Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item MODELING POTENTIAL HABITAT OF CHESAPEAKE BAY LIVING RESOURCES(2012) Schlenger, Adam James; North, Elizabeth; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quantitative understanding is needed to identify the impacts of climate change and eutrophication on the habitat of living resources so that effective management can be applied. A systematic literature review was conducted to obtain the physiological tolerances to temperature, salinity, and dissolved oxygen for a suite of Chesapeake Bay species. Information obtained was used to define required and optimal habitat conditions for use in a habitat volume model. Quality matrices were developed in order to quantify the level of confidence for each parameter. Simulations from a coupled oxygen and hydrodynamic model of the Chesapeake Bay were used to estimate habitat volumes of juvenile sturgeon (Acipenser oxyrinchus) and to assess sensitivity of habitat to environmental factors. Temperature and salinity define spring and fall habitat and a combination of salinity, temperature and dissolved oxygen influence habitat in summer. Both fixed criteria and bioenergetics habitat volume models yielded similar results.Item Downscaled Climate Change Forecasting and Maryland's Forests(2011) Juchs, Stephanie; McIntosh, Marla S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Effective planning and management of forests in a changing climate requires valid and robust predictions of future climate change that are context-specific since climate changes vary by region. Climate models are often used to predict future trends in temperature and precipitation at the global level, but are most useful if downscaled to predict change at regional levels. Monthly temperature and precipitation were predicted using three downscaled regional climate models for the 1990s and the 2050s. Comparison of the 1990's predictions to weather station data from across Maryland indicated inherent model biases affecting accurate predictions, which were used to adjust the model-projected climate variables for the 2050s. The projected daily temperatures were also used to calculate projected growing degree days and frost days. The degree of climate change in Maryland projected by these regional models for the next half-century would have profound impacts on forests across Maryland.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.