Nitrogen pollution of stormwater ponds: Potential for toxic effects on amphibian embryos and larvae

Runoff from impervious surfaces associated with areas of residential, commercial and industrial development is commonly managed through the construction of stormwater ponds that are designed to slow runoff and reduce pollutant inputs to streams. It has been suggested that stormwater ponds may also provide habitat for wildlife. However, wildlife attracted to ponds may be exposed to pollutants entering ponds in runoff. To assess the potential toxicity of nitrogen pollution of stormwater ponds to pond-breeding amphibians we monitored nitrogen levels in waters of eleven ponds in Baltimore County, Maryland. Levels of NH 3 , NO − 2 and NO − 3 exceeded lowest sublethal effects concentrations reported in the literature in <2% of the water samples collected, and when relatively high concentrations did occur they were restricted to only a portion of the pond. Water sampling during and following rain events also indicated little input of nitrogen to stormwater ponds through runoff. While the number of amphibians recorded at ponds varied from three to six species, there was no relationship between nitrogen levels and amphibian occurrence at ponds. Overall, nitrogen pollution of stormwater ponds in our study area appears to represent little or no direct risk to developing embryos and larvae of pond-breeding amphibians, although indirect effects and interaction of inorganic nitrogen with other pollutants warrant further investigation.