Influence of wastewater-treatment effluent on concentrations and fluxes of solutes in the Bush River, South Carolina, during extreme drought conditions

Abstract

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

Urban Influences on Stream Chemistry and Biology in the Big Brushy Creek Watershed, South Carolina

“…However, HCO À 3 and DOC concentrations were higher, rather than lower, downstream of the WWTP during October (data not shown). Low temporal variability in concentrations of many solutes under baseflow conditions at sites upstream of the WWTP is consistent with results of a study of the Bush River, South Carolina (Andersen et al, 2004). The large temporal variation in river chemistry downstream of the WWTP (Figs.…”

“…2 and 4). These effects are consistent with effects of WWTP effluent on river chemistry in the lower piedmont of South Carolina (Andersen et al, 2004). Differences in solute concentrations immediately upstream and downstream of the WWTP in early October generally were consistent with the differences observed during the summer.…”

“…There are many causes of these elevated concentrations. For example, industrial and wastewater treatment plant (WWTP) point sources add significant amounts of solutes, especially nitrate, sulfate, phosphate, chloride, and sodium, to streams (e.g., Andersen, Lewis, & Sargent, 2004;Cameron, Hall, Veizer, & Krouse, 1995;Ceasar et al, 1976;Flintrop et al, 1996;House & Denison, 1997;Jarvie, Whitton, & Neal, 1998;Roy, Gaillardet, & Allegre, 1999). In some urban residential areas, septic tanks and lawn fertilizers may increase phosphate or nitrate concentrations in streams (e.g., La Valle, 1975;Hoare, 1984;Wernick et al, 1998).…”

The impacts of drought on freshwater ecosystems: an Australian perspective

“…All of these changes have served to exacerbate the impacts of natural drought and to delay ecological recovery from drought. While the effects of low flow and water extraction in drought-affected rivers can be offset partly by industrial and sewage wastewater discharges into the rivers, the hydrologic benefits may be compromised by declines in water quality (Andersen et al, 2004;Aravinthan, 2005). Rather bizarrely in some systems, such as the Murray River in southeastern Australia, in times of natural low flow or even drought, large volumes of water may be delivered to downstream irrigators, generating 'anti-droughts' (Boulton, 2003;McMahon & Finlayson, 2003).…”

Patterns in the linkage of water quantity and quality during low‐flows

“…This equation implies a lower dilution during low‐flow provided that the chemical load a [G/T] and background concentration b [G/L 3 ] do not change. A general dilution effect was found for a variety of other water quality parameters (Andersen, Lewis, & Sargent, ; Nosrati, ; Sprague, ). In contrast, Golladay and Battle () found lower concentrations for ammonium, dissolved organic carbon, and dissolved inorganic carbon during low‐flow.…”