Bacterial Stressors: What Value Should Be Given to Stormwater Bmps Such As Retention Ponds and Constructed Wetlands During Tmdl Development
Abstract:Research has shown stormwater runoff from urban areas can have high concentrations of microbial indicator organisms. Stormwater best management practices (BMPs) are often considered effective tools to mitigate the affects of urbanization on receiving waters. Microbial indicator organism make up the greatest number of reported receiving water impairments, resulting in many questions on the fate of indicator bacteria passing through stormwater BMPs. The U. S. EPA's, Office of Research and Development investigated the processes occurring within two commonly used BMPs, constructed wetlands and retention ponds. This research focused on creating pilot-scale systems to determine the environmental mechanisms that affect effluent indicator bacteria concentrations and to provide better information for the prediction of bacterial indicators for models when developing and meeting Total Maximum Daily Loads (TMDLs). Research results indicate water temperature, light, and a combination of other environmental factors influence bacteria indicator concentrations. Results from this research suggest that both constructed wetlands and retention ponds lower microbial concentrations in urban stormwater runoff. Bacteria inactivation generally followed the first-order, KC* model which includes irreducible or background concentrations of a stressor. Indeed, sediment analyses indicated bacteria can accumulate and could have the potential to be reintroduced by turbulent flow or lack of maintenance within these BMPs. Developing microbial inactivation models to predict effluent concentrations from constructed wetlands and retention ponds will aid in reducing the uncertainty and add to the accuracy of surface water quality models in determining bacterial TMDL allocations. First-order models that do not consider irreducible concentrations may underestimate actual bacterial concentrations. The relationship between turbidity and bacteria suggests stormwater management practices that substantially reduce turbidity may also provide the greatest improvement in reducing concentrations of bacteria in stormwater runoff.
Document Type: Research Article
Publication date: October 1, 2007
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