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Fecal Source Characterization of Impaired Urban Streams Impacted by Municipal Stormwater Discharges
Citation:
Shanks, O., A. Diedrich, Mano Sivaganesan, A. Sharifi, AND J. Willis. Fecal Source Characterization of Impaired Urban Streams Impacted by Municipal Stormwater Discharges. ASM Microbe 2022, Washington, DC, June 09 - 13, 2022.
Impact/Purpose:
Polluted urban stormwater is a major cause of surface water impairment in the United States. Under Section 402(p)(3) of the Clean Water Act, permits are required for municipal separate storm sewer system (MS4) discharges in census designated urban areas or in jurisdictions where the population is greater than 100,000. As a result, more than 7,500 local communities are required to develop, implement, and mitigate stormwater management programs with the goal to reduce the discharge of pollutants. In collaboration with the Washington DC Department of Environment and Energy, this study employed advanced host-associated molecular methods to characterize the amount and sources of fecal pollution in urban streams impacted by MS4 discharges. Findings demonstrate the utility of combining microbial source tracking with high-resolution global information system mapping to improve stormwater management. Information covered in this abstract was prepared based on high priority research needs in the EPA Research Action Plan (SSWR Research Area 3, Output #1, Product 1).
Description:
More than 80% of the United States population resides in communities with municipal stormwater systems. These systems are designed to collect, transport, and discharge stormwater from a defined catchment area into local surface waters. Discharges may contain unsafe levels of fecal waste originating from various sources ranging from sewer cross-connections to local wildlife making it challenging to manage potential public health risks, especially in densely populated urban areas. Paired measurements of six water quality parameters (e.g. pH, turbidity, water temperature), 12-hour cumulative precipitation (mm), stream flow (L/min), five land use indicators determined by global information system (GIS) mapping, E. coli (MPN/100ml), and genetic markers (log10 copies per reaction) indicative of human (HF183/BacR287 and HumM2), ruminant (Rum2Bac), canine (DG3), and avian (GFD) fecal sources were assessed in 231 stream samples. Stream samples were collected twice per month (n = 24 sampling days) and after rain events (n = 9) from seven low-order tributaries of the Anacostia River in Washington D.C. over a 12-month period. Almost 50% of stream samples (n = 103) were impaired, exceeding the local E. coli single day maximum regulatory level (410 MPN/100ml). A censored data analysis approach identified several fecal source pollution trends. Canine, ruminant, and avian mean log10 fecal score ratios (FSR) were always significantly elevated after rain events irrespective of catchment (FSR ≥ 0.378). In contrast, human FSR values exhibited variable trends often indicating no significant shift regardless of precipitation amount (95% Bayesian credible intervals include 0). Avian average log10 fecal scores were the only pollutant source with a significant correlation to catchment land use indicators (p ≤ 0.039) suggesting that bird waste accumulates on urban landscapes between rain events and is washed off and discharged into receiving waters during subsequent storms. Overall, findings demonstrate that combining microbial source tracking with high-resolution GIS mapping complements routine E. coli monitoring to improve stormwater management in urban areas.
