Biology
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Item Marsh-ing Through Time: Resolving the temporal and spatial variability of tidal marsh sediment dissolved organic carbon sorption(2021) Morrissette, Hannah; Hood, Raleigh; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal marsh ecosystems are among the most economically and ecologically valuable environments in the world, providing critical ecosystem services and a continuous exchange of carbon between these systems and their surrounding environments. Tidal marshes are an important overall net carbon sink, while simultaneously being a substantial source of dissolved organic carbon (DOC) to estuaries and the coastal ocean. The temporal and spatial variability in these carbon fluxes is large, difficult to measure, and currently considered to be one of the most daunting challenges to carbon exchange quantification. Sorption, despite being known as a dominant DOC exchange process at the sediment-water interface, is still understudied in tidal marsh ecosystems, with exchange kinetics largely unquantified. This research combined observational data with sediment flux modeling to answer a suite of questions addressing sorption speed, its variability, and its impacts to DOC fluxes between sediments and adjacent waters. Sediment flux models must incorporate sorption processes to more accurately simulate DOC fluxes between tidal marsh sediments and adjacent waters. Kinetics of these processes were quantified for the first time through a set of 24 hour sorption laboratory experiments, from which results showed that the majority of sorption processes occur rapidly, within 15 minutes of sediment exposure to water. Sorption rate parameters were determined through a numerical modeling study that simulated the laboratory experiments. These rates were used to parameterize a sediment flux model that included sorption processes formulated with varying degrees of complexity. The sorption kinetics of individual pools of DOC (colored and non-colored) were also measured, revealing that these separate pools sorb quickly but independently of one another, with preferential adsorption of humic colored DOC over time, and preferential desorption of native non-colored DOC over time. Sorption kinetics were also shown to be spatially variable within a marsh site, with adsorption decreasing with sediment depth and distance from the creek edge. This research provided important new information on sorption in tidal marsh sediments that allows these processes to be incorporated into models, which will, ultimately, facilitate efforts to simulate and quantify coastal carbon fluxes.Item TEMPORAL AND SPATIAL VARIABILITY OF METHYLMERCURY ACCUMULATION IN SMALL STREAM ECOSYSTEMS(2018) Oster, Jacob Matthew; Heyes, Andrew; Lapham, Laura L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Maryland has state-wide fish consumption advisories for mercury, and there is a need to explain these trends. I explore two tools for characterizing MeHg conditions in Maryland. The first explores benthic macroinvertebrates as vectors of MeHg from sediments to fish. I examined macroinvertebrate communities over two years from two first-order streams differing in land-use and historical stream water MeHg concentrations. I assessed temporal and spatial variability in invertebrate populations in conjunction with an assessment of the distribution of MeHg in water and sediment. I tested a second tool, an autonomous continuous water sampler that would allow MeHg to be measured without laborious expeditions. I observed differences in concentrations of MeHg across trophic levels between watersheds and identified a candidate organism as a bioindicator of MeHg exposure risk and watershed MeHg condition, as well as a potential sampling mechanism for MeHg in aquatic ecosystems.Item Intact bacterial hopanoids as specific tracers of bacterial carbon in marine and estuarine environments(2009) Taylor, Karen Ann; Harvey, H. Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intact bacteriohopanepolyols (BHPs) and their degrative products were investigated in surface sediments and particulate organic matter from the Bering Sea, Western Arctic Ocean and Chesapeake Bay to trace the inputs of bacterial carbon sources and the dominant microbial processes operative during organic matter recycling. Despite cold temperatures and the dominance of diatoms, cyanobacteria are ubiquitous and inhabit the deeper layers of the euphotic zone in the Bering Sea, where their contributions to sediments were directly traced. As a small but important contribution to the total system chlorophyll, cyanobacteria represent a previously undocumented fraction of the organic carbon pool in this region. In the Western Arctic, soil derived bacterial sources were abundant and include a fraction that likely degraded on land prior to being transported into the Arctic Ocean. Bacterial signatures in Chesapeake Bay transition along the salinity gradient with intact hopanoids reflecting a diverse range of potential bacterial sources.Item Light available to the seagrass Zostera marina when exposed to currents and waves(2009) McKone, Katie Lynn; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquatic organisms are regularly exposed to varying degrees of hydrodynamic forces such as currents and waves. Seagrasses, which are rooted in the sediment, have flexible leaves, allowing them to sway back and forth with waves and deflect with currents. Furthermore, seagrasses can acclimate to local hydrodynamic forces exerted upon them by changing their morphology, which may benefit the organism via reduced drag, but may also bring disadvantages such as increased self-shading. We examined the interaction between water flow and morphology of the seagrass Zostera marina, and how this interaction affects light availability to the plant. We also assessed carbon and nutrient content of Z. marina, as the uptake of these constituents has been linked to hydrodynamic conditions and sediment composition. Our results indicate that local hydrodynamics and sediment composition induce morphological variation in the seagrass Z. marina, and that this variation influences light availability to the seagrass canopy.Item Modeling The Impact Of Sediment Resuspension And Flocculation On The Fate Of Polychlorinated Biphenyls(2008-07-11) Chang, Chihwei Andrew; Baker, Joel E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrophobic organic contaminants (HOCs) are important pollutants in urban estuaries. HOCs include polycyclic aromatic hydrocarbon (PAH), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). Sorption to resuspended particles and sediments plays an important role controlling the water column residence times and spatial distributions of HOC in aquatic environments. Pollutant residence times and the time required to reach sorptive equilibrium are highly dependent on the chemical character, the surrounding environment, and particle types and compositions. If rates of sorption are slow relative to particle residence times, HOC behavior may be described using kinetically-limited partitioning behavior. In this study, a flocculation model that simulates flocculation of activated carbon, organic carbon, and inorganic solids ranging in diameter from 2 to 1000 μm has been developed. A multi-class flocculation-based contaminant fate model is adapted to describe desorption kinetics for contaminants associated with flocculated particles during a resuspension event. The model is effective in predicting transport of hydrophobic organic contaminants among different size flocs, water, and two sediment layers. The model also demonstrates the impact of fractal geometry, bottom shear stress, particle composition, floc size, fraction of organic carbon (fOC), fraction of activated carbon (fAC), organic carbon partition coefficient (KOC), and total suspended solids (TSS) on contaminant desorption rate and residence time. Under different scenarios, this model's results support the importance of multi-floc cluster, sediment-water interaction, and of flocculation for the contaminant desorption rate in the water column. In a floc-rich environment flocculation is an important mechanism redistributing contaminants among flocs. When flocculation is considered in a dynamic particle environment that includes sediment resuspension, settling, and kinetic-limited HOC partitioning, the steady state total PCB concentration in the water column is decreased by 20 % and water column HOC residence time decreased by 36%. When activated carbon is added to contaminated sediments, the total PCB concentration in the water column decreases by 90% (123.4 to 11.4 ng/L). If the activated carbon coagulates with the resuspended sediment, this decrease is partially offset by some activated carbon being entrained in slowly-settling flocs, and the steady-state PCB concentration is 61 ng/L.Item Sediment Biogeochemistry Across the Patuxent River Estuarine Gradient: Geochronology and Fe-S-P Interactions(2007-12-21) OKeefe, Jennifer; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although salinity and redox gradients are defining features of estuarine biogeochemistry, compositional changes in sediment characteristics associated with these factors are poorly described in U.S. coastal plain estuaries. Understanding the basics of nutrient sources and sinks, in the context of these defining characteristics, is required to make efficient and effective management decisions regarding estuarine eutrophication. In this study, detailed analysis of long-term nutrient burial has been used as a tool to understand the trajectory of nutrient cycling at 7 stations along an oligohaline to mesohaline transect in the Patuxent River estuary. Sediment mass accumulation rates were determined for 3 of the 7 sites. Cores analyzed for total P, total N, organic C, biogenic silica, δ13C, and δ15N did not provide evidence of historical nutrient reduction actions taken in this watershed. Burial rates of Fe-S mineral phases and inorganic P (IP) indicated pyrite formation limited the availability of Fe-oxides for adsorption and retention of IP.Item The effect of sea level rise on seagrasses: Is sediment adjacent to retreating marshes suitable for seagrass growth?(2005-12-13) Wicks, Elinor Caroline; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Salt marsh retreat resulting from sea level rise creates new subtidal substrate (old marsh peat) for seagrasses, which is usually unvegetated. The hypothesis that sediment characteristics of old marsh peat are limiting to <em>Zostera marina</em> was tested in Chincoteague Bay, Maryland and in controlled experiments. A unique aspect of the study site is an eroding dune within the marsh that supplies sand to the subtidal. The organic content and sulfide concentrations of old marsh peat were not limiting <em>Z. marina</em> growth and seagrasses were able to colonize the old marsh peat if a layer of sand covered it. The lack of <em>Z. marina<em/> in old marsh peat may be due to a plant morphology that is highly susceptible to dislodgement. These findings suggest that seagrass distribution may be negatively affected by sea level rise as seagrasses may be unable to migrate shoreward due to unsuitable sediments adjacent to retreating marshes.Item PCB Desorption from Resuspended Hudson River Sediment(2005-08-03) Schneider, Abby Ruth; Baker, Joel E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)From the late 1940's until 1977 two General Electric Plants discharged 200,000 - 1.3 million pounds of polychlorinated biphenyls (PCBs) into the upper Hudson River. Field studies and detailed modeling efforts indicate that PCB release from sediments under realistic mixing conditions determines the efficiency of both 'natural recovery' and proposed dredging operations. In this study, Hudson River sediment was resuspended into clean water in large mesocosms. The desorption rates of individual PCB congeners were determined by measuring dissolved PCB concentrations using solid-phase microextraction. Immediately following the initiation of resuspension, large particles with an average median diameter of 140 ± 14 mm were lifted into the water column. Dissolved PCBs rose rapidly and after two hours of resuspension 6 to 38% of the PCBs in the water column were in the dissolved phase. Rate constants for this rapid release ranged from 0.04 to 0.34 hour-1 and decreased significantly as log Kow of the PCBs increased. Both the total suspended solids concentration and dissolved PCBs reached steady state in 24 hours. At steady state the flocs volume median diameter averaged 112 ± 3 mm, porosity averaged 0.90 ± 0.02, and 15-50% of the resuspended PCBs were dissolved. The PCB concentration on resuspended particles was an average of two times greater than the bulk sediment PCB concentration and 8% of the resuspended mass did not settle after twenty hours without mixing. At steady state the particle-water PCB partition coefficients were similar to values measured in the Hudson River and constant across the range of congeners examined. With only one-day quiescence between resuspension events the percent of dissolved PCBs at steady state decreased significantly from the first to the third resuspension event (p = 0.02). When quiescent time was increased to four days, there was no change in the percent dissolved PCBs at steady state for the low molecular weight congeners (Log Kow ≤ 5.85, p = 0.45). This analysis suggests there was a large release of PCBs from particles when they were initially resuspended; however, chronic resuspension resulted in less PCB release per event due to the slow recharge of a labile pool.