Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

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 give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    EVALUATION OF THE INFLUENCE OF NITROGEN ON PRIMARY PRODUCTION USING RETROSPECTIVE DATA, REGRESSION ANALYSIS, AND MODELING
    (2012) Ziombra, Katherine Elizabeth Davis; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Anthropogenic activities have negatively affected water quality in the Chesapeake Bay and its tributaries. The Potomac River (PR), the largest tributary, is a primary study site for water quality research and new management strategies. The Blue Plains Wastewater Treatment Plant (BP), located in the tidal fresh portion of the PR, is the largest total nitrogen (TN) point source. Retrospective examination of water quality data for the PR revealed relationships among discharge, N loading and concentration, light and primary production. Regression analysis revealed BP (TN) load was an important variable influencing production, coupled with local dissolved inorganic nitrogen concentrations and photic depth prior to installation of biological nutrient removal (BNR) at BP. After 100% BNR implementation, BP TN did not influence production. Four existing primary production models were evaluated for applicability to tidal fresh systems. Regression analysis demonstrated all models were significant but the BZpI0t model provided the most robust results.
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    Community Metabolism and Energy Transfer in the Chesapeake Bay Turbidity Maximum in 2007 and 2008
    (2010) Lee, Dong-Yoon; Hood, Raleigh R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The estuarine turbidity maximum (ETM) is a zone of elevated organic matter concentrations and it is an important habitat for bacteria, zooplankton, and early-life-stages of fish. In an effort to identify the key mechanisms controlling production, we measured plankton community metabolism on a series of high-resolution spatial surveys in the upper Chesapeake Bay. The spatial patterns of metabolism revealed the highest primary production and community respiration rates downstream of the ETM region, and net heterotrophy in winter and spring. Also, strong correlations between plankton community metabolism and phytoplankton pigment concentrations, including chlorophyll-a and dinoflagellate indicating pigment peridinin, were observed. These correlations suggest that mixotrophic dinoflagellates were key organisms linking detrital and algal organic matter to higher trophic levels. It is hypothesized that the physiological advantages of mixotrophic dinoflagellates (i.e., autotrophic, heterotrophic) combined with the physical conditions in the ETM which enhance the quantity and quality of organic matter give rise to the high secondary production in the upper Chesapeake Bay.
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    Effect of pH on phytoplankton and bacteria production
    (2009) Johns, Desmond Justine; Stoecker, Diane K; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In recent decades eutrophication has fueled intense phytoplankton blooms that frequently negatively impact ecosystems. Dramatic pH elevations are commonly overlooked during such blooms, which may also be harmful. Cyanobacteria blooms in the Sassafras River, MD were sampled during Autumn 2008 and measured for primary and bacterial production (PP and BP), and differences in bacteria communities composition were examined. pH elevations above 8.8 in the field corresponded to decreased PP, but had no effect on BP. Laboratory experiments demonstrated that negative effects of pH were dependant on light intensity; PP increased with pH at moderate light intensities, but decreased at low irradiance. There was some evidence that BP is affected by high pH, although bacteria community differences as determined by DGGE were not. Negative effects of high pH are probably most important during spring and summer in low salinity environments when pH fluctuations are more common and last longer.