UMD Theses and Dissertations
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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 Examination of a GIS-Based Water Quality Model using USGS Gaged Watersheds in Maryland(2007-06-13) Shivers, Dorianne E.; Moglen, Glenn E; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Water quality models are important tools used by the Maryland Department of the Environment (MDE) in developing Total Maximum Daily Loads (TMDLs), which serve as water quality standards. The MDE tool, which spatially interpolates output from the Chesapeake Bay Program Watershed Model (WSM), is often used because it requires little time, data, or training. In contrast, the WSM requires extensive time, data, and training to run. This study examines if the MDE tool provides accurate estimates of pollutant loads and whether the mid-level complexity model AVGWLF provides comparatively more accurate estimates. The accuracy of the models was assessed based on qualitative comparisons, t-tests, and Nash-Sutcliffe coefficients. The MDE tool was found to more accurately predict total nitrogen and total sediment loads and the AVGWLF model was found to more accurately predict total phosphorus loads. The study also found that a consistent method for calculating observed loads needs to be developed.Item Quantifying Fine Sediment Sources in the Northeast Branch of the Anacostia River, Maryland, Using Trace Elements and Radionuclides(2006-12-11) Devereux, Olivia Harcourt; Needelman, Brian A; Prestegaard, Karen L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fine sediment sources were characterized in an urban watershed, the Northeast Branch of the Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible sediment sources and suspended sediment collected at the watershed outlet during storm events. Methodology for selecting tracers was developed so the sediment fingerprinting method could effectively determine the relative quantity of sediment contributed by each source to the suspended fraction. The amount of enrichment of trace elements in sediment sources and suspended sediment was determined by calculating enrichment ratios, which are ratios of the normalized concentration of elements in the sample relative to their average normalized concentration in the Earth's upper continental crust. Streambanks contributed the highest relative quantity of sediment in the fall and spring while upland areas contributed mostly during winter. Street residue contributed 12% on average and was the source most concentrated in anthropogenically enriched elements.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 Characterization and Mobilization of Arsenic in Various Contaminated Materials(2005-08-03) Peterson, Michael Clayton; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Arsenic is a potentially toxic contaminant of concern even at relatively low concentrations in the environment. The complex chemistry of arsenic in the environment is influenced by a variety of chemical and physical factors. The presence of iron minerals is believed to be particularly important to arsenic mobility. Extraction methods were used to evaluate arsenic and iron in a variety of contaminated materials including mine tailings and soils. The contaminated materials were also evaluated for arsenic mobilization in batch experiments while pH and redox potential were monitored. A relationship between arsenic and iron was observed to occur in most, but not all, of the arsenic-contaminated samples. The most mobile fractions of arsenic were shown to be highly correlated with a simulated human oral bioavailable extraction method in the samples evaluated. The mobilization of arsenic by the simulated bioavailable extraction method was associated with a negligible mobilization of iron.