UMD Theses and Dissertations

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Subject: search.filters.subject.Patuxent River

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Now showing 1 - 4 of 4
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    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.
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    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.
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    Factors Regulating Variability in Water Quality and Net Biogeochemical Fluxes in the Patuxent River Estuary
    (2006-08-10) Testa, Jeremy Mark; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Net biogeochemical production and transport rates for several variables were computed for the Patuxent River estuary from 1985 to 2003 using a box model. Monthly rate estimates were analyzed for temporal patterns and variability in response to climatic factors and nutrient management. The middle estuary was the most productive estuarine region and was characterized by strong pelagic-benthic coupling. Phytoplankton biomass in this region peaked in spring as fueled by seaward nutrient inputs. Nutrients regenerated from decomposition of this spring bloom were required to support summer productivity. Improvements of sewage treatment in the watershed resulted in declining point source nutrient loads to the estuary, but water quality did not improve in the mesohaline estuary. Poor water quality in the middle estuary was maintained by persistent non-point nutrient loads, while degrading water quality in the lower estuary correlated with increasing DIN inputs from Chesapeake Bay, high river flow, and declining herbivorous grazing.
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    ICHTHYOPLANKTON COMMUNITY STRUCTURE AND FEEDING ECOLOGY IN THE PATUXENT RIVER ESTUARINE TRANSITION ZONE
    (2004-08-02) Campfield, Patrick Anthony; Houde, Edward D.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Surveys were conducted during spring-early summer of 2000 and 2001 to investigate the spatiotemporal structure of ichthyoplankton assemblages, including hatchery-released American shad <i>Alosa<i> <i>sapidissima<i>, and feeding of larval fishes in the Patuxent River, Chesapeake Bay. Ichthyoplankton, zooplankton, and hydrographic data were collected across the Patuxent's estuarine transition zone, including the salt front and Estuarine Turbidity Maximum region. Recaptured American shad larvae cohort mortality (<i>M<i> = 0.20 to 3.01d<sup>-1</sup>) and growth (<i>G<i> = -1.28 to 0.87 mmd<sup>-1</sup>), low dispersal (±0.4kmd<sup>-1</sup>), and feeding habits similar to co-occurring species, suggest that the best production will result from larval shad releases upriver of the salt front in early to mid-May. Two ichthyoplankton assemblages were distinguished: 1) riverine characterized by anadromous species and 2) estuarine characterized by naked goby <i>Gobiosoma<i> <i>bosc<i>. Temperature, dissolved oxygen, salinity-associated variables (e.g., salt-front location), and the larval prey <i>Bosmina<i> <i>longirostris<i> (Cladocera) concentrations were indicators of larval abundance. Abundance, taxonomic diversity, and dietary overlap and potential for competition among larval taxa were highest within and up-estuary of the salt front of the estuarine transition zone.