 130+13 635+22 12+15 19530+630 SR-8A grab 15+5 795+17 1+8 18260+510 SR-8B grab 1680+86 2460+48 180+10 11820+390 SR-9 grab 110+10 195+11 3 + 1 1 11600+390 G-1 grab 17+5 470+25 - 14610+760 G-2 grab 83+13 620+35 51+6 12090+660 G-3 grab 13+5 1 10+9 1+4 8230+450 G-4 grab 870+94 1280+67 160+10 9880+530 G-5 grab 115+14 210+14 2+5 6260+360 G-6 grab 79 + 14 1890+100 5+9 15930+870 G-7 grab 415+46 535+31 1 0+5 7790+440 G-8 grab 580+64 850+47 40+8 9780+550 325 S p l . No . I n te r - Gamma A c t iv i t y ( p i c o c u r i e s / k g ) val --------------------------------------------------------------------- ------- (cm) Cs -13H Cs-137 Co-60 K-40 ( deca y-corrected to"_d'ate o f c o l l e c t i o n ) G-9 grab 180+20 315+17 9+4 5480+300 G-10 grab 220+26 535+32 8+7 16230+880 G-1 1 grab 210+24 670+36 6+6 14920+790 G-12 grab 490+55 1070+58 29+9 18480+990 G-1 3 grab 160+24 71+44 - 16010+920 G-14 grab 450+48 960+51 22+5 16420+860 G-1 5 grab 145+15 190+10 2+2 4610+240 G-1 6 grab 280+32 390+22 - 5080+290 G-1 7 grab 105+13 135+10 - 13520+710 G-1 8 grab 160+18 225+12 2+3 7950+410 G-19 grab 265+21 330+17 2+2 3940+210 G-20 grab 275+30 445+23 5+2 5490+280 G-21 grab 29+7 79+8 8+7 11770+630 G-22 grab 330+37 790+43 8+8 12240+660 G-23 grab 140+17 440+26 6+7 9290+510 G-24 grab 27+3 76+5 3+2 2350+130 G-25 grab 43+8 4 80+26 7+7 14350+750 G-26 grab 100+13 480+27 7+7 11940+635 G-27 grab 58+10 175+13 _ 14260+760 326 S p l . No. I n te r - Gamma A c t iv it y ( p i c o c u r i e s / k g ) val ----------------------------------------------------------------------------- (cm) Cs -134 Cs -137 Co-60 K-40 ( decay- coFreeted to date o f c o l l e o t i o n T TMI-1A 0-5 4+4 TMI-2A 0-5 105+11 5-10 43+7 SH-2A 0-2 16+6 2-14 - SH-2-1 0-8 - SH-2-2 0-9 1 + 10 H-3 0-4 26+7 4-16 33+14 16-28 - 28-32 15+9 32-38 19+13 38-59 - 59-76 5+9 C-4 0-2 210+14 2-17 79 + 19 17-41 - 41-50 - 50-79 - 79-85 — SF-5 0 - 2 . 5 41+7 120+8 7+7 5560+197 375+17 71+10 9780+360 250+11 6+9 8480+290 110+8 6 + 1 0 16920+490 - - 14020+680 66+12 22+10 17380+560 270+20 10+18 17120+620 430+15 6 + 1 2 19100+580 455+29 1 1+23 17380+730 380+29 8+17 15460+570 350+18 1+15 15870+540 160+23 19+21 10025+530 47+12 - 6260+290 430+20 - 17460+590 665+20 9+13 18620+620 615+3 6 22+9 20420+680 485+33 - 17230+590 465+27 - 19400+540 370+21 - 16020+430 545+59 - 16230+940 64+8 14+1 1 10820+360 327 S p l . No. I n te r - Gamma A c t iv i t y ( p i c o c u r i e s / k g ) val ----------------------------------------------------------------------------- (cm) Cs-134 Cs -137 Co-60 K-40 CORE E CORE 38 0-5 28+13 350+11 - 13120+380 5-10 22+1 5 387+29 - 13650+680 10-15 26+21 385+41 - 15440+930 15-20 18+13 420+27 - 16390+710 20-25 - 530+43 - 14430+850 25-30 - 495+30 - 15530+710 30-35 - 530+28 - 15480+660 35-40 - 495+26 - 16700+670 0-2 - 590+40 - 14900+800 2-4 - 600+20 - 18200+500 4-6 - 660+20 - 16670+420 6-8 - 810+30 - 14600+600 8-10 - 916+72 - 17300+1200 10-12 - 700+50 - 18020+1020 12-14 - 510+80 - 13300+1700 14-16 - 540+60 - 14600+1300 16-20 - 320+30 - 13500+600 O J i o C \J - 290+36 - 18100+760 00 C \J 1 C M - 200+26 - 17200+690 C \J on I CO C M - 84+27 - 19500+600 32-36 - 72+24 - 15700+600 36-40 - 28+31 - 17800+700 CO i — — _ 18200+900 328

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Creator Donoghue, Joseph Francis (author)

Core Title Estuarine sediment transport and Holocene depositional history, Upper Chesapeake Bay, Maryland

Degree Doctor of Philosophy

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,physical oceanography

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c29-346354

Unique identifier UC11220972

Identifier DP28554.pdf (filename),usctheses-c29-346354 (legacy record id)

Legacy Identifier DP28554.pdf

Dmrecord 346354

Document Type Dissertation

Rights Donoghue, Joseph Francis

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Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

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