Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Sediment connectivity between the lower Susquehanna River and upper Chesapeake Bay(2019) Russ, Emily; Palinkas, Cindy; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Excess fine sediment is one of the main pollutants contributing to water quality degradation in the upper Chesapeake Bay. Recent management efforts have focused on reducing sediment inputs within the Bay watershed to achieve water quality standards set in the Chesapeake Bay Total Maximum Daily Load (TMDL). However, the models used to develop the TMDL did not account for the evolving sediment loads to and storage in the Bay, which include reduced sediment capacity in the Conowingo Reservoir, the last reservoir on the Susquehanna River, increased shoreline protection measures, and resurgence of SAV in the upper Bay in a region known as the Susquehanna Flats. The overall goal of this dissertation is to assess the current sediment dynamics of the upper Bay and specifically evaluate the connectivity of sediment transport from the Susquehanna River through the Flats into the upper Bay. First, I evaluated sedimentation on the Susquehanna Flats over seasonal to decadal time scales using radioisotopes within the context of submersed aquatic vegetation (SAV) biomass and geomorphology. Seasonal-scale sedimentation variability was related to river discharge, sediment supply, and geometry over the SAV bed, while decadal-scale sedimentation was influenced by flood events and changes in SAV biomass abundance. Next, I analyzed sediment geochemical patterns in the upper Bay using statistical analyses. Elements associated with aluminosilicate minerals, rare earth elements, and heavy metals explained the most variability in the dataset due to changes in grain size, salinity, and anthropogenic input, respectively. A sediment-provenance analysis was performed using the sediment-geochemistry data and indicated that the Susquehanna is the dominant source of fine-grained material throughout the upper Bay. Finally, I developed an updated sediment budget through quantitative analysis of sediment sources (Susquehanna River and shoreline erosion) and sinks (Susquehanna Flats and mainstem sediment-accumulation rates). Conservation-management practices have reduced Susquehanna River sediment loads at low flows, but sediment loads at high flows have increased, consistent with a decreasing scour threshold for bottom sediments in Conowingo Reservoir as it has filled. Increases in shoreline stabilization have reduced shoreline erosion inputs.Item Impact of breakwaters on sediment characteristics and submerged aquatic vegetation(2011) Barth, Nicole; Palinkas, Cindy M; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examined the impact of breakwaters, with varying ages (1-19 y) and in 3 salinity regions of Chesapeake Bay, on sediment characteristics and submerged aquatic vegetation (SAV). Sediment and SAV characterisitcs were determined at an adjacent-exposed and a breakwater-protected site in 24 locations. A mesocosm experiment was also conducted to evaluate SAV response to 4 organic-content treatments for 3 SAV species (Ruppia maritima, Vallisneria americana, and Zannichellia palustris). Breakwater effects on sedimentation were site-specific, some sites, having no apparent affect, while others where sandy shoreline erosion was dominant, an increase in grain size and sedimentation rate was observed. At other sites breakwaters facilitated fine-sediment deposition. SAV responses in the mesocosms, were highly variable with organic content. Therefore, SAV biomass in breakwater-protected area was related to the amount and type of sediments that the breakwater retained. Site evaluations should be conducted before breakwater construction if SAV colonization is desired.Item NITROGEN CYCLING AND CONTROLS ON DENITRIFICATION IN MESOHALINE SEDIMENTS OF CHESAPEAKE BAY(2009) Owens, Michael Sean; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nitrogen is a key nutrient in the eutrophication of coastal and estuarine systems. In shallow water systems, sediment recycling can be an important source of nutrients for phytoplankton growth. The balance between nitrogen recycling and denitrification regulates the importance of sediments as a nitrogen source. To assess controls on denitrification, we conducted intensive seasonal measurements of sediment water exchange and denitrification using sediment core incubations. Peak rates of denitrification were observed in fall and spring (>100 μmol N-N m-2 h) followed by a decrease to 10 μmol N m-2 h in summer. Although denitrification rates were stimulated by labile organic carbon additions from the water column, the overall efficiency of the process sharply declined as temperature increased and bottom water O2 declined. Macrofauna activity was shown to enhance sediment transport of O2 by >5 fold, increase organic matter decomposition and maintain a high rate of denitrification efficiency.