The primary objective of this study was to determine the salinity effect on nutrient release and the denitrification rate in a sediment-water system. To accomplish this objective, bench-scale microcosm studies of York River sediments and Occoquan Reservoir sediments were conducted. Seawater and freshwater were mixed in various ratios to simulate seasonal, salinity-varying environments in the Chesapeake Bay and its tributary estuaries. Experiments were conducted under aerobic, anaerobic, and anoxic conditions. The results showed that high salinity can cause flocculation of particles and result in lower concentration of phosphate under aerobic conditions, but the flocculation effect was not obvious under anaerobic conditions. The release of ammonia was governed by the salinity; the increasing salinity accelerated the release of ammonia by ion exchange. The denitrification rate under anoxic conditions in the system was not influenced by the salinity. / Master of Science

This study examined the consequences of the opening and operation of a new highway north of Richmond, Virginia with respect to contamination of the aquatic environment with heavy metals (Zn, Cd, and Pb), and the effects of these metals on the biota of roadside streams. Sixteen sites located on six small, soft-water streams that were crossed by the highway, encompassing six reference sites located upstream of the highway, six sites located directly at the highway, and four sites located downstream of the highway, were sampled over a two and a half year period, allowing both spatial and temporal analyses. Traffic densities on the highway averaged about 12,000 vehicles per day (vpd). Significant increases in the metals concentrations of sediment, benthic invertebrates, fish whole-bodies, and fish tissues (liver, kidney, and bone) were noted over the course of the study, although the increase varied in magnitude, and were not always consistent. Sediment metals concentrations followed a dynamic plateau. Fish whole-body concentrations of Cd and Pb increased steadily over the course of the study. Spot-sampling for the same parameters along another nearby, more heavily traveled highway (50,000 vpd) indicated that increases in metals concentrations in the different ecosystem components at the study streams would have been greater had there been more traffic. A number of biotic parameters were investigated to determine whether metals contamination was affecting the biological integrity of the study sites. These were: benthic macroinvertebrate diversity and density; the percentage of the aquatic insect community that was composed of chironomids; and fish community diversity, density, and biomass. Only benthos density, the percent chironomids, and fish species diversity showed changes that could be related to metals contamination. Indications from spot sampling along the more heavily traveled highway were that if more contamination had been experienced, more biotic parameters would have been disturbed, and to a larger extent. Fish community structure analyses using the Pinkham-Pearson coefficient of similarity indicated that fish community structure became increasingly altered at highway sites, and to a lesser degree downstream sites, over the study period. / Ph. D. / incomplete_metadata