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Oxygen uptake rates by fine benthic organic matter were measured on samples from two Appalachian mountain streams to determine the effects of land use patterns on microbial respiration. Both Coweeta Creek in western North Carolina, and Wolf Creek in western Virginia, flow through national forest, agricultural land and scattered residential areas. Seven sites were sampled at six to ten week intervals over one year. Land use was determined using infrared aerial photographs. ARC/INFO was used to obtain land use areas for various land uses. Oxygen uptake rates were measured using a Gilson differential respirometer, at ambient temperature and 20°C. Temperature was the most important factor influencing oxygen uptake rates in both streams, with oxygen uptake rates consistently lower at ambient temperatures than 20°C. Oxygen uptake rates were higher in Wolf Creek than Coweeta Creek and were higher at sites that drained agricultural areas. Nitrates increased as the percent of agriculture increased in Wolf Creek, but not in Coweeta Creek. Nitrates were positively correlated with oxygen uptake / Master of Science

Utilizing field and modeling methodology, the effects of benthic micro-communities and physical transport mechanisms on sediment nutrient flux were investigated for two nearshore sediment types on Virginia’s Eastern Shore. Subtidal sandy mineral sediments were conducive to water transport and subsequently influenced by groundwater discharge to a greater degree than less permeable organic silt-clay sediments. Sediment ammonium and dissolved inorganic phosphorus (DIP) fluxes were strongly dependent on benthic aerobic respiration rates for silt-clay sediments as compared to sandy substrates. In situ studies indicated a significant decrease in ammonium and DIP fluxes as a result of nutrient uptake by benthic microalgal communities. The importance of advective solute transport mechanisms within nearshore sediments was demonstrated by a one-dimensional, steady-state model for a conservative substance. By incorporating dispersive and advective transport mechanisms, model predictability for chloride sediment flux was significantly improved as compared to a diffusion based model. Model results indicated that velocity associated transport of solutes, driven by elevated upland hydraulic heads, are significant and can dominate over diffusive flux in sandy sediment. In contrast, silt-clay sediment solute fluxes were dominated by dispersive processes. The importance of sedimentary nutrient flux in a shallow coastal embayment was demonstrated by short water column DIN and DIP turnover times with respect to sediment nutrient fluxes, by the significance of ammonium and DIP sediment nutrient fluxes with respect to phytoplankton nutrient assimilation demands, and by the relative importance of benthic respiration with respect to water column primary productivity. In order to evaluate water quality impacts of groundwater discharge on a larger scale, a surface, groundwater, and in situ groundwater discharge water quality survey was conducted in a shallow estuarine embayment. Sediment inorganic nitrogen fluxes were elevated adjacent to agricultural fields without benefit of a vegetative buffer. Nitrogen contributions from direct groundwater discharge and groundwater derived creek inputs appear to be of significant importance in terms of water quality and phytoplankton nitrogen assimilation demands. In summary, this study highlights the importance of nearshore sediments with regards to estuarine nutrient water quality and ecological processes. Neglecting groundwater discharge as a nutrient source and transport mechanism and potential biotic effects occurring at the sediment-water interface may lead to serious misinterpretation of data and error in water quality strategies. / Ph. D.