mid-Chesapeake Bay Research Articles

Elevation Changes in Restored Marshes at Poplar Island, Chesapeake Bay, MD: II. Modeling the Importance of Marsh Development Time

Tidal marshes in the Chesapeake Bay are vulnerable to the accelerating rate of sea-level rise (SLR) and subsidence. Restored and created marshes face the same risks as natural marshes, and their resilience to SLR may depend upon appropriate design and implementation. Here, the Coastal Wetland Equilibrium Model (CWEM) was used to assess the resilience of tidal marshes at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (PI) in mid-Chesapeake Bay, MD, where dredged material from navigation channels is being used to create new tidal marshes planted with Spartina alterniflora in the low marsh and S. patens in the high marsh. The site is microtidal with low inorganic sediment inputs, where the rate of marsh elevation change is dominated by the production of organic matter and, therefore, is proportional to net ecosystem production (NEP). The model demonstrated the importance of marsh development for surface elevation gain. In created marshes, the buildout of belowground biomass adds volume and results in faster growth of marsh elevation, but the gains slow as the marsh matures. Elevation gain is the lessor of the recalcitrant fraction of NEP sequestered in sediment or the rate of increase in accommodation space. Marshes can keep up with and fill accommodation space with sequestered NEP up to a tipping point determined by the rate of SLR. The PI low marsh platform was forecasted to drown in about 43 years after construction at the current rate of SLR. Marsh loss can be mitigated by periodic thin layer placement (TLP) of sediment. CWEM was used to simulate PI marsh responses to different TLP strategies and showed that there is an optimal design that will maximize carbon sequestration and resilience depending on the trajectory of mean sea level.

Beneficial use of sediments to restore a Chesapeake Bay marsh island

Despite rapidly expanding interest in the use of natural coastal habitats for their ability to protect against erosion and flooding, implementation of coastal natural infrastructure (NI) projects has been limited to date. Uncertainty over how the benefits of NI will change over time as they mature and adapt to changing environmental drivers, and a lack of well-documented demonstrations of NI, are often cited as roadblocks to their widespread acceptance. Here, we begin to fill that knowledge gap by describing implementation and early (3 years post-implementation) monitoring results of an NI project at Swan Island, MD. Swan is an uninhabited marsh island in mid-Chesapeake Bay, United States whose position renders it a natural wave break for the downwind town of Ewell, MD. Prior to project implementation, Swan had experienced significant losses in areal extent due to subsidence and erosion. To reverse this trend, the island was amended with dredged sediments in the winter of 2018–2019. The overarching goal was to preserve the Island’s ability to serve as a wave break and make it more resilient to future sea level rise by increasing the elevation of the vegetated platform, while also increasing the diversity of habitats present. A monitoring program was implemented immediately after sediment placement to document changes in the island footprint and topography over time and to evaluate the extent to which project goals are met. Data from the initial three years of this effort (2019 through 2022) indicate an island that is still actively evolving, and point to the need for rapid establishment of vegetative communities to ensure success of coastal NI.

Elevation Changes in Restored Marshes at Poplar Island, Chesapeake Bay, MD: I. Trends and Drivers of Spatial Variability

Tidal marshes provide numerous ecosystem services, but are threatened by recent increases in global sea level rise (SLR). Marsh restoration and creation are important strategies for mitigating marsh loss, restoring ecosystem services, increasing coastal community resilience, and providing much needed habitat for threatened species. Dredged material resulting from navigation channel maintenance can provide a substrate for these restoration projects. Few studies, however, have addressed the sustainability of these marshes. The Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island, where fine-grained, nutrient-rich dredged material from upper Chesapeake Bay is being used to create > 302 ha of tidal marshes, provides a case study. The low supply of inorganic sediment is counteracted by abundant nutrients, stimulating high rates of organic matter production and elevation change. Using > 10 years of data from 39 surface elevation tables, we found that the mean low marsh rate of elevation change (7.7 ± 3.21 mm year−1) was double the mean high marsh rate (3.6 ± 0.47 mm year−1) and exceeded the natural reference marsh (3.0 ± 2.28 mm year−1) and relative SLR (5.7 mm year−1). By stimulating organic matter production, the high nutrient substrate appears to offset the low inorganic sediment inputs in mid-Chesapeake Bay. Spatial variability was correlated with initial elevation, but was also influenced by local factors that may affect sediment redistribution within the marshes.

Seasonality and Characterization Mapping of Restored Tidal Marsh by NDVI Imageries Coupling UAVs and Multispectral Camera

Salt marsh evolution is strongly affected by tidal processes and ecology, which regulate sediment accretion and erosional rates. A balance between marsh erosion and deposition in a restored tidal wetland is crucial for analyzing restoration strategies to adopt in a natural context. Here, we present an integrated approach monitoring salt marsh seasonal changes over several months in a microtidal restored salt marsh of the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (MD, USA). The project is undertaken at a restoration site where sediment dredged from the shipping channels in the upper Chesapeake Bay is being used to restore a tidal marsh habitat in mid-Chesapeake Bay. We flew an Unmanned Aerial Vehicle (UAV) with an RGB and a multispectral camera to obtain a high-resolution map of the planimetric position of vegetation and to monitor the health of the marsh vegetation in diverse seasons. Due to its extension of 400 m by 400 m, a total of four flight plans were necessary to cover the entire marsh flying at a 40 m altitude obtaining a 2 cm Ground Sample Distance (GSD). This technique provides reliable results at a very low cost, enabling an accurate assessment of the marsh platforms to be conducted over time, due to both the very high spatial resolution and the precise georeferencing of the images for the comparisons. Our results show seasonal variability in the two dominant species colonizing the low marsh, Spartina alterniflora, and high marsh, Sporobolus pumilus. While the lower marshes showed a higher variability along seasons, the up-land vegetation showed persistent green foliage during cold seasons. Detecting salt marsh evolution and seasonality coupled with field measurements can help to improve the accuracy of hydrodynamic and sediment transport models. Understanding the drivers of salt marsh evolution is vital for informing restoration practices and designs, in order to improve coastal resilience, and develop and coastal management strategies.

High-Resolution Monitoring of Tidal Systems Using UAV: A Case Study on Poplar Island, MD (USA)

Tidal processes regulating sediment accretion rates and vegetated platform erosion in tidal systems strongly affect salt marsh evolution. A balance between erosion and deposition in a restored salt marsh is crucial for analyzing restoration strategies to be adopted within a natural context. Marsh morphology is also coupled with tidal mudflats and channel networks and this makes micro-tidal systems crucial for a detailed assessment of restoration interventions. Here, we present a methodological approach for monitoring channel morphodynamics and vegetation variations over a time frame of six years in a low tidal energy salt marsh of the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (Maryland, USA). The project is a restoration site where sediment dredged from the shipping channels in the upper Chesapeake Bay is used to restore a tidal marsh habitat in mid-Chesapeake Bay. Aerial surveys with an Unmanned Aerial Vehicle (UAV) have been performed for the high-resolution mapping of a small tidal system. Flight missions were planned to obtain a Ground Sample Distance (GSD) of 2 cm. Structure-from-Motion (SfM) and Multi-View-Stereo (MVS) algorithms have been used to reconstruct the 3D geometry of the site. The mapping of channel morphology and an elevation assessment on the mudflat were performed using orthomosaics, Digital Terrain Models (DTMs) and GNSS survey. The results highlight that the workflow adopted in this pilot work is suitable to assess the geomorphological evolution over time in a micro-tidal system. However, issues were encountered for salt marsh due to the presence of dense vegetation. The UAV-based photogrammetry approach with GNSS RTK ground surveys can hence be replicated in similar sites all over the world to evaluate restoration interventions and to develop new strategies for a better management of existing shorelines.

Sulfate-Reducing Bacterium Desulfovibrio desulfuricans ND132 as a Model for Understanding Bacterial Mercury Methylation

We propose the use of Desulfovibrio desulfuricans ND132 as a model species for understanding the mechanism of microbial Hg methylation. Strain ND132 is an anaerobic dissimilatory sulfate-reducing bacterium (DSRB), isolated from estuarine mid-Chesapeake Bay sediments. It was chosen for study because of its exceptionally high rates of Hg methylation in culture and its metabolic similarity to the lost strain D. desulfuricans LS, the only organism for which methylation pathways have been partially defined. Strain ND132 is an incomplete oxidizer of short-chain fatty acids. It is capable of respiratory growth using fumarate as an electron acceptor, supporting growth without sulfide production. We used enriched stable Hg isotopes to show that ND132 simultaneously produces and degrades methylmercury (MeHg) during growth but does not produce elemental Hg. MeHg produced by cells is mainly excreted, and no MeHg is produced in spent medium. Mass balances for Hg and MeHg during the growth of cultures, including the distribution between filterable and particulate phases, illustrate how medium chemistry and growth phase dramatically affect Hg solubility and availability for methylation. The available information on Hg methylation among strains in the genus Desulfovibrio is summarized, and we present methylation rates for several previously untested species. About 50% of Desulfovibrio strains tested to date have the ability to produce MeHg. Importantly, the ability to produce MeHg is constitutive and does not confer Hg resistance. A 16S rRNA-based alignment of the genus Desulfovibrio allows the very preliminary assessment that there may be some evolutionary basis for the ability to produce MeHg within this genus.

Remote sensing reflectance and inherent optical properties in the mid Chesapeake Bay

We used an extensive set of bio-optical data to examine the relationships between inherent optical properties and remotely sensed quantities in an optically complex and biologically productive region of the Chesapeake Bay. Field observations showed that the chlorophyll algorithms used by the MODIS (MODerate resolution Imaging Spectroradiometer) ocean color sensor (i.e. Chlor_a, chlor_MODIS, chlor_a_3 products) do not perform accurately in these Case 2 waters. This is because, at high concentrations of chlorophyll, all MODIS algorithms are based on empirical relationships between chlorophyll concentration and blue:green wavelength remote sensing reflectance ( R rs) ratios that do not account for the typically strong blue-wavelength absorption by non-covarying, dissolved and non-algal particulate components. We found stronger correlation between chlorophyll concentration and red:green R rs ratios (i.e. R rs(677)/ R rs(554)). Regionally-specific algorithms that are based on the phytoplankton optical properties in the red wavelength region provide a better basis for satellite monitoring of phytoplankton blooms in these Case 2 waters. Our estimates of f/ Q (proportionality factor in the relationship between R rs and the ratio of water backscattering, b b, and absorption, a, coefficients, b b/( a + b b)) were not considerably different from f/ Q previously estimated for same measurement geometry but Case 1 waters. Variation in surface b b significantly affected R rs magnitude across the visible spectrum and was most strongly correlated ( R 2 = 0.88) with observed variability in R rs at 670 nm. Surface values of particulate backscattering were strongly correlated with non-algal particulate absorption, a nap ( R 2 = 0.83). These results, along with the measured backscattering fraction and non-algal particulate absorption spectral slope, indicate that suspended non-algal particles with high inorganic content are the major water constituents regulating b b variability in the studied region of the Chesapeake Bay. Remote retrieval of surface a nap from R rs(670) could be used in conjunction with inversion of UV-blue wavelengths to separate contribution by non-algal particles and colored dissolved organic matter to total light absorption, and monitor non-algal suspended particle concentration and distribution in these Case 2 waters.

Drag Coefficients with Fetch-Limited Wind Waves*

Air‐sea fluxes of momentum and heat were measured simultaneously with surface wind waves and nearsurface currents in mid Chesapeake Bay during summer 1998 under low wind conditions. The data were collected using a Gill sonic anemometer and a Sontek Acoustic Doppler Velocimeter with a pressure sensor mounted on a temporary fixed tower in 8.8 m of water. The analyzed data show that the neutral drag coefficients depend upon both wind speed and wave age. They are better correlated to wave age than to wind speed. Data scatter is significantly larger in low winds than in high winds. Under light winds, the neutral drag coefficients increase with decreasing wind speed and have values much higher than those for relatively higher wind speeds. At higher wind speeds, neutral drag coefficients increase with increasing wind speed. Regardless of wind speed, neutral drag coefficients always decrease with increasing wave age. Neutral drag coefficients are lower than the results of similar field studies when fit to wind speed alone, but they statistically agree with other studies if they are fit to wave age. The momentum transfer mechanism is investigated using a parametric wave model with a seastate-dependent form drag and a reference system moving with the waves. The relationship between modeled drag coefficient and modeled wave age agrees well with the relationship derived from the data.

Nitrogen-fixing phylotypes of Chesapeake Bay and Neuse River estuary sediments.

Sediments often exhibit low rates of nitrogen fixation, despite the presence of elevated concentrations of inorganic nitrogen. The organisms that potentially fix nitrogen in sediments have not previously been identified. Amplification of nifH genes with degenerate primers was used to assess the diversity of diazotrophs in two distinct sediment systems, anoxic muds of Chesapeake Bay and shallow surficial sediments of the Neuse River. Phylogenetic analysis revealed that sequences obtained from mid-Chesapeake Bay, which receive high organic loading and are highly reducing, clustered closely with each other and with known anaerobic microorganisms, suggesting a low abundance of aerobic or facultative diazotrophs in these sediments. Sulfate reduction dominates in the surface, but methanogenesis becomes more important with depth. A thin (<1 cm) oxidized layer is present only in the spring. No archaeal nifH sequences were obtained from Chesapeake Bay. Sequences of nifH amplified from surficial sediments of the Neuse River were distant from Chesapeake Bay sequences and included nif phylotypes related to sequences previously reported from marine mats and the Spartina rhizosphere. Differences in environmental site characteristics appear to select for different types of sediment diazotrophs, which is reflected in the phylogenetic composition of amplified nifH sequences.

Reductive dechlorination of 2,4-dichlorophenol and related microbial processes under limiting and non-limiting sulfate concentration in anaerobic mid-Chesapeake Bay sediments

The effects of sulfate, added electron donors, and metabolic inhibitors on reductive dechlorination of 2,4-dichlorophenol (DCP) in anaerobic sediment from a relatively unpolluted site in the mesohaline region of Chesapeake Bay were investigated. The onset of ortho reductive dechlorination of DCP was often rapid in sulfate-depleted sediments and the metabolite, 4-chlorophenol, persisted for >44–60 days at nearly stoichiometric levels, relative to the DCP lost, with no further degradation or dechlorination observed. Dechlorination rates increased by a factor of 6–10 after re-feeding DCP, suggesting enrichment of dechlorinators. Sulfate inhibited reductive dechlorination greatly in fresh sediments, but only partially in aged, methanogenic or DCP-acclimated sediments. Exogenous H 2 stimulated rates of reductive dechlorination in the absence, but not presence of sulfate. Molybdate severely inhibited reductive dechlorination and also significantly inhibited methanogenesis in sulfate-depleted sediments. Direct inhibition of methanogenesis with bromoethane sulfonic acid did not negatively affect dechlorination rates, suggesting that molybdate may have inhibited production of electron donors for methanogenesis and reductive dechlorination. These results demonstrate a potential for rapid dechlorination of DCP in relatively uncontaminated estuarine sediments and reveal confounding effects of a putative ‘specific’ metabolic inhibitor, molybdate.

Reductive dechlorination of 2,4-dichlorophenol and related microbial processes under limiting and non-limiting sulfate concentration in anaerobic mid-Chesapeake Bay sediments

The effects of sulfate, added electron donors, and metabolic inhibitors on reductive dechlorination of 2,4-dichlorophenol (DCP) in anaerobic sediment from a relatively unpolluted site in the mesohaline region of Chesapeake Bay were investigated. The onset of ortho reductive dechlorination of DCP was often rapid in sulfate-depleted sediments and the metabolite, 4-chlorophenol, persisted for >44-60 days at nearly stoichiometric levels, relative to the DCP lost, with no further degradation or dechlorination observed. Dechlorination rates increased by a factor of 6-10 after re-feeding DCP, suggesting enrichment of dechlorinators. Sulfate inhibited reductive dechlorination greatly in fresh sediments, but only partially in aged, methanogenic or DCP-acclimated sediments. Exogenous H2 stimulated rates of reductive dechlorination in the absence, but not presence of sulfate. Molybdate severely inhibited reductive dechlorination and also significantly inhibited methanogenesis in sulfate-depleted sediments. Direct inhibition of methanogenesis with bromoethane sulfonic acid did not negatively affect dechlorination rates, suggesting that molybdate may have inhibited production of electron donors for methanogenesis and reductive dechlorination. These results demonstrate a potential for rapid dechlorination of DCP in relatively uncontaminated estuarine sediments and reveal confounding effects of a putative 'specific' metabolic inhibitor, molybdate.

An Exotic Nematode Parasite of the American Eel

Abstract We investigated reports from commercial fishers of parasitized American eels (Anguilla rostrata) in the Patuxent River (located in the mid-Chesapeake Bay) and discovered that some eels were infected with an exotic swim bladder nematode, Anguillicola crassus. Here, we (1) describe the dispersal of this blood-feeding nematode, endemic to the Japanese eel (A. japonica), in Europe and North America; (2) discuss what is known of the effects of this parasite on eels; (3) summarize current knowledge of the life cycle and identification of this parasite; and (4) present new data on the range of A. crassus in the eastern United States. We examined the swim bladders of 329 American eels from 4 sites in the mid- and upper Chesapeake Bay as well as 150 eels from 4 sites in the Hudson River in New York. Prevalence ranged from 10% to 29% in the Chesapeake Bay and from 0% to 12% in the Hudson River. Maximum intensity of infection was 24 for Chesapeake Bay eels and 3 for Hudson River eels. We urge our U.S and Ca...

Sexual Competition Among Male Blue Crab, Callinectes sapidus.

Experiments and field data on blue crab, Callinectes sapidus, from mid-Chesapeake Bay between 1991 and 1994 were used to test whether large males have advantages over small males in accessing females and in sperm competition. In the field, large males were paired more often, especially with large, more fecund females. However, the variance in the relationship between male and female size in mating pairs was high, suggesting that mating with large females may not be the primary determinant of male reproductive success. Large males had proportionately longer chelipeds, which may provide an advantage in aggressive interactions for females or in struggles to control females. Previous work indicates that sperm competition may occur in blue crabs and that ejaculate size may influence a male's ability to compete during sperm competition. Large males stored more seminal fluid and spermatophores and passed a larger volume of ejaculate to each mate than did small males. Ejaculate volume averaged 47% of a male's stored supply. However, ejaculate volume increased with the duration of copulation but decreased with successive matings, such that males needed about 15 days between matings to pass similar-sized ejaculates to successive mates. Pre-copulatory mate guarding may serve as a time to replenish ejaculate contents, and thus its duration also influences a male's performance in sperm competition.

Onshore-offshore pattern and variability in distribution and abundance of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 138:15-25 (1996) - doi:10.3354/meps138015 Onshore-offshore pattern and variability in distribution and abundance of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay MacGregor JM, Houde ED The pattern and daily variability of kilometer scale, onshore-offshore distributions of bay anchovy Anchoa mitchilli eggs and larvae were determined from 4 d of repetitive sampling on a transect in mid-Chesapeake Bay. The 13 km transect ran from nearshore to the most offshore area of the Bay, passing through a river-plume front. Most spawning by bay anchovy occurred offshore. Eggs and recently hatched larvae were 30 to 200 times more abundant offshore than at inshore and frontal stations. Few eggs and larvae occurred below the pycnocline, where oxygen levels often were too low for survival or normal development. Mean larval lengths and relative (but not absolute) abundances of large (>=5.5 mm standard length) larvae increased in an offshore to inshore direction. Apparent larval mortality rates, which were both size- and area-specific, were highest offshore and higher for small length classes. There was no indication that anchovy eggs or larvae were concentrated in the frontal region, but gelatinous predators and zooplankton suitable as larval prey tended to increase at the front. While significant transport of larvae from offshore to inshore may occur, most larvae of all sizes were offshore, indicating that recruitment of anchovy is most dependent on processes in the offshore region. Bay anchovy . Eggs . Larvae . Onshore-offshore distribution . Mortality rates . Chesapeake Bay Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 138. Publication date: July 25, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Virtual reality of planktivores:a fish's perspective of prey size selection

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 140:271-283 (1996) - doi:10.3354/meps140271 Virtual reality of planktivores: a fish's perspective of prey size selection Luo J, Brandt SB, Klebasko MJ Traditionally, field studies of size selective predation by visual-feeding planktivorous fish compare the size distribution of prey in stomachs to that of zooplankton measured in the field. However, the size frequency of prey perceived by a fish may differ from that measured by researchers using integrative plankton nets. In this study, a mechanistic spatial foraging model was developed to test the hypothesis that size-selective predation by visual-feeding planktivorous fish can arise simply by random encounters with prey. Our model was based on movement of a single predator and a size structured prey population distributed in 3-dimensional space. The model assumed that a predator's encounters with prey was a function of prey size and predator swimming speed. Upon encounter, the predator either selected prey by random choice or the largest apparent size. The size frequency and distance distribution of prey encountered, selected, and captured were estimated using Monte Carlo techniques. The model performance was initially evaluated with hypothetical prey size frequencies, and different light attenuation coefficients, capture efficiencies, visual distances and predator swimming speeds. Simulation results showed that the size frequency of prey encountered randomly by a predator is very different from the size frequency of the ambient prey in the environment. The size frequency of prey selected by random choice only differed from that selected by apparent size choice when visual distance was greater than reactive distance. Prey distance distribution, which was defined as frequency of prey encountered at different distances, showed that as prey density increased predators selected prey at closer distances by the largest apparent size choice than by random choice. We also tested the model specifically for the bay anchovy Anchoa mitchilli. Ambient zooplankton size frequencies found in mid-Chesapeake Bay were used to predict the size frequencies of zooplankton consumed by fish. Predicted prey size frequency in the diet matched the size frequency of zooplankton found in bay anchovy stomachs. We conclude that prey size selection by fish can be described mechanistically by differential random encounter from a fish's perspective, and that behavioral choice plays a minor role in prey size selection. Spatial foraging model · Prey size selection · Visual-feeding planktivore Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 140. Publication date: September 12, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Population biology of bay anchovy Anchoa mitchitli in the mid Chesapeake Bay

Population biology of bay anchovy Anchoa mitchitli in the mid Chesapeake Bay

Bay anchovy Anchoa mitchilli production and consumption in mid-Chesapeake Bay based on a bioenergetics model and acoustic measures of fish abundance

Bay anchovy Anchoa mitchilli production and consumption in mid-Chesapeake Bay based on a bioenergetics model and acoustic measures of fish abundance

Microbial processes affecting alanine and glutamic acid in anoxic marine sediments

Abstract The utilization of glutamic acid and alanine in anoxic marine sediments was studied using sediments collected from a tidal flat on the Atlantic Ocean side of Virginia's Eastern Shore (Bordens-take Bay) and a site in the mid-Chesapeake Bay. At both sites volatile fatty acids (VFAs) were produced as intermediates in the catabolism (or oxidation) of both amino acids. In contrast, methylated amines were not produced as metabolic intermediates from either amino acid. The addition of 20 mM molybdate to sediment slurries (to inhibit bacterial sulfate reduction) led to the continuous production of VFAs from both amino acids, indicating that the majority of this VFA production from these amino acids occurred by fermentative processes. Non-catabolic uptake of these amino acids (presumably into bacterial bio-mass) also appeared to be an important process in removing alanine and glutamic acid from these sediment slurries. A kinetic model used to analyze these data indicated that ∽ 85% of the alanine catabolism occurred by fermentative processes, with remineralization by sulfate reducing bacteria accounting for the difference. In contrast, all of the glutamic acid catabolism appeared to occur by fermentation. Calculations using data on VFA and ΣCO2 production in molybdate inhibited sediments also suggested that acetate and formate were the predominant VFAs produced by the fermentation of alanine, and perhaps glutamic acid as well. The oxidation of dissolved, free amino acids appeared to account for a significant fraction of the ammonium production in these anoxic marine sediments, although amino acids represented less than ∽ 2% of the carbon sources/electron donors used by sulfate reduction. These observations suggest that the general pathway of amino acid utilization in anoxic sediments involves their oxidation by fermentative bacteria to produce compounds such as VFA or H2 which are then themselves used as substrates by either sulfate reducing or methanogenic bacteria. As such, dissolved free amino acids appear to play an important role as intermediates in carbon and nitrogen cycling in these environments.

Spawning, fecundity, hatch-date frequency and young-of-the-year growth of bay anchovy Anchoa mitchilli in mid-Chesapeake Bay

Spawning, fecundity, hatch-date frequency and young-of-the-year growth of bay anchovy Anchoa mitchilli in mid-Chesapeake Bay

The effects of sediment slurrying on microbial processes, and the role of amino acids as substrates for sulfate reduction in anoxic marine sediments

In sediment slurry experiments with anoxic marine sediments collected in Cape Lookout Bight, NC, and a site in mid-Chesapeake Bay, the rates of sulfate reduction and ammonium production decrease with increasing dilution of sediment with oxygen-free sea-water. The effect of sediment dilution on the rates of these processes can be described by a simple mathematical relationship, and when these rates are corrected for sediment dilution they yield values which agree well with direct measurements of these processes. In sediment slurry studies of amino acid utilization in Cape Lookout Bight sediments, the fermentative decarboxylation of glutamic acid (to γ-aminobutyric acid) or aspartic acid (to alanine or β-alanine) did not occur when either of these amino acids were added to Cape Lookout Bight slurries. The addition of glutamic acid did however lead to a small (∼1) transient build-up of β-aminoglutaric acid. Measured rates of glutamic acid uptake in these slurries also decreased with increasing sediment dilution. Molybdate inhibition experiments demonstrated that dissolved free amino acids represent 1–3% of the carbon sources/electron donors used for sulfate reduction in Cape Lookout Bight sediments. The direct oxidation of amino acids by sulfate reducing bacteria also accounts for 13–20% of the total ammonium produced. Glutamic acid, alanine, β-aminoglutaric acid, aspartic acid and asparagine are the major amino acids oxidized by sulfate reducing bacteria in Cape Lookout Bight sediments.