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As the human population in the piedmont of South Carolina grows, the release of treated effluents from wastewater-treatment plants (WWTPs) will increasingly affect the chemical composition and biogeochemical processes of the region's rivers. We examined the impact of WWTP effluent on the solute chemistry of one such river, the Bush River, South Carolina, which experienced extremely low flow during the drought of 1998–2002. Two WWTPs discharge into the river and accounted for at least 70% of the river flow during the summer of 2002. The response of river solute concentrations to discharge from the downstream WWTP followed the expected dilution pattern. In contrast, the response to discharge from the upstream WWTP only followed the expected pattern for nonnutrient solutes (e.g., chloride and sodium). Concentrations of total dissolved nitrogen, nitrate, phosphate, and sulfate were all far below those expected from simple mixing calculations. At downstream sampling localities, however, conservative ions such as chloride and sodium had concentrations well below those predicted by mixing calculations. Instream biological processes associated with very low flow conditions, such as denitrification and sulfate reduction, may have caused the observed decrease in some nutrients. The cause of the discrepancy between the observed and predicted concentrations of conservative solutes remains unclear. Fluxes of solutes were much higher below the downstream WWTP. Our results indicate that the treated effluents of WWTPs have a significant impact on the biogeochemistry of piedmont rivers during drought periods. The impact is particularly large in rivers with small discharges. Extreme low flow conditions, however, may actually increase the opportunity for biological activity to remove dissolved nutrients from river water.
C. Brannon Andersen is an associate professor of earth and environmental sciences and associate director of the River Basins Research Initiative at Furman University. His main research interests focus on biogeochemical processes controlling the aqueous chemistry of rivers and the impact of urbanization on the water quality of rivers in the piedmont of the eastern United States.Gregory P. Lewis is an assistant professor of biology at Furman University. He has broad interests in watershed biogeochemistry and linkages between terrestrial and aquatic ecosystems. He has conducted research on influences of forest insect defoliations, forest species composition, wetlands, and man-made impoundments on the nutrient chemistry of streams and rivers in the eastern United States.
Kenneth A. Sargent is a professor of earth and environmental sciences and director of the River Basins Research Initiative at Furman University. His main research interests focus on the hydrologyand geochemistry of watersheds, particular those undergoing rapid urbanization, and the transport of sediment in urbanized systems.