Stormwater ponds are common features of modern stormwater management practices. Stormwater ponds often retain standing water for extended periods of time, develop vegetative characteristics similar to natural wetlands, and attract wildlife. However, because stormwater ponds are designed to capture pollutants, wildlife that utilize ponds might be exposed to pollutants and suffer toxicological effects. To investigate the toxicity of stormwater pond sediments to Hyla versicolor, an anuran commonly found using retention ponds for breeding, we exposed embryos and larvae to sediments in laboratory microcosms. Exposure to pond sediments reduced survival of embryos by approximately 50% but did not affect larval survival. Larvae exposed to stormwater pond sediment developed significantly faster (x = 39 days compared to 42 days; p = 0.005) and were significantly larger at metamorphosis (x = 0.49 g compared to 0.36 g; p < 0.001) than controls that were exposed to clean sand. Substantial amounts (712-2215 mg/l) of chloride leached from pond sediments into the water column of treatment microcosms; subsequently, survival of embryos was negatively correlated (r (2) = 0.50; p < 0.001) with water conductivity during development. Our results, along with the limited number of other toxicological studies of stormwater ponds, suggest that road salt contributes to the degradation of stormwater pond habitat quality for amphibian reproduction and that future research should focus on understanding interactions among road salts and other pollutants and stressors characteristic of urban environments.
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.
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