Theses and Dissertations from UMD
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Item BAHAMIAN OOLITIC ARAGONITE SAND IMPACT ON WATER QUALITY AND MITIGATION OF PHOSPHATE AND PHOSPHORUS REMOVAL AND RECOVERY IN RECIRCULATION AQUACULTURE SYSTEMS(2021) Rodgers, Steven R; Place, Allen R; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recirculating aquaculture systems (RAS) require management of water conditions to ensure animal health and limit nutrient discharges. Oolitic aragonite sand (OAS) forms from whiting events off the coast of the Bahamian Islands is a sustainable, renewable and effective in controlling water quality. Cyanobacteria mediate the precipitation of aragonite by capturing CO2, internally forming CO32-, which reacts with Ca2+ in seawater forming CaCO3 precipitations. Studies in freshwater, brackish and marine waters maintained stable pH and alkalinities. Initially, OAS removed phosphate rapidly, slowing afterwards. The OAS removed phosphate at rates of 716, 705 and 215 mg PO4/ kg OAS for freshwater, brackish and marine water, respectively. A system with daily P additions showed a removal capacity of 77.8 mg P /kg OAS. Treatment of phosphorus exposed OAS with 1.0% and 2.0% citric acid solutions show phosphate removals ranging from 17.3% to 93.5%. The citric acid increases the OAS surface area 1.66 times to 4.628 m2/g OAS, confirmed by SEM. Microbiome analysis show similar bacterial phyla exist on the naïve OAS and the OAS used in different salinities. Under anaerobic conditions, the control of system conditions were favorable for denitrification and anammox processes to occur. In freshwater, a loss of 215.8 gram of nitrogen (a loss of 90.5%) of the added nitrogen to the system occurred. In marine conditions, a loss of 253.04 g nitrogen, representing an 87.6% loss, occurred. Microbiome analysis identified phyla known to function as denitrifiers, though lacking known phyla for anammox bacteria. Losses of nitrogen in both salinities is likely due to denitrification, as oppose to anammox. OAS in RAS holding Eastern and Pacific oysters, showed dissimilar responses. The water quality remained in acceptable ranges for oyster growth. The survival in Eastern oysters (≥80%) contrasted with the Pacific oysters (≤56%). Weight increases occurred only with the Eastern oysters. Both species shows increases in shell length, width and height, but unchanged or decreases in weight. Reduced somatic growth and limited shell development occurred, perhaps due stresses from nitrogen spikes in the systems. OAS shows no positive advantage with oyster growth.Item Understanding Urban Stormwater Denitrification in Bioretention Internal Water Storage Zones(2016) Igielski, Sara Jasmine; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Free-draining bioretention systems commonly demonstrate poor nitrate removal. In this study, column tests verified the necessity of a permanently saturated zone to target nitrate removal via denitrification. Experiments determined a first-order denitrification rate constant of 0.0011 min-1 specific to Willow Oak woodchip media. A 2.6-day retention time reduced 3.0 mgN/L to below 0.05 mg-N/L. During simulated storm events, hydraulic retention time may be used as a predictive measurement of nitrate fate and removal. A minimum 4.0 hour retention time was necessary for in-storm denitrification defined by a minimum 20% nitrate removal. Additional environmental parameters, e.g., pH, temperature, oxidation-reduction potential, and dissolved oxygen, affect denitrification rate and response, but macroscale measurements may not be an accurate depiction of denitrifying biofilm conditions. A simple model was developed to predict annual bioretention nitrate performance. Novel bioretention design should incorporate bowl storage and large subsurface denitrifying zones to maximize treatment volume and contact time.Item THE DISTRIBUTION AND FUNCTION OF DENITRIFICATION GENES: EXPLORING AGRICULTURAL MANAGEMENT AND SOIL CHEMICAL IMPLICATIONS(2016) Bowen, Holly; Yarwood, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Denitrification is a microbially-mediated process that converts nitrate (NO3-) to dinitrogen (N2) gas and has implications for soil fertility, climate change, and water quality. Using PCR, qPCR, and T-RFLP, the effects of environmental drivers and land management on the abundance and composition of functional genes were investigated. Environmental variables affecting gene abundance were soil type, soil depth, nitrogen concentrations, soil moisture, and pH, although each gene was unique in its spatial distribution and controlling factors. The inclusion of microbial variables, specifically genotype and gene abundance, improved denitrification models and highlights the benefit of including microbial data in modeling denitrification. Along with some evidence of niche selection, I show that nirS is a good predictor of denitrification enzyme activity (DEA) and N2O:N2 ratio, especially in alkaline and wetland soils. nirK was correlated to N2O production and became a stronger predictor of DEA in acidic soils, indicating that nirK and nirS are not ecologically redundant.Item Denitrification, N2O emissions, and nutrient export in Maryland coastal plain streams(2014) Gardner, John Robert; Fisher, Thomas R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Small streams are hotspots for denitrification, emissions of a potent greenhouse gas nitrous oxide (N2O), and are also highly connected to their watersheds via groundwater flowpaths. In-stream, reach scale denitrification and N2O production as well as biogenic nitrogen gases delivered by groundwater were investigated in one small agriculturally impacted watershed. Groundwater was an important source of biogenic N2, but most N2O was produced in-stream and emissions were relatively high. In addition, agricultural streams significantly contribute to nutrient loading and degradation of downstream aquatic ecosystems. Export and transport mechanisms of nitrogen and phosphorus were investigated during base and stormflow in three watersheds with varying amounts of agricultural and forested land use. Quickflow, which is associated with storms, transported most of the phosphorus and ammonium in the agricultural watersheds, but quickflow had little impact on nutrient concentrations and export in the forested watershed.Item The Impact of Agricultural Wetland Restoration on Adjacent Temporary and Perennial Streams(2013) McDonough, Owen Thomas; Palmer, Margaret A; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wetlands are known for the ecosystem services they provide, including hydrologic storage, sediment retention, nutrient processing, habitat provision, and carbon sequestration. Since European settlement, however, it is estimated that > 50% of wetlands within the conterminous United States have been lost, with a majority of loss attributed to drainage of freshwater wetlands for agriculture. In efforts to offset loss and restore ecosystem services, agricultural wetland restoration has become common. How wetland restoration impacts adjacent stream ecosystem structure and function, however, is poorly understood. Additionally, many freshwater wetlands have historically been considered geographically isolated and disconnected from adjacent surface waters. Recent U.S. Supreme Court rulings have called into question the jurisdictional status of so-called isolated wetlands and non-perennial streams, making investigation of wetland-stream connectivity particularly critical. Comparing native forested, historical (i.e., prior-converted cropland), and hydrologically restored freshwater wetlands within the headwaters of the Choptank River watershed (Delmarva Peninsula, Maryland, USA), I examined the impact of agricultural wetland restoration on within-wetland structure and function and influences on adjacent temporary and perennial streams. In Chapter 1, I present evidence that recently restored wetland soils, although similar to historical wetland soils in physicochemical properties and denitrification potential, may be sediment and nutrient sinks. Chapter 2 shows that so-called isolated Delmarva bay wetlands may in fact be intimately linked to perennial stream networks via temporary stream flow and that land use influences connectivity. In Chapter 3, I investigate the role of temporary stream sediment drying and wetting on denitrification potential in restored and forested wetland-stream pairs and find that alterations in flow regime, a likely outcome of both land use change and climate change, may alter the capacity of temporary streams to denitrify. Chapter 4 considers the impact of cultivation on perennial stream dissolved organic matter (DOM) quantity and quality, and suggests agricultural wetland restoration may be a tool to recover more natural fluvial DOM. Results from this research suggest geographically isolated wetlands may be both hydrologically and ecologically linked to adjacent temporary and perennial streams and that cultivation and subsequent restoration of historical wetlands exerts strong influence on these connections.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.Item Whole stream nitrogen uptake and denitrification in a restored stream of the Chesapeake Bay(2007-08-10) Klocker, Carolyn Ann; Kaushal, Sujay S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Little is currently known about the effects of stream restoration practices on in-stream processing and nitrogen removal. This study quantified nitrate retention in a survey of two restored and two unrestored streams in Baltimore, MD using unenriched nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length was significantly correlated to surface water velocity, which was lowest in restored streams. In situ denitrification rates in Minbank Run were 153 mg NO3--N m-2 d-1, and approximately 40% of the daily load of nitrate could be removed over a distance of 220.5 m. Stream restoration projects that decrease water velocity and increase residence time may lead to considerable rates of nitrate removal through denitrification.Item The effect of benthic microalgal photosynthetic oxygen production on nitrogen fluxes across the sediment-water interface in a shallow, sub-tropical estuary(2005-08-15) Burton Evans, Jessica Landis; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Benthic microalgae (BMA) are a highly productive component of benthic ecosystems. BMA production and nitrogen fluxes were examined in four sub-basins of Florida Bay, in both seagrass and seagrass-free patches, as well as seasonally in a persistent seagrass-free patch in eastern Florida Bay. BMA biomass and oxygen production was highest in seagrass-free sediments with little seasonal variability. Despite high porewater NH4+ concentrations there was little NH4+ efflux. As in temperate estuaries, sub-tropical BMA production and N-assimilation act as a filter to prevent the release of nutrients to the water column. Microelectrode measurements revealed that BMA production causes a doubling of the depth to which O2 penetrates, increasing suitable conditions for nitrification and coupled denitrification. However, the presence of H2S in surface sediments can inhibit nitrification, and there is little nitrogen removal from Florida Bay by denitrification. As a result, BMA N-assimilation is an important nutrient sink in this oligotrophic estuary.