UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item QUANTIFYING NITROGEN REMOVAL POTENTIAL OF BOTTOM CAGE (C. VIRGINICA) AQUACULTURE(2022) Shenoy, Stefenie; Harris, Lora A; Testa, Jeremy M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While management strategies for human-caused nutrient pollution have improved over the last decade, eutrophication and its ecological effects remain primary concerns in many coastal marine systems. In-water nutrient removal techniques are being explored for potential use as a management strategy, including oyster aquaculture operations. Where abundant, oysters have been shown to exhibit denitrifying potential beyond that which is assimilated into shell and tissue biomass. While nitrogen cycling dynamics are well studied and modeled on natural and restored reefs, equivalent processes within oyster aquaculture operations are less defined. This study adapts an existing mechanistic model of oyster filtration, biodeposition, and particle transport to capture the influence of an aquaculture farm on local sediment-water chemical fluxes. Modifications included (1) revising the spatial domain to represent an array of bottom cages, and (2) integrating an existing bioenergetics module to mechanistically couple simulated seston removal from the water column via filtration and subsequent biodeposition by simulating oyster growth. Model simulations included a variety of oyster densities, farm sizes, natural reef, and no oyster scenarios. Two seasonal sampling campaigns of a bottom cage aquaculture site provided model forcing and validation data. Model output revealed complex relationships among oyster density and distribution, farm size, oyster growth and biodeposition. The estimated rates of net nitrogen removal suggest increased potential for oyster aquaculture operations to receive credits above what is currently being realized, and the calculations of such removal for management purposes should consider lease-specific configurations and environmental parameters.Item Methane Dynamics in Marine Systems(2015) Gelesh, Lauren; Lapham, Laura; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Laboratory and field experiments were performed to investigate methane (CH4) in marine systems. Laboratory experiments explored the impact of aerobic CH4 oxidizing bacteria on the dissolution process of CH4 hydrate. The pure culture, Methylomicrobium album, grew at high pressure (34 atm), but not at low temperature (15°C). Hydrate was formed in media containing culture, but was not stable to perform dissolution experiments. The culture used was found to be unsuitable for hydrate dissolution experiments. Field experiments were performed in the Chesapeake Bay estuary, where CH4 concentrations were measured in bottom water and sediment pore-water. Results showed that bottom water CH4 concentrations increased to 40μM in mid-July, which coincided with decreasing oxygen concentrations and decreasing CH4 concentrations, which coincided with increasing oxygen concentrations in the fall. These observations supported the hypothesis that estuarine emissions of CH4 are being enhanced by seasonal hypoxia and that estuarine CH4 emissions may be currently underestimated.Item Geomorphic, hydraulic, and biogeochemical controls on nitrate retention in tidal freshwater marshes(2012) Seldomridge, Emily; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are ideal sites for nitrate retention because of their position within the landscape (near the head of tide); they receive water, discharge, nutrients (N and P), and sediment loads directly from contributing watersheds. Nitrate retention (the difference between nitrate inputs and outputs in an ecosystem), however, is difficult to predict due to the complex interactions between flow processes and the multiple retention processes. The goal of the study was to evaluate both external and internal controls on nitrate retention, and to determine whether scaling procedures could be identified to estimate nitrate retention for an entire ecosystem. The external controls included temperature, dissolved oxygen concentrations, and incoming nitrate concentrations. Internal controls are the interactions among geomorphic, hydrologic, and biological systems within individual marshes that influence nitrate retention. This study was conducted in the upper Patuxent River Estuary where the ecosystem is composed of hundreds of individual marshes that are connected to the estuary through tidal inlets; marsh inlet geomorphology governs water and nitrate fluxes into the marshes. This study therefore took a mass balance approach to determine geomorphic, hydrologic, and biological influences on nitrate retention. Nitrate retention was measured over a 4-year period in three tidal freshwater wetlands, selected to represent a range of marsh sizes. An examination of the mass balance data suggest that nitrate retention is an outcome of complex interactions among inlet geomorphic characteristics, hydrologic flux, and biogeochemical processes. In cases where nitrate concentrations and temperatures are greater than critical (limiting) values, an emergent behavior in which nitrate retention is a simple function of water volume is observed. The wetland ecosystem is composed of numerous, small wetlands that process a small percentage of total nitrate; approximately 50% of retention is processed by the large marshes that comprise only 4% of the total population, but over 80% of the marsh area; therefore, any processes that affect tidal water volumes in large marshes is likely to affect net nitrate retention. The growth of vegetation in these large channels reduced ecosystem nitrate retention.