Chesapeake Bay Sediments Research Articles

Climatic variability in the eastern United States over the past millennium from Chesapeake Bay sediments

Salinity oscillations caused by multidecadal climatic variability had major impacts on the Chesapeake Bay estuarine ecosystem during the past 1000 yr. Microfossils from sediments dated by radiometry ( 14 C, 137 Cs, 210 Pb) and pollen stratigraphy indicate that salinity in mesohaline regions oscillated 10‐15 ppt during periods of extreme drought (low fresh-water discharge) and wet climate (high discharge). During the past 500 yr, 14 wet-dry cycles occurred, including sixteenth and early seventeenth century megadroughts that exceeded twentieth century droughts in their severity. These droughts correspond to extremely dry climate also recorded in North American tree-ring records and by early colonists. Wet periods occurred every ~60‐70 yr, began abruptly, lasted <20 yr, and had mean annual rainfall ~25%‐30% and fresh-water discharge ~40%‐50% greater than during droughts. A shift toward wetter regional climate occurred in the early nineteenth century, lowering salinity and compounding the effects of agricultural land clearance on bay ecosystems.

Hydrophobic organic contaminants in surficial sediments of baltimore harbor: Inventories and sources

AbstractThe heavily urbanized and industrialized Baltimore Harbor/Patapsco River/Back River system is one of the most highly contaminated regions of the Chesapeake Bay. In June 1996, surficial sediments were collected at 80 sites throughout the subestuarine system, including historically undersampled creeks and embayments. The samples were analyzed for a suite of hydrophobic organic contaminants (HOCs) consisting of 32 polycyclic aromatic hydrocarbons (PAHs) and 113 polychlorinated biphenyl (PCB) congeners. Total PAH and total PCB concentrations ranged from 90 to 46,200 and 8 to 2,150 ng/g dry weight, respectively. There was enormous spatial variability in the concentrations of HOCs, which was not well correlated to grain size or organic carbon content, suggesting nonequilibrium partitioning and/or proximity to sources as important factors explaining the observed spatial variability. High concentrations of both classes of HOCs were localized around major urban stormwater runoff discharges. Elevated PAH concentrations were also centered around the Sparrow's Point Industrial Complex, most likely a result of the pyrolysis of coal during the production of steel. All but 1 of the 80 sites exceeded the effects range‐low (ERL) for total PCBs and, of those sites, 40% exceeded the effects range‐medium (ERM), suggesting toxicity to marine benthic organisms would frequently occur. Polychlorinated biphenyl homolog patterns most closely resembled Aroclor 1260 at sites around areas of high concentration of industrial outflows and urban runoff. Conversely, those sites further from suspected municipal and industrial discharges had patterns resembling that of Aroclor 1254. We suggest the heavier chlorinated pattern is indicative of near‐source emissions of PCBs. The lighter chlorinated PCB patterns observed are similar to those found in mainstem Chesapeake Bay sediments and may reflect a more weathered pattern or one derived, in part, from air‐water exchange of gaseous PCBs. Using principal component analysis, differences in PAH signatures were discerned. Higher molecular weight PAHs were enriched in signatures from sediments close to suspected sources (i.e., urban stormwater runoff and steel production complexes) compared to those patterns observed at sites further from outfalls or runoff. Due to varying solubilities and affinities for organic matter of the individual PAHs, partitioning of the heavier weight PAHs may enrich settling particles with high molecular weight PAHs. Lower molecular weight PAHs, having lower affinity for particles, may travel from the source to a greater extent.

Seasonal variability of shallow biogenic gas in Chesapeake Bay

Methane gas in Chesapeake Bay sediments occurs in buried paleodrainage channels incised during the last glacial sealevel lowstand. Repeat acoustic surveys of two Chesapeake Bay sites during the past year (with a 2–15 kHz chirp sonar profiler and 100 kHz sidescan sonar) show that the top of the zone of acoustically opaque gas bubbles in the sediments fluctuates vertically by up to 0.5 m, apparently in response to seasonal temperature changes. The vertical movement of the gas layer is most apparent in the main channel of the bay, where the methane gas is very close to the seafloor. In areas where the gas is seen to be very near the seafloor on the chirp profiler records, the sidescan sonar data show corresponding high backscatter. This does not appear to be the result of differing sediment types. It is not likely that the sidescan signal is penetrating the seafloor at the shallow outer grazing angles of the sidescan swath, therefore, the gas must extend to the water–sediment interface. The areas of high backscatter caused by the gas are observed to change seasonally, expanding during the summer high-temperature period and shrinking during the winter low-temperature period.

Estuarine cycling of carbonyl sulfide: production and sea–air flux

Abstract A 3 year field and laboratory study of estuarine carbonyl sulfide (OCS) was undertaken during 1991–1994 to more accurately quantify the variability of coastal OCS fluxes and to investigate mechanisms that lead to elevated OCS concentrations in coastal waters. Results from the water column of the Chesapeake Bay show no definitive seasonal trends in the sea–air flux of OCS, although these fluxes are over 50 times more than those from the open ocean. In contrast, fluxes of OCS from estuarine sediments were found to be highest in the summer, and contribute up to 75% of the total sources of OCS in this estuary. Laboratory incubations of Chesapeake Bay sediments using different carbon substrates, inhibitors, and temperature show that OCS production is coupled to microbial sulfate reduction. These results explain the high sediment porewater concentrations and high sediment–water fluxes in the summer, and combined with the field data, provide evidence that anoxic sediments can be an important component of the OCS budget in coastal waters.

Fluxes of copper‐complexing ligands from estuarine sediments

Most studies of the organic complexation of Cu in natural waters have focused on distributions and processes in the water column, where a significant fraction of Cu‐complexing ligands may be biologically produced. We present direct evidence for a flux of Cu‐complexing ligands from estuarine sediments, demonstrating that sediments are a significant, yet previously unrecognized source of the ligands. Fluxes of Cu‐complexing ligands from Chesapeake Bay sediments range from 300 to 1,200 nmol m−2 d−1, exceeding fluxes of total dissolved Cu by 3→40‐fold, suggesting that any Cu fluxing from the sediments is likely to be organically complexed. Our results indicate that benthic fluxes may supply from 10 to 50% of the standing stock of Cu‐complexing ligands in Chesapeake Bay and suggest that such fluxes may strongly influence the biogeochemistry of Cu in shallow water environments and potentially in the ocean as a whole.

A Sediment Chronology of the Eutrophication of Chesapeake Bay

Chesapeake Bay sediments were examined for biogeochemical evidence of eutrophication trends using two mesohaline sediment cores. Measurements of 210Pb geochronology and sediment profiles of organic carbon, nitrogen, organic phosphorus, inorganic phosphorus, and biogenis silica (BSi) were used used to develop temporal concentration trends. Recent sediments have 2–3 times as much organic carbon and nitrogen as sediments from 80 to 100 yr ago, but the increases result from both changes in organic matter deposition and time-dependent changes in organic matter decomposition rates. Despite increases in phosphorus loading, no major changes in phosphorus concentration were noted throughout most of the century; anthropogenic phosphorus deposition, though not evident in sulfidic mid-bay sediments, must occur in more oxidizing sediment environments in both the northern and southern bays. Temporal trends in BSi concentrations are much less evident and the lack of substantial increases in this century suggest that BSi inputs may be capped by late spring-summer Si limitation.

Carbon cycling in mesohaline Chesapeake Bay sediments 2: Kinetics of particulate and dissolved organic carbon turnover

Temporal and depth variations in benthic carbon metabolism rates were examined in relation to particulate organic carbon (POC) deposition rates and particulate and dissolved organic carbon degradation kinetics in two sediments from the mesohaline region of Chesapeake Bay. The depth distribution of a single pool of metabolizable POC (MPOC) in mid-Bay sediments was estimated by curve-fitting of dry weight POC profiles (1-G approach). Estimated MPOC pools accounted for 3-4% of total POC content in the upper 10 cm of sediment. First-order MPOC decay constants of 10 yr -1 during the warm season were estimated from the ratio of MPOC pool size to weighted-average MPOC deposition rate derived from mid-water column sediment trap deployments. These results indicated that the MPOC pool defined by the 1-G approach corresponded to the most readily degradable component of coastal marine phytoplankton detritus. Transient-state kinetic models of MPOC turnover, based on observed MPOC deposition rates and temperature-dependent mineralization, predicted MPOC accumulation in sediments during the spring followed by depletion during the summer. The models also predicted an early summer maximum in MPOC mineralization rate associated with the degradation of MPOC accumulated during the spring, in agreement with the seasonal pattern of sulfate reduction rates in mid-Bay sediments. Model results suggested that MPOC deposition during the summer is important in maintaining high rates of benthic carbon metabolism throughout the warm season. Steady-state and transient-state models of depth-dependent POC degradation suggested that particle mixing influences the depth distribution of MPOC concentration and turnover rate within the upper 4-6 cm of mid-Bay sediments. However, because of the rapid rate of MPOC decay, random particle mixing is unlikely to transport significant quantities of MPOC below 4-6 cm. A steady-state diagenetic model was used to test the hypothesis that downward diffusion of acetate produced by anaerobic decomposition of MPOC in the upper 4-6 cm fuels sulfate reduction deeper in the sediment. The results suggest that because of the very rapid turnover of acetate pools (≥ 2 hr -1 ), acetate diffusion does not influence the depth distribution of carbon metabolism in the sediment. Therefore, sulfate reduction occurring at depths below 4-6 cm must be fueled by decomposition of some portion of the large pool of relatively refractory sediment POC. Degradation of this material is likely responsible for =1/3 of total warm season benthic carbon metabolism.

Aliphatic amines in Chesapeake Bay sediments

Abstract Aliphatic amines were determined in sediments and sediment pore waters from several contrasting sites in Chesapeake Bay. The aliphatic amines diethylamine, sec-butylamine, n-propylamine, and i-propylamine were detected in a limited number of pore-water samples at concentrations generally less than ~ 0.6 μM. The occurrence of these amines showed no obvious correlation to other sediment geochemical parameters. Whole sediment (HF/HCl-extractable) aliphatic amines were less than ~ 0.8 nmol gdw . Isoamylamine and 2-methylbutylamine were the only amines that could be detected and quantified in sediment extracts, although diethylamine was below our detection limit in selected samples. When compared to other measured nitrogen pools in the sediments, these observations suggested that aliphatic amines may not represent a significant fraction of the nitrogen that is remineralized in these sediments, although more detailed concentration and rate studies are needed to verify their role in sediment nitrogen cycling. These aliphatic amines also did not appear to represent a major component of the uncharacterized nitrogen in these sediments.

Carbon cycling in mesohaline Chesapeake Bay sediments 1: POC deposition rates and mineralization pathways

Organic carbon cycling in sediments at two locations in the mesohaline Chesapeake Bay was analyzed using available data on sediment sulfate reduction, sediment oxygen consumption, and particulate organic carbon (POC) deposition and burial. Estimates of POC deposition based on the sum of integrated sediment metabolism and POC burial compared well with direct estimates derived from chlorophyll-a collection rates in mid-water column sediment traps. The range of POC deposition estimates (15-31 mol C m -2 yr -1 ) accounted for a large fraction (36-74%) of average annual net primary production in the mesohaline Bay. The difference between rates of POC deposition and permanent burial indicated that 70-85% of deposited carbon is mineralized on the time scale of a year. Carbon mineralization through sulfate reduction accounted for 30-35% of average net primary production, and was likely responsible for 60-80% of total sediment carbon metabolism. Oxidation of reduced sulfur accounted for a large but quantitatively uncertain portion of SOC in mid-Bay sediments. Our results highlight the quantitative significance of organic carbon sedimentation and attendant anaerobic sediment metabolism in the carbon cycle of a shallow, highly productive estuary.

Fluxes of dissolved organic carbon from Chesapeake Bay sediments

Benthic fluxes of dissolved organic carbon (DOC) were measured over an annual cycle at two contrasting sites in Chesapeake Bay. At an organic-rich, sulfidic site in the mesohaline portion of the Bay (site M) DOC fluxes from the sediments ranged from 1.4 to 2.9 mmol/m 2/d. Measured benthic DOC fluxes at site M corresponded to ~3–13% of the depth-integrated benthic C remineralization rates (ΣOCR), and agreed well with calculated diffusive DOC fluxes based on porewater DOC profiles. This agreement suggests that DOC fluxes from site M sediments were likely controlled by molecular diffusion. The second site that was studied is a heavily bioturbated site in the southern Bay (site S). The activity of macrobenthos did not appear to enhance DOC fluxes from these sediments, since measured benthic DOC fluxes (< 0.5 mmol/m 2/d) were lower than those at site M. The ratios of benthic DOC fluxes to ΣOCR values at site S were also slightly smaller than those observed at site M. Benthic DOC fluxes from Chesapeake Bay sediments do not appear to significantly affect the transport of DOC through this estuary, although uncertainties in the reactivity of DOC in estuaries makes this conclusion somewhat tentative at this time. However, when these results are used to make a lower limit estimate of the globally integrated benthic DOC flux from marine sediments, a value similar to that previously calculated by Burdige et al. (1992) is obtained. This observation further supports suggestions in this paper about the importance of benthic DOC fluxes in the oceanic C cycle.

Interaction of triorganotin compounds with chesapeake bay sediments and benthos

AbstractTriorganotin compounds can interact with various segments of natural water systems. In sediments, for example, these compounds can undergo speciation, and can also become injurious to benthos. The interaction of tributyltin (TBT) and triphenyltin (TPT) compounds with sediments have been studied using extraction techniques in addition to directly observing these compounds in sediments using Mössbauer spectroscopy. The effect of these compounds on benthos has also been examined. The results of these studies are reviewed with particular regard to studies on sediments from the Chesapeake Bay, USA.

Inorganic sulfur turnover in oligohaline estuarine sediments

Inorganic sulfur turnover was examined in oligohaline (salinity < 2 g kg-1) Chesapeake Bay sediments during the summer. Cores incubated for < 3 hr exhibited higher sulfate reduction (SR) rates (13–58 mmol m-2 d-1) than those incubated for 3–8 hr (3–8 mmol m-2 d-1). SR rates (determined with35SO 4 2- ) increased with depth over the top few cm to a maximum at 5 cm, just beneath the boundary between brown and black sediment. SR rates decreased below 5 cm, probably due to sulfate limitation (sulfate < 25 μM). Kinetic experiments yielded an apparent half-saturating sulfate concentration (Ks) of 34 μM, ≈ 20-fold lower than that determined for sediments from the mesohaline region of the estuary. Sulfate loss from water overlying intact cores, predicted on the basis of measured SR rates, was not observed over a 28-hr incubation period. Reduction of35SO 4 2- during diffusion experiments with intact core segments from 0–4 and 5–9 cm horizons was less than predicted by non-steady state diagenetic models based on35SO 4 2- reduction in whole core injection experiments. The results indicate that net sulfate flux into sediments was an order of magnitude lower than the gross sulfur turnover rate. Solid phase reduced inorganic sulfur concentrations were only 2–3 times less than those in sediments from the mesohaline region of the Bay, despite the fact that oligohaline bottom water sulfate concentrations were 10-fold lower. Our results demonstrate the potential for rapid SR in low salinity estuarine sediments, which are inhabited by sulfate-reducing bacteria with a high affinity for sulfate, and in which sulfide oxidation processes replenish the pore water sulfate pool on a time scale of hours.

Isolation and Diversity of Actinomycetes in the Chesapeake Bay

Chesapeake Bay was investigated as a source of actinomycetes to screen for production of novel bioactive compounds. The presence of relatively large populations of actinoplanetes (chemotype II/D actinomycetes) in Chesapeake Bay sediment samples indicates that it is an eminently suitable ecosystem from which to isolate actinomycetes for screening programs. Actinomycetes were isolated from sediment samples collected in Chesapeake Bay with an isolation medium containing nalidixic acid, which proved to be more effective than heat pretreatment of samples. Actinomycete counts ranged from a high of 1.4 x 10 to a low of 1.8 x 10 CFU/ml of sediment. Actinomycetes constituted 0.15 to 8.63% of the culturable microbial community. The majority of isolates from the eight stations studied were actinoplanetes (i.e., chemotype II/D), and 249 of these isolates were obtained in a total of 298 actinomycete isolates. Antimicrobial activity profiles indicated that diverse populations of actinoplanetes were present at each station. DNA hybridization studies showed considerable diversity among isolates between stations, but indicated that actinoplanete strains making up populations at nearby stations were more similar to each other than to populations sampled at distant stations. The diversity of actinoplanetes and the ease with which these organisms were isolated from Chesapeake Bay sediments make this a useful source of these actinomycetes.

Inorganic sulfur cycling in mid and lower Chesapeake Bay sediments

Inorganic sulfur cycling in mid and lower Chesapeake Bay sediments

Sulfide release from estuarine sediments underlying anoxic bottom water

Independent measurements of dissolved sulfide (DS) production in and release from mesohaline Chesapeake Bay sediments underlying anoxic bottom water were made during summer. DS accumulated under benthic chambers at a rate of 27.3rt8.2 mmol m-2 d-l. Rates of DS release ranged from 60 to 80% ofdepth-integrated@-12 cm) sulfate reduction (SR) rates (average 39.Ok9.0 mmol m-2 d-l) determined with 35S0, 2 -. The balance between DS production, accumulation in pore waters, and sediment-water exchange was examined by steady siate and transient state transport-reaction modeling, with a DS sediment diffusion coefficient derived from that determined for sulfate by the instantaneous source technique. The results indicate that DS transport is influenced by processes other than vertical molecular diffusion, most likely gas bubble ebullition driven by methane production beneath the SR zone. Although such processes may significantly reduce porewater DS accumulation (i.e. promote DS release), the models show that most (65-95%) DS formation during summer is not stored in the DS pool regardless of the transport processes occurring. The observed rates of DS production and release correspond to a potential oxygen demand of l2 g 0, m-z d-l, equal to or greater than estimated rates of eddy-diffusive bottom-water reaeration during summer stratification. Thus, sulfur cycling alone can maintain anoxia in these subpycnocline waters during summer under quiescent water conditions. Anoxic sediment metabolism is a quantitatively significant component of the carbon cycle in shallow-water aquatic ecosystems (Jorgensen 1983), and sulfate reduction (SR) is the principal terminal microbial process in anoxic sediments where sulfate is abundant (Capone and Kiene 1988). The reoxidation of reduced sulfur formed by SR influences oxygen balance in shallow coastal systems, accounting for at least half of sediment oxygen consumption (SOC) under waters <20 m deep (Jorgensen 1982). In coastal systems subject to vertical water stratification, SOC linked to sulfur cycling

Beryllium-10 in Chesapeake Bay sediments: An indicator of sediment provenance

In a plot of 10 Be vs . Fe, central Chesapeake Bay sediments can be segregated into distinct units. This plot reveals an unexpected, statistically significant difference between sediments on the eastern and western flanks of the main channel, implying different origins. Although the 10 Be concentrations in sediments from these two regions span as much as an order of magnitude range, the 10 Be/Fe ratios vary by an amount approximating analytical error alone. The large concentration ranges are ascribed to hydraulic sorting, which can produce variance in composition while not affecting ratios between grain surface components such as Fe and Be. On the basis of 10 Be/Fe signatures, sediments on the western flank of the main channel appear to have been derived from the Susquehanna or another Piedmont/Appalachian river. Sediments on the eastern flank may have been transported from the south, by landward flowing bottom currents, or may be relicts of a Pleistocene estuarine system. Conditions under which 10 Be may prove a useful tool in sediment provenance studies elsewhere are discussed.

Testing sediment toxicity in chesapeake bay with the amphipod Leptocheirus plumulosus: An evaluation

AbstractOrganisms selected for testing the toxicity of estuarine sediments must exhibit sensitivity to toxicants while remaining tolerant of wide ranges of salinities and sediment characteristics. The amphipod Leptocheirus plumulosus Shoemaker is an ecologically important infaunal inhabitant of Chesapeake Bay sediments. Leptocheirus plumulosus was exposed to a range of salinities and sediments varying in physical composition for up to 28 d in separate experiments to determine effects of natural environmental variables on amphipod survival and reproduction. No significant differences in adult survival were observed among salinity treatments ranging from 1.5 to 32 ppt or among sediment treatments varying in particle size and organic content. Significant effects on reproductive end points were detected, indicating the potential for incorporating sublethal end points into the bioassay. Acute 96‐h LC50 values for aqueous cadmium at a salinity of 6 ppt were determined for Leptocheirus plumulosus and the amphipod Hyalella azteca Saussure, an organism commonly used in freshwater sediment toxicity tests. The LC50 values were 0.30 mg Cd per liter and 0.19 mg Cd per liter for Leptocheirus plumulosus and Hyalella azteca, respectively.

Ammonium recycling versus denitrification in Chesapeake Bay sediments

Contemporaneous measurements are reported for nitrification, denitrification, and net sediment— water fluxes of NH4+ and NO3− in the mesohaline region of Chesapeake Bay. Seasonal cycles over a 2‐yr period were characterized by a midsummer maximum in NH4+ efflux to the overlying water and a May peak in NO3− removal from water by sediments. Coherent temporal patterns for nitrification and denitrification were observed, with relatively high values in spring and fall and virtual elimination of both processes in summer. Indirect measurements indicate that nitrification was limited by the shallow O2 penetration (&lt;1 mm) here compared to reports for other marine sediments (2–6 mm). In addition, a strong positive correlation between the two processes suggested that denitrification was generally controlled by nitrification. Comparisons of NO3− fluxes and net nitrification rates (nitrification minus NO3− reduction to NH4+) revealed that measurements of denitrification with the acetylene block method systematically underestimated actual rates. Rates of N2 loss in denitrification were similar to NH4+ recycling fluxes to the overlying water in spring and fall, but in summer negligible denitrification contributed to enhanced NH4+ recycling. These results suggest that inhibition of denitrification in eutrophic estuaries such as Chesapeake Bay may reinforce the effects of nutrient enrichment by allowing increased rates of NH4+ recycling.

Temporal and spatial distribution of beryllium-7 in the sediments of Chesapeake Bay

The sediment inventory of 7Be was determined at six stations in the main stem of Chesapeake Bay nine times between April, 1986, and September, 1987. The inventories ranged from < 0·20−7·32 dpm cm −2. Comparison to the atmospherically supported 7Be inventory (range 2–4 dpm cm −2) showed significant focusing of 7Be in the sediments in the zone of the turbidity maximum during the summer, and suggested that the spatial distribution of 7Be in the sediments of the lower Bay was determined largely by horizontal redistribution of bottom sediments. The processes causing this redistribution of 7Be in the lower Bay apparently had a recurrence frequency greater than the sampling frequency in this investigation. The temporal pattern of 7Be accumulation at the six stations over the first year of this investigation allowed estimation of sedimentation rates, which suggested that the processes governing the distribution of 7Be in Chesapeake Bay sediments were similar to the processes determining sedimentation patterns over about the past 100 years.

Determination of DI- and Tributyltin in Sediment and Microbial Biofilms Using Acidified Methanol Extraction, Sodium Borohydride Derivatization and Gas Chromatography with Flame Photometric Detection

Abstract A method for the relatively rapid determination of di- and tributyltin species in sediment and microbial biofilms is presented. Di- and tributyltin species were detected in Chesapeake Bay sediments using this method. Microbial biofilms grown on glass slides exhibited substantial accumulation of tributyltin species from solution. This method should have useful application to sediment analysis of di- and tributyltin species and for studies on the accumulation and fate of tributyltin in microbial biofilms.