Microbial Source Tracking of a Stormwater Detention Basin Overlying the Edwards Aquifer Recharge Zone, San Antonio, Texas

The Edwards Aquifer is the primary water resource for over 2 million people in Texas and faces serious challenges including fecal contamination of water recharging the aquifer. Fecal contamination enters hydrologic systems via failing septic systems, wastewater treatment plant effluent, and livestock waste facilities, among other sources. Effectiveness of best management practices (BMPs) such as detention basins in protecting water quality remains poorly understood. Fecal source identification is therefore crucial for implementation of BMPs that can mitigate pollution. Microbial source tracking (MST) has proven valuable in identifying contamination sources. For this study, the inlet and outlet of a detention basin overlying the aquifer's recharge zone were sampled following storm events using automated samplers. Quantitative polymerase chain reaction and IDEXX methods were used to quantify occurrence of MST markers and fecal coliform bacteria in collected water samples. Markers included those associated with E. coli (EC23S857), Enterococcus (Entero1), humans (HF183), canines (BacCan), and birds (GFD). Fecal coliforms, EC23S857, and Entero1 were detected following each storm event. GFD was the most frequent host-associated marker detected (91% of samples), followed by BacCan (46%), and HF183 (17%). Wilcoxon signed rank tests indicated significantly lower outlet concentrations for fecal coliforms, EC23S857, and Entero1, but not for HF183, GFD, and BacCan. Higher GFD and BacCan outlet concentrations may be due to factors independent of basin design, such as the non-point source nature of bird fecal contamination and domestic dog care practices in neighborhoods contributing to the basin. Mann-Whitney tests showed marker concentrations were not significantly higher during instances of E. coli water quality standard exceedance and that fecal coliform concentrations were not significantly different based on marker detection. Results suggest management efforts should focus on dog and bird-associated fecal pollution. Future work will investigate additional basins in the Edwards Aquifer Recharge Zone with varying land use regimes.