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1986
The York River: A Brief Review of Its Physical, Chemical and Biological Characteristics
Michael E. Bender Virginia Institute of Marine Science
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Recommended Citation Bender, M. E. (1986) The York River: A Brief Review of Its Physical, Chemical and Biological Characteristics. Virginia Institute of Marine Science, William & Mary. https://doi.org/10.21220/V5JD9W
This Report is brought to you for free and open access by W&M ScholarWorks. It has been accepted for inclusion in Reports by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. The York River: A Brief Review of Its Physical, Chemical and Biological Characteristics
·.by
· Michael E. Bender .·· Virginia Institute of Marine Science School ofMar.ine Science The College of William and Mary Gloucester, Point; Virginia 23062 The York River: A Brief Review of Its Physical, Chemical and Biological Characteristics
by
· Michael E. Bender Virginia Institute of Marine Science School of Marine Science The College of William and Mary Gloucester Point, Virginia 23062 LIST OF FIGURES Figure Page 1. The York River ...... 5 2. The York River Basin (to the fall line) .. 6 3. Mean Daily Water Temperatures off VIMS Pier for 1954- 1977 [from Hsieh, 1979]...... • . 8 4. Typical Water Temperature Profiles in the Lower York River approximately 10 km from the River Mouth . . . 10 5. Typical Seasonal Salinity Profiles Along the York River. 11 6. Salinity Distribution along the York During March, July and October 1982 • • ~ . . . • . . • • ...... • 12 7. Salinity and Di.ssolved Oxygen During Periods of Strati- fication and·Destratification, August 1981, 1982 . 14
8. Salinity Distributiori Al~ng the Axis of the York- August 1982 [from Ruzecki & Evans, 1985] . . . • . 15 9. Surface to Bottom Dissolved Oxygen Differences vs Tidal Range - York River Approximately 10 km From the Mouth. . 17 10. Surface to Bottom Dissolved Oxygen Differences (May - September) from 1972 - 1981 Approximately 10 km from the River Mouth. . . • ...... • . . . 19 11. Surface and Bottom Phosphate Concentrations in the Lower York (monthly moving averages over 3 years) [calculated from Jordan et al., 1975]. . . . • • • 20 12. Surface and Bottom Nitrogen Concentrations in the Lower York (monthly moving average over 3 years) [calculated from Jordan et al., 1975]...... 22 13. Sampling Stations for Water Quality and Plankton [from Jordan et al., 1975] ...... 28 14. Seasonal Abundance of Dinoflagellates, Cryptophytes and Diatoms in the lower York [from Jordan et al., 1975] 29 15. Temporal Distributions of Nine Dinoflagellate Species 1973-74 [from Jordan et al., 1975] ...•...•. 30
i ----~------·------··------·----~---·------··-···-----·
LIST OF FIGURES (continued)
Figure Page 16. Seasonal Occurrence of Dominant Zooplankton in the Lower York [modified from Jordan et al., 1975] • . . • . . • . 32 17. Seasonal Abundance of Four Common Polychaete Species vs Substrate [from Virnstein, 1975] ...... 37 18. Sampling Stations of Hinde for Benthic Invertebrates [from Hinde, 1976] ...... •...... 38 19. Benthic Species Diversity (H1) vs Sampling Location [from Hinde, 1976] ...... 40 20a,b,c. York River Oyster Habitat [from Haven et al., 1981] .. 44,45,46 21. Hard Clam Densities in the Lower Chesapeake Bay [from Haven and Loesch, 1975] ....•...•.. 48
22. Hard Clam Densities in t~e Lower York and Poquoson Flats [from Haven and Loesch, 1975] ...... 50 23. York River - Catch Per Unit Effort - Striped Bass, White Perch, Atlantic Croaker and Spot [from Wojcik and Austin, 1982]...... • . . . . 55 24. York River - Catch Per Unit Effort - Weakfish, American Shad, Summer Flounder, Hogchoker and Channel Catfish [from Wojcik and Austin, 1982] ...... • . . . 57 25. York River - Catch per Unit Effort - White Catfish, Bay Anchovy and American Eel [from Wojcik and Austin, 1982]. 58 26. Beach Seine and Trawl Sampling Stations [from Jordan et al., 1975]...... 59 27. Seasonal Occurrence of 10 Fish Species [from Jordan et al., 1975]...... 61 28. Number of Fish Species vs. Year, Month and Strata [from Jordan et al., 1975] ...... 62 29. Seasonal Sand Shrimp Abundance vs. Cross Sectional Strata, April 1972- December 1974 [from Jordan et al., 1975]. . . . 64 30. Seasonal Sand Shrimp Abundance vs. Longitudinal Strata, April 1972- December 1974 [from Jordan et al., 1975]. . 65
i i 31. Number of Fish Species vs. Cross-sectional Strata, April 1972 - December 1974 [from Jordan et al ., 1975]. . . . 67 32. Number of Fish Species vs. Longitudinal Strata, April 1972- December 1974 [from Jordan et al., 1975]. . . . 68 33. York River Commercial Catch (1963-81) Finfish (total) A1 ewi fe, Blue Crabs and Hard Clams • . . • • . . . . . 71 34. York River, Commercial Catch (1963-81) Swellfish, Croaker, Spot and Grey Trout...... • ...... • . . 72 35. York River, Commercial Catch (1963-81) Bluefish, Striped Bass, American Shad and Oysters (from private grounds} . 73 36. Moving Averages (3) of Concentrations of Precipitated Coprecipitated and Organic Copper in the <63-um Fraction of Sediments from the York River Estuary [from Huggett et a1 • , 197 4] . . • ...... • . 83 37. Moving Averages (3) of Concentrations of precipitated Coprecipitated and Organic Zinc in the <63-um Fraction of sediments from the York River Estuary [from Huggett et al., 1974] ...... : ...... 84 38. The Distribution of Copper in Oysters From Virginia's Major Rivers [from Huggett et al., 1974] ...... 85
iii LIST OF TABLES
Table Page 1. Diversity and Descriptive Statistics of Benthic Communities in the Lower York [from Hinde, 1981] . . • . . • • . • . . . 41 2. Aromatic Hydrocarbons in Sediments [from Voudrias, 1981] . . 80 3. York River Aliphatic Hydrocarbons [from Hinde, 1981] . 81 4. Copper, Cadmimum and Zinc Levels in Oysters [data from State Health Department] • . • . . • ...... 86
iv 1
Executive Summary
The purpose of this paper is to provide an overview of the physical, chemical and biological characteristics of the York River, Virginia. The river is formed by the confluence of the Mattaponi and Pamunkey rivers at West Point, Virginia. It is tidal over its entire length and flows to the western shore of Chesapeake Bay. The salinity structure and chemical characteristics of the lower York River are extremely dynamic. Stratification of the water column in summer months causes oxygen depletion in the deeper waters of the river and nutrients are regenerated during these periods. Episodes of stratification and destratification are, related to the neap-spring tidal cycle. Low oxygen tensions in the deeper portions of the river, during periods .. : of stratification, limit fish and crab populations in these areas and may 'cause mortalities of benthic fauna. The extent to which the nutrients that are regenerated are utilized phytoplankton is not known with certainty. However, there are indications that the nutrients are rapidly assimilated by phytoplankton in the York and in other estuaries exhibiting destratification cycles. Insufficient historical data precludes an analysis of whether the degree of oxygen depletion in the deeper segments of the York has changed with time. Data collected over the last 10 years do not indicate a deterioration in conditions, however, prior to 1970 data are too sparse to make comparisons. The conditions which result in oxygen depletion are natural but the degree of depletion can be augmented by man's activities that contribute oxygen demanding wastes and/or nutrients. 2
Phytoplankton populations in the river vary seasonally, their most striking feature being the sproadic occurrence of "red tides" caused by blooms of various species of dinoflagellates. These motile, non-toxic organisms can develop very dense populations with chlorophyll levels exceed ing 100g/l. A bay wide decline in submerged aquatic vegetation has been observed over the last 15 years. The declines in areal coverage by these plants began in the upstream areas and have progressed "down-river." Communities in the York have declined in a similar manner. Although the exact cause of the declines is not known it is believed due to increased turbidity levels resulting from erosion and increased phytoplankton growth.
Copepods are th~ most consistently abundant members of the zooplankton community but larval stages of. decapods, molluscs and polychaetes are also important. Benthic animal populations are dominated by polychaete worms. The type of substrate present plays an important role in determining community structure. Oyster populations in the lower river are limited by disease and predators. Commercial harvests come mainly from private grounds located upstream where average salinities are less than 15°/oo. The lower river supports a hard clam fishery of 10-20 patent tong boats. Landings reported for the river average about 200,000 pounds/year. Fish populations of the York are composed of resident, anadromous and catadromous species. As in the Bay proper, populations of many important species have shown dramatic fluctuations in abundance as a function of time. The causes of these population fluctuations are known for only a few species. 3
Finfish are harvested commercially in the York by pound nets, fixed and drift gill nets, fish traps and by haul seining. Major species include; bluefish, grey trout, croaker, spot, flounder, eels, striped bass and American shad. Large fluctuations in landings for individual species occur with time. In general, trends in harvest from the York follow those ob served for the state as a whole. The estimated dockside value of commercial fishery landings from the York was 1.6 million in both 1980 and 1981. Finfish landings account for about one-third of the total value, blue crabs are usually the most economi cally important species followed by oysters and clams. 4
Introduction
The objective of this paper is to provide an overview of the physical, chemical and biological characteristics of the York River, Virginia. The York River (Figure 1) is formed by the confluence of the Mattaponi and Pamunkey rivers at West Point, Virginia. It has a drainage basin of 69,000 km2, of which nearly 70% is forested and another 22% is in cropland and pasture (Figure 2). Less than two percent of the land area is clas sified as urban. Average total freshwater inflow to the river is estimated at 70 m3;sec,with flows near the fall line on the Pamunkey River at Hanover averaging 27.3 m3;sec, and at Beulaville on the Mattaponi 16.4 m3;sec (Hyer, 1977). Recorded flow extremes at Hanover range between 1,140 m3;sec to 0.3 m3;sec, with extremes at Beu~av;lle of 480 m3;sec to 0.2 m3;sec. Discharges ·are higher than average from January-April and less than average from July September. The entire length of the York is tidal and tides extend 96 km up the Mattaponi and 60 km up the Pamunkey. Tidal waves.move upstream at about 22 km/hr. As the wave progresses upstream its amplitude increases, with a mean tidal range near the mouth of 0.7 m and 0.9 mat West Point. Tidal ranges continue to increase in the tributaries to their fall lines, reaching 1.2 m in the Mattaponi and 1.0 min the Pamunkey. Average tidal currents increase from 30 em/sec at the mouth to 54 em/sec at West Point but then decreases as one moves up the tributaries (Hyer, 1977). The salinity structure of the York River is influenced by the interac tion of freshwater discharge and tidal flux. Salinity gradients between the Figure 1 , (~ ~ ,-J) . FALL LINE •/\ r-\\ J, ... \-""'f) Hanover
Figure 2 Downstream sub-basin of York drainage basin. 7 surface and bottom waters tend to increase with increasing freshwater dis charge in the spring and to decrease in the summer and fall. However, as will be discussed later, the salinity structure of the lower river is ex tremely dynamic and apparently controlled more by tidal forces than freshwater inflow. During low flow conditions, salt water intrudes from West Point, 20 to 30 km up the tributary streams. The climate of the area is humid subtropical with a mean temperature of 15°C. Annual precipitation is 112 cmjyear, and of this less than 25 em is in the form of snow. The major industries in the basin are lumbering, pulp and paper, petroleum refining, electric power production, agriculture, fishing, tourism and the military. Major environmental characteristics of the system will be summarized in the following sections with emphasis on the lower river.
Physical and Chemical Characteristics
Water Temperature Water temperatures in the lower York River have been recorded more or less continuously since 1954 at a station located at the end of the Virginia Institute of Marine Science (VIMS) at Gloucester Point tide gauge pier. The sensor is located 2.2 m below mean low water and the river bottom is 4.2 m below mean low water. Hsieh (1979) summarized the data collected from this monitoring station as mean daily average temperatures (Figure 3). January had the lowest average temperatures with a mean of 3.5°C. Maximum tempera tures were observed in August with a mean of 26.2°C. 0 0 . II" ("> UPPER RHO LOWER LJHIT 0 0 . .J y f") AVERAGE VALUES
c.> 0 .,c~. 0 ('"~
0 0 0 N w >o a a:u. 0 . !f)
0 0 . -0
a u. "'
0a 0
u0 0 • a ~o~.~o~c----~3o~.~o~o--~~~o.ro~o--~9~~.~~~o~~,~z~o.~o~o--~I~o.~o~o--~:~s=c~.c=o~~2~1~o~.o~o~~2q~o~.~oo~~2~o~.7co~~3roo~.~o~o---3TJ-o.-ft-o---3~~-n-c-~---1:~~ ELAPSED T1 HE tOOl'Sl ... _.... ·,; 3 ·~'· 00
Figure 3. Mean daily average temperatures for: 1954 to 1977 and +,1 standard deviation.
co 9
Some degree· of thermal stratification is usually present in the lower York. Typical profiles of temperature vs depth are shown in Figure 4. These data were obtained during 1972 at a station located midstream in the river between Allens Island and Goodwin Neck. Stratification is usually strongest in the spring and early summer when the water is warming. During the late summer and autumn when the water is cooling, periods of homothermy and inverse stratification also occur.
Salinity The salinity structure of the York River is controlled by freshwater inflow and tidal mixing. The degree of stratification is usually greatest in the spring and summer, and lessens during the fall and winter. A typi
cal seasonal cycle showin~ the distribution of salinity with depth and distance in the river is shown. in Figure 5. High spring runoff depresses ·salinities in the upper water strata, as flows decrease during the summer saltwater intrudes further upstream and the degree of stratification decreases. The water column usually becomes more homogeneous in the fall and winter. Figure 6 presents data from 1982 for.comparison to the typical seasonal cycle. The vertical structure is not, however, determined simply by freshwater inflow. Haas (1977), showed that the lower York and Rappahannock rivers oscillated between conditions of considerable vertical salinity stratifica tion and homogeneity on a cycle that was closely correlated with the spring neap tidal cycle. Homogeneity was most highly developed about 4 days after sufficiently high spring tides while stratification was most highly developed late in the spring-neap cycle. An example of this mixing by tidal AUGUST JAN APRIL MAY OCTOBER JULY s 0 0 I . i I 0 0 I I 0 0 I 5 I 0 G \ \ e 0 Cl) . \ 0: LLJ \ t- 10 e ... 0 LLJ \ ~ \ z 0 0 \ ~ \ t- 0 0 D. I LLJ 15 I 0 0 •I I 0 0
20 0
...... 25 30 35 0 0 5 10 15 20 TEMPERATURE ° C Typical Water Temperature Profiles in the Lower York Figure 4 River approximately 10 km from the River Mouth 11
Figure 5 Typical Seasonal Salinity Profiles Along the York River
SPRING
~ 20· 10
CJ) a: SUMMER IJJ t IJJ ~ z :I: t o. 10 IJJ 0
FALL 20~----~------~------0 \ \
WINTER
,•• 10 20 30 40 50
KILOMETERS FROM THE MOUTH 12
Figure 6 Salinity Distribution along the York During March, July and October 1982
17 10
MARCH
C/) a:: 20 10 LLJ.... 15 LLJ ::E 10 z :I: 1-a. LLJ JULY 0
\ 10
10
OCTOBER
10 20 30 40 50
KILOMETERS FROM THE MOUTH 13 forces is shown i·n Figure 7 which compares August of 1981 (post-spring tide} with August of 1982 (near neap tide}. The stratification/destratification cycle in the York appears to result from two or three conditions associated with the neap-spring cycling of tides (Ruzecki and Evans, 1985}. In the lower York (from Gloucester Point to the mouth} destratification results from importation of fresher water at the mouth during spring tides (see Figure 8). The increased excursion of Bay water, freshened from large up-Bay tributaries, during spring tides, coupled with phase differences in tides at the mouth of the York (flooding starts in the York while the adjacent portion of the Bay is still ebbing} results in this importation. The consequence is a strong reduction or even reversal of the horizontal pressure gradient which drives the normal two layered estuarine circulation. Pressure gradient relaxation allows tur bulent mixing, now enhanced .by increased tides, to erode the pycnocline. ·The greatest erosion occurs during maximum spring tides. Once started, the now weakened pycnocline continues to erode with smaller amounts of tidal energy until complete vertical homogeniety is achieved 3-4 days after maxi mum spring tides. Additionally, intrusion of fresher water at the mouth blocks higher salinity bottom water from entering the river from the Bay proper. Restratification of the lower York starts the following day with the intrusion of higher salinity deep water from the Bay. Upriver from Gloucester Point, the York estuary experiences periodic destratification in two reaches. In the reach extending 25 km upstream from Gloucester Point, destratification 3-4 days after spring tides is hypothesized to result from increased vertical motion, induced by basin configuration, and increased turbulent mixing, both of which are amplified during spring tides. 14 Figure 7 Salinity and Dissolved Oxygen During Periods of Strati fication and Destratification, August 1981, 1982
SALINITY 0/oo AUG. 1981 20 0 10 20 15
10 CJ) rx: w ..... 24 w :!! SALINITY %o AUG. 1982 z
:J: 6 ..... 0.. w 5 0 10 \
DISSOLVED AUG. 1981 OXYGEN moll 20 0 5 4
10
DISSOLVED AUG. 1982 OXYGEN moll 20 0 10 20 30 40 50 KILOMETERS FROM THE MOUTH 15
17 ::szm: 82 SBE It • ""' ''•"' Yl II .. • ·•"'"' ,., CJ$ CJ • •
17 1llli 82 SBF It 22 JZIIt 82 SSE It
•• fttlfll Yl .... ,,.,. Yl ,. .. ll ,. .. II ...... ,, .,,. 'riJ rtil Yll roo r!l J'l C.l:J CJ • a 23 Jlll[ 82 SBE " .,.. tr•M Yl ,. .. II .,, ,,. I'IJ .,~ I'll .,, rtJ .,~ .,, "" 1'14 • • 19 :!ZIII 82 SSE " 24 Jlll[ 82 SSE " II"' froM Yl liM fttM 'If II .. ll .... II .. II . .,, .,,. -· .,, .,,. ....
2~:!Zlll 82 SBE
II
.,, 1'14 1'/J .,,~ Yll
Figure 8 Salinity Distribution Along the Axis of the York August 1982 (Ruzecki and Evans 1986) 16
In the upper· reach of the York, the segment within 10 km of West Point, destratification appears to be the result of river flow modulation during the neap-spring tide cycling. The modulation, resulting from elevated local mean sea levels during spring tide, tends to reduce flow for the week prior to spring tide and increase flow during the three days subsequent to spring tides. The result is an apparent pulsing between stratified and homogenous conditions. The reach located 15 to 30 km upstream from Gloucester Point is a region of persistent stratification which is maintained by strong gravita tional circulation. This stratification-destratification cycle has important biological consequences in the lower York River as it affects both dissolved oxygen and nutrient levels in the river.
·Dissolved Oxygen· Dissolved oxygen concentrations observed during periods of stratification-destratification are shown in Figure 7 along with the salinity distribution discussed above. As can be seen from the figure, oxygen levels in the deeper waters are significantly depressed during periods of stratification. The degree of oxygen depletion observed in the deeper waters is probably a function of temperature, length of isolation and the amount of organic matter present. Figure 9 illustrates the effect of mixing, as expressed by tidal range, on the degree of oxygen stratification observed in the lower York during 1974 and 1978. During these studies differences between surface and bottom DO concentrations as great as 7 mg/1 were observed, as tidal range increased surface to bottom concentration gradients decreased. 17
Surface to Bottom Dissolved Oxygen Differences vs Tidal Figure 9 Range - York River Approximately 10 km From the Mouth
(/) z 0 0 0· ~ a r =-0.83 >a: w (/) m 0 1.0 0.... a: 0 a: a. (/)
?i0 v -:E -w (.!) z 0 SUR FACE TO BOTTOM DO DIFFERENCE 18 The existence of these mixing events make yearly comparison, for pos sible trends in dissolved oxygen levels, more difficult because data collection was not designed to account for this phenomenon. Therefore, in VIMS' regular surveys of the river periods of stratification were not in cluded during some years. Figure 10, which compares yearly surface and bottom DO levels, was constructed utilizing those years which included surveys during the stratified period. Dissolved oxygen minima were usually observed in August, and bottom DO levels during this period were frequently 4 to 5 mg/1 below surface levels. Differences between surface and bottom concentrations generally increased in magnitude between May and August. During the period of these observations, i.e. from 1972 through 1981, dif ferences between years were not observed. Nutrients An extensive data set to characterize the nutrient regimes of the lower York was collected between April of 1972 and January of 1974. In this study samples were collected on a monthly basis at several stations in the lower York River (Jordan, et al. 1975). Data from Jordan's study were summarized for this presentation by computing moving averages of surface and bottom nutrient concentrations over the nearly 3 year period of observation. Surface and bottom phosphate concentrations are shown in Figure 11. Both surface and bottom orthophosphate levels increased gradually during the summer to a maxima in September, then declined during the fall and main tained relatively constant low levels until early summer. Concentrations of dissolved organic phosphate remained relatively constant throughout the year and surface to bottom differences were slight. Particulate organic phos phate levels were higher in both surface and bottom waters during the late Figure 10 Surface to Bottom Dissolved Oxygen Differences (May - Septe~ber) from 1972 - 1981 Approximately 10 km from the R1Ver Mouth 10 o SURFACE 9 • BOTTOM 0 \ 8 \ 0 o, I o, I . o, 0 "o \ \ 7 0 0 y, ' \ 1\0 \ \ ~\ \· \ \ \ I ' \ \ b I \ \ \ \ ..,o \ I o, 0 6 \ 0 o-~ . 'I \ b 0 0 0 0 \ 0 0 \ \ I \I 0 0 \ I 0 ' '/ \ I '\ \1 \ I 5 \ 0 \ I \ \ I 0 ,J 0 0 c 4 3 2 1972 1973 1974 1977 1978 1979 198i 20 Surface and Bottom Phosphate Concentrations in the Figure 11 lower York (monthly moving averages over 3 years) (calculated from Jordan et al., 1975] 50 ., .._=BOTTOM 0a.._ 40 o =SURFACE ...... 0 01--· :J:... ::( 30 0::: 0 20 10 '· ... 30 a..0 - -tr --o.... ', 0 _.3___0 --a ..... , (!)'o::.:O:::CII ,--.A---- • • • • • '"' ... ___-8 CIS o • • a 0 50 ., 0 a.. 40 c)_ a::: ...... 30 0 01 t-= :::( 0::: 20 100 80 a.. I _J- 60 c:t' ... 01 ...0~ 40 MONTH 21 summer. Concentrations in the bottom waters were higher from May through December, reflecting most probably the settling of planktonic organisms. Trends in total phosphate concentrations reflect a combination of the or thophosphate and particulate organic variations. Seasonal variations in the various forms of nitrogen are shown in Figure 12. Nitrate-nitrite concentrations were relatively constant, in both surface and bottom samples, during the winter, levels decreased in the spring to a minima during the late summer. Ammonia levels increased from minimum during the winter months and peaked during the late summer and fall, with concentrations in the bottom waters much higher than the surface in the summer. Dissolved organic nitrogen usually accounted for a major fraction of the total nitrogen present. Surface and bottom differences were slight from May through December, with bottom concentrations exceeding those at . \ the surface during the winter and early spring. Particulate organic ·nitrogen levels,. (not shown) varied widely from month to month with no definite seasonal pattern. D'Elia et al. (1981) have shown that oxygen depletion in the bottom waters of the lower York can result in the release of both phosphate and ammonia. Similar releases have been known for many years in stratified lakes and in the deep ocean. The seasonal cycles reported here indicate that regeneration is occurring in the bottom waters. Mixing of these bottom enriched waters during destratification will bring nutrients to the surface where they may be utilized by phytoplankton. 22 100 _..o ,. .... p.- --0 ...... 1:1'::, , / ..,. / 0 50 z ,. J'"' + N 0 z 0 200 • =BOTTOM o =SURFACE ...... 150 Ct .,.... -o-- -.a._. ::, .... ~ .. .., ,.0...... lOO ; :I: / ~' ~ z - .J>' ~ 0 -~- 50 o- --o------tr-0 0 350 ...... g z 250 0 U) 150 800 .-o--.. 0".... ~ ' " ~ ..... 'O.... MONTH Figure 12 Surface and Bottom Nitrogen Concentrations in the lower York (monthly moving average over 3 years) [calculated from Jordan et al., 1975] 23 Biological Characterization Phytoplankton Studies yielding information on the species composition and seasonal changes of the phytoplankton community of the lower York River began with a series of 24 sampling cruises conducted in the Chesapeake Bay region between January, 1960 and January, 1961 (Patten et al., 1963). Two stations were located in the lower York River, one at a point 300 m off the VIMS pier and one at the river mouth. Samples for net phytoplankton determinations were obtained from oblique hauls with a #20 bolting cloth net attached to a Clarke-Bumpus sampler. Samples for total phytoplankton determinations were taken from the i ~I surface water with a Kemmerer bottle. Aliquots of unconcentrated, live I]~I :i'j material were examined in Sedgwi.ck-Rafter cells, and species determinations, !l' 'in many cases tentative, were made. l~~~ I The species lists for both net and total phytoplankton identified in ! } the 1960 samples are included in Patten et al., 1963. However, the York ! River data are pooled with data from the Chesapeake Bay stations, so the composition of the river flora is obscured. The abundance data for two groups of species, diatoms and flagellates, are presented for each station separately, and indicate that in the York River, .diatom populations dominated in the winter and early spring, while flagellates peaked in the summer. Population levels of both groups were generally low in the fall. On an annual basis, it was concluded that diatoms and flagellates are of comparable significance in the surface waters of the lower Chesapeake Bay region. This conclusion departed from results of earlier investigations of Chesapeake Bay phytoplankton (Wolfe et al.,1926, Cowles, 1930 and Morse, 24 1947}, in which·diatoms were found to be generally dominant, especially in the winter, and in which a bimodal pattern of abundance, with spring and autumn peaks, was noted. This discrepancy was attributed to the exclusive use of net collections in the earlier studies. It was further noted that in the experience of the present investigators, nannoplankton in most seasons numerically exceeded the net plankton by as much as 103or more times. Using the species data from this study, Patten (1966) divided the annual phytoplankton cycle into five parts, summer (SU, mid-June to mid September), fall-winter (FW, mid-September through January), winter-spring {WS, February and March), spring bloom (SB, first half of April), and post bloom (PB, mid-April to mid-June), and listed the dominant species found in each part. On an annual basis, flagellates dominated (at least according to his numerical indices) at . all. times, particularly in the surface layers. Diatom populations did not achieve as large numbers in the winter of 1960-61 ·as they had in the winter of 1959-60 (reported in Patten et al., 1963). The vertical distribution of organisms was homogeneous during the FW and WS periods, but was stratified during the SU, SB, and PB periods, with greater numbers of individuals near the surface. Diatoms tended to increase in relative importance with increasing depth, during periods of stratification. From June, 1962-May, 1963, "total phytoplankton" counts were once again performed on samples taken from 0.6 m and 3 m depths at the VIMS pier sta tion (Fournier, 1966). Dominant species were listed, and the annual abundance cycles of flagellates and diatoms were plotted, this time in terms of cells per ml. The flagellates were dominant from June through December, and in May, but were overshadowed at 0.6 m by diatoms from late December to late April--a pattern similar to that reported for 1960 (Patten, et al., 25 1963). At 3m flagellates were always numerically more important than were diatoms. From June-August, 1963, "total phytoplankton" counts were performed in conjunction with eight productivity experiments, and included depths of 0, 2, 6, 10, 14, 18 and 22 feet (Patten and Chabot, 1966). Thus from January, 1960 through August, 1963, a large amount of plankton data was accumulated, and general seasonal patterns of species abundance emerged. Extensive species lists for diatoms were compiled, but are limited mostly to species that were retained by plankton nets. Temperature ranges for most of these species were recorded. Lists of flagellates were also compiled, but are admittedly incomplete since the "total phytoplankton" samples were observed in Sedgwick-Rafter mounts of live material, resulting )n ~nderestimation due to counting difficulties, and the formalin used to preserve the net samples destroyed unarmored forms. During the period August, 1963-September, 1966, no phytoplankton sam pling programs were undertaken .. The next major phytoplankton sampling program was conducted by Mackiernan (1968) in the period September, 1966-N~vember, 1967. Her samples were taken weekly, from the end of VIMS pier, and in most cases consisted of No. 20 plankton net hauls. Dinoflagellates were studied in detail, while other phytoplankton and zooplankton organisms encountered were recorded alive, when possible, under higher magnification than was possible with the Sedgwick-Rafter mounts used in earlier studies. In discussing the seasonality of the phytoplankton, Mackiernan divided the year into four floral periods: winter (early December to mid-April), spring (mid-April through May), summer {June through September), and fall {October and November). In common with the results of th~ earlier studies, 26 she found that ·diatoms dominated the net phytoplankton during the winter period, followed by dinoflagellate peaks in the spring and summer. Dinoflagellates and, at times, euglenoid flagellates continued to dominate the phytoplankton until the fall when temperatures declined steadily and diatom blooms developed. Mackiernan divided the dinoflagellate species into five groups; year round species with constant abundance, year-round species that varied in abundance, winter cold-water species, summer warm-water species, and transi tion species of the spring and fall. In connection with this categorization, she tabulated temperature ranges for the species that she had found. In considering temperature and salinity as factors that could influence the temporal distribution of phytoplankton species, she concluded that both factors were im~,ort.ant, and that certain species may not appear unless both temperature and salinity requirements are satisfied. Between August, 1969 and November, 1970, Gibson (1971) processed 10 sets of phytoplankton samples, four of which were taken in the lower York River, near VIMS . Samples were taken from the river surface with a screen sampler, and from 1 m depth with a 1 liter F.rautschy bottle, and were preserved with formalin. Settled concentrates were counted, and percent of the total number counted was determined for each species. In all, 98 species were identified. Diatoms dominated the flora in the surface samples between August, 1969 and June, 1970, while dinoflagellates peaked in August, 1970. Surface samples generally had higher concentrations of organisms than did the as sociated 1 m samples, while diversity at the surface was generally less than at 1 m. These results were confirmed in a study initiated in February, 1971 (Stofan et al., 1972), in which four stations were _sampled. Surface 27 n1icrolayer samples showed higher cell densities and lower species numbers than subsurface samples. Jordan, et al. (1975) conducted phytoplankton studies in the lower York from April of 1972 to December of 1974. Data on total phytoplankton popula tions were obtained monthly from the 7 stations shown in Figure 13. He found surface to bottom differences in cell counts for the channel stations (Stations 1-4). Motile flagellate species (Cryptophyta, Pyrrophyta, Chlorophyta) were usually more abundant in the surface samples while diatoms were more numerous in the bottom samples. On some occasions differences between stations were observed. The most notable being lower populations near the VEPCO cooling water outfall. After careful analysis of the data he concluded that the lower phytoplankton populations were not due to losses on passage throug~ th~ condensers but rather due to lower popula tions in the source water which was drawn from an intermediate depth. Qualitatively, species composition varied little from station to sta tion, if only major species were considered. On several dates more species were present at Station 1 than at the other stations, but these were repre sentatives of the Chesapeake Bay community and were present in small numbers. The phytoplankton were dominated by three major species groups; Cryptophyta (Chroomonas sp.), Pyrrophyta of the genus (Katodinium, Gleonodinium, Gymnodinium, Gonyaulax, Proocentrum, Peridinium and Cochlodinium) and Bacillariophyta (Skeletonema, Cyclotella, Rhizosolenia, Asterionella and Nitzschia). The temporal distributions of these three phytoplankton groups are shown in Figure 14. Plots of mean counts for the most important species of dinoflagellates are shown in Figure 15. The most consistently abundant species was 2 3 VEPCO Figure 13 Sampling Stations for Water Quality and Plankton [from Jordan et al., 1975] 29 TOTAL DINOFLAGELLATES 2000 E '0::: LLI Ill 1000 :1: ::> z 0 TOTAL DIATOMS 6000 4000 2000 1973 Seasonal Abundance of Dinoflagellates, Cryptophytes Figure 14 and Diatoms in the lower York [from Jordan et al., 1975] OINOFLAGELLATES=RETRAt~SFORMED MEAN In ( X+l) NO./ml, STA.I-4, SURFACE fgly!!WJ ~yaulox Glonodinium Prorocentrum .§.!!.: ~ .§!: minimum Proroeentrum Cochlodmium Gymnodinium I Peridinium Kotodinium I rofundotum ~ ~ splendens tnquefrum I 1000 1000 1000 1000 1000 1000 1000 1000 I 0 z 0 w 0 Figure 15 Temporal distributions of 9 dinoflagellate·opecies, 1973-1974. 31 Katodinium rotundatum, which was present in surface samples in all months except Sept~mber. Most of the species, however, were more restricted in seasonal distribution. Prorocentrumn minimum and Peridinium triquetrum preferred the colder months, and were essentially absent in the summer and fall. The others appeared for short periods in the summer and were absent for the remainder of the year. The dominant diatom genera in the winter and spring were Skeletonema and Cyclotella. Zooplankton and Meroplankton Most of the available data on the zooplankton of the York River are found in the studies by Burrell (1968, 1972) and Jordan, et al. (1975). Burrell's first study was conducted in conjunction with an examination of the York-Pamunkey fish nursery grounds and involved the examination of ·monthly samples · taken from September, 1965 through December, 1966. Most data was collected at stations located in the upper York River, although the river mouth was sampled occasionally. In Burrell's second study, nine stations· in the York and Pamunkey rivers and three in Chesapeake Bay ~ere occupied monthly from January, 1968 through December, 1969. Sandifer (1972), as part of his study on the meroplankton of the York, identified and quantified the decapod larvae present in the samples taken in Burrell's 1968-69 study. Jordan, et al. (1975) sampled 4 to 6 stations in the lower river on a monthly basis between April of 1972 to December of 1974. A summary s~owing the seasonal occurrence of dominant zooplankton in the lower York derived from these studies is shown in Figure 16. 32 Figure 16 Seasonal Occurrence of Dominant Zooplankton in the Lower York River J F M. A M J J A S 0 N D Copepoda Aeartia tonsa Aeartia clausi .,._...,_ ___-l.,..._. Pseudodiaptomus coronatus -s 1> Pseudocalanus minutus ..,._...,_ __...... ,.,. EuPytemozta affinis Cladocera Podon sp. Rot ifera Ctenophora Mnemiopsio l.eidyi Tint inn ida Meroplankton Polychaeta Po lydora sp. Pectinaria sp. .. .. Decapoda ~ ~on septemspinosa Cll .... Uca spp. • Neopanope tena.na say'I .. ... Panopeus herbstii Cl ... Gallinectes sapidUs ...... Barnacle larvae Pelecypod larvae Gastropod larvae 33 The quantitative data presented in Burrell (1972} show that the two most important species of copepods in the lower York are Acartia tonsa and Acartia clausi. ~ tonsa abundance peaked in the fall and~ clausi was present only in the winter and spring. The greatest numbers of copepod species occurred in the spring and fall, as did peaks in numerical abundance of individuals. In all, 12 species of copepods were recorded from the lower river. Sandifer (1972} identified 19 species of decapod larvae in samples from the lower York River. In most cases fewer than 10 individuals of any species per 1,000 liters were collected. Larvae of Crangon septemspinosa were present during most of the year, while larvae of other species were most abundant during the summer and essentially absent for the remainder of the year. 'Benthos The benthic populations of the York River estuary are of both direct and indirect importance to man. Certain members of the benthic community are of direct commercial value, e.g. clams, while.others serve as important food organisms of higher trophic levels. Besides being of value in these regards, benthic animals play an important role in mixing and cycling of materials from sediments to the overlying water. Benthic and related communities, e.g. epifauna of eel grass, of the lower York have been studied by numerous investigators over the past several years (Academy of Natural Sciences of Philadelphia, 1957; Warinner and Brehmer, 1966; Haven et al., 1966; Wass et al. 1967; Feeley, 1967; Marsh, 1970; Orth, 1971; Boesch, 1971, 1972, 1976; Boesch et al., 1976a and b; Bender et al., 1974; Jordan et al., 1975 and Hinde, 1981}. In this review 34 we will attempt·to summarize the major findings of these studies conducted on the benthic community of the lower York River. Boesch et al. (1976), summarized long term populations trends from a station located in 9 m of water near VIMS. They observed that populations of most macrobenthic species in this polyhaline mud-bottom community were quite variable seasonally and over long time periods. The dynamics of the populations reflect life histories of the species and long-term habitat changes. Few common species were persistent and most were either irruptive, annuals, or euryhaline opportunists responding to habitat changes. The most persistant species were Acteocina canaliculata, Oqyrides limicola, Micropholis atra and Harmothoe ~· Populations showing reduced abundance after Hurricane Agnes in 1972 include, Nephtys incisa, Edwardsia eleqans, Cirriformia grandis and Cerapus tobularis. Five species, Parapionospis pinnata, Pseudeurythoe sp, Leacon americanus, Heteromastis ·filiformis and Glycinde solitaria, increased in abundance after the hur ricane and have continued as important members of the community (VIMS, unpublished data). Haven et al. (1966) studied animal-sediment relationships in the lower York. They established stations at four depths and evaluated the number of individuals and biomass at each station monthly for a period of one year. Species diversity did not differ between any of the four depths but the number of individuals found at the various stations did show a trend toward increasing abundance in shallow water. Dominant species at the deep station 12.2 m were Cirriformia filiqera, nematodes, Sarsiella zostericola and Acteocina canaliculata. The number of individuals, species, and biomass were lower at the 6.1 m station than any other station sampled during the study. Copepods, nematodes, Acteocina canaliculata and Nephtys incisa made ·--~------... ·------· 35 up the majority·of the individuals found at this station. Stations at 1.5 and 3.0 m were quite similar in terms of species composition, with the same five species ranking high at each station. These were nematodes, Phoronis architecta, Loxoconcha impressa, copepods and Acteocina canaliculata. Boesch (1971) studied the benthic populations of the lower Chesapeake Bay and the York and Pamunkey rivers. In this study 10 stations were estab lished from the Bay mouth extending to the oligohaline section of the Pamunkey. Analyses of station similarity and faunal affinity showed that communities were virtually continuous along the estuarine gradient and that species were generally distributed independently. Community structure analyses indicated that complexity was fairly constant throughout the long polyhaline zone but decreased to a low in the oligohaline zone. Dominant species in the lower York as determined by ranking according to the method of McNaughton (1967), were Tharyx setiqera, Heteronastus filiformis, Nephtys ·incisa, Harmothoe sp.A, Amphiodia atra, Pseudoeurythoe paucibranchiata and Cirratulus qrandis. Virnstein (1975) sampled 7 stations in the lower York River, from May, 1972 to November, 1974. Samples were collected quarterly on two transects, one off the VEPCO plant and the other between the Coast Guard station and VIMS. A total of 15,000 individuals were identified to 120 taxa. Polychaetes were the most abundant organisms in terms of both species and numbers. Cluster analysis to identify species associations showed two major groupings, shallow stations with sandy sediments and deeper stations with muddy sediments. Seasonal associations were also noted. Four of the top six species identified were the same for both sediment types: the polychaetes Paraprionospio pinnata, Glycinde solitaria and Heteromastus fi 1 i formi s and the opisthobranch gastropod Acteocina canaliculata. '• 36 Abundance varied· from 173-6,000/m2, numbers of individuals were usually lower in August. The number of species was most often maximum in May, while August was usually the month with the minimum number of species. Species diversity (H') fluctuated around 3.5 bits/individual at the shallower sandy stations and 3.0 at the deeper muddy stations. Numerical abundance of even common species was quite variable with time and substrate as is shown in Figure 17. In September, 1976, Hinde sampled a grid of 133 equally spaced stations in the vicinity of the refinery at Yorktown. The dimensions of the grid were approximately 4.5xl.5 Km, with stations located about 250 meters apart in depths ranging from 0.6 to 23 meters (Figure 18). Benthic animals were collected at all stations with a 0.1 m2 Smith-Maclntyre grab. Samples for hydrocarbon analysis were ta~en from selected stations. A total of 20,032 benthic animals representing 10 phyla and distributed ·among 124 species were collected during the study. Polychaete annelids dominated the macrofauna comprising 67% of the total, while phoronids ranked second with 15%. Molluscs and crustaceans accounted for 5 and 8% of the fauna, respectively. Diversity values (H') varied widely over the grid from a low of 0.81 at a mud station to a high of 4.36 at a muddy sand station. Highest densities occurred at those muddy sand stations having a solid substrate (either oyster shell or hydroids) supporting an epifaunal community. Five habitat types were identified; sand, muddy sand, transitional, mud and mud with hydro ids. Attempts using both parametric and non-parametric techniques, to corre late diversity values with three of the quantitative hydrocarbon parameters (pristane;c ; pristane/phytane and total aliphatic hydrocarbons) proved 17 .. ---.•- --- 37 100 40 P. pinnoto ? A. conolicu/oto 1~ MUD : I I I I I I I 75 r/ I I 30 I I I I I I I I I I I I A I I I I 50 I I 20 I I II ~ 25 10 ('J E 0 0 F M A N F M A N I() 0 ...... cj 40 ·z 40 H. filiformis G. solitario 30 30 20 20 f' I 10 10 I I ,o.._.J I A , "' ' ,..4 ' '0--0" 0 0 M A N F M A N F M A N M A N F M A N F M A N 1972 1973 1974 1972 1973 1974 seasonal Abundance of Four Common Polychaete Species Figure 17 vs Sub~trate [from Virnstein, 1975] ----- __ --- - ...... ------.CJ ------~c.R' lfoulleol "'"•• 1/2 ,,II II II II II • MolCimolly Contaminated 11 II 0 lntermediatefy Contaminated II h G Minimally Contaminated ~ \\ ~'0 ,, J:1 Uncontaminated .... ,.. GOODWIN NECK C?..~ ~',, (II ' Figure 18 w [fromSampling Hinde, Stations 1976] of Hinde for Benthic Invertebrates co 39 unsuccessful. However, a perspective plot of H' values, as viewed from on shore (Figure 19) indicated a depression in diversity values in the vicinity of the refinery. To test whether the apparent depressions in diversity were in fact related to the refinery outfall, the grid was subdivided into nine blocks representing areas upstream from, adjacent to and downestuary from the refinery and three sediment types, mud, muddy sand and sand. The results of these tests are shown in Table 1. Statistically significant differences were noted between the refinery stations and both upstream and downstream muddy-sand strata. High diver sities were indicated in the downestuary sand strata and in the upestuary mud strata. Although these differences were identified, Hinde (1981) con cluded that routine operation_s a~ the refinery have not had drastic or very extensive effects on the benthos. Oysters Oysters occur in the York River from the junction of the Mattaponi and Pamunkey rivers all the way to the mouth. Today they are scarce on the public rocks in the lower half of the river largely due to the disease MSX (Andrews and Wood, 1967). Predatory drills are usually abundant in the lower third of the river extending upriver as far as Page Rock. Because of drills, few spat setting on cultch survive in the zone from Gloucester Point to the mouth of the river. The impacts of MSX and drills on oysters are controlled by salinity. Drills do not survive in areas with average salinities less than 15 °joo and the incidence of MSX is also reduced at this salinity. MSX is virtually absent when salinities average below 12 0/oo. Thus, because of the combined impacts of drills and MSX on young and -- 1 Figure 19 Benthic Species Diversity {H ) vs Sampling Location [from Hinde, 1976] Table-1 Means (H') and Variances (s;,) of H' Values for Each of Nine Subdivisions of the Sampling Grid Upestuary Stratum Refinery Stratum Downestuary Stratum 7 3A 3B 3C Mud 6 Stratum l ii'=2.60 ii'=2.20 ii'=2.29 . 5 2 2 2 SH,c0.26 SH,=0.36 SH,=0.30 4 Muddy Sand 2A 2B 2C 3 2 2 . 2 Stratum ii'=3.os SH,m0.03 ii'=2.71 SH,=0.24 ii'=3 .45 SH,=0.25 Sand lA lB lC 2 2 2 2 Stratum ii'•2.54 SH, .. 0.30 H'a2.45 SH,=0.22 ii'aJ.OO Sh,=0.08 1 S T U V D E F G r'---1--~---K--L--~ j.___O___ p__ Q_.Jj tlA,lBa0.59 N.S. tlB,lC=3.00** t2A,2Ba7.08** t2B,2C=2.55* t3A,3Ba:2.49* tJB,J8.54 N.S. tlA, lC =16. 95** t2A 2c"' 8.84** ' 42 adult oysters, productive oyster grounds today are restricted to a region in the upper third of the estuary from about Capahosic to Bell Rock. Prior to the outbreak of MSX in 1960, the lower river was used to moderate degree by private growers for growing James River seed to market size. The Baylor bottoms below Gloucester Point had been unproductive for many years prior to 1960. Before 1928 the York was said to produce up to 400,000 bushels of oysters annually (Glatsoff et al., 1947). However, since 1935 the York river has had a history of poor setting and low oyster production (Haven, et al., 1978). From 1962-1975 the York River accounted for 0.2% of the oyster harvest from public rocks in Virginia. The public oyster grounds of Virginia were surveyed between 1976 and 1981 by Haven, et al. (1981) .. The objective of their study was to determine the potential suitability of the public oyster grounds, called Baylor Grounds after their original surveyor, for the culture of molluscs. They classified bottom types within the originally surveyed Baylor Grounds, considered the areas productive potential as influenced by disease and predators, and also evaluated the influence of hydrographic factors on productivity. There are 2,449 acres of public oyster grounds in the York River, the location and bottom types found within the surveyed areas are shown in Figures 20a, 20b, and 20c. Based on a consideration of the major factors influencing potential productivity, Haven, et al. (1981), classified 1,089 acres as having high to moderate potential for oyster culture and 1,359 acres as having low potential. In the lower York (Figure 20c) 223 acres were classified as high to moderate, in the middle reach (Figure 20b) 382 acres were expected to have high potential, with 476 acres classified as 43 moderate and in the upper reach (Figure 20a) 8 acres were believed to have moderate potential. Oyster production in the lower and middle reaches is, however, limited by the disease MSX and plantings of non-resistant seed oysters will most certainly not be successful. Samples from the middle section of the river in 1978 showed oyster abundance at about 46 bushels/acre. Privately leased oyster grounds in the York account for about 13,000 acres held by over 350 leases. Two industrial corporations lease a significant percentage of the private grounds in the York making it unique in respect to all other Virginia river systems. A large pulp and paper company located at West Point, leases about 2,800 acres and an additional 800 acres are held by two executives of the corporation. A Virginia holding company leases 1,162 acres for an oil company, whose headquarters are located in another state. Total acreage held by these two companies accounts for 30% of all leased ground in the York River. In the past the holdings of the pulp and paper company were subleased to a private corporation which produced oysters.on rocks under the trade na~e 'Sea Rae Oysters'. This practice ended during 1972 and in 1974 another company subleased a portion of the holdings (Haven et al., 1978). To our knowledge the lease held by the oil company has never been used for oyster production on a commercial scale. 44 1 INDEX I i' :! < ~ ,.' I ~. I ~ I I ! I I I I ..p1•2e' 9 o,.,., llodl ITm ,... 111114 ..... Btrlor Lh•t ..... ,. oOOO Figure 20a York River Oyster Habitat 2 --·-0·- G]'l - ...... ~ ..,1_,,... -- •• ,1.\.'- ) l Figure 20b York River Oyster Habitat ~------l 3 111110(1 ! () i 1I~ .'\ ';. t I I '\'c...•., I I ~- # -r,.,. TU(J 'OfU -~ YORK RIVER UCMT~J I ~,., .. I + + ' Figure 20c York River Oyster Habitat 47 I! Hard Clams 1- ·clams was correlated with substrate, and that sediment preference followed ! this order: shell, sand, sand/mud, mud. Abundance in shell was believed to I oe related to larval setting behavior, as larvae prefer to attach their byssus to a firm substrate lightly covered by sediment. Clams are preyed upon by a number of fish, crabs and waterfowl. Gulls and rays feed on the adult clams while juv~niles and newly set spat are consumed by crabs, demersal fish and waterfowl. The clam is also an important commercial species although harvests in the Bay are limited by irregular recruitment. Nearly 95% of all hard clams landed commercially are taken with patent tongs. Figure 21 shows the dis tribution of hard clams in lower Chesapeake Bay. Commercial harvest is generally limited to those areas with medium to high density. Patent tongers harvest from 1,000 to 3,000 clams per day from areas with medium 48 ;\' ,0;}\ . ~~~{$~ .::Y CHESAPEAKE BAY ~ .... . I.. . p ··· CAPE o p ATLANTIC CHARLES~ p OCEAN D NO CLAMS f:f::';:f::j LOW DENSITY ~ LDW WITH ~ SCATTERED MEDIUM ~ MEDIUM WITH ~SOME HIGH • HIGH DENSITY LOW- LESS THAN 23buAJcre MEDIUM- 24 to 55bu.lacre HIGH- OVER 56bu.Alcre Figure 21 Hard Clam Densities in the lower Chesapeake Bay [from Haven and Loesch, 1975]1 49 abundance and up to 7,500 per day from high abundance areas (Haven, et al., 1973). Haven, et al. (1973) have indicated that the Virginia hard clam in dustry has operated near maximum sustained yield in recent years . Catch per unit effort has declined as the number of licenses has increased with the total harvest reaching a plateau in the mid to late sixties. An extensive survey of hard clam abundance in the lower York River was conducted between 1969 and 1973 by Haven, et al. (1973). A total of 67 stations in the York and the adjacent areas of York Spit and south along the Poquoson Flats were sampled during their study. Sampling was conducted along 50 foot transects with a towed hydraulic dredge. Clam density was estimated as follows: low, catch was 6 or less clams per 50 linear feet; medium, catch was between 14 to 21 clams per 50 linear feet; high, catch was 29 or more clams per 50 linear feet. In terms of expected harvest per · acre the above limits can be equated to : 1) low density~ 14 bushels/acre; 2) medium density ~ 32 but ~ 49 bushels/acre; high density ~ 67 bushels/acre. Abundance was generally low in shallow water .( 2 to 6 meters) along the south side of the river with medium abundance encountered near Yorktown, Goodwin Island and Tue Point (Figure 22). Medium to high abundance was recorded in shallow water along the north side of the river from its mouth to Sarah Creek. In water deeper than 6 meters clam density was generally low, espe cially below Gloucester Point. Just upstream from Gloucester Point, clams were more abundant in these deeper waters. The growth rates of hard clams in the York and James rivers were also studied by Haven et al. {1973). They observed that growth rates were 30' 7SO 15' GlOU~INES 0 0 + + 0 37° ~~~T ~ 0 I • 15 0 0 0 0 q. +C) 0 Cl ~ 0 0 + 0 0 0 0 0 0 YORKTOWN. 0 + 0 0+ 0 0 + r - 0 ~GOODWIN0&1 + OR-t 0 + <~'.o ~~·. 0 ~ 0 0 0 0 0 POQUOSON FLATS 370 1 10 + + Figure 22 Hard Clam Densities in the lower York River and Poquoson Flats area Abundance code: high-closed circles ;medium-half closed circles; low-open circles; and no decision-crosses. lJ1 0 51 generally higher in the Hampton Flats area (of the James River) than in the Gloucester Point-Yorktown area. Clams reached harvestable size for lit tlenecks (-60 mm) and cherrystones (-70 mm) at 2.5 and 4.5 years, respectively for Hampton Flats while about 4 to 8 years were required in the York River. Good recruitment of hard clams as determined by high abundance, low average length, and high percentages of littlenecks and cherrystones was indicated along the north shore of the lower York and in the vicinity of the Coleman Bridge. Moderate recruitment was indicated for York Spit and for the lower river in waters deeper than 6 meters. Poor recruitment was indi cated for the south shore of the lower river. Submerged Aquatic Vegetation The Chesapeake Bay, with its extensive littoral zone and broad salinity ·regime supports many different species of submerged aquatic vegetation (SAV). These plants play important roles in the Bay's ecology providing: I ( 1) food sources, (2) habitat, {3) acting as nutrient buffers, and (4) trapping sediments. The distribution and ecological significance of these communities has recently been the subject of an extensive series of studies which are summarized in four papers in the 1982-EPA Technical Studies report on Chesapeake Bay. A review of historical data and aerial photography has shown that submerged aquatic vegetation (SAV) was in the past very abundant throughout the Chesapeake Bay. Current evidence indicates a pattern of SAV decline that includes all species in all sections of the Bay. A marked decline has l ,l,, 52 occurred throughout the estuary since the mid-1960's. At present the abun dance of Bay grasses is estimated to be at its lowest level in recorded history. Surveys have not indicated a significant decline in SAV distribution in other areas along the East Coast and for this reason it is believed that water quality problems specific to the Bay region are affecting the dis tribution of these plants. Research conducted during the EPA-program indicates that the SAV decline parallels a general increase in nutrients, chlorophyll ~ concentrations, and turbidity in the upper Bay and major tributaries. The decline first occurred in the freshwater portions of the Bay and has moved "down-river". The upper-Bay, western-shore and lower-Bay communities have been most severely impacted. The distribution of SAV in the York River has been studied by several investigators (Marsh, 1970, 1973; Orth, 1971, 1976; Orth, et al. 1979). ·rn 1971 extensive beds of Zostera and Ruppia were present on the south shore of the river from Goodwin Islands to Yorktown. On the north shore SAV beds , were found from the Guinea Marshes to as far upriver as Clay Bank, 30 km f ,I from the mouth of the York River. By 1974, only.small scattered beds were 1: evident on the south shore, while on the north shore significant reductions in SAV density were observed from the Guinea Marshes to Gloucester Point l with almost complete loss from G.loucester Point to Clay Bank. In 1978 no I significant vegetation was observed from Gloucester Point to Clay Bank, and beds on the north shore of the lower river were reduced by almost 50% in areal coverage between 1974 to 1978. Vegetation along Goodwin Neck and Goodwin Islands also declined between 1974 and 1978. The ecological implications of the decline in SAV abundance in the Bay are difficult to assess. It has been estimated that these communities in 1960 were responsible for about 33% of the organic matter fixed in the 53 upper-Bay and by 1978 their contribution had decreased to only 4%. If these decreases occurred without other sources making up the deficits, serious consequences, e.g., reduced abundance of organisms higher up the food chain, may have resulted. Grass beds serve as major blue crab nursery areas sup porting very large populations of juvenile blue crabs throughout the year. In the lower Bay during comparable months up to 10,000 times as many blue crabs were found at vegetated · sites compared to unvegetated stations. Studies in both the upper and lower Chesapeake Bay have shown that infaunal abundance and diversity is higher in vegetated than unvegetated areas (Boynton and Heck, 1982). Therefore, in addition to their role in primary production, grass beds provide a very valuable habitat for an important commercial species. Fish and Crustaceans The fishes of the York River can be grouped in four major categories: (1) resident species, those which spawn and remain in the York River system; (2) anadromous species, those which utilize the freshwater portion of the river,as a spawning and nursery area and migrate fom the system as juveniles or young adults; (3) catadromous species, those which spawn offshore but utilize the river as a nursery area and feeding ground; and (4) strays, those species which occasionally wander into the York River. The study of fish populations, particularly, in estuarine waters is complex. Within the estuary individual species may be distributed on the basis of salinity, bottom characteristics , depth, etc. Population abun dance may be influenced by a variety of factors, e.g., fishing pressure, success of spawning and recruitment, species competition, effects of pollu tion, etc. In addition, sampling problems such as gear selectivity and the ;[ 54 timing of the sampling effort when dealing with migratory species further complicate population assessment. In the Chesapeake Bay populations of many important species have shown dramatic fluctuations in abundance as a function of time. The causes of these population fluctuations are known for only a few species. In order to provide a predictive mechanism for adult population abun dance, VIMS has for many years been conducting trawl surveys which estimate the size of juvenile fish populations. The theory being that if one knows the life-histories of the species involved you can project the relative size of adult population in future years. Although, the information derived from this effort may not indicate the cause of population fluctuations coupling the abundance data with other information, e.g., hydrography etc. may lead to a better understanding of the causative factor. Data on the relative abundance of juvenile fishes in the York and ·pamunkey rivers are available from VIMS trawl surveys conducted since 1955. Certain species are better sampled by the gear used and for those species less vulnerable comparisons between years although relative must be made with greater care. Stations in the trawl surveys are located at ap proximately 5 mile intervals along the York and Pamunkey rivers. In the yearly data presented here the five year moving average of the number of individuals captured per 0.25 nautical mile is shown (Wojcik and Austin, 1982). Figures 23, 24 and 25 depict the relative abundance (CPU-catch per unit effort) for the major species of interest. Figure 23, depicts the relative abundance of striped bass, white perch, croaker and spot. Striped bass are not adequately sampled by bottom trawls & 55 Striped Bass White Perch ::::> Cl. (.) 20 w (!) <( ct:: w ~ (!) z 0 100 !, >0 Atlantic Crooker ~ Spot 0~------~------~------r------r------~----~ 1970 1975 1980 1955 1960 1965 Figure 23 : } -----::.=---:·::~~.:::..::.:...~.::.:..-~~'."'~~-:::-.::::.:~::"~:~~=-::~:·:::-....::.....-:--~.::::::::::-.:-_~:::~:::-::=::.oo:-::-..:::,:-:. .:.:.:::.:: .. :.:...:_ __ ::______..:. ..::~:... ..:==.:- .:.:.....__ .._------_...... _ ____ ~------"T ") ' 56 '! "1 ~ l and therefore i·n comparison to some other species juvenile abundance in I dicies are never high. Juvenile white perch were most abundant during the .I I mid-sixties, decreasing in abundance in the mid-1970's, since 1974 popula d tions have shown a steady increase. Croaker and spot abundance follow similar trends, both these species being relatively scarce prior to 1970. Periods of abundance and scarcity for these species have been shown to be dependent in part on winter temperatures in the Virginia tributaries of the Chesapeake Bay where the young of the year over-winter (Joseph, 1972 and Norcross &Austin, 1981}. The relative abundance of weakfish, American shad, summer flounder, hogchoker and channel catfish are shown in Figure 24. Weakfish spawn at the mouth of the Chesapeake Bay and seaside of Virginia's Eastern shore in the spring. Peaks in juvenile abundance occurred in the early 70's, declining in the mid-70's and increased to record levels during 1979 and 1980. · Commercial harvest of weakfish from the York follows the trends observed in juvenile abundance. Juvenile shad are poorly sampled by the trawl gear and even when stocks are high CPU figures are very low. Populations of summer flounder have increased in recent years as indicated by these surveys of juvenile populations and commercial landing statistics. The hogchoker is the most consistently abundant species in the York River. An intensive survey of the fish and major decapod populations of the lower York River was made between March of 1972 and December of 1974. This investigation was conducted to provide background information prior to the expansion of the VEPCO power .station located in the lower York River. Samples were collected at monthly intervals from 12 strata in the lower river by trawl and from 9 beach seining stations (Figure 26}. ' I, ~ 57 Weakfish 20 10 American Shad :::> a.. u - w 0 (!) <( 4 wex: Summer Flounder ~ (!) z > 0 ~ 0 400 Hogchoker 200 o~------5 Channel Catfish 0+------~------.------.------.r------~----~ 1955 1960 1965 1970 1975 1980 Figure 24 58 ·20 White Catfish 10 0 ::::> a.. Bay Anchovy u w 100 (!) <( a:: w ~ (!) z > 0 :::E 0 American Eel 2 o+------.------.------.------.------~----- 1955 1960 1965 1970 1975 1980 Figure 25 - t \ I I · AI Cl 1 [.....-- _....,.. - ' ------I Bl ,/I -_:.--1 / A2 ------I I C2 I I 82 I I ,- I ----L--/ I I Figure 26 Beach Seine and Trawl Sampling Stations V1 \0 ~-~~------~---...... ---'"""'""',..._,.~---.fl"';".....,...__4 60 During the ·34 months of sampling at the beach seining stations 49 species were captured, but only 9 were present consistently: the Atlantic silverside, Menidia menidia; the tidewater silverside, Menidia bervllina; the mummichog, Fundulus heteroclitus; the striped killifish, Fundulus ma,jalis; the spot, Leiostomus xanthurus; the bay anchovy, Anchoa mitchilli; the sheepshead minnow, Cyprinodon variegatus; the northern pipefish, Syngnathus fuscus; and the summer flounder, Paralichthys dentatus. Of these, only ~ xanthurus and ~ dentatus cannot be considered to be resident species, since they migrate out of the river in winter to spawn offshore or in the Bay. Fish species that were captured only by beach seine were: ~ variegatus; the Atlantic needlefish, Strongylura marina; the striped mullet, Mugil cephalus; and the white mullet, Mugil curema. Seasonal occurrence of the major species sampled during the 3 year period is presented in Figure 27, which shows the percentage of the beach ·seine stations at which a species occurred as a function of season. The number of species captured per station (3 replicate hauls) ranged from zero to ten. Greater numbers of species were captured from April to September, as water temperatures increased. Species diversity (H') ranged from o to 2.7 which is characteristic of other estuarine fish populations. The biomass of fish captured peaked during the late spring and early summer. Figure 28, shows the number of species caught at each station during the survey. Similar plots of biomass, species diversity, and number of individuals indicate little difference between the sites sampled. However, certain stations were preferred by some species indicating perhaps more favorable habitats at these sites. Trawl surveys were conducted in 12 different strata of the lower York River as shown previously in Figure 26. The lower river was divided into 4 61 ,Figure 27 Seasonal Occurrence of 10 Fish Species B. tyronnus 40 40 w (.) z 4 0::: C. variegotus :::> (.) 20 20 (.) 0 0~ 0 0 s F w s s F 90 90 /\ I \ I \ w \ (.) I 60 I \ z 60 I \ 4 I \ 0::: I \ :::> I \ (.) I \ \ (.) I I \/ A. mitchilli 0 30 30 0~ lj ~' 0 0 s F M. menidio 100 ,_,,.' -0------o- ----o ~ w 0"' (.) z M. beryl/ina 4 0::: ::::> (.) 50 (.) 0 0~ 0 w s s F Figure 28 Number of Fish Species vs. Year, Month and Strata NORTH SHORE SOUTH SHORE 25 10 20 5 15 0 10 10 5 ..... ~ ...... ---~- 5 •. v ___ , -__ '-:···' .. , •··•• ~:-.. - 0 ~~ ....., ·· .... ·· ····· .... - 0 (f) w 25 u- 10 w a.. 20 (f) 5 15 u. 0 0 10 10 0: w CD 5 5 ~ :::> z 0 0 10 5 "" "' ...... 0 10 M A M J J A S 0 N 0 J F MONTH 5 3/72 - 2/73 0 0'\ ------3/73 - 2/74 N M A M J J A S 0 N 0 J F ...... 3/74 - 12/74 MONTH •':rrtMC -~---·-""' ,._._.,__ -·-"-...--~ .... - -·-~---~ ""-· --- ...,· . .sv;.---,--"'-·~~·~-""""'~'"' """'"""-'--...t'-"'·"--:.-...... ,-:-- ,_.__ · -··- ~..-.. - ~ ,.~_.- ·- - ?,_ ~,...,__ ...,.._ ....,.,_4',..._-::"".:::~::,::.:-.' I -~-· 63 strata as a function of distance from the mouth, within each of these seg ments samples were collected from the north and south shoal areas and from the channel. Sampling effort was determined based on the area covered by each substratum but no fewer than 3 samples (trawls) were collected in each area. Trawls of 5 minute duration with a 4.9 m semi-balloon otter trawl constituted a sample. In addition to determining the abundance of fin fishes the distribution of three major crustacean species was determined from the trawl data. The seasonal abundance of sand shrimp, Crangon septemspinosa, is shown in Figures 29 and 30. Sand shrimp were most abundant in the channel from April to May of 1972 and from October of 1972 through March of 1973. In April and May abundance increased dramatically in the shoal strata, popula tions then declined remaining relatively low throughout the rest of the study. Longitudinal distribution was variable, abundance in upstream strata ·was higher in · 1972 while the lower strata appear to have been favored in 1973. The distribution of Palaemonetes sp. (grass shrimp) followed similar but not identical patterns to sand shrimp. Channel strata were preferred during the fall of 1972 and winter of 1973, but no peaks in abundance on the shoals were observed as was noted in the spring of 1973 for sand shrimp. In general grass shrimp were more abundant in the upstream strata. Blue crabs were evenly distributed in all substrata from April to December of 1972, preference for the channel stations was indicated during the winter of 1973 but not in 1974. Populations were more abundant in the upstream strata. Seventy-eight fish species were collected during the trawl surveys. Monthly totals ranged from a high of 40 in July 1972 to a low of 15 in March 64 40 )0 20 10 0 .. J J .. s 0 N 0 J , 1972 19U 40 )0 zo D 10 0 , .. J J .. s 0 N 0 197S 1974 40 )0 H. ·sHOt.l. 20 CHANH[I. c 10 0 S. SHOAL 0 • J J .. s 0 N 1974 Hean ( retransfonne-d ln(x + 1)) nu:abers of Crangon Figure 29 septemspinosa per tow for cross-sectional strata in the lower York River April 1972-December 1974. 65 0 40 )0 D ZO 10 0 A .. A s 0 II 0 , .. "" 0 40 10 0 A .. A s 0 II 0 , .. lt74 0 , )0 zo 10 0 s --r-0 N 0 A .. A I 9?4 M.an (r~trans(onHd tn(x + I)) n .... ben of~ srt>teoasL)ino~a per tow for tong 1 t udinal strata '" Figure 30 th• lo~r York River April 1972-Decemb~r 1974. ,------ 1 66 ! of 1974. Figures 31 and 32, illustrate the variation in the mean number of species per station for each stratum. In general, fewer species were present in the winter, while species abundance increased in the summer and early fall. While there were no pronounced upstream-downstream differences, there were distinct channel-shoal differences. Generally during the summer months fewer species were collected from the channel stations coinciding with seasonal lows in dissolved oxygen. " The average catch in terms of number of individuals varied erratically from season to season and year to year. There were no consistent patterns of distribution either upstream-downstream or from channel to shoal. During both of the two winters sampled abundances were quite low during late January and early February but during the rest of the year peaks appeared sporadically, both with respect to time and location. catch in terms of biomass was also erratic from year to year but showed ·some distinct patterns within years. During both 1973 and 1974 the channel stations had consistently higher biomass than the shoals and higher biomass was also indicated in the upstream strata. Consistent patterns in species diversity .were evident from year to year, with low values in the winter_ and peaks in the late summer and fall in all strata. Shoal diversities reached maximum values during the next two months. There was little upstream-downstream difference in diversity. Six species dominated the fish fauna of the lower river, ~ mitchilli, ~ xanthurus, ~ undulatus, ~ maculates, ~ dentatus and ~ tau accounted for 87% of the biomass and 95% of the number of individuals collected. 67 A ~ 10 I 0' 1 II I J 1 s 0 H 0 "' i97Z i9H D :: 10 1'0 .. s 6 H 0 .. i9U " 1974 zo I~ 10 l0' s 0 N D " "' lt74• Mean num~r of sp~ie! pPr atat1on for cross-sectional Figure 31 •trata in the low.r York River, April 1972 to O.ce=ber 1974, l .,. 68 0 A ~ [ 10, 0 .. .. 0 N D , II lt71 ' ltfJ • 20 15 10 s 10 .. s 0 N 0 J f II ttH D c ~ 10 ' ! 0 A .. A s 0 N D lt74 H.an number or species per station Cor lcn&&tudLr.al strata In the low.r York R&ver Apr&! 1972 to O.c~ber Figure 32 1974. 69 Commercial Fisheries Landings The National Marine Fisheries Service and the Virginia Marine Resources Commission cooperate in the collection of commercial fisheries landing data for Virginia. Landing data are collected on an areal basis, for the York River there are three areas for which landings are recorded and these have been combined in this report. Statistics on landings must be viewed with caution for several reasons: .(1) they do not necessarily reflect effort; (2) they are based in part on tax records and undoubtedly underestimate the catch; and (3) harvest from a specific location may or may not be reported in that area. The commercial landings for the major species of interest in the York River are shown in Figures 33, 34 and 35 for the period of 1963 through 1981. In calculating the total finfish harvest data through 1977 included the menhaden fishery. Since that time due to restrictions on fishing, catch ·of this species is not included in the total. Fluctuations in catch of both menhaden and alewives account for the large peaks in harvest observed in 1965, 70 and 77. The catch of alewives has declined Bay wide since 1969 due in part to overfishing by foreign fleets in the Atlantic. The harvest of blue crabs from the York is shown along with the James ..... River for comparison purposes (Figure 33). Peak harvests of nearly 6 mil lion pounds were recorded in 1966 and 1971. Catch declined dramatically in 1973 and reached a low point in 1975, since that time steadily increasing harvests have been recorded. Portions of the James River were closed to crabbing in 1976 and 1977 due to contamination with Kepone, however, as can be seen from the figure catches declined in both rivers prior to this closure. In general landings of blue crabs for the York follow trends j observed for the total catch in Virginia. Total landings of blue crabs in ! I l I lI l! j,'I ·~ . 1 70 Virginia declined from 48 million pounds in 1971 to a low of 25 million in 1976, during this period a similar but proportionally larger decline was observed in the York. The reasons for the apparently greater decline in York River catches during this period are not known. Landings of hard clams reported for the York River fluctuated from a high of 600,000 pounds in 1974 to a low of just 7,000 pounds in 1978 {Figure 33). Since, 1978 the harvest has increased steadily to near average levels for the period. In 1974 the harvest from the York accounted for nearly half of the total recorded for Virginia. Low harvest reported in 1976 and 1977 correspond to decreased catch in the state as a whole. Commercial landings for swellfish, croaker, spot and grey trout from the York are shown in Figure 34. As can be seen from the figure large variations in catch occur as a function of time. The harvest for all of these species in the York follows the pattern observed for the total catch ·in Virginia. Fluctuations in abundance of croaker and spot are known to be related to the survival of young fishes during the winter. Cold winters cause extensive mortalities of young of the year fish and production during subsequent years is low. The catch of bluefish, striped bass, American shad and oysters, from private grounds for the York is shown in Figure 35. Harvest of these species generally follow trends observed for the total catch of the species in Virginia. On a comparative basis landings of striped bass were somewhat low'er for the York in the early 70's and shad catch was proportionally higher in the late 70's, i.e., when compared to the state totals. Harvest of oysters from both private and public grounds declined dramatically through out Virginia in the early 1960's due primarily to the oyster disease MSX. The disease was first recognized in Virginia in the (8422) 6000 TOTAL FINFISH 3000 ALEWIFE 40001.J 2000 \ I (/) \ I \ Cl z :::> 2000 0 Q_ u.. 0 (/) Cl Oi, I 0 z I I I I I I I I I I I I I I I I I I oJ. 1 I I I I I I I II~0 I I I I I I 0 63 70 80 63 70 80 ....., ,..... Figure 33 600 ( 1500) (2000) SWELLFISH 900 CROAKER 400l 600 en I I 0 z ::::> 2001 I I 1\ 300 0 a.. u.. 0 en 0 0 z 0;, I I I Tl I I"''"''''''' I :I: (.) t- 200 300 I I I I I I I I I I I I I I I 1 1 1 1 1 1 0 0 II I I I I I I I I I r I 1 I I I 1 1 1 63 70 80 63 70 80 ~ Figure 34 N _;;_-:----.:;:.....,_~-~-~~-:__..:=- ---- •. -~ - --- . #IJ ... 600 300 BLUEFISH STRIPED BASS 400 200 (/) 0 z :::> 100 0 Q_ u.. 0 (/) 0 0 z 0 I 'PRIVATE' OYSTERS ~ -z I (.) ~ AMERICAN SHAD 80 63 70 80 -..,J Figure 35 w ------~· ~ 74 spring of 1959. ·It spread rapidly, killing, in the next few years, most of the oysters in the high salinity regions of the Bay. Market oyster catch dropped from 3.5 million bushels in 1960 to under 1 million bushels by 1967. In the York the harvest of oysters declined from a high of 2 million pounds ( 300,000 bushels) in 1964 to a low of just 40,000 pounds in 1974. Improved harvest from private grounds have been recorded since the low in 1974 due primarily to planting of oysters in lower salinity regions wh~re MSX is less of a problem. Special Topics Petroleum Hydrocarbons Several investigations of the fate and effects of petroleum hydrocar bons have been conducted in the vicinity of the lower York River. Bender et al. (1974) studied the effects of an oil spill on benthic animals in the lower York River. The spill occurred in May of 1971 when a number of slicks of oil (cracking residue thinned with No. 2 fuel oil to the consistency ~f No. 6 fuel oil) washed onto the.sand beaches and Spartina marshes near the mouth of the York River. Control and oiled stations were sampled from July of 1971 to April of 1973. The effect of the spill was most evident when comparing numbers of species or species richness of benthic animals. The control stations averaged 33 species in July after the spill while the contaminated station had only 14. Recovery in terms of both species richness and faunal similarity was shown by April of 1973. However, the number of individuals remained lower at the spill site suggesting that complete recovery had not yet occurred. 75 Hyland (1973) conducted bioassays with water-accommodated No. 6 fuel oil on some of the dominant benthic species found in the lower York. In replicated experiments neither, Nassarius obsoletus, ~otea triloba, Nereis succinea, nor Modiolus emissus showed mortality which could be attributed to the presence of the oil. Three species, Spiochaetopteus oculatus, Gammarus mucronatus, and Paqurus lonqicarpus had 48 hour Lc50 values of 4.9, 0.4 and 0.6 mg/1, respectively. The four species which were not affected by the accommodated oil in this laboratory study also did not reveal population depressions following the oil spill in the river. Bieri and Stamoudis (1977) studied the uptake of No. 2 fuel oil by oysters and clams in a controlled spill conducted in the York River at Cheatham Annex. Their results showed that accommodated petroleum hydrocar bons in water reached their maximum concentrations a few hours after the ·spill and most were below detection 25 hours after the spill. In oysters uptake of hydrocarbons continued in some cases past 100 hours for both branched aliphatic and aromatic hydrocarbons. Residues of normal alkanes in oysters, up to about heptadecane, decreased very.rapidly and were very low or below background 25 hours after ~he spill. They demonstrated that uptake after 6 hours must be via ingestion of adsorbed hydrocarbons, many of which have undergone modification prior to uptake by the oysters. Clams acquired hydrocarbons at much lower concentrations than the oysters. Hershner (1977) studied the effects of petroleum hydrocarbons on salt marsh grasses and gastropods by repeatedly dosing a marsh with small amounts of No. 2 fuel oil. The study site was located just north of the mouth of the York River in Mobjack Bay. The marsh was dosed with oil twice monthly from November of 1973 until August of 1974. 76 Spartina alterniflora was the only grass species to show effects from the oil dosing. This result was attributed to the grass's location in the marsh, i.e. along the edges where it received the highest dose of oil. A substantial proportion of the S. alterniflora complement in the marsh was killed by the oil dosing. The remaining grass stand evidenced sublethal effects including delayed development in the spring, increased densities and reduced mean weights per stem. The second annual cohort of shoots, usually produced in late summer and early fall, was suppressed almost entirely. Oil which entered the roots and rhizomes of dead ~. alt~rniflora was maintained in a relatively undegraded state for at least seven months after being dosed. The population size and distributions of three species of snails were also determined in this study. Populations of Littorina irrorata were most severely affected by the oil. Changes in both the size and distribution of ·its population closely followed the changes in the marsh grass community. N. obsoletus showed some changes in distribution due to the oil, while populations of Melampus bidentatus were unaffected. The most severe long term impact of these chronic spills was the ero sion of th« underlying peat and sediment after the marsh grass had been killed. Recovery of ~. alterniflora during two growing seasons after the oiling ceased was slight. Lake (1977) examined the chemical fate of petroleum compounds in four marsh organisms during the chronic dosing of the marsh. The animals studied included Modilus demissus (a mussel), £. virqinica (the Eastern oyster), ~ irrorata (a snail) and N· succinia (a polychaete). All the organisms con tained components of the dosing oil and analysis revealed that some organisms accumulated or selectively retained some aromatic hydrocarbons and ±&1&4& c LL L S&ZUA:~i&i Mi d:Z 77 that patterns of loss of petroleum fractions seemed to depend upon the organism. Concentrations of petro-sulfur compounds were determined, in mussels and oysters, for a period between 2-15 weeks after dosing. Sulfur compounds found in the dosing oil included benzothiophenes, dibenzothiophenes and their alkyl derivatives. In samples of oysters and mussels taken two weeks after dosing ended, no petro-sulfur compounds with molecular weight below methyl benzothiophene were found. Fifteen weeks after dosing no sulfur compounds below dibenzothiophene (oysters) and methyl dibenzothiophene (mussels) could be detected. Loss rates for these compounds seemed to follow the patterns observed for the aromatic hydrocarbons. Concentrations of aromatic hydrocarbons in control mussels were 0.02 ppm (wet weight) and 0.01 ppm (wet weight) in oysters. A tributary of the York River, Cub Creek located at Cheatham Annex, was ·utilized during the 70's in a long term study of the fate and effects of oil spills in marsh ecosystems. Detailed results of this study were reported by Bender, et al. (1981). The study determined the ecological effects, chemi cal fate and microbial responses of marsh systems to spills of fresh and artificially weathered South Louisiana crude oil. The effects of the spills on primary production by phytoplankton were short lived, with recovery to control levels occurring within 7 days after the spills. Effects on the standing crop of marsh plants were severe during the. first year following the spills and substantial differences were still evident during the second year. Growth during the third year was much improved, with both oil treatments showing standing crops equal to or greater than the control. Long term effects, i.e. population reductions, were observed on most members of the benthic animal community. The fresh 78 crude was clearly more toxic than the aged crude to only three members of the benthic community. The fate of identifiable petroleum hydrocarbons in water, biota and unconsolidated sediments as a function of time was studied. Accommodation rates of the two different crude oils to water were substantially different. Water collected 6 hours after the fresh spill contained very low concentra tions of hydrocarbons while hydrocarbons in the 6 hour sample from the weathered oil had reached their maximum concentrations. Peak concentrations of total aromatics in water were similar in both spills and decreased rapidly to background levels. Tissue concentrations of aromatics in fish followed the pattern observed for the water, i.e. peak concentrations ear lier in the weathered oil spill. Concentrations of aromatics in oysters were higher in the weathered treatment and depuration was slower. Levels of autochthonous heterotrophic bacteria capable of degrading ·petroleum hydrocarbons evidenced significant and rapid increases following the oil spillages. The duration of the responses was longest within the intertidal sediments and was construed as indirect evidence for the con tinued presence of spill-derived petroleum hydrocarbons in the sediments. Detrimental effects on micro?ial biomass related to possible toxicity of the crude oils was not observed. On the basis of viable count data, significant short or long term reductions of bacterial populations involved in the mineralization of chitin or cellulose did not occur. voudrias (1981) conducted a study of the hydrocarbon concentrations in sediments from three Eastern Virginia estuarine creeks. Two of these creeks are tributaries of the York and the other is a tributary of the Poquoson River. The objective of his study was to determine whether differences in hydrocarbons levels in bottom sediments could be related to the presence of 79 marinas and other activities at two of the sites as compared to a control. The control station selected was Carter Creek about 25 km upstream from the mouth of the York. Sarah creek located near the mouth of the York and White House Cove, on the Poquoson, were selected as sites which were expected to show contributions of petroleum hydrocarbons from boating activities. Sediments from the creeks with marinas contained significantly higher levels of both aromatic and aliphatic hydrocarbons than did the control. Differences in the concentrations of certain "oil-pollution" indicators such as 17 , 21 -hopane homologs, phytane, and low molecular weight hydrocarbons were indicative of light petroleum fractions. Table 2, summarizes the aromatic hydrocarbon content at the three sites studied by Voudrias and one station at the mouth of the York (Bieri, et al. 1981). Hinde (1981) in her study of benthic animal populations in the vicinity ·of the refinery analyzed 19 sediment samples for hydrocarbons. Concentrations of total aromatic hydrocarbons, pristane;c17 and pristane/phytane ratios for these samples are listed on Table 3, station locations are shown in Figure 18. Heavy Metals The distribution of certain heavy metals in York River sediments and oysters has been studied by Huggett, et al. (1973 and 1975) . . Figure 36, shows the distribution of precipitated-coprecipitated copper in York, Mattaponi and Pamunkey rivers. As can be seen from the figure there appears to be an unnatural source of copper between 7.5 and 22 km from the mouth. In this segment of the river concentrations are 3 to 4 times higher than those on either side. Levels are also higher in the Pamunkey 80 Table 2 Summary of Sediment Aromatic Hydrocarbons Content ).lg/g of Dry Sediment White Sarah House Carter York Creek Creek Creek River 2-Methylnaphthalene .02 • 01 .003 1-Methylnaphthalene .006 .004 Biphenyl .06 :01 .001 2,6-Dimethylnaphthalene .03 .007 Acenaphthene .008 • 01 2,3,5-Trimethylnaphthalene .02 .01 .001 Fluorene :05 .02 .004 Dibenzothiophene .05 .03 .003 Phenanthrene .26 .20 .03 .004 Anthracene • 10 .05 .02 3-Mehtylphenanthrene .20 .09 .02 2-Methylphenanthrene .07 .04 • 01 Methylenephenanthrene .08 .06 .008 9-Methylphenanthrene • 11 .06 .008 1-Methylphenanthrene • 07 .05 .009 Fluoranthene 1.60 • 70 .20 .012 Pyrene 1.40 .60 • 10 .013 2,3-Benzofluorene .21 .09 .04 Benzo(a)anthracene .95 .40 • 10 .008 Chrysene 1. 60 .60 .09 .013 Benzo(e)pyrene 1.20 .40 .20 .011 Benzo(a)pyrene 1.30 .40 .08 .011 Perylene .90 .20 .20 .016 9,10-Diphenylanthracene .60 .30 .09 Benzo(ghi)perylene .90 .30 . 07 .013 Total Resolved Aromatics 23.6 9.5 2.50 UCM 8.0 0 0 Total Aromatic Hydrocarbons 31.0 9.5 2.50 &&iC aaa, && an CE&it. Table 3 ·York River Sediment Hydrocarbon Levels Prist/Phyt Station TAH*(~g/g) Prist/C 1 cl 0.72 10.3 9.2 c .. 0.10 4.5 3.6 Es 3.23 10. 1 4.7 Fl 0.24 3.2 2.2 Gs 1.17 10.2 7.5 r .. 0.98 6.8 6~9 Ll 1.70 0.4 0.8 Ls 3.04 10.8 4.9 M2 0.31 8.6 5.7 Ms 0.56 7.9 7.8 M.. 0.66 7.9 6.8 Ms 2.79 7.9 5.8 Nl 0.16 3.2 3. 1 Ns 0.16 9.2 6.2 10.0 Q.. 1.08 9.2 8.8 13.7 R7 0.97 6.6 7.6 Ss 0.13 4.5 7.0 Tl 3.42 *Total aliphatic hydrocarbons, resolved peaks only. 82 which receives drainage from abandoned pyrite mines. Zinc levels, shown in Figure 37, were greatly elevated in the Pamunkey, but show a regular decrease from the most upstream stations towards the mouth of the river. Oysters collected from the York and other Virginia estuaries exhibit concentration gradients for the metals Cu, Cd and Zn with increasing con centrations as one proceeds upstream (Huggett, et al. 1973). Figure 38, shows the distribution of copper in oysters as an example. Levels of Cd, Cu, and Zn in oysters from 4 stations in the York have been monitored twice yearly by the State Health Department since 1974. Table 4 shows the average metal levels in oysters at these stations. Summary and Discussion The salinity structure and chemical characteristics of the lower York River are extremely dynamic. Stratification of the water column in summer months causes oxygen depletion in the deeper waters of the river and - nutrients are regenerated during these periods. Episodes of stratification and destratification are related to the neap-spring tidal cycle, the water column appears to destratify about 4 days after spring tides. After these mixing periods the water column restratifies and oxygen concentrations in the lower waters gradually decrease. Low oxygen tensions in the deeper portions of the river limit fish and crab populations in these areas and may cause mortalities of benthic fauna. The extent to which the nutrients that are regenerated are utilized phytoplankton is not known with certainty. However, there are indications that the nutrients are rapidly assimilated by phytoplankton in the York and in other estuaries exhibiting destratification cycles. 83 Figure 36 Precipit~ted-copre<:ipitated E 0. 0. ~· 30 0.. 0.. 0 u Or~nic 15 30 YORK RIVER >.IATTAPONI AND PA>.IUNI Moving avenges (3) of concentrations of prrcipitated-coprecipitated and organic copper in me <63·1'm fraction of scdimrnu from me York River and estuary collected in June 1973• •, York River. o, Mattaponi River. •, Pamunkry River. 84 Figure 37 Prec:ipltated-coprec:lpltatld Q.~ cJ z N 0 0 15 160 YORK RIVER MAnAI'ONI ANO rAMUNKEY RIVERS OIST ANCE FROM MOUTH, km Movlnl averages (3) of concentrations of prccipitatcd-coprccipitatcd and organic rlnc in the <63-l'm fraction of sediments from the York River and estuary coUcctcd in June 1973• •· York River. o, Mattaponi River. •· Pamunkcy River. 85 Figure 38 ""''""" .,(, :- :-:-r-:- :. -The distribution of copper In oysten from Virginia's major rivers (from Proceedings of 7th National Shellfish Sanitation Conference). 86 Table 4 Mean Heavy Metal Levels in Oyster (~g/g) (1974-1981) Station (Km from mouth) 11 41 ___.2Q_ Copper 20 40 95 Cadmimum 0.6 1.4 1.3 960 Zinc 525 880 87 The existence of the stratification-destratification cycle in the York must be recognized in sampling programs designed to monitor and/or model water quality. Quantitative or qualitative fluctuations in other chemical constituents, particularity those associated with sediments, may result from the cycle. Insufficient historical data precludes an analysis of whether the degree of oxygen depletion in the deeper segments of the York has changed with time. Data collected over the last 10 years do not indicate a deterioration in conditions, however, prior to 1970 data are too sparse to make comparisons. The conditions which result in oxygen depletion are natural but the degree of depletion can be augmented by man's activities that contribute oxygen demanding wastes and/or nutrients. Prior to 1984 point source loadings of BOD in the lower York were estimated at 700 kg/day. In the spring of 1984 additional loadings from the ·operation of the York River sewage treatment plant increased the BOD load by about 1,000 kg/day. Model studies conducted by VIMS indicate that increased loading from this source should not be expeted to have a significant impact on oxygen levels in the lower estuary. However, considering the present state of the system, this and any additional loadings should be viewed with caution and potential impacts carefully monitored. Phytoplankton populations in the river vary seasonally, their most striking feature being the sporadic occurrence of 'red tides' caused by blooms of various species of dinoflagellates. These motile, non-toxic organisms can develop very dense populations with chlorophyll levels exceed ing 100 ug/1. A bay wide decline in submerged aquatic vegetation has been observed over the last 15 years. The declines in areal coverage by these plants 88 began in the upstream areas and have progressed "down-river". Communities in the York have declined in a similar manner. Although the exact cause of the declines is not known it is believed due to increased turbidity levels resulting from erosion and increased phytoplankton growth. Copepods are the most consistently abundant members of the zooplankton community but larval stages of decapods, molluscs and polychaetes are also important. Benthic animal populations are dominated by polychaete worms. The type of substrate present plays and important role in determining community structure. Benthic populations near the refinery outfall have been studied and slight, although statistically significant, depressions in diversity were found in 1976. Oyster populations in the lower river are limited by disease and predators. Commercial harvests come mainly from private grounds located ·upstream where average salinities are less than 15 °joo. The lower river supports a hard clam fishery of 10-20 patent tong boats. Landings reported for th river average about 200,000 pounds/year. Fish populations of the York are composed af resident, anadromous and catadromous. species. As in the Bay proper populations of many important species have shown dramatic fluctuations in abundance as a function of time. The causes of these population fluctuations are known for only a few species. Finfish are harvested commercially in the York by pound nets, fixed and drift gill nets, fish traps and by haul seining. Major species include; bluefish, grey trout, croaker, spot, flounder, eels, striped bass and American shad. Large fluctuations in landings for individual species occur j &&&£ &IE A iii ~ . ~ ----~-~ -~- ~------~·--·-·-·------ 89 with time. In· general, trends in harvest from the York follow those ob served for the state as a whole. The estimated dockside value of commercial fishe~y landings from the York was 1.6 million in both 1980 and 1981. 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