Evaluating the Impacts of Wastewater on Aquatic Biota in the Red River Basin

Abstract

The capture and reuse of wastewater is a promising strategy for increasing water availability, but the environmental benefits and costs are poorly quantified. In water-limited river basins, wastewater outfalls are an important component of stream flows and may buffer ecosystems from drought. How does wastewater influence the biodiversity of fish and macroinvertebrate communities? We investigated two competing hypotheses. First, we hypothesized that if wastewater flows buffer aquatic communities from drought, then measures of biodiversity should be higher at sampling sites near wastewater outfalls than at sites not near wastewater outfalls. On the other hand, if wastewater outfalls negatively impact water quality or homogenize flow regime, then measures of biodiversity may be lower at sites near wastewater outfalls. To test these competing hypotheses, we calculated a suite of biodiversity indices at 320 biological sampling sites in the Red River basin and analyzed for significant differences in communities based on proximity to wastewater outfalls. We found that wastewater outfalls had varied impacts on biodiversity in fish and macroinvertebrate communities, and in most cases the effects were not significant. Findings from this study could be used to provide insight to management decisions on wastewater reuse initiatives in beneficial subbasins while minimizing harmful ecological impacts.