Influence of rafted oyster aquaculture on sediment processes draft final report

[From the U.S. Government Printing Office, www.gpo.gov]

Ref. No. [UMCEES]CBL 92-033

NA90AA-D-CZ795

Task 21

INFLUENCE OF RAFTED OYSTER AQUACULTURE

ON SEDIMENT PROCESSES

DRAFT FINAL REPORT

to:

Maryland Department of Natural Resources
Tidewater Administration
Maryland Coastal Research Division
DNR Contract No. C224-91-004

AUTHORS:

Jon H. Tuttle
The University of Maryland System
Center for Environmental and Estuarine Studies
Chesapeake Biological Laboratory
Solomons, MD 20688-0038

QL and
430.7
.09 Robert B. Jonas
T88 Department of Biology
1992
George Mason University
Fairfax, VA 22030

TABLE OF CONTENTS

ABSTRACT i

LIST OF TABLES ii

LIST OF FIGURES iii

PROJECT RATIONALE AND OBJECTIVES I

BACKGROUND 3

Ecosystem Rationale for Oyster Replenishment 3
Oyster Replenishment as a Bioremediation Tool 8
Replenishment Strategies: Oyster Reef vs. Oyster Aquaculture 9
Field and Ecosystem Modeling Validations I I
Potentially Negative Impacts 13

METHODS 14

Study Site Description 14
Coring Device Design and Sediment Collection 18
Hydrographic Measurements 19
Pore Water Collection 21
Chemical Determinations and Porosity 22
Biochemical Oxygen Demand 23
Dark Assimilation of Carbon Dioxide 24
Sulfate Reduction 25

RESULTS 26

Weather and Hydrographic Data 26
Sediment Characteristics 29
Carbon: POC and PON 29
Carbon: Biochemical Oxygen Demand 34
Carbon: POC by Combustion 39
Dark Assimilation of Carbon Dioxide 42
Sulfur: Sulfate Profiles 52
Sulfur: Sulfate Reduction 61
Sulfur: Sulfide Profiles 69
Sulfur: Total Reduced Sulfur 71

DISCUSSION

EXECUTIVE SUMMARY US Department of Commrece
Technical Findings NOAA Coastal Services Center Library
2234 South Hobson Avenue
Recommendations Charleston, SC 29405-2413

ACKNOWLEDGEMENTS

REFERENCES 83

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LIST OF TABLES

Table 1. Weather conditions and other observations made at the Pintail Point Farm oyster
aquaculture facility on sediment sampling days.

Table 2. Hydrographic and secchi disk data collected at the Pintail Point Farm oyster
aquaculture facility on days when sediments were sampled. Oysters were rafted at stations 2
and 3. Station 6 was located in the main channel of the adjacent Wye River. ND indicates
no data collected.

Table 3. Mean particulate organic carbon, particulate organic nitrogen, and molar carbon:
nitrogen ratios in the surficial 2 cm of sediment at stations 1 through 3.

Table 4. Comparison of sediment POC measured directly, calculated by regression and
estimated from loss on combustion.

Table 5. Loss of POC between the 0-2 cm and 4-6 cm segments of cores collected July 12 to
September 15, 1991.

LIST OF FIGURES

Figure 1. Current state of production (carbon flow) in the Chesapeake Bay ecosystem.
Adapted from Draft 1989 State of the Bay report.

Figure 2. Schematic diagram of the Deep Cove Creek rafted oyster aquaculture site.

Figure 3. Porosity profiles of sediments at stations 1-5.

Figure 4. POC, PON, and POC:PON molar ratios in surficial sediments.

Figure 5. Five-day and twenty-day biochemical oxygen demand in surficial sediments.

Figure 6. Comparisons of five-day and twenty-day biochemical oxygen demand values at
stations 2 and 3 with values at the other stations.

Figure 7. Intercomparison of five-day and twenty-day biochemical oxygen demand values
among stations where rafts were not present.

Figure 8. Regression of surficial sediment weight loss on combustion on POC determined by
elemental analysis.

Figure 9. Distributions of POC in sediments at stations 1-5.

Figure 10. Distributions of total inorganic carbon (TIC) in sediments at stations 1-5.

Figure 11. Rates of dark assimilation of CO, as a function of sediment depth at station 1.

Figure 12. Rates of dark assimilation of C02 as a function of sediment depth at station 2.

Figure 13. Rates of dark assimilation of CO, as a function of sediment depth at station 3.

Figure 14. Rates of dark assimilation of CO, as a function of sediment depth at station 4.

Figure 15. Rates of dark assimilation of CO, as a function of sediment depth at station 5.

Figure 16. Depth-integrated areal rates of dark assimilation of CO, over the study period.

Figure 17. Depth profiles of pore water sulfate concentration at station 1.

Figure 18. Depth profiles of pore water sulfate concentration at station 2.,

Figure 19. Depth profiles of pore water sulfate concentration at station 3.

Figure 20. Depth profiles of pore water sulfate concentration at station 4.

Figure 21. Depth profiles of pore water sulfate concentration at station 5.

Figure 22. Sulfate reduction rate as a function of sediment depth at station 1.

Figure 23. Sulfate reduction rate as a function of sediment depth at station 2.

Figure 24. Sulfate reduction rate as a function of sediment depth at station 3.

Figure 25. Sulfate reduction rate as a function of sediment depth at station 4.

Figure 26. Sulfate reduction rate as a function of sediment depth at station 5.

Figure 27. Depth-integrated areal sulfate reduction rates over the study period.

Figure 28. Depth profiles of pore water HS- concentration at station 1.

Figure 29. Depth profiles of pore water HS- concentration at station 2.

Figure 30. Depth profiles of pore water HS- concentration at station 3.

Figure 31. Depth profiles of pore water HS- concentration at station 4.

Figure 32. Depth profiles of pore water HS- concentration at station 5.

Figure 33. Distributions of total reduced sulfur in sediments at station 1.

Figure 34. Distributions of total reduced sulfur in sediments at station 2.

Figure 35. Distributions of total reduced sulfur in sediments at station 3.

Figure 36. Distributions of total reduced sulfur in sediments at station 4.

Figure 37. Distributions of total reduced sulfur in sediments at station 5.

Figure 38. Depth-integrated areal total reduced sulfur content of sediments over the study
period.

PROJECT RATIONALE AND OBJECTIVES

Comparison of historical Chesapeake Bay oyster standing stocks with those existing

now indicate that an important mechanism for removing phytoplankton biomass from Bay

water has all but disappeared (Newell 1988; Newell et al. 1989). The Bay ecosystem appears

to have changed such that a substantial portion of primary production is now dissipated by

bacterial metabolism (Baird and Ulanowicz 1989), leading to increased oxygen consumption

-n the water column and sulfide production in sediments. These microbial processes have

been chiefly responsible for increasing the intensity, duration, and spatial extent of hypoxic

and anoxic conditions in mesohaline Bay waters (Tuttle et al. 1987a). A simple, benthic

suspension feeding model predicts that rafted oyster population densities sufficient to reduce

current phytoplankton biomass by 40% are theoretically sustainable (Gerritsen et al. 1989).

All these observations lead to the hypothesis that increasing Bay oyster stocks, by rafted

oyster mariculture or by augmenting oyster reef densities, could substantially improve water

quality in the Chesapeake Bay and/or its tributaries and, at the same time, revitalize the

declining shellfish industry in Maryland.

Field studies conducted by our laboratory in 1989 and 1990 at the St. George Oyster

Company oyster mariculture facility in St. Mary's County, Maryland, demonstrated that

rafted oysters can remove significant quantities of phytoplankton carbon and biochemical

oxygen demand from the estuarine water column (Jonas and Tuttle 1991; Tuttle and Jonas, in

preparation). The field data are consistent with the trophic consequences of increasing oyster

densities predicted by a quasi-equilibrium, mass action model of the exchanges transpiring in

the mid-Bay ecosystem (Ulanowicz and Tuttle, in press). Despite mounting evidence of the

efficacy of increasing oyster stocks as a useful bioremediation technique to augment the

nutrient reduction strategy, it remains unclear whether increased loading of sediments with

oyster feces and pseudofeces would significantly increase oxygen demand in the sediments.

If so, many of the benefits gained from removing excess phytoplankton from the water

column could be negated.

Based on information gained using a variety of techniques, many of which we have

applied over the past eight years to examine the formation and maintenance of anoxia in the

mesohaline Chesapeake Bay, we report here on the influences of oyster rafting mariculture on

underlying estuarine sediments in comparison with similar, nearby sediments outside the raft

area. Our goals were to establish whether oyster fecal loading substantially increases

sediment oxygen deficits and to examine how this loading quantitatively and qualitatively

affects key estuarine microbial sediment processes on a seasonal basis.

To attain these goals, our objectives were:

1. To compare the quantity and quality of organic carbon reaching the

sediments beneath and away from rafting areas;

2. To determine integrated microbial metabolism in these sediments;

3. To compare rates of sediment sulfate reduction, the key bacterial process

occurring in Chesapeake Bay sediments during the periods of rapid oyster

growth; and,

4. To assess sediment oxygen demand in sediments beneath and away from

rafting areas.

BACKGROUND

Ecosystem Rationale for Oyste Replenishment

Recent studies on Chesapeake Bay water quality and assessments of the current state

of the mid-Bay's ecosystem (Malone et al. 1986; Tuttle et al. 1985, 1987a, 1987b; Jonas

1987; Jonas et al 1988a, 1988c; Baird and Ulanowicz 1989; Jonas and Tuttle 1990; Baird et

al. 1991) all suggest that there has been a major shift in the trophic food web structure of the

Bay's ecosystem. Especially during the warmer months of the year, the ecosystem now

appears to be dominated by bacteria and their associated physiological processes rather than

by grazer-based food webs. This trophic shift is particularly evident in the water column

where increased phytoplankton production resulting from anthropogenic inputs of nitrogen

and phosphorous is consumed to a major degree by free-living bacteria. In the mesohaline

reaches of the Bay, for example, abundances of these microorganisms reach and remain at 10

to 20 x 101 cells 1;'. Such sustained abundances, which have been observed over several

years and locations throughout the mid-Bay region (Malone et al. 1986; Tuttle et al. 1987a;

Ducklow et al. 1987; Jonas and Tuttle 1990; Malone et al. 1991), are high compared to other

coastal environments (Williams 1984). These elevated bacterial abundances are responsible

for high rates of pelagic oxygen consumption and represent one of the primary factors driving

the development and maintenance of hypoxia and anoxia commonly observed in the mainstern

and subestuaries of the Bay (Tuttle et al. 1987a).

High levels of microbially labile dissolved organic carbon (DOC) fueling the

production and metabolism (and thus, oxygen consumption) of the pelagic, heterotrophic

bacteria derive from: 1) direct release of DOC by living phytoplankton (Malone et al. 1991);

2) indirect release of DOC through grazing and excretion by zooplankton (e.g. Caron et al.

1988; Roman et al. 1988); and 3) DOC release from decaying phytoplankton cells (Tuttle et

al. 1987a; Jonas and Tuttle 1990; Bell 1990). About I I % of mainstem mid-Bay total DOC

(typically 3.5 mg C L-'; Malone et al. 1991) consists of highly labile organic carbon (0.38

mg C L:' measured as dissolved, 5-day biochemical oxygen demand; Jonas and Tuttle 1990)

which in turn is composed of such substances as carbohydrates, amino acids, and short chain

organic acids (Bell et al. 1988; Jonas et al. 1988a; Bell 1990). Like bacterial abundances,

rates of oxygen-consuming metabolism of this labile organic carbon are also unexpectedly

high compared to other estuarine systems. In the mid-Bay mainstem, for example, dissolved

monosaccharide concentrations average I to 2 jM (0.07 to 0.14 mg C L;'), dissolved free

amino acid (DFAA) concentrations approach I IAM, and their metabolism can average 225 n

mol L;' h-' (16.2 ILg C L;' h@') and 20 n mol 1;' h-', respectively (Bell 1990). Thus, dissolved

monosaccharides, comprising up to 37% of labile DOC, represent a preferred source of

carbon and energy for pelagic bacterial metabolism and production in the mid-Bay and exhibit

a very rapid turnover ranging from 8.9 to 4.3 h.

Recent inter-ecosystem comparisons of the Chesapeake Bay with other coastal

environments suggest that the Bay is stressed, giving rise to increased recycling of materials

(i.e. fixed carbon and nutrients) via short intense loops (Baird et al. 1991). Thus, although

there have been suggestions that secondary producer-based bacterial food webs may be

-mportant links to higher trophic levels in aquatic ecosystems, this phytoplankton/bacterial

food web ("microbial loop") is probably unproductive in terms of transferring carbon and

energy to harvestable biological resources. Factors such as increased food web length (Baird

and Ulanowicz 1989) and the apparent lack of efficient bactivors (small animals which

consume bacteria) seem to result in Bay planktonic food webs in which the bacteria act as an

organic carbon sink in which carbon and plant nutrients are rapidly recycled (Ducklow et al.

1986; Baird and Ulanowicz 1989; Malone and Ducklow 1990; Fig. 1). The amount of

phytoplankton net production "lost" through mid-Bay water column microbial metabolism

alone has been estimated at 50, 30, 28 and 25% in summer, fall, winter, and spring,

respectively (Baird and Ulanowicz 1989). Indeed, the 1989 State of the Bay Report

concludes: "...only a small percentage of the plant production eventually reaches the

economically important finfish and shellfish levels. The task of managers is to restore the

Chesapeake to a balanced ecosystem in which as much of this energy as possible is funneled

into important and useful biological yields -- oysters, striped bass, and waterfowl, among

others. In the Bay's current state, much of the plant production does not reach these higher

levels but ends up decomposing on the Bay bottom, robbing the water of much needed

oxygen."

Recent evidence indicates that increased carbon flow through microbial loop

communities is occurring in Bay sediments as well as in the water column. Sulfate reduction,

a process confined chiefly to sediments and catalyzed by obligately anaerobic bacteria, has

increased in mid-Bay sediments since colonial times (Cooper and Brush 1991). Directly

measured rates of sediment sulfate reduction (sulfide production) in the mid- and lower Bay

are among the highest found in marine environments (Tuttle et al. 1987a, 1987b; Roden and

Tuttle in press, in revision) and rates in the upper Bay are substantial, even at limiting

sediment pore water sulfate concentrations (Roden and Tuttle in review).

Although there are probably multiple causes for this shift in trophic structure of the

Chesapeake Bay ecosystem, it is likely that a key factor has been the decline in abundance of

benthic suspension feeders, such as oysters and clams, and consequent reduction in cropping

The Bay Pyramid

Ft s

Sunlicht

Senthos
(Hurnan
Ac
/ livitles)
Zooplankton Nutrients

Primary Production

TO tal
Decomposition
I by Bacteria
Annual Prodwdon of Elomass
(tons cubw In mesottallne `5
@IN

Figure 1. Current state of production (carbon flow) in the Chesapeake Bay ecosystem.
Adapted from Draft 1989 State of the Bay report. (Thanks to Dr. J.A. Mihursky, CRQ.

of phytoplankton. Baird and Ulanowicz (1989) noted that deposit-feeding organisms now

dominate the benthic community of the Bay and that water clarity, once maintained by large

populations of filter feeders, has decreased. Low dissolved oxygen concentrations, high rates

of sediment deposition, overharvesting and parasitic diseases (e.g. MSX and Dermo) have all

contributed to this decline of benthic suspension feeders. Newell (1988) estimates that

Chesapeake Bay standing stocks of the American oyster, Crassostrea virginica, declined from

188 x 10' kg dry weight (-355 million bushels) in the late 19th century to about 1.9 x 10' kg

dry weight (-4 million bushels) currently. Oyster landings in the 1800's amounted to about

20 million bushels annually from the northern, mesohaline portion of the Bay, whereas

current harvests are of the order of 0.5 million bushels or less.

Calculations based on oyster abundances in the Bay and laboratory-determined oyster

feeding rates (Newell 1988; Newell et al. 1989) suggest that oyster abundances in the late

19th century were sufficient to filter the entire volume of the Maryland portion of the Bay in

three to six days. Current oyster stocks filter the same volume in about 325 days. Thus, a

major biological mechanism for removing phytoplankton and organic detritus has been nearly

eliminated from large areas of the Bay.

Although deposit-feeding macrobenthic invertebrates may have replaced the oyster to

some extent (Baird and Ulanowicz 1989), it is possible that benthic biomass is actually

reduced due to the loss of oyster feces and pseudofeces (Haven and Morales-Alamo 1986;

Holland et al. 1987; Jordan 1987). Large segments of the macrobenthos may depend either

on the organic materials deposited by oysters or the large surface area provided by oyster

shell. In either event, inhospitable bottom water and sediment chemical conditions probably

limit annual recolonization success.

It is reasonable to conclude that oysters, key filter feeders, were but are no longer a

quantitatively important component of the trophic structure of the Chesapeake Bay ecosystem.

Based on calculations such as those discussed above and on the current trophic state of the

Bay, we (Tuttle et al. 1987b) and others (Newell 1988; Newell et al. 1989; Gerritsen et al.

1989) have proposed that replenishing oyster populations should have a major positive impact

on Bay water quality as well as a revitalizing influence on the nearly extinct Chesapeake Bay

shellfish industry.

Qyste ftlenishment as -4 Bioremediation Tool

Given the likely condition that the magnitude of bacterial biomass, production, and

metabolism in Chesapeake Bay is ultimately related to the amount of internal organic carbon

production (autochthonous primary production) and external inputs (allochthonous carbon

from terrestrial sources), it is theoretically feasible to control bacterioplankton communities

by:

1. decreasing autochthonous production through nutrient reduction strategies

and allochthonous carbon inputs by effective waste treatment and land

management practices (bottom-up or supply side controls) and by

2. redirecting a portion of autochthonous production and allochthonous carbon

through ecosystem compartments at higher trophic levels than the microbial

loop (top-down or demand side control).

The first of these strategies, already implemented as the cornerstone of Bay cleanup

efforts and targeted primarily at decreasing phytoplankton biomass and production, would be

expected to decrease microbial loop biomass and production as well with a concurrent

decrease in oxygen consumption and improved water quality (eg. higher dissolved oxygen

levels in deep waters, increased water clarity). Unfortunately, it is becoming increasingly

apparent that nutrient reduction goals (40% reduction of N and P inputs) are probably not

attainable, particularly in the case of N where substantial inputs as NO. enter the Bay

watershed from air pollution (see eg. Blankenship 1990, 1991). Furthermore, there is no

reason to conclude & priori that the V=ortio of primary production metabolized by

microbial communities would be altered, even if nutrient reduction goals were attained (i.e.

even less production would be available for transfer to higher trophic levels, such that stocks

of desirable species could be decreased).

The second strategy, a bioremediation procedure relying on higher trophic level

consumers (oysters) whose population density could be directly managed, would permit a

greater proportion of primary production to be captured by species more desirable than

microorganisms. This top-down control scheme has, in fact, been proposed as a practical

means to augment the nutrient reduction strategy (Gerritsen et al. 1989; Ulanowicz and

Tuttle, in press).

Replenishment Strategies: Oyste Reef versus Oy AQuacul

Oyster standing stocks could be increased by replenishing historic oyster reefs,

establishing new reefs, or by raft mariculture of oys ters. Although our arguments are based

on delineating those practices which will optimize water quality improvement, we are well

aware of political and sociological considerations which may ultimately drive the

implementation of oyster replenishment strategies.

Gerritsen et al. (1989) used a simple, benthic: suspension feeding model to predict the

ability of suspension feeding bivalves to remove excess phytoplankton production from Bay

waters, thereby improving water quality and decreasing oxygen deficits caused by decaying

phytoplankton. Their model predicts that benthic oyster populations increased to a density

sufficient to remove 40% of the phytoplankton standing crop (requiring an oyster biomass

about ten-fold greater than that which existed historically in the Maryland portion of

Chesapeake Bay) would be unsustainable due to problems of crowding, food limitation, and

periodic hypoxic and anoxic conditions. In contrast, rafted oyster mariculture population

density sufficient to meet the 40% nutrient reduction (i.e., 40% phytoplankton biomass

removal) target of Maryland's Chesapeake Bay Initiatives are theoretically sustainable. It

should be pointed out that this model scenario assumes the use of oyster replenishment alone

to meet established water quality goals. If on the other hand oyster replenishment were used

to augmen nutrient reduction strategies (Ulanowicz and Tuttle, in press), oyster biomass

supplementation could be reduced and oyster replenishment to the benthos would become an

effective option.

There are other factors, however, which argue for oyster aquaculture. Viewed most

simply, rafting of oysters within the mixed zone of the water column removes the oyster in

the "Bay Pyramid" (Fig. 1) from its usual benthic position to the level between primary

production and bacterial decomposition processes. In this new position, the oyster

"competes" with bacterioplankton and, if successful, oysters could sequester a substantial

amount of organic carbon from immediate bacterial metabolism. Redirecting the carbon flow

by increasing oyster populations would be expected to reduce suspended particulate matter

(including phytoplankton, bacteria, and detritus) and oxygen demand while improving water

clarity and increasing a harvestable fisheries resource. Rafted aquaculture is also likely to

alleviate two major problems faced by bottom dwelling oysters. First, bottom dwelling

oysters are particularly subject to deleterious influences of hydrogen sulfide arising from

sulfate reduction in the sediments or from inundation by advected anoxic water. Secondly,

oysters in more saline regions (e.g., the mesohaline Bay) are threatened by the parasitic

disease MSX and Dermo, chronic infections often fatal to the animals before they reach

market size. By suspending oysters near the surface, away from sediments, the threat of low-

dissolved oxygen concentrations is greatly reduced or eliminated, and the more rapid oyster

growth rates attainable in rafted aquaculture should lessen the effects of parasitic diseases.

Field and Ecosyste Modeling Validations

Although simple modeling exercises such as those discussed above suggest that

increased oyster populations could improve Bay water quality and restore balance to the Bay's

ecosystem, field evidence and ecosystem effects confirming the efficacy of this proposed

bioremediation strategy has been lacking. Dining 1989 and 1990, however, our laboratory

conducted at the St. George Oyster Company in St. Mary's County, MD, a small-scale

demonstration study aimed at determining how rafted oyster mariculture influences

phytoplankton and bacterioplankton biomass and production, water column nutrients, and

organic carbon lability. Details of this work may be found elsewhere (Jonas and Tuttle 1991;

Ulanowicz and Tuttle, in press) or are in preparation (Tuttle and Jonas, in prep), but several

key findings are worthy of mention here. We compared parameters measured within a raft

field with measurements made in adjacent, open water areas.

Over a late May - early October period, phytoplankton biomass was reduced in the

raft field (60,000 oysters in a 300 m' area) an average of 50% (range 17% to 72%) with a

concommitted reduction in primary production (average 44% reduction). Thus, suggestions

that raft mariculture should decrease phytoplankton biomass but might leave primary

production unaffected (Gerritsen et al. 1989) or even increased (Tenore et al. 1982) seem

unfounded. Bacterioplankton abundances were reduced significantly but less dramatically

(average 20%, range 10 to 40%) than phytoplankton. Bacterial production and metabolism

(glucose turnover), however, were nearly identical in rafted and open water areas despite

decreased abundances in the former, indicating increased cell-specific rates of both processes.

This finding is consistent with observations that bacterioplankton in Bay waters respond

primarily to labile DOC (Jonas and Tuttle 1990; Malone et al. 1991). Indeed, filterable

(functionally dissolved) 5-day biochemical oxygen demand (BOD) was decreased an average

of only 9 % (range 20 % decrease to 21 % increase) within the oyster raft field. Total BOD,

however, was reduced an average of 30% within the rafts area and particulate BOD was

decreased by an average of 47% (maximum of 64%), comparable to decreases in

phytoplankton biomass and production.

A quasi-equilibrium, mass action model designed to assess the influence of increasing

oyster densities on the mid-Bay ecosystem (Ulanowicz and Tuttle, in press) predicts

qualitatively similar changes resulting from decreasing oyster stock exploitation by 23 %

(oyster biomass increased by 150%). Although smaller in magnitude (the aquaculture oyster

densities were much greater), the predicted changes (decreases of 11 %, 6 %, and 5 % for

phytoplankton abundance, bacterioplankton abundance, and suspended POC-attached bacterial

mass, respectively) were all in the same direction as parameters measured at the aquaculture

facility. Interestingly, the ratio of phytoplankton abundance decrease:bacterioplankton

abundance decrease (about 2:1) was stffdngly similar to that measured in the field. Other

desirable changes predicted by the model included: decreased gelatinous zooplankton (-89%);

increased benthic diatoms (+ 29 %), mesozooplankton (+ 5 %), carnivorous fishes (+ 18 %),

filter feeding fishes (+5 %); and virtually unchanged DOC (+ I %). Thus, the evidence so far

supports the contention that increasing oyster populations in the Bay and/or its tributaries will

positively impact the Bay's ecosystem and yield improved water quality.

Potentially Negative Impac

Despite proposed, predicted, and measured benefits of an oyster replenishment

strategy, there are several possible negative impacts associated with increased oyster densities.

One of these, namely increased phytoplankton production in the vicinity of the oysters, has

been discounted (Jonas and Tuttle 1991; Ulanowicz and Tuttle, in press). Another, increased

nutrient concentrations (particularly N) arising from oyster excretion or from increased

sediment flux, has not been confirmed by our 1990 study of water quality and pelagic

microbial processes at the St. George Oyster Company (Tuttle and Jonas, in prep). Indeed,

levels of ammonia and nitrate + nitrite were not elevated in an oyster raft area compared to

nearby open waters.

Perhaps of greatest concern is the possibility that increased oyster densities could,

through increased deposition of highly labile organic material (oyster feces and pseudofeces)

increase sediment microbial processes and, thereby, increase sediment oxygen demand and

sediment nutrient regeneration. In one sense then, what had been a problem of excess

oxygen consumption and nutrient regeneration in the water column could be relocated to the

sediments. This shift appears to occur in mariculture raft areas of Spanish rias (Tenore et al.

1982) where sediments beneath rafts exhibit higher rates of anaerobic microbial processes

(e.g. sulfate reduction) than sediments in rias where aquaculture is not conducted. The

Spanish ria environments, however, are not nearly so productive as the Chesapeake Bay.

Interestingly, ammonia regeneration in sediments underlying rafted rias is less intense than in

open rias, probably due to decreased bioturbation in the former (Tenore et al. 1982).

The potential for increased carbon loading to sediments by increased oyster densities

has been pinpointed as the critical outstanding question which needs to be addressed before

oyster augmentation as a water quality improvement strategy can be implemented (Gerritsen

et al. 1989). The work reported here was undertaken to directly investigate this potential

problem. We have hypothesized that sediments underlying rafted oysters will receive greater

quantities of microbially labile organic matter than outlying sediments and that key, anaerobic

processes, such as sulfate reduction, will be increased. Both aerobic decomposition of the

newly deposited material and sulfide produced from sulfate reduction should increase oxygen

demand beneath the rafts. Accordingly, we selected for measurement parameters to assess

sediment carbon quantity (POC) and quality (PON and BOD), overall sediment microbial

activity (dark assimilation of carbon dioxide), and sulfate reduction (rates and pool sizes of

sulfate and sulfide).

METHODS

S
Auddy Site De%@doon

Our proposal identified the St. George Oyster Company oyster aquaculture facility,

located along the Potomac River in St. Mary's County, MD and operated by the Stewart

Petroleum Company, as our study area. We intended to examine sediments beneath "oyster

bag" raft arrays set along the eastern shore of Piney Point Creek where we had conducted in

1990 a study of the influence of rafted oyster aquaculture on water quality; phytoplankton

biomass and production; bacterioplankton biomass, production and metabolism; and water

column carbon quality (Tuttle and Jonas, in prep). This site had the advantages that: we had

already collected a substantial body of water column data to serve as a backdrop for our

sediment study; the oyster raft experimental study area, consisting of adjacent rows of oyster

bag rafts, bags without oysters, and surrounded by open water on all sides, remained virtually

-unmanipulated" by aquaculture personnel through an agreement we had with the St. George

Oyster Company; the site was within 1/2 hour of our laboratory in Solomons; and outside

access to the site by land was controlled by Stewart Petroleum which owned the property.

Unfortunately, the St. George Oyster Company was closed by Stewart Petroleum in February

1991, just before our sediment study was to begin. We are unsure of the causes which

forced the closure, but continued financial losses incurred by the ambitious St. George Oyster

Company undertaking and possibly infection of the aquacultured oyster stock by the disease

Dermo and/or MSX (caused by the parasitic protozoans, Perkinsus marinus and

Haplospofidium nelsoni, respectively) may well have been key factors.

We are indebted to our grant officer, David Bleil of the Maryland Department of

Natural Resources Tidewater Administration, for identifying and arranging for our access to

an alternate aquaculture site located at Pintail Point Farm (near the Wye River Institute) on

Maryland's Eastern Shore. Unfortunately, this site is more than two hours from our

laboratory and had lower oyster densities and smaller oysters than the Piney Point Creek site.

Perhaps more importantly, however, financial and research personnel constraints on the

project inhibited us ftom making pelagic measurements of the sort we had done previously at

the St. George facility, and it was inappropriate at such a late date for us to interfere with

operations (e.g., moving oyster trays and aerating the water) critical to the success of the

commercial enterprise. On the positive side, the sediments at Pintail Point Farm (Deep

Cover Creek, Paynter and Burreson 1991) were softer and less shell-littered, both of which

facilitated coring. Moreover, the cove environment was more protected than at Piney Point

Creek, thus minimizing sediment resuspension events, and the oysters at this lower salinity

site were not infected with MSX or Dermo (Paynter and Burreson 1991).

The oyster raft area of the Deep Cove Creek site is shown schematically in Fig. 2.

Two oyster raft fields were located approximately 5 m from each other and 15 m out from

the northerly shore. Water depth throughout the cove ranged from about 1 m (station 1) to 2

m (station 4) at mean low tide. The raft stations 2 and 3 were located in the approximate

center of each of the two raft fields. Oyster culture employees set out smaller oysters in the

field surrounding station 3 for initial grow up, and then moved these oysters to the raft field

surrounding station 2 for further growth. The larger oysters at station 2 were transported to

high salinity sites in Virginia for final grow out before they were sold commercially. This

scheme is employed to take advantage of the observations that the young oysters could be

grown disease-free at the low salinity site but higher growth rates could be achieved at high

salinity sites, so long as the oysters were not held at the latter for time periods long enough

for Dermo infection to occur (Paynter and Burreson 1991).

The oysters were rafted in mesh trays (Paynter and Burreson 1991) similar in size and

design to the "bread tray" rafts used by St. George Oyster Company in 1989 (Ulanowicz and

@@AIPOT FROM
ACqJACULTURE :3L-:-rTLj?jt pr

NI A

OYSTER
C R A r-TS

4)
Ob 0
4:P QQ

C 0
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P7ARM

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Sta. 4-

Figure 2. Schematic diagram of the Deep Cove Creek rafted oyster aquaculture site (not to
scale).

Tuttle, in press). The maximum number of oysters rafted in the cove was 600,000

individuals (K. Paynter, personal communication).

Intermittent terrestrial input from an aquaculture waste pond settling at the cove's head

influenced our selection of control (away from rafts) stations. Station 1 was located about 50

in down-cove from the raft field around station 2 in order to assess effects of this input.

Station 4 was established about 35 m out from the cove mouth side of the raft field

surrounding station 3. Thus, stations 1-4 formed a transect along the main axis of the cove

which permitted us, within the bounds of original project resources, to assess oyster-related

influences against the background of potential effects of non-oyster inputs. We also

established a third control site (station 5) midway into a second cove whose mouth was

adjacent to the mouth of the rafted cove. This cove received runoff from agricultural fields

at its head and on its southern shore, but it was unaffected by aquaculture pond input and, to

our knowledge, had not been used for oyster aquaculture.

Coring Device Design and Sedime Collecfion

In order to sample soft sediments such as those of the oyster raft fields from a small

skiff, we needed to design and fabricate light, easy to use hand-held coring devices. These

were constructed chiefly of light, inexpensive PVC tubing. The core barrel consisted of a 15

cm length of thin-walled, I in. ID PVC plumbing pipe fitted with a threaded male PVC

connector. The core barrel was screwed into a 1" ID brass flapper valve with its plug

removed. The flapper valve retained cores in the core barrel liner during retrieval. Core

barrel liners were cut from 2.5 cm ID plexiglass stock (Read Plastics, Rockville, MD) to a

length of 20-25 cm. One end was beveled to serve as a cutting edge. The core liner, which

fit easily but snugly into the core barrel, was held in place by a strip of duct tape wrapped

around the bottom of the core barrel and the protruding core liner. The core handle,

consisting of a thick-walled, I" ID, 1.75 m length of PVC pipe, was connected to the top of

the flapper valve by another threaded male PVC connector. The overall length of the

assembled corer, about 2 m, was sufficient for most coring at the depths encountered at the

site. For deeper samples, an additional 1.4 m length of pipe could be easily fitted to the

handle by means of male and female connectors.

A synopsis of sampling visits is shown in Table 1. Full suites of measurements were

made on June 10 (station 2 only) and on all subsequent visits (stations 1-4, occasionally 5).

Cores were collected by lowering the core barrel to the sediment surface, followed by a

rapid, even push of the corer into the sediment to a depth of about 15-20 cm. The cores

were retrieved gently into the skiff and the bottom of the liner immediately plugged with a

#51h rubber stopper. The liner was then carefully removed from the core barrel and the top,

filled to overflowing with overlying water was carefully stoppered to exclude air. Collected

cores were placed upright in core racks and transported to the laboratory in coolers containing

ambient temperature cove water. Eleven to 12 cores collected at each station were required

for a full suite of measurements.

Hydrogmj2hic Measurements

Temperature, salinity, dissolved oxygen (DO), and Secchi disk depth were determined

routinely at each station. Salinity was measured using a YSI Model 33 salinity meter, and

temperature and DO with a YSI Model 57 digital dissolved oxygen meter.

Table I . leather conditions and other observations made at the Pintail Point Farm"
oyster aquaculture facility on sediment sampling days.

DATE WEATHER CONDITIONS OTHER OBSERVATIONS
May-29 ------- Fair-and-hot,-calm ------------- Dissolved-oxygen-in-rafted-cove-lower ---------
than in unrafted cove where the minimum %
oxygen saturation ( 67% ) was found at the
head of the cove.

June 10 Fair and warm, calm.

July 12 Fair and warm. Wind light Air bubblers in operation between the two
from west ( into rafted oyster raft areas ( Stations 2 and 3
cove ).

Aug I Fair and warm. Wind light Additional air bubblers installed along
and northerly across the main axis of the oyster raft areas.
rafted cove Bubblers in operation. "Red tide" observed
at Station 4 and offshore into mouth of cove.

Sep 6 Rainy and cool. Wind gusty Oyster rafts removed from Station 2 ( largest
from the southwest. Water oysters ) area. Rafts still in place at
surface of unrafted cove Station 3. Bubblers not in operation.
most affected by wind.

Sep 27 Fair and cool. Wind moderate Some rafts of larger oysters have been placed
from north ( across both back at Station 2. Only a few oyster rafts at
coves Station 3. Bubblers not in operation.

Nov 15 Fair and warm, calm. All rafts removed from Station 2 area. Still a
few rafts at Station 3. Bubblers not in
operation.

Pore Water Collection

Collection of sediment pore water was required for analysis of free sulfide (HS7),

sulfate, and total inorganic carbon (TIC). Upon returning to the laboratory, three cores from

each station were selected for pore water collection. Overlying water was carefully removed

with a syringe from the top of the core as the core surface was gassed with O,-free N, A #4

rubber stopper was inverted into the bottom of the liner and a 1.5 cm thick-walled PVC tube

was applied against the stopper as a core pusher. Two cm thick segments of sediment were

extruded directly into a gassed-out 50 mf centrifuge tube which was then tightly capped to

prevent air intrusion. Two additional segments from replicate cores were removed to the

tube. A total of 6 tubes were filled with sediments from each station so that profiles over a

12 cm depth at 2 cm intervals were obtained.

Capped tubes of pooled sediment were centriftiged at 3000 to 4000 rpm with an IEC

swinging bucket rotor for 30 to 40 min. For pore water HS and sulfate analyses, the caps

were removed, the pore water surface was gassed with 02-free N2, and 5 to 8 mL of pore

water was taken up into a gassed-out syringe. The contents of the syringe were filtered

through a N,-purged, in-line filter (0.22 Jim pore size membrane) into a pre-weighed

scintillation vial containing 0.5 mL of 10% (w/v) zinc acetate to fix HS_ as ZnS. The vial

was then weighed again so that a dilution factor to allow for the zinc acetate could be

determined.

A portion of the zinc acetate-treated pore water was removed for immediate HS_
analysis or held overnight at 40C for analysis the following day. The remainder was filtered

(0.22 gm pore size membrane) to remove precipitated ZnS and the filtrate was stored at 40C

in a plastic scintillation vial for subsequent sulfate analysis.

An additional portion of untreated pore water was removed to a small plastic vial

fitted with a tight cap. The vials were stored frozen and analyzed later for TIC.

Chemical Determinations and Porosijy

Pore water HS and total reduced sulfur (TRS) in sediments were measured according

to the colorimetric method of Cline (1969). Samples analyzed for TRS consisted of

appropriately diluted material from zinc acetate traps used to collect reduced sulfur from

chromium distillations (see below).

Sulfate was measured with a Dionex Model 2020i ion chromatograph operated in the

30 u Siemens detector range. Ions were separated on an APS-4 column (Dionex) and eluted

with filtered (0.45 jim pore size membrane) 2.8 mM NaHC03/2.25 MM Na,C03. The

column was regenerated with 0.025 N H,SO,.

Porosity of sediments is defined as the water content (by weight) of I g of wet

(whole) sediment. Two cm thick segments were cut from fresh cores into pre-weighed

aluminum pans and the wet weight determined. The segments were then dried to constant
weight at 75 " C.

POC and PON content of the surficial sediments (0-2 cm) was determined by

elemental analysis of dried sediments, ground to a powder with a mortar and pestle. POC
was also estimated from gravimetric loss from dry sediments after combustion at 450-C.

TIC in pore water was estimated by acidifying samples and quantifying purged C02with a

carbon analyzer fitted with an infrared detector (CBL Analytical Services).

Biochemica OUgen Demand

Five-day and 20-day biochemical oxygen demand (BOD-5 and BOD-20, respectively)

estimates were made using a newly-developed procedure for sediments. A 2 cm thick

surficial sediment segment was cut from a freshly coflected core into a 150 mL beaker to

which was added 90 mL of a nutrient-buffer solution prepared just prior to use from the two

sterile stock solutions described below. Solution A had the composition: NaCl, 24 g;

MgSO, - 7H20, 7 g; KCI, 0.7 g; MgC12 - 6H,O, 5.3 g; deionized distilled water, I L.

Solution A was sterilized by autoclaving. Solution B was composed of: K2HPO, 21.75 g;

KH2P041 8.5 g; NaHP04 - 7H20, 33.4 g; KN03, 3.2 g; deionized-distilled water, I L. The

pH was adjusted to 7.2 and the solution was filter-sterilized (0.22 ktrn pore size membrane).

Solution A was diluted for use to the salinity of sample site surface water (usually about 8

ppt) with deionized-distilled water and solution B was added at the rate of 1 mL/L of diluted

solution A to prepare the nutrient-buffer solution.

The diluted sediment was vigorously stirred and aerated for 30 min. to oxidize free

sulfide which in the reduced sediments could contribute greatly to BOD. Two mL portions

of well stirred sediments were transferred to each of 3-150 mL glass stoppered bottles,

followed by an "inoculum" of I mL of surface water collected at the aquaculture site. The

bottles were then filled with additional nutrient-buffer solution and DO was measured with a

stirring DO probe. Two 4 mL portions of diluted sediments were filtered through pre-

weighed GF/F glass fiber filters. The collected sediment was washed with two 5 mL

portions of deionized water and dried to a constant weight. The dry weight data were used to

normalize BOD data to unit weight of dry sediment.

BOD samples were incubated in the dark at 200C and their DO content was measured

at 5 and 20 days. Controls consisted of "inoculated" nutrient-buffer solution lacking

sediments. BOD values for nutrient-buffer solution were subtracted from values for diluted

sediments. Replicate cores from each station were analyzed for BOD.

D Assimilation _o_f Carbon Dioxide

Dark CO, assimilation as a measure of integrated microbial metabolism was

determined by measuring the rate of NaH`CO, assimilation in duplicate intact sediment cores

collected at each station and incubated at in situ temperature in the dark. The methods were

similar to those described by Radway et al. (1987), but with some important modifications.

Overlying water was removed to a depth of 2 cm above the sediment surface.

Measurements were started by injecting with a Hamilton syringe 10 AL (10 AQ portions of

NaH"C03 (ICN Radiochemicals) into the sediments through silicone-sealed ports in the side

of the core liner. Injections began 1 cm beneath the sediment water interface and were

repeated at 2 cm intervals to a depth of 11 cm. Following incubation for 12 h (optimal

incubation time was determined from time course measurements up to 24 h with station 2

sediments collected on June 10), the cores were frozen and held at -700C until alkaline

extraction of radiolabeled organic material was done.

For analysis, frozen core segments were sliced directly into tared, 125 ml, wide

mouth flasks which were then re-weighed to estimate sediment wet weight. Purging of

thawed, acidified sediment with air to remove remaining MC-labeled inorganic carbon and

boiling alkali extraction of labeled organic material was done according to Radway et al.

(1987). Radioactivity of extracts was quantified using a Packard 3340 Minaxi liquid

scintillation counter (LSQ operated in the DPM mode. Water was added to 10 niL Instaget

(Packard Instruments) to form a gel so that the samples did not phase during counting.

Dark CO, assimilation rates were calculated from turnover constants

corrected for isotope discrimination (factor = 1.06). The turnover constants were also

corrected for amount of radiolabel recovered when cores were frozen immediately after they

had been injected (T = 0 correction). This correction factor, determined on a sediment dry

weight basis, varied in magnitude with the turnover constant. For example, when extracted

DPM was 0.075% of DPM injected into a segment, the T = 0 correction accounted for 65%

of the turnover constant. When extracted DPM exceeded 1.2% of injected DPM, the T = 0

correction accounted for only 4.6% of the turnover constant. Turnover constants, adjusted

for the T = 0 correction, were corrected for porosity (to convert to a "whole" or wet

sediment basis) and multiplied by the TIC pool size of the appropriate segment. Assimilation

rates used to construct core profiles have the units:

ng Carbon/g Wet Sediment x Day.

Areal rates were calculated by multiplying the per gram rate of each individual segment by

wet weight of that segment and then summing the segment values to obtain an integrated

value for the entire 12 cm core. These integrated values are expressed as:

mg Carbon/m' x Day.

Sulfate Reductio

Sediment sulfate reduction was assessed by "S- radiotracer methods (Jorgensen 1978).

Initial core preparation and injection procedures were identical to those for CO, assimilation

measurements (see above), except that injections consisted of 10 to 15 FL portions (1.2 to 2.0

ACi) of carrier-free Na2'SO, (ICN Radiochemicals). Incubations were for 4 h as determined

from time course incubations (0, 1, 2, 4, and 6 h) conducted with station 2 sediments

collected on June 10. Sulfate reduction was stopped by injecting 200 gL of 30% (w/v) zinc

acetate into the sediments through the same injection ports through which radioactivity had

been added. This procedure "fixed" reduced sulfur by retarding its reoxidation. Fixed cores
were immediately frozen and held at -70 -C.

Total reduced "S was liberated by acidic chromium reduction (Zhabina and Volkov

1978; Fossing and Jorgensen 1989; Roden and Tuttle, in press). Cores were removed from

the freezer, gently warmed so that they could be extruded from the core liner, and 2 cm thick

segments cut and placed into tared 125 mL three-neck boiling flasks. The flasks were rapidly

Te-weighed, connected to distillation apparatus, and reduced "S was distilled into collection

traps containing 100 mL of 10% (w/v) zinc acetate.

Radioactivity of Zn"S was quantified by LSC counting of LSC 2 ml, of trap contents

in 7 mL of Instagel. The TRS content of the trap material was measured as described above.

Calculations made to determine sulfate reduction rates were similar to those used for the dark

CO, assimilation measurements (see above). T = 0 corrections averaged 2.8% of sulfate

reduction turnover constants. Sulfate reduction rates for core profiles have been expressed

as: n mol S/9 Wet Sediment x Day. Areal rates are in the units: in mol S/m@ x Day.

RESULTS

Weather and Hydroanhic Data

Weather conditions and hydrographic data collected during each of the visits to the

sample sites are recorded in Table 1 and 2. All samples were collected during mid-
to late-morning. Highest water temperatures, sometimes exceeding 300C, occurred in May,

although temperatures remained at 240C or above throughout the season until late September.

Salinity during the entire period ranged from about 6.8 ppt to 10.0 ppt. Surface water

dissolved oxygen, when unaffected by operation of air bubblers, followed a pattern in the

rafted cove of lowest DO at the head to highest values at the mouth (stations 1-4, May 29).

Lowest observed DO (Table 2) occurred near the bottom of the channel of the Wye River at

a depth of about 3 meters, suggesting that oxygen consuming in situ processes were at least

as intense in the river as in the aquaculture cove area. Highest summertime DO in surface

water occurred at station 4 on August 1. This coincided with the observation of an apparent

"Red Tide" extending from station 4 to the mouth of the rafted cove.

Although DO values were sometimes low, < 3.5 mg/l, they were not biologically

critical, at least during daylight hours, even without mechanical aeration. Bottom water DO

tended to be lower than at the surface and this was true of both rafted and unrafted stations.

When mechanical aeration commenced on July 12, bottom and surface water DO appeared to

increase within the rafted cove areas relative to station 4 (Table 1). Mechanical bubbling was

discontinued on or before September 6 even though oysters were still being rafted at station

3. Substantial DO sags were not noted in the period after June 10.

Secchi depths ranged from about 37 to 101 cm (Table 2). Highest Secchi depth values,

indicating greatest water clarity, occurred in November likely as a result of natural seasonal

variation in phytoplankton standing stocks. Usually there were no apparent significant

differences in Secchi depth between rafted and unrafted areas. This suggests that oysters did

Table 2 Hydroqraphic and secchi disk data collected at the Pintail Point Farm
oyster aquaculture facility on days when sediments were sampled. Oysters
were rafted at Stations 2 and 3. Station 6 was located in the main channel
of the adjacent Wye River. ND indicates data not collected.

SURFACE BOTTOM SURFACE BOTTOM SURFACE BOTTOM SECCHI
TEMP TEMP SALINITY SALINITY DO DO DEPTH
DATE STATION deg C deg C ppt ppt mg/L mq/L cz

May 29 1 29.9 ND 7.0 ND 3.10 ND >70
2 30.1 28.9 6.9 6.9 3.51 3.42 69
3 29.7 28.6 6.8 6.9 3.30 3.75 85
4 30.5 28.1 6.9 7.0 6.35 5.22 68
5 31.3 30.8 7.1 7.1 6.16 5.60 50
6 29.6 27.3 7.1 7.5 8.44 2.89 ND

June 10 2 25.9 25.4 6.9 6.9 5.85 4.48 45

July 12 1 26.9 26.6 7.0 7.0 6.79 5.70 53
2 27.4 27.3 7.0 7.1 6.79 5.65 52
3 27.8 27.5 7.1 7.2 6.41 5.33 52
4 28.2 27.5 7.1 7.1 7.49 6.13 57

Aug 1 1 26.8 26.4 8.3 8.3 5.65 4.95 53
2 27.0 26.6 8.4 8.4 6.34 4.91 54
3 27.1 26.8 8.8 8.8 6.35 6.09 56
4 27.3 26.5 8.8 8.8 10.00 6.08 45

Sep 6 1 24.3 24.2 8.2 8.1 6.16 4.75 43
2 24.9 25.0 8.2 8.2 5.91 5.61 42
3 25.1 25.2 8.2 8.2 5.81 5.56 39
4 25.0 25.2 8.4 8.5 6.10 5.32 47
5 24.7 ND 8.2 MD 6.59 ND 37

Sep 27 1 20.3 20.3 7.8 7.8 5.09 5.10 55
2 20.7 20.8 7.8 7.9 5.80 5.62 52
3 20.5 20.6 8.0 8.0 6.07 5.85 52
4 20.7 20.6 7.8 8.0 6.70 5.69 65
5 20.2 ND 7.3 ND 6.43 ND 40

Nov 15 1 8.5 8.5 9.9 10.0 12.40 12.01 97
2 8.3 8.3 9.8 9.9 13.24 13.16 98
3 8.0 8.2 9.4 9.6 13.05 10.71 101
4 8.9 8.3 9.3 9.5 12.27 11.80 101
5 8.2 8.0 9.2 9.2 12.42 11.24 90

not detectably influence water clarity as determined by this relatively crude method.

Sgdimen Chaja=jjs@ju

The sediments consisted of "clayey" sand material at all stations except station 4

which was noticeably sandier. All stations, except station 4, appeared to be chemically

reducing below 2 cm, as evidenced by a black appearance of the sampled cores. Surficial.

sediments, even in the rafted areas, often contained macrofauna, usually polychaete worms.

At station 4, however, bioturbation, as indicated by worm tracks, was often apparent to a

depth of at least 4 cm. Undecomposed or only partially decomposed leaves were sometimes

encountered in cores taken at stations 1 through 3. These leaves were found at various

depths, even as deep as 12 cm.

Porosity of the sediments exhibited a high degree of uniformity from sampling date to

sampling date at individual stations (Fig. 3). Surface porosities were in the range of 0.75 to

0.80 at stations 1, 2, 3 and 5. Throughout the sediment profile, stations 1 and 2 were

similar, as were stations 3 and 5. However, the profile for station 4 showed lower values

than any of the others. The differences between station groups were most noticeable at the

bottom of the sampled profile (10-12 cm). Mean porosity values were 0.67 to 0.68 at

stations I and 2 (Figs. 3a and 3b), 0.60 to 0.62 at stations 3 and 5 (Figs. 3c and 3e), and

0.55 at stafion 4 (Fig. 3d).

: POC and PON

POC and PON, measured by elemental analysis, were analyzed only in the 0-2 cm

core segments. POC decreased from station I to 4 (Fig. 4a). The pattern for PON was

0
A B c

E 6
LU

U-
q:

F-
Z10
U,

q:
W
< 12
0 D E
LU
2
0 2
Uj

0 4
w MEAN �STD
'a
:E 6

LU
C) 8

12 7- -7-
0.5 0.6 0.7 0.8 0.9 0.5 0.6 0 7 0.8 0.9

POROSITY (ml WATER/g WET SEDIMENT)

Figure 3. Porosity profiles of sediments at (A): station 1, (B): station 2, (Q: station 3,
(13): station 4, and (E): station 5.

4b..

POC PON (Molar Ratio) PON (mg N/g DRY SEDIMENT) POC
C)
z

C3 ro 4 0) w m 4@1 0 N.) w .4 cn 0) 0

x x x x x x A 4 x
z

K) c- X.
LJ C
>

-S
L] C.0

LIJ -4
0 -A
2.-1 All
(n
CA)

similar except that PON was highest at station 2 on two occasions (Fig. 4b). It is noteworthy

that station 5, having sediment characteristics most resembling station 3, consistently had both

lower POC and PON values than station 3 (Figs. 4a and 4b). The consistency of this pattern

suggests an oyster signal in the sediments at station 3.

The surficial sediments at all station were carbon rich compared to the Redfield Ratio,

C/N = 8 (Fig. 4c), although station I appeared to be the most enriched (Fig. 4a, Table 3).

At station 2, POC was relatively constant until removal of oyster rafts on September 6, after

which POC declined slightly. PON decreased simultaneously, although the decrease in PON

was slightly greater than that of POC as evidenced by an increasing POC/PON ratio (Fig.

4c). These data suggest that while oysters were present the surficial organic matter was of

higher nutritional quality. Overall the POUPON ratio at station 2 was lower than at other

locations (Table 3).

POC at station 3 was variable. The relatively high values of POC and PON on

November 15 might reflect deposition of primary production from a fall phytoplankton

bloom. At station 4 the trends in both POC and PON were negative after July 12, except for

September 27 when both were elevated. The POC/PON ratio at station 4 showed the least

variability. Trends in the data from station to station (Table 3) are suggestive of two effects.

Decreasing POC from station 1 to 4 implies organic inputs from upland sources such as the

aquaculture sedimentation pond located in the drainage basin of the cove. Superimposed on

this gradient is an oyster effect as evidenced by the lower POC/PON ratio at station 2 and

higher POC and PON at station 3 than at station 5.

Table 3. Mean particulate organic carbon, particulate organic nitrogen,
and molar carbon : nitrogen ratios in the surficial 2cm of sediment
at stations 1 through 5.

POC (mg C/g Dry Sed) PON (mg N/g Dry Sed) C:N (Molar Ratio)
----------------- ----------------- ----------------
STATION MEAN STD MEAN STD MEAN STD

51.2 0.8 5.1 0.1 11.8 0.3
2 44.6 2.1 5.0 0.4 10.4 0.4
13 37.5 1.6 4.1 0.3 10.8 0.3
4 29.7 3.2 3.2 0.4 10.7 0.1
5 32.1 3.0 3.4 0.3 10.9 0.3

Carbon: Biochemical OUgen Deman

Five-day BOD data are shown in Fig. 5a. Excluding the August I sampling date

when values were skewed by an undetermined amount of BOD in the diluent (see Methods),

BOD ranged from 0.75 to 2.75 ing C/g dry weight of sediment. Highest values were always

found at station 2 except on November 15 when almost identical values were found at stations

2 and 3. Five-day BOD at stations 1 and 3 were similar except on November 15 when it was

substantially higher at station 3 than at station 1. Station 4 BOD-5 was always lower than at

station 1 and was usually lowest, except on August 1 where the data may be in error. On the

final three sampling dates (September 6 - November 15) BOD-5 was higher at station 5 than

at station 4 but they varied in the same pattern on the different dates. There was a trend of

decreasing BOD-5 at each station over time (note August 1 possible error) until November 15

when it increasing at all stations. This observation supports our hypothesis of increasing rate

of deposition of fresh phytoplankton derived organic carbon during this period. This effect

could not be due to oysters since most had already been removed (Table 1).

The carbon in the surficial sediments at station 2 was clearly more labile than at other

stations (Fig. 5a) even though POC was not the highest (Fig 4a and Table 3). This

conclusion is supported by the POC/PON ratios at station 2 (Fig. 4c, Table 3). The BOD-5

data suggest the same pattern as do the POC/PON data, that of decreasing organic matter

lability (nutritional quality) in the down-cove direction but with an intermediate oyster signal

of increased lability.

Our goal in estimating both 5 and 20 day BOD was to develop an index of BOD

lability, i.e. high BOD-5 to BOD-20 ratios would indicate increased carbon lability. On

E 2.5-

<
>
2- < >
< >
<
>
M 1.5- >

E
U? 0.5-
0
0 A
6 149 161 1 9@' 3 249 270 319-
CD -
E 5-

Cn <
4- <
>@ <
3- X <

E 2-

C@
0 < A
CO 0
100 161 193 213 249 270 -319

80-
X
C@ > IN
0 60-
0

40-
U?
0
0 >
20 >

>
0
1@1 193 213 249 270 319

JULIAN DAY
1 2 2 7 3 71 4 El 5

Figure 5. Five-day and twenty-day biochemical oxygen demand (BOD-5 amd BOD-20,
respectively) in surficial (0-2 cm) sediments. Bar codes represent different stations.

several occasions, however, high amounts of BOD in diluent water resulted in very low or

zero DO before the end of the 20-day incubation period. Obviously these 20 day values are

not then useful. Reasonable data were accumulated from the July 12 (Julian Day 193) and

September 27 (Julian Day 270) sampling trips. On these two dates, the trend in BOD-20 was

the same as that for BOD-5 and the ratios of BOD-5/BOD-20 were not substantially different

among the stations (Fig. 4c).

With the exception of one occurrence at station 3 (November 15), BOD-5 at station 2

always exceeded, by as much as 3 times, that at all other stations (Fig. 6a). This increased

sediment BOD clearly indicates an organic signal in surficial sediments associated with the

presence of oysters in the overlying water. Similarly, BOD-20 at station 2 also exceeded that

at other locations except on November 15 (Fig. 6c). At station 3, the other oyster-raft site,

BOD was greater than at station 4, the down-cove, unrafted, control site. However, station 3

BOD was variable compared to BOD at stations I and 5, the up-cove and out-cove control

sites, respectively (Figs. 6b and 6d). On August I (Julian Day 213) BOD at station 3 was

2-3 times greater than at station 1, but at other times they were about the same. The oyster

signal in BOD was not nearly as clear at station 3 where smaller oysters were rafted. Even

where a fairly strong oyster effect was observed it appeared to be gone by November 15 in

both cases. The oysters effects on labile sediment carbon seem to be local in geographic

extent and of short-term duration.

From an experimental design perspective, there is a question as to the efficacy of

station I as an up-cove control site. Terrestrial carbon inputs seemed to elevate BOD at that

site compared to station 4 and 5 (Figs. 7a and 7b). There is no reason to suspect that station

5 has been influenced by oysters in the recent past. The data shown in Fig. 7c suggest no

mop

400 400

LO
0 300- 300-
U? CO LO 0
LO LO
0 If 0
c'! 200- 200 -
Cf)
C\1
F-
U) CO
100- 00
0
0-0
0-0

4-
0 1 1111 0
1 @9 161 193 213 249 270 319 193 213 249 270 3@9
400 400
C D
C\j C14
0 0 300- 0 300-
C@ CO C\1 0
LO
0 LQ
0 @i
c6 200- CO 200 -
m
C\1
< <
U) U)
U) 100- - 100-
0
0
0-0
1-0
01
IL -,'oL!l ------ 0
0 T T
193 213 249 270 319 193 213 249 270 319

JULIAN DAY
1 0 2 F@ 3 El 4 F] 5

Figure 6. Comparisons of five-day and twenty-day biochemical oxygen demand values at
stations 2 and 3 with values at the other stations. Panel (A): BOD-5 at station 2
compared to BOD-5 at stations 1, 3, 4, and 5; (B): BOD-5 at station 3 compared to BOD-5 at
stations 1, 4, and 5; (C): BOD-20 at station 2 compared to BOD-20 at stations 1, 3, 4, and
5; and (D): BOD-20 at station 3 compared to BOD-20 at stations 1, 4, and 5. Bar codes
represent different stations.

300 M1 E12 E23 [14 5 A
250

U?
0 0C 200
0
0 LO
CO -
150

100-1
W 4- 11. 1
0

50
0 L
300
1 Z12 E3 74 D 5 B
250,

CM 0 200
CD
0 LO
-ti 150

W 100
(n
0

0
50-
-0

0
300 ii 5 day 20 day C
250

0
0 m 200-11
1
03 to
150

100
I-RO
50

0
149 161 193 213 249 270 319

JULIAN DAY

Figure 7. Intercomparison of five-day and twenty-day biochemical oxygen demand values
among stations where rafts were not present. Panel (A): BOD-5 at station 1 compared to
BOD-5 at stations 4 and 5; (B): BOD-20 at station I compared to BOD-20 at stations 4 and
5; and (Q: BOD at station 4 compared to BOD at station 5. Bar codes represent different
stations in panels (A) and (B) and BOD- 5 and BOD-20 in panel (C).

significant differences in BOD between stations 4 and 5.

Carbon: POC 4 Combustion

From a practical perspective determination of organic content of the sediments by

weight loss after combustion is an inexpensive and rapid technique useful for processing

multiple samples. Carbon contents of synoptic surficial sediment samples analyzed by

elemental analysis and, separately, by combustion weight loss were compared (Fig. 8, Table

4). Although there is some scatter in the data, particularly at low carbon concentrations,

these two estimates yielded comparable results (r' = 0.83).

In order to validate conversion of down-core combustion loss data to POC values and

to characterize the oxidation state of the sediment POC, we compared mean measured POC

(elemental analysis), mean POC calculated from the regression shown in Fig. 8 and POC

values calculated from combustion data assuming the carbon was at the oxidation state of

carbohydrate (combustion loss * 12/32). The results (Table 4) indicate that, when data from

all stations were used, the three methods yielded very similar results. Therefore, it is

reasonable to conclude that the POC, on average, is at or near the oxidation state of

carbohydrate. POC profiles were generated using this assumption about POC oxidation state.

When we compared the stations individually, calculated POC values differed from

combustion loss POC values at four of the five stations (Table 4). Stations I and 2 evidenced

higher regression based POC values than were suggested by the carbohydrate-based

calculations, whereas, these ratios of the values were lower than expected at stations 4 and 5.

Similar relationships held for ratios of measured POC against combustion loss POC only at

stations I and 5. This suggests that at station 1, and possibly station 2, POC was more

130

Y = 1.874X + 24.637

Z 120 2 =0.825
r
W
n 22 0
0
W C)
110
0 00
0
0)
0) 100
E 0
z 0
0
90 0
W

CIO
2
0
80
z
0 00 0
(1)
U) 70
0
0

60 -

20 25 30 35 40 45 50 55
TOC (mg C/g DRY SEDIMENT)
Figure 8. Regression of surficial sediment weight loss on combustion on POC determined by
elemental analysis.

Table 4. Comparison of sediment POC 0-2cm depth ) measured
directly ( by CHN analysis calculated by regression
( see Fig. 8 ) and estimated from loss on combustion
(assuming lost material had the composition : CHOH

MEAN
MEAN COMBUSTION MEAN CALCULATED MEASURED
CALCULATED LOSS POC MEASURED POC: POC:
POC (AS CHOH) POC COMBUSTION COMBUSTION
mg C/g. mg C/g mg C/g LOSS POC LOSS POC
STATION n DRY SED DRY SED DRY SED % %

1 5 50.30 47.57 51.22 105.7 107.7
2 5 46.96 45.06 44.76 104.2 99.3
3 4 38,42 38,66 37,45 99*4 96,9
4 5 26-30 29.57 29.74 88.9 100.6
5 3 34.41 35.66 32.10 96.5 90.0

-------------
ALL DATA 22 39.76 39.66 39.76 100.2 100.2

reduced than carbohydrate, and at station 5, and possibly station 4, it was more oxidized.

Station 1 was carbon rich throughout the sediment profile when compared to all other

stations (Fig. 9a). Station 2 was enriched only at the surface, and showed the greatest

decrease in carbon with depth (Fig.9b). Stations 3 and 5 had very sin-filar profiles (Figs. 9c

and 9e), while station 4 sediments had the lowest carbon content throughout the 0 - 12 cm.

horizon (Fig. 9d). Whereas there may be an oyster signal of increased carbon at stations 2

and 3 (note variance in 0 - 4 cm. horizon at station 3), this effect appears to be small and is

masked by the non-oyster related, down-cove gradient in POC.

Station 2 exhibited an unusually large decrease in carbon between the surface and the

6 cm horizon (Fig . 9b). We investigated this further by comparing decreases in POC from

the surface to the 6 cm. horizon on each sampling date. The largest declines were seen at

station 2 and sometimes at station 3 (Table 5). This effect could be explained by carbon

enrichment in the surficial sediments (i.e. deposition by oysters) or by increased microbial

metabolic activity at depth. On the average, the difference at station 2 was nearly twice that

at any other station.

Dark Assimilation Qf Carbon Dioxide

Total inorganic carbon (TIC) was measured to determine the size of the inorganic

carbon pool which is necessary to convert "CO, uptake rates to actual carbon assimilation

values. The TIC content of sediment pore waters represents the balance between

assimilatory/dissimilatory microbial processes and diffusion (abiotic: transport within the

sediments). Increases in TIC with depth indicate an imbalance between microbial organic

carbon degradation and the sum of TIC assimilation and diffusive processes. Assimilatory

0 A B K3 C W, 0
2

E
0
- 6
W
>
LL
a: 8
W >
z

q:
W
> >

Z 0
W D E

W 2
> 0

4
W
0

6
W 0 0

10
lit,

12 ............

15 20 25 30 35 40 45 50 15 20 25 30 35 40 45 50

COMBUSTION LOSS POC (mg C/g DRY SED)

4 5 6 7 8 AVG
13 > 0 0 10,

Figure 9. Distributions of POC in sediments at (A) station 1, (B) station 2, (C) station 3,
(D) station 4, and (E) station 5. Different symbols represent different sampling days whose
number codes are as follows: July 12 (4); August 1 (5); September 6 (6); September 27 (7);
and November 15 (8).
0@1 I
0

0 0

TABLE 5. Loss of POC ( determined from combustion of dry sediment ) between
the 0-2cm and 4-6ca segments of cores collected July 12 to September
15, 1991.

POC LOSS (mg C/g Dry Sediment) on SAMPLE DATE
-----------------------------------------------
STATION 07-12 09-01 09-06 09-27 11-15 K EAR STD

1 3.75 2.68 3.56 5.32 1.27 3.32 1.33
2 6.81 10.39 6.29 8.58 6.05 7.62 1.64
3 6.31 HD 7.21 4.20 2.58 4.06 2.59
4 6.75 4.69 3.02 3.58 4.59 4.53 1.28
5 ND ND 5.59 2.76 2.98 2.27 2.10

process and diff-usion out of the sediments would tend to decrease TIC whereas dissimilatory

processes would increase TIC.

TIC profiles for the five stations are shown in Fig. 10. In nearly every case, TIC

increased with depth. Profiles for stations I and 4 showed the least scatter from cruise to

cruise (Fig. 10a and 10d), but TIC increased more substantially with depth at station 1. The

variability in TIC among sampling dates was particularly evident at stations 2 and 3 (Fig. 10b

and 10c). The profiles for station 5 were similar to stations 2 and 3 on the same sampling

dates, indicating a similar balance in carbon dynamics at these three stations (Figs. 10b, 10c

and l0e). The trend at station 2 was for high TIC values, particularly in surficial sediments

when temperatures were high and oysters were present (samplings 3 - 5, Fig. 10b). Aeration

in the water column (see Table 1) tended to depress surficial TIC. Stations 2 and 3, affected

by deposition from oysters tended to have similar TIC profiles, except on July 12 (sampling

4) when the station 3 profile resembled that of station 4. Because smaller oysters were rafted

at station 3, this relationship was probably due to insufficient oyster biomass to generate a

detectable signal at this early date.

Dark CO, assimilation profiles are reported in Figures 11 - 15. Assimilation rates

were generally high in the surficial sediments (100 - 300 ng C/gd) but declined rapidly with

depth to less than 50 ng C/gd below the 6 cm horizon. A notable exception occurred in

station 2 sediments on July 12 (Fig. 12b) where rates in the 10 - 12 cm segment of one of the

replicates exceeded 1. 1 jug C/gd. This was probably the result of methanogenesis (bacterial

autotrophic metabolism). This explanation is supported by sulfate depletion in sediments

below 9 cm on this day at station 2 (see Fig. 18b). Dark CO, assimilation profiles at station

4 (Fig. 14) differed from those at other stations in that maximum surficial rates (except on

0 A- B C

4
-E
W 6
(P

U-
a: 8
W
F-
z

W 1>

Z 0
W D E
> 3

W
2
W
4

4
W
5 >

F-
CL 6
W 6

8
7 11@

10
8

12
0 50 100 150 200 250 0 50 100 150 200 250

TOTAL INORGANIC CARBON (ug C/ml)

Figure 10. Distributions of total inorganic carbon (TIC) in sediments at (A) station 1, (13)
station 2; (C) station 3; (D) station 4; and (E) station 5. Different symbols represent
different sampling days whose number codes are as follows: June 10 (3); July 12 (4); August
1 (5); September 6 (6); September 27 (7); and November 15 (8). Lines are drawn through
symbols for July 12 and September 6 to highlight the extremes at station 3.

Station 1
0- A C
El 0

El
-E 4- C
0 0 0 El

LU 6-
C)
< 0
LL
CE 8-
LU
F-
z
a: 10
LU
< July 12 Aug 1 Sep 6
12
0 100 280 300 0 100 280 300 0 100 200 300
z
Uj 0 -
0 DI D El 0 E
LU 2 -
Cn
3: 0 El El 304.420
0 4 -
w
0 El 0

6 -

D 7

10 -
Sep 27 0 Nov15
12 - I . I I
0 1@0' 280' 300 0 180 280' 300

C02 Assimilation, ng C/g day

Figure 11. Rates of dark assimilation of C02 as a function of sediment depth at station 1.
Different symbols represent values for individual cores and the line depicts the average. The
number in panel (E) gives the magnitude of an officale rate.

Station 2
0 - A B C
El El 0 0 0

2 -

0 El

-E F-I
0
LU 6 -
0 D
<
U-

Uj
0
'r-

z
cc lu -
LU 0 1156.14 El
June 10 July 12 Aug I
< 12
0 100 200 300 0 100 200 300 0 100 200 300

w 0
D 0 0 E F-I 0 F
LU 2
U)
3: 0 0 0
0 4
Ui
C"

6
CL
LU

Sep 6 Sep 27 Nov 15
12 @ I I i I , , . ' '-' I, - I I I . I @ I I I ; ' . I
0 100 200 360 0 100 200 300 0 100 200 300
C02 Assimilation, ng C/gd

Figure 12. Rates of dark assimilation of CO, as a function of sediment depth at station 2.
Different symbols represent values for individual cores and the line depicts the average. The
number in panel (B) gives the magnitude of an officale rate.

Station 3
0 A B C
El 0 0 D 0 0
2 0 0
4
E
0 1:1 0 Ej
1-
UJ 6

0 0
U-
q: 8
Ir-
z 0

Cr '0
LU
1--
< July 12 Aug 1 Sep 6
12
0 100 2@O '300 0"1@0 . . . 280 . . . 300 0 180 280 'Ino
z
W 0
D E
343.42
LU 2

C
0
-J 4
LU
0 El

l--6
LU 0
8 0
10

12 Sep 27 Nov 15
0 1@0' 200 3 0 0 100 200 30'0
Cq Assimilation, ng C/g day

Figure 13. Rates of dark assimilation of CO, as a function of sediment depth at station 3.
Different symbols represent values for individual cores and the line depicts the average. The
number adjacent to panel (E) gives the magnitude of an officale rate.
Li

Station 4
0- E 1) A 1:1 B C
2 0
41
E
-C_

LWLJ6
0
< I El 0 D 0
U-
T- 8
F- El 0 11
z
LL,

irl 0
w
!;@ E] 0 E
July 12 Aug 1 Sep 6
12 1 1 . @ I I . I @ I I I @ ; I @ . I . I . I
0 100 200 300 0 100 200 300 0 100 200 300
z
W 0
D E

w
2 -

0
J4
w
CO
'r
F- 6

w 0 01

013 C 7

10
Sep 27 0 Nov 15
12 , i , 1 @ 1 , , I i . I . I I I I I
0 100 200 300 0 100 200 300
C02 Assimilation, ng C/g day

Figure 14. Rates of dark assimilationof C02 as a function of sediment depth at station 4.
Different symbols represent values for individual cores and the line depicts the average.

Station 5
E 0 -
0
A B
w 0

u- 2
Cr
w
0 0
z
Cc 4
w
< 0

6
z
w

0
w 8 -

0
-j
w 10 -
M

CL Sep 6 Nov 15
w 12
0 0 100 200 300 0 1@0 2@O 300

C02Assimilation, ng C/g day

Figure 15. Rates of dark assimilation of CO, as a function of sediment depth at station 5.
Different symbols represent values for individual cores and the line depicts the average.

August 1) never exceeded 100 ng C/gd and rates at depth were the same or higher than at

other stations (note the station 2 exception, see above).

It appears that the dark CO, assimilation measurement, except for times when

methanogenesis is occurring, estimates microbial respiratory activity which causes increasing

TIC levels particularly at stations 1, 2, 3, and 5. The more uniform depth profiles at station

4 indicate reduced respiratory activity in the upper 6 cm of the sediments (compare Fig. 14

with Figs. 11 - 13 and 15). This relationship is more readily apparent when areal dark CO,

assimilation rates are compared (Fig. 16).

There were no clear patterns among the stations in areal dark CO, assimilation rates

integrated from 0 - 12 cm depth (Fig. 16a). In the upper 6 cm, however, the down-cove

effect, decreasing rates from station 1 to station 4, could be seen from July 12 through

September 27. Data for August 1 and September 27 suggest a possible oyster effect at station

2 , but this difference was probably not significant (Fig. 16b). In general, microbial

respiratory activity in the top 6 cm of sediment was higher in stations I - 3 than at stations 4

and 5, but possible oyster effects at stations 2 and 3 were small in magnitude and/or masked

by the down-cove gradient previously described- Interestingly, temperature seems not to have

greatly affected darkC02 assimilation during sampling period.

Sulfur: Sulfate Profiles

Under anoxic conditions in marine sediments such as those studied here, sulfate

reduction is the major microbial metabolic process consuming organic matter (anaerobic

respiration) (Roden and Tuttle, in press). Sulfate concentrations must be known in order

to calculate sulfate reduction rates from the radiotracer experiments, but they are of

30 -
A
CY 0-12 cm
E 25 -

E 20 -

0
15

E
10 -

5 A
0
0

14 - B
N 0-6 cm
E
12 -

E 10

8 -

6 -
E
vp
cn
4
< IR
2

100

0
80
S9
E
E
60
< 04
0 E
C.) 40

CD 20
CL

0
Rl
1@1 193 213 249 270 319
Julian Day
E Stal 9, Sta 2 7 Sta3 El Sta 4 Sta 5

Figure 16. Depth-integrated areal rates of dark assimilation of CO, over the study period.
Panel (A): integrated over 12 cm depth; (B): integrated over the 0-6 cm depth interval; (Q:
ratio of areal rate over 0-6 cm to that over 0-12 cm.
V

importance in their own right in that their level is indicative of the balance between sulfate

supported anaerobic respiration and sulfide oxidation. In general, in sediments with active

sulfate reduction, sulfate concentrations in sediment pore water are expected to be high at the

surface and to decrease with depth. On the other hand, if substantial sulfate depletion is

evident in pore waters of surficial sediments, sulfate reduction exceeds sulfide oxidation

and/or influx of new sulfate from overlying water.

Sulfate profiles for the five stations are shown in Figures 17 - 21. The overall pattern

indicates depletion of sulfate with depth except occasionally at station 4. At station I the

profiles from July 12 to September 27 were almost identical (Fig. 17) suggesting a

quasi-equilibrium between reductive and oxidative plus diffusion processes. On November 25

sulfate concentrations had increased, however, indicating that the balance shifted in favor

of oxidative processes and/or diffusion. High salinity on this date (Table 2) supports

increased diffusion of sulfate into sediments.

Sulfate profiles at station 2 (Fig. 18) were qualitatively similar to station I profiles

(Fig. 17) but differed quantitatively. Specifically, throughout the profiles sulfate was more

depleted than at station 1 indicating increased rates of sulfate reduction at this oyster raft site.

Even in the 0 - 2 cm horizon in the presence of aeration, sulfate concentrations were

substantially lower on July 12 and August I at station 2 (Figs. l8b and 18c) than at station 1

(Figs. 17a and 17b). In the deeper horizons on July 12 (Fig. 18b) sulfate had nearly

disappeared below 7 cm and on August I (Fig. 18c) below 5 cm. After removal of oysters

from station 2 (September 6, Table 1) sulfate concentrations in the pore waters above 6 cm

depth increased dramatically (Fig. 18d) such that the concentrations were even higher than at

station I (Fig. 17c). This strongly implicates oysters in the overlying water as a source of

Station 1

...........
1 ->vx A
-.1-11.1 .. ... ......... . .............................
3 -Y\
5-

9 M@
July 12

.. ........... I..-, . . . . . . ................ . .
E 77j B
0
3
W 5-

7
_70
-7Z
Ir 9
Ui
F_ Aug 1
z

Cr
Ui
C
3-

5
z 7
LU 9
Z>
Fn 11 -V Sep 6
LU
U)

D
0

LU
m 5 T@,@@_
7-=
9 -
Ui
Sep 27

. ...... . .. E

............ .. ....................
3
5 ...... . .....

. . .... . .............. .
................... .......................... . ..
7 in-'..........."..-I.-I., . ........
................ ....... . .
...... . ..... ............... .--.-
... ............. . .. ...................... .

..........
...........
...........
.............
9
11 Nov 15
0 16 1@ 14
So 2,CONCENTRATION (mM)
4

Figure 17. Depth profiles of pore water sulfate concentration at station 1.

Station 2

.............. .
A
3-

7
9
June 10

B
3
E 5
7
W 9
C)
< July 12
LL
CE
W
C
z 3
Cc 5 -5"
W 7
9V
Aug 1

z
.......................... .. .
W
D
3-
5-
W
7 -__P

Sep 6
0
i
W
CO
E
3
...... ....I
5-
W 7-
9
Sep 27

.......... F
3
. . . . . . . . . . . . . . .
. ..........
5 . ...
7

- - - - - - - - - - - -
Nov 15

0 2 4 6 8 10 12 14
So 2-CONCENTRATION (MM)
4

Figure 18. Depth profiles of pore water sulfate concentration at station 2.

organic matter fueling increased sulfate reduction in July and August. Sulfate continued to

increase in pore waters at station 2 throughout the remainder of the study (Figs 18d - 18f).

In fact, by November 15 the profiles at stations 1, 2, 3 and 5 were very similar (Figs. l7e,

18f, l9e and 21b).

At station 3, where the smaller oysters were rafted and which had less total biomass,

sulfate concentrations were high relative to station 2 and were reasonably constant to a depth

of 9 cin (Figs. 18b and 19a). However, by August 1 the profile at station 3 (Fig. 19b) was

almost identical to that at station 2 on the same date (Fig. 18c). On September 6, when

oysters were still present at station 3, sulfate concentrations were lower than at station 2,

particularly in the upper 7 cm. This supports the contention that oyster deposition is

responsible for increased sulfate reduction and, therefore, sulfate depletion. Oysters were

kept at station 3 until almost the end of the study (Table 1). In this respect the persistent

sulfate depletion in sediments at this station (Figs. 19d and l9e) compared to stations 1 (Fig.

17d and l7e) and 2 (Figs. l8e and 18f) strongly illustrate that oysters increase the rate of

anaerobic sediment microbial processes.

Comparison of sulfate profiles at stations 3 and 5 on September 6 (Figs. 19c and 21a)

and November 15 (Figs. l9e and 21b) indicates that, although they were qualitatively similar,

sulfate was more depleted at station 3. Because these sediments were so similar in character,

this depletion further supports the conclusion of an oyster effect.

Sulfate profiles at station 4 differed from those at an the other stations (Fig. 20).

Apart from July 12 (Fig. 20a) there was little or no sulfate depletion throughout the entire

depth profile. This is probably due to the sandy nature of these sediments, lack of oyster

influences and reduced input of allochthonous organic material in this down-cove area.

Station 3

...................
A
3

5-
....... . .....
7-
......... .
9-
11 July 12

1 -1ZZ11A),
E 3
Q
5 V
Ui
71
<
LL 9V
CE I 10 Aug 1
U.j
1--
z
CI: 1
LU 3
< 5 fl
7
94
Sep 6

3: 3 - \\w"\7@V
0 5-
LLJ 7
m
-r 9
i Sep 27
a-
LLJ

... . . .......... E
. ...............
3 ..... ....... . . . . . . . . ....
...........
5
. ............
.............
7

9. . . . .... ..
Nov 15
0 10, 12 14

So ZCONCENTRATION (mM)
4

Figure 19. Depth profiles of pore water sulfate concentration at station 3.

--p uopvjs It, uo!ILAua:)uoo ;)ILjlns mium wod jo s;)Igoid tpd;D(I -OZ ain2ij

(INW) NOliVHiN30NOaz;"OS

t, L z 1 0 8 9 V z 0

..............
..........
SL AON
. ...... ......................... .... .. .... -6
. . ... ... ...... . ... . ...... ..... ..
.......................... .............. .............. . . . ......... .... ...... .

. .... . .....
........... . ... .... ........
. .. . . ..... . .. .. ... ...................... .... . .........
........................
. . ............
......... ....... .
......... . . . .......... ...............
..... . .... .
... . . . . . . . New

......... ..
3 ........... ........... ........ . .. .....................................

LZ des

... .. ... ... ... -- ...........
L m
................ . . ......... . ...0

(n
cl m

9 des M

>
i
m
E.... . . . . . . .. . .. . ...... .
.42

LBnV
... . ......
-n
>

. .. .............. ..... .......

z I Ainr

........... . .... -.4

. ..... ...........
v

t, U01juls

Station 5

.... ........ %@
.. .. ... ............. A

... . .... . .... . .. .. .. ..... ..... .... . .............. ...
3

E
0 5
W
L)
< 7
U-

AO@
W

W Sep 6

z
W
................ . ... ...
.... ......... ..................... . ............... .............................
................... .......... .. . ... ...............
...... ........
B

W
U) . ....... . ...... ... ..... ... .. ... ........................ .... ..... .. ....... .................. . ..........
. ... ........ ..........................
........... ........ . ...........

....... ............ .................... .
.................... -.- . ... . . . ............................ ... ... ... ... .. ... ... ... ... ...........
-.....................
................. ............................... . .... . ..
..................
..........
W . ...... .. . .. . .. ....... ..............
CO 5

. . .. ....... ........ .... .. . . ...................... . .
........ . . ............ ......
.............. . .........
.............
EL
........... .............. . ................. .
I.. ... .. . .................... ...... ... ...............
. . . . . ........... .........
W ........... .. ... . .... .... .......
........................-
. . . . ...................

.. ......
. .. ............. ...
.. ... .......
..... ...r. . ........
ggi,
Nov 15

0 2 4 6 8 10 12 14

So 2-CONCENTRATION (mM)
4

Figure 2 1. Depth profiles of pore water sulfate concentration at station 5.

Sulfur: Sulfa Reduction

Profiles of measured sulfate reduction rates are shown in Figs. 22 - 26. On the final

two sampling dates sulfate reduction rate profiles were similar at all stations examined.

Sulfate reduction rates were low, with mean values not exceeding 50 nmol S/gd throughout

the sediment profiles. Maximum rates of sulfate reduction occurred during summer, warm

weather conditions, probably indicating effects of temperature, redox condition and

the availability of suitable substrates supporting sulfate reduction.

On June 10 the sulfate reduction profile at station 2 was bimodal, having peaks near

the sediment water interface and at 8 - 10 cm. (Fig 23a). On July 12 sulfate reduction was

bimodal at station I (Fig. 22a) but at station 2 (Fig. 23b) sulfate reduction was highest near

the surface and declined with depth. The replicate values were highly variable in the top 8

cin of the cores from station 2. The mean profile is probably more representative of sulfate

reduction rates than is the core which yielded the lower rate estimates since sulfate at station

2 was highly depleted with depth on that date (Fig. l8b). The station 3 profile (Fig. 24a)

was markedly different from stations I and 2. Sulfate reduction occurred mainly below 8

cm, in agreement with sulfate profiles which indicated depletion, particularly in the deeper

sediments (Fig. 19a). Despite high rates of sulfate reduction at stations 1, 2 and 3, rates at

station 4 on July 12 were low throughout the sediment column, never exceeding about 40

nmol S/gd (Fig. 25a).

On August I rates at the sediment surface at station I had decreased from July 12, but

the minimum in the 4 - 6 cin horizon remained evident and rates below 6 cin increased (Fig.

22b). Stations 2 and 3 (Figs. 23c and 24b) exhibited very similar sulfate reduction profiles

Station 1
0 A B
0 El F1
2

El 0

4
E
C.)
Lu 6
C)
< 0 El 0
LL
CC
w 8

z 0 El El 0
Cc 10
LIJ
< July 12 Aug 1
12
Z 0
LU C D

w 2 j

0 4

CL
w

0 El

10
12 Sep 27 T r Nov'15,
1 '0 200 0 100 200
0 0
SO,2-HEDUCTION RATE (nmol S/gd)

Figure 22. Sulfate reduction rate as a function of sediment depth at station 1. Different
symbols represent values for individual cores and the line depicts the average.
0'

Station 2
0
A B C
0 El 308.56
2

El 317.74

4-11
E !j -
0

< 0
U-
8

0
z
10

< June 10 July 12 Aug 1
LL,
R
z 0
LU D E
U0 2

0 4
-j

ca
7- 6

0 8

10 -
12 Sep 27 Nov 15
0 100 200 0 100 200
S04 2REDUCTION RATE (nmol S/g day)

Figure 23. Sulfate reduction rate as a function of sediment depth at station 2. Different
symbols represent values for individual cores and the line depicts the average. The numbers
in panel (B) give values for officale rates.

Station 3

F-1 0 227.52

209.10 1:1

4-
E
0
w 6
<
U-
cr
w 8
z 0 11 0 0
Er 10 - -
w
0 307.30 DD 0 El
< July 12 Aug 1 Sep 6
12 - - - - - - - -7-

z 0-
w D E
C

2
w

0 4-
w
M
6
(L 0
w
8

0 0
10-

Sep 27 Nov 15
12 1 . I . I I I . I . i i
0 100 200 0 100 200

S04 REDUCTION RATE (nmol S/9 day)

Figure 24. Sulfate reduction rate as a function of sediment depth at station 3. Different
symbols represent values for individual cores and the line depicts the average. The numbers
in panels (A), (B), and (C) give values for officale rates.

Station 4
0- A B C
1:1 0 E)

4-
E

Lu 6 -
< ED
U-
8 -

z
I--

Cr 10
LU
1@ -I July 12 Aug I Sep b
12

z 0
w D E
Z>
F5 2
Uj

0 4
LLj
03
6

Lij
8

Sep 27 Nov 15
12 , , i I . I I i L
0 100 200 0 100 200
S04 2REDUCTION RATE (nmol S/g day)

Figure 25. Sulfate reduction rate as a function of sediment depth at station 4. Different
symbols represent values for individual cores and the line depicts the average.

Station 5
0
A
E 07

w
0 2
<
U-
Cr.
LU
z 4
w
< ED 0

z 6
w
El 0

w
8
3:
0

10
a_
w C :1
Sep 6 Nov 15
12
0 100 200 0 100 200
Sq2-REDUCTION RATE (nmol S/g day)

Figure 26. Sulfate reduction rate as a function of sediment depth at station 5. Different
symbols represent values for individual cores and the line depicts the average.

with maxima within the 2 - 4 cm horizon. Decreased surficial rates at these two stations may

have been due to oxygen input at the sediment water interface due to mechanical bubbling of

the overlying water (Table 1). Despite relatively high rates at station 2 and 3 sulfate

reduction at station 4 remained low (Fig. 25b).

Unfortunately, data for stations I and 2 on the September 6 were lost due to improper

processing of cores. At station 3 (Fig. 24c), however, sulfate reduction rates remained high

in contrast to the companion station 5 (Fig. 26a). Station 4 continued to evidence low sulfate

reduction rates (Fig. 25c). Similarities in the magnitude and trend in the sulfate reduction

rate profiles at stations 2 and 3 compared to stations 1, 4 and 5 during the summer indicate a

marked oyster effect.

By September 27 sulfate reduction rate profiles at stations 1, 2 and 3 appeared to be

qualitatively similar (Figs. 22c, 23d and 24d). However, mean rates in the deepest 6 cm at

station 3 were noticeably higher than at the other two stations. This may represent an effect

of oysters having been removed later from station 3 than from station 2 (Table 1).

Relationships among sulfate reduction rates in time and space are most easily seen by

comparing depth integrated data (Fig. 27). At station 1 sulfate reduction rates decreased

consistently over the period July 12 to November 15 (Julian Day 193 to 319) (Fig. 27a).

Data for station 2 followed a similar pattern of change with a peak occurring on July 12. In

contrast, sulfate reduction rates at station 3 peaked on August 1, whereas, integrated sulfate

reduction at station 4 remained low throughout the study. Although sulfate reduction was

measured at station 5 on only two occasions, the sulfate reduction rate patterns were not

inconsistent with those at stations I and 3.

Oyster rafting had a substantial, although transient, effect on sediment sulfate

14-
0-12 cm Depth
Cts 12-
m
C
0 -COV 10
: -
t5 _E
U) 8 -
CD 0 6 -
Cr E K
K
42) E 4 - K
K
Cz K
>1
2 L >@ K
K
K
K Ell i
CO

14
0-6 cm Depth
12-1
Cr
C P 10
0
E
8
KI
><
K
0 6
CI: E J
K K
4 K K
Cz K
x >d A
75 2 4
0 L >'< ><

C 100
0
4- -
Q
80
E <
K <
60 </ <
Cj </ <
Ca K < <
KK
40 < K >< <
U) < <
(0
CD 20 <
C.) 0
CL
161 193 213 249 270 319
Julian Day
M Sta 1 @2 Sta 2 7 Sta 3 F-I Sta 4 ZSI Sta 5

Figure 27. Depth-integrated areal sulfate reduction rates over the study period. Panel (A):
integrated over 12 cm depth; (B): integrated over the 0-6 cm depth interval; (Q: ratio of
areal rate over 0-6 cm to that over 0-12 cm.
a2i

reduction. When oysters were present at station 2 (Table 1) sulfate reduction rates there were

substantially higher than at either of the control stations I and 4. This effect was most

noticeable in the upper 6 cm of the sediments (Fig. 27b). After oyster removal from the raft

area at station 2, sulfate reduction rates in the sediments there were not significantly different

from rates at any of the control stations.

Our conclusions are reinforced by comparing sulfate reduction rates at station 3 with

those at stations 1, 4 and 5. Presumably the oysters at station 3 were smallest on July 12 and

increased in size (biomass) as time progressed. It is interesting in this respect that the

integrated rate of sulfate reduction at station 3 on July 12 was about the same as at station I

and its distribution in the sediments was also similar to that at station 1 (Figs. 27a - 27c).

Only 3 weeks later, however, the sulfate reduction rate at station 3 was substantially greater

than at station 1, and this effect was most noticeable in the upper portions of the sediment.

This is consistent with increased deposition of labile organic material to the sediment surface.

Oysters were removed from station 3 at a date later than when they were removed from

station 2. It is significant that from August 1 through September 27 sulfate reduction rates at

station 3 were higher than at any of the other stations. However, by November 15 the rates

were very similar across the rafted cove transect with a possible trend of decreasing sulfate

reduction from the head of the cove to its mouth.

Sulfur: Sulfide Profiles

Distribution of HS- in sediment pore water supports the sulfate reduction rate data and

sulfate distribution profiles (Figs. 28 - 32). At station 1, HS- tended to accumulate at depth

rather than at the sediment surface (Fig. 28). When oysters were present at stations 2 and 3

Station 1

A
3-0
5
7-1
9 July 12

E B
0
3
W
0 5 -zzzzzzZZA-)
U_ 7
cc: ..., ..........
W 9-
Aug 1
z 11

W 1 C
3-
5-
........... . ..
z 7-
W 9-1
.. . .......... Sep 6
W
D7@
.............. ....................
0 3-
W 5 ........ . ........
......... .....
7-
... ........ ......
9-
W Sep 27

E
3
5
...... . ...
7
. . . . . .. . . . .. .
.............
. . .... ... .
...........
9
11 N ov 1 5
0 0.5 1'5 2 2.5

HS-CONCENTRATION (mM)

Figure 28. Depth profiles of pore water HS- concentration at station 1.

(Figs. 29 and 30) HS- tended to accumulate near the surficial sediments, and, were it not for

mechanical aeration, it might well have contributed to anoxic conditions in the water column.

Also in concert with sulfate reduction rate data, when oysters were removed from stations 2

and 3 (before September 6 and 27, respectively), HS rapidly disappeared from surficial

sediments and the profiles had the same patterns as at station I (Fig. 28). In this respect,

comparison of the HS profile on September 6 at station 3 (Fig. 30c) with station 5 (Fig.

32a) also demonstrates an effect of the oysters.

Although station 4 was only about 35 meters from the oyster rafts, HS concentrations

were very low throughout the sediment profiles during the entire sampling period (Fig. 3 1).

The only case in which a substantially higher than background value was detected was on

July 12 in the 10 - 12 cin segment (Fig. 3 1 a).

Sulfur: Total Reduce Sulfur

The general distribution pattern for TRS was an increase with depth in the sediment

profile Figs. 33 - 37). Despite differences in sulfate reduction rates and HS- concentrations,

TRS in the sediments was reasonably similar at most of the stations (Figs. 33 - 38). A

possible exception was at station 4 where TRS appeared to be lower overall (Fig. 38d).

Nevertheless, there appeared to be an increase in TRS at stations 2 and 3 (Figs. 38b and 38c)

at the same time that areal sulfate reduction rates peaked (Figs. 27a and 27b).

The fact that TRS levels in the sediments were relatively similar at all the stations may

be related to inputs of metals which can react with sulfide, forming insoluble metal sulfides

such as FeS whose oxidation is very slow. Thus, at station 4 where sulfate reduction rates

were low most of the sulfide produced would accumulate as metal sulfide. The failure of

Station 2

i iii-mw A
3 M@@
5
7
9 June 10

1 B
...... . . . ...... .. ............. ...... ... ...
3-
E 5
7 -
W 9 _m5NxXXXXAXP
July 12
L.L
X
W ........ .... .
1 _K11171171111117 C
z 3-1V//Z//////Z/ZZI.)
cc 5 q2zzzz///@
W 7 -@77=77V
Augl

W D
3
5
W . . .............
U) 71
9
3: Sep 6
0

W
m E
m 3
(L 5
W
0 7 \\\\7715 . .. ....... ......... .
9
Sep 27

F
3
5
7
9 Nov15
11 t=m '
0 0.5 1 1.5 2 2.5

HS -CONCENTRATION (mM)

Figure 29. Depth profiles of pore water HS- concentration at station 2.

Station 3

A
3
5 4
7-0

July 12

..............-
B
... . .... . ..... .... . .... . .
E
3-
5-

U_
CC 9-
W 11 Aug 1
_P I T I
z

CC
W 1 C
< 3
5 -
7-9
9 -
Sep 6
F5
W
U)
D
0
1 3
W
5
7-0
.......... . .. ....
(L 9-
Sep 27 1

E
34
5
7-0

Nov 15 i

2 5
0 05 1.5

HS -CONCENTRATION (mM)

Figure 30. Depth profiles of pore water HS- concentration at station 3.

Station 4

A
3
5
7 4"
9-1
July 12

1 4. B
3-1
W 5 41
7-1
U-
Cc 9-0
LU Aug 1

cc:
W C
< 3-1
5
z 7
Ui 9-3
2
Sep 6
LU T

0
3-0
m 5
m 7
a_ 9
W
Sep 27

E
34
5
7
9
Nov 15

0 05 1 1.5 2 2.5

HS-CONCENTRATION (mM)

Figure 31. Depth profiles of pore water HS- concentration at station 4.
1-1
4*.'@

Station 5

E A
U
.* 3 -
Lij

< 5 -
I I
rr
W
z 9 -
CC
LU
Sep 6

F-
z
LU

LU 3 -
U)
3: 5
0
-j
W 7
9-0
CL
W Nov 15

0 0.5 1 1.5 2 2.5

HS- CONCENTRATION (mM)

Figure 32. Depth profiles of pore water HS- concentration at station 5.

Station 1
0 -
A 0 7 B
2- July 12 Aug 1 1

E 4 -
Q
LU 0 El
6 -

LU 8 -
F-
z 0 Ej
a: 10 -
LU
F-
<
12

Z 0-
W C D

Q
Lj 2- Sep 27 Nov 15
U)
3: 4-
0
-i
uj 11 0 0 0
C13

CL
LU 8-
Q
0 0 0

10-

12
0 60 120 180 0 6@ 1 @O 180
TOTAL REDUCED S (mmol/kg WET SEDIMENT)

CORE 1 CORE 2 MEAN

11 0

Figure 33. Distributions of total reduced sulfur (TRS) in sediments at station 1.

Station 2
0
A B C

1:3
E 4
0
0 0
W
6
LL 0 0
cr_
W 8
z
cr 10 -
W
June 10 July 12 Aug 1 0 0
12
z 0 -
W D E

W 2 -
(D
3: CORE 1 o
0 4 -
-j CORE 2 o
M
-r 6 CORE 3
LU

F- 0 ED 0 CORE 4
a_
W
8 - CORE 5 A,

0 0 MEAN
10 - 27 Nov 15
12
o 60 120 180 0 60 1@0 180
TOTAL REDUCED S (mmol/kg WET SEDIMENT)

Figure 34. Distributions of total reduced sulfur (TRS) in sediments at station 2. Note in
panel (A) that 5 replicate cores were examined as part of a time course sulfate reduction
I @d

experiment.

Station 3
0
A B C

D
E 4
0

w
6
<
U-
CC J
w 8

z 0 D El 0

CE: 10
w
0 11
12 July 12 Aug 1 Sep 6

z 0
w D E

C) 2 7:
w
E-] 0
CORE 1 o
0 4
-j CORE 2 o
w 0 10
M MEAN
6 7
-r
0 0
W 8

0 E], 0

Sep 27 Nov 15
12
0 60 120 180 0 6@ 1 @O 180

TOTAL REDUCED S (mmol/kg WET SEDIMENT)

Figure 35. Distributions of total reduced sulfur (TRS) in sediments at station 3.
C

0 Station 4

El El 0 11 0
2 - July 12 Aug 1 Sep 6
ET
E 4
w 0
Q 6

U-
cc
w 8
z 0 El
cc: 10 -
w
Cl 0

Z 0
w D E

w 2 - Sep 27 Nov 15

0
4 CORE 1 0
-j CORE 2 o
w C 0 El
co 6 - MEAN

(L 0
w 8 -

10 -

12
0 60 120 180 0 60 120 180
TOTAL REDUCED S (mmol/kg WET SEDIMENT)

Figure 36. Distributions of total reduced sulfur (TRS) in sediments at station 4.
00

Station 5
0 A
E 11 0
0

w
2-

U-
Ir Ej
w
z 4-
a:
w
El 1:1 .(D

6-
z
w
2
0 D 0 E 0
w
8 -

w E] 0
M
10
a_
w
12 Sep 6 11 0 Nov 15
0 60 120 180 0 60 120 180

TOTAL REDUCED S (mmol/kg WET SEDIMENT)

CORE 1 CORE2 MEAN

0 0

Figure 37. Distributions of total reduced sulfur (TRS) in sediments at station 5.

20-
A Station 1 B Station 2

15-

10-

/T
CE 0
0 20-
E C Station 3 D Station 4

15-
U_
_j
(0 10-

Z) 5-

W
a:
0
161 193 213 249 270 319
0 20-
E Station 5 JULIAN DAY
15- 0-4cm 0-6cm E 6-12cm El 0-12cm

0
161 1@3 2@3 249 270 319

JULIAN DAY

Figure 38. Depth-integrated areal total reduced sulfur (TRS) content of sediments over the
study period. Bar codes indicate the depth intervals over which values for individual
segments were integrated.
8 LA
A

metal sulfides to continue accumulating at the other stations where the sulfate reduction rates

were much higher probably means that the supply of metals available to react with sulfide is

depleted and, thus, HS_ accumulates. This contention is supported by the data for station 2

(Figs. 34a, 34b and 38b) where TRS increased about two-fold between June 10 and July 12

and remained relatively constant thereafter.

REFERENCES

Baird, D. and R.E. Ulanowicz. 1989. The seasonal dynamics of the Chesapeake Bay
ecosystem. Ecol. Monogr. 59:329-364.

Baird, D., J.M. McGlade and R.E. Ulanowicz. 1991. The comparative ecology of six
marine ecosystems. Phil. Trans. R. Soc. Lond. B333:15-29.

Bell, J.T. 1990. Carbon flow through bacterioplankton in the mesohaline Chesapeake Bay.
MS. Thesis, Univ. of Maryland. 126 pp.

Bell, J.T., D. Gluckman, R.B. Jonas and J.H. Tuttle. 1988. Fine-scale zonation in
microbial turnover of labile dissolved organic substrates in Chesapeake Bay. EOS, Dec.
1987.

Blankenship, K. 1990. Energy and the Chesapeake. Chesapeake Citizen Report, Sept.-Oct.,
pp. 1-5.

Blankenship, K. 1991. Air pollution a growing Bay concern. Bay Journal. 9:1-5.

Caron, D.A., J.L. Goldman and M.R. Dennett. 1988. Experimental demonstration of the
roles of bacteria and bactivorous protozoa in plankton nutrient cycles. Hydrobiologia 159:27-
40.

Cline, J.D. 1969. Spectrophotometric determination of hydrogen sulfide in natural waters.
Limnol. Oceanogr. 14:454-458.

Cooper, S.R. and G.S. Brush. 1991. Long-term history of Chesapeake Bay anoxia.
Science 254:992-996.

Ducklow, H.W., D.A. Purdie, P.J. LeB. Williams and J.M. Davies. 1986.
Bacterioplankton: A sink for carbon in a coastal marine plankton community. Science
232:865-876.

Ducklow, H.W,m E.R. Peele, S.M. Hill and H.L. Quinby. 1987. Fluxes of carbon
nitrogen and oxygen through estuarine bacterioplankton. pp. 511-523, In: Lynch, M.P. and
E.C. Krome (eds.), Perspectives on research in the Chesapeake Bay. Chesapeake Research
Consortium Publ., Gloucester Point, Virginia.

Fossing, H. and B.B. Jorgensen. 1989. Measurements of bacterial sulfate reduction in
sediments: evaluation of a single-step chromium reduction method. Biogeochem. 8:205-222.

Gerritsen, J., A. Ranasinghe and A.F. Holland. 1989. Comparison of three strategies to
improve water quality in the Maryland portion of Chesapeake Bay. Rept. to MD Dept.
Natural Resources, Appendix C. 20 pp.

Haven, D. and R. Morales-Alamo. 1986. Aspects of biodeposition by oysters and
invertebrate filter-feeders. Limnol. Oceanogr. 11:487-498.

Holland, A.F., A.T. Shaughnessy and M.H. Hiegel. 1987. Long-term variation in
mesohaline Chesapeake Bay benthos: spatial and temporal patterns. Estuaries 10:227-245.

Jonas, R.B. 1987. Chesapeake Bay dissolved oxygen dynamics: Roles of phytoplankton and
microheterotrophs. pp. 75-80, In: Mackieman, G.B. (ed.), Dissolved oxygen in the
Chesapeake Bay: processes and effects. MD Sea Grant Publ. College Park, MD.

Jonas, R.B. D. Gluckman, J.H. Tuttle and J.T. Bell. 1988a. Distribution and metabolism of
amino acids in Chesapeake Bay: water column maxima. AGU-ASLO Ocean Sciences
Meeting. New Orleans. LA, 18-22 Jan. 1988. Published in EOS: Transactions, American
Geophysical Society, Vol. 68, Dec. 1987.

Jonas, R.B., J.H. Tuttle, D.L. Stoner and H.W. Ducklow. 1988c. Dual-label radioisotope
method for simultaneously measuring bacterial production and metabolism in natural waters.
Appl. Environ. Microbiol. 54:791-798.

Jonas, R.B., J.H. Tuttle, J.T. Bell and D.G. Cargo. 1988c. Organic carbon, oxygen
consumption and bacterial metabolism in Chesapeake Bay. Presented at Chesapeake Research
Consortium Conference, Understanding the Estuary: Advances in Chesapeake Bay Research/
29-31 March 1988, Baltimore, MD.

Jonas, R.B. and J.H. Tuttle. 1990. Bacterioplankton and organic carbon dynamics in the
lower mesohaline Chesapeake Bay. Appl. Environ. Microbiol. 56:747-757.

Jonas, R.B. and J.H. Tuttle. 1991. Improving Chesapeake Bay water quality: Influences of
rafted oyster aquaculture on microbial processes and organic carbon. In: New perspectives
on the Chesapeake Bay. Chesapeake Research Consortium Publ.

Jordan, S.J. 1987. Sedimentation and remineralization associated with biodeposition by the
American oyster Crassostre virginic (Gmehne). Ph.D. dissertation, Univ. of MD, College
Park, MD.

Jorgensen, B.B. 1978. A comparison of methods for the quantification of bacterial sulfate
reduction in coastal marine sediments. 1. Measurement with radiotracer technique.
Geomicrobiol. 1: 11-27.

Malone, T.C. and H.W. Ducklow. 1990. Microbial biomass in the coastal plume of
Chesapeake Bay: phytoplankton-bacterioplankton relationships. Limnol. Oceanogr. 35:296-
312.

Malone, T.C., W.M. Kemp, H.W. Ducklow, W.R. Boynton, J.H. Tuttle and R.B. Jonas.
1986. Lateral variation in the production and fate of phytoplankton in a partially stratified
estuary. Mar. Ecol. Prog. Ser. 32:149-160.

Malone, T.C., H.W. Ducklow, E.R. Peele and S.E. Pike. 1991. Picoplankton carbon flux
in Chesapeake Bay. Mar. Ecol. Prog. Ser. 78:11-22.

Newell, R.I.E. 1988. Ecological changes in Chesapeake Bay: Are they the result of
overharvesting the American oyster Crassostrea iftinica? Ln: Understanding the estuary:
Advances in Chesapeake Bay Research. CRC Publ. 129.

Newell, R.I.E., J. Gerritsen and A.F. Holland. 1989. The importance of existing and
historical bivalve populations in removing phytoplankton biomass from Chesapeake Bay. Ln:
Abstracts of the Tenth Biennial Int. Est. Res. Conf.

Paynter, K.T. and E.M. Burreson. 1991. Effects of Perkinsus marinus infection in the
eastern oyster, Crassostrea Wrginica: 11. Disease development and impact on growth rate at
different salinities. J. Shellfish Res. 10:415-431.

Radway, J.C., J.H. Tuttle, N.J. Fendinger and J.C. Means. 1987. Microbially mediated
leaching of low-sulfur coal in experimental coal columns. Appl. Environ. Microbiol.
53(5):1056-1063.

Roden, E.D. and J.H. Tuttle. Sulfide release from estuarine sediments underlying anoxic
bottom water. Limnol. Oceanogr. In press.

Roden, E.D. and J.H. Tuttle. Inorganic sulfur turnover in oligohaline estuarine sediments.
Limnol. Oceanogr. In review.

Roden, E.D. and J.H. Tuttle. Inorganic sulfur cycling in mid and lower Chesapeake Bay
sediments. Mar. Ecol. Prog. Ser. In revision.

Roman, M.R., H.W. Ducklow, J.A. Fuhrman, C. Garside, P.M. Glibert, T.C. Malone and
G.B. McManus. 1988. Production, consumption and nutrient cycling in a laboratory
mesocosm. Mar. Ecol. Prog. Ser. 42:39-52.

Tenore, K.R., L. Boyer, R. Cal, J. Corral, C. Garcia-Fernandez, N. Gonzalez, E. Gonzalez-
Gurriaran, R. Hanson, J. Iglesias, M. Krom, E. Lopez-Jamar, J. McClain, M. Parnatmat, A.
Perez, D. Rhoades, G. diSantiago, J. Tietjens, J. Westrich and H.L. Windom. 1982.
Coastal upwelling in the Rias Bajas, NW Spain: Contrasting the benthic regimes of the Rias
de Arosa and de Muros. J. Mar. Res. 40:701-768.

Tuttle, J.H., T.C. Malone, R.B. Jonas, H.W. Ducklow and D.G. Cargo. 1985. Nutrient-
dissolved oxygen dynamics: Roles of phytoplankton and microheterotrophs under summer
conditions. Final Rept. U.S. E.P.A. Ref. No. Univ. of MD [UMCEES]CBL 85-039.
Chesapeake Biological Laboratory, Solomons, MD, U.S.A. 121 pp.

Tuttle, J.H., R.B. Jonas and T.C. Malone. 1987a. Origin, development and significance of
Chesapeake Bay anoxia. pp. 442-472, In: Majumdar, S.J., L.W. Hall, Jr. and H.M. Austin
(eds.), Contaminant Problems and Management of Living Chesapeake Bay Resources. PA
Academy of Science Press.

Tuttle, J.H., T.C. Malone, R.B. Jonas, H.W. Ducklow and D.G. Cargo. 1987b. Nutrient-
dissolved oxygen dynamics in Chesapeake Bay: the roles of phytoplankton and microhetero-
trophs under summer conditions, 1985. U.S. E.P.A., CBP/TRS3/87. 158 pp.

Ulanowicz, R.E. and J.H. Tuttle. The trophic consequences of oyster stock rehabilitation in
Chesapeake Bay. Estuaries. In press.

Williams, P.J. leB. 1984. Bacterial production in the marine food chain: the emperor's new
suit of clothes? pp. 271-299, In: Fasham, M.J.R. (ed.), Flows of energy and materials in
marine ecosystems: Theory and practice. Plenum Press, New York,

Zhabina, N.N. and I.I. Volkov. 1978. A method of determination of various sulfur
compounds in sea sediments and rocks. pp. 735-746, In: Krumbein, W. (ed.),
Environmental biogeochernistry and geomicrobiology, Vol. 3. Ann Arbor Sci. Publ., Ann
Arbor, MI.

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