Watershed-scale analysis of pollutant distributions in stormwater management ponds

Stormwater management ponds have become a common Best Management Practice in urban and suburban landscapes. Stormwater management ponds are designed to hold runoff from impervious surfaces and allow the settling of sediments and associated pollutants. Various semi-aquatic and aquatic wildlife species have been documented using stormwater management ponds as habitat, but these wetland-like systems are not managed to adhere to freshwater habitat pollutant guidelines. To address the potential for pollutant exposure for wildlife, we used a random sample of 68 stormwater ponds and estimated the proportion of ponds in a third-order watershed that exceed toxicity guidelines for trace metals and polycyclic aromatic hydrocarbons in sediments and chloride in surface waters. Ninety-six percent of ponds exceeded consensus-based threshold effect concentrations for at least one trace metal. Concentrations of at least one of the PAHs measured exceeded the threshold effects concentration in 63% of the ponds. Nine percent of ponds exceeded chronic toxicity levels of chloride on all sampling dates, and 21% exceeded acute toxicity concentrations on at least one sampling date. More studies are needed to evaluate toxic effects of pollutants in stormwater management ponds and the potential for interactive effects of pollutants on wildlife.