Urban stormwater runoff significantly alters the stream water quality and biointegrity. Best management practices (BMPs) are commonly used to mitigate the impacts of urban stormwater runoff. The objective of this study was to examine the effects of wet and dry ponds, two commonly used BMPs, on urban stream water quality and biological quality, with a focus on benthic macroinvertebrates - the most commonly used group of organisms in stream bioassessment. Twenty first and second order streams located in the Piedmont ecoregion of northern Virginia which receive drainage from moderately to highly developed urban subwatersheds were sampled. The subwatersheds fell into two categories: (a) with a mixture of wet and dry ponds (14 streams), (b) with no wet and dry ponds (6 streams). Also sampled as reference sites were 6 streams from a nearby and otherwise comparable forested watershed located in the same ecoregion. Grab water samples were collected to determine the following water quality parameters: total suspended solid (TSS) and concentrations of nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), soluble reactive phosphorus (SRP), and total phosphorus (TP). Macroinvertebrates were sampled from one riffle and one run at each site using a modified single-habitat approach of the US Environmental Protection Agency’s Rapid Bioassessment Protocols.
Results/Conclusions
Streams draining watershed with no BMPs showed higher TSS (6.0±0.3 mg/L; Mean±SE) than streams draining watershed with BMPs (5.1±0.4 mg/L) and reference sites (3.2±0.6 mg/L). In addition, concentrations of NO3-N and SRP were lower in streams draining watershed with BMPs (NO3-N, 0.39±0.04 mg/L; SRP, 0.016±0.005 mg/L) and reference sites (NO3–N, 0.38±0.04 mg/L; SRP, 0.009±0.004 mg/L) as compared to streams draining watershed with no BMPs (NO3-N, 0.84±0.27 mg/L; SRP, 0.058±0.029 mg/L), although there were no significant differences in NH4-N and TP concentrations among these streams. Currently, analysis of macroinvertebrate data is being performed to evaluate differences among streams. The outcome of this study will help clarify the efficacy of urban BMPs in mitigating stressors in urban runoff and have important implications for urban stormwater management.
