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Naturally high total dissolved solids and upstream agricultural runoff often mask the influence of urban land cover on stream chemistry and biology. We examined the influence of headwater urbanization on the water chemistry, microbiology, and fish communities of the Big Brushy Creek watershed, a 96 km 2 drainage basin in the piedmont of South Carolina, USA. Concentrations of most major anions and cations (especially nitrate, sulfate, chloride, sodium, potassium, and calcium) were highest in the urban headwaters and decreased downstream. Generally, the highest concentrations of suspended coliform bacteria occurred in the urban headwaters. In contrast, stream habitat quality and the abundance, species richness, and species diversity of fishes did not differ significantly between urban and rural sites. Discharge of wastewater treatment plant effluent at one rural location caused an increase in concentrations of many solutes and possibly the abundance of benthic algae. We hypothesize that atmospheric dry deposition and domestic animal wastes are important sources of stream solutes and of coliform bacteria, respectively, in the urban headwaters. The lack of significant differences in fish abundance and diversity between urban and rural sites may indicate that urban development in the Big Brushy Creek watershed has not yet degraded habitat conditions greatly for stream fishes. Alternatively, agriculture or other land uses may have degraded stream habitat quality throughout the watershed prior to urbanization.

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

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