Microbial source tracking in a coastal residential canal system

Coastal residential canal communities are an important yet overlooked component of global coupled natural and human systems and are acutely vulnerable to anthropogenic pollution. This study monitored water quality in a coastal canal community, with a comprehensive approach that included multiple water quality metrics: nutrient levels, enterococci concentrations, and microbial source tracking. Enterococci were detected in 50.6 % of samples (<10.00 to 175.00 MPN/100 mL), and the human-associated HF183 fecal marker was detected in 10.9 % of samples (<100.00 to 196.67 gene copies/100 mL). Enterococci were strongly associated with wet-weather events, whereas HF183 was slightly lower after wet-weather. The canine-associated DogBact marker (40.91 %; <103.34 to 250.01 gene copies/100 mL) was not significantly affected by wet-weather conditions, although it was elevated in the winter months. The gull-associated LeeSeaGull marker (75.54 %; <36.67 to 495.00 gene copies/100 mL) was prevalent nearly constantly and increased as days preceding rainfall increased. Although enterococci were not correlated with the host-associated markers, enterococci measurements were consistently below the USEPA's marine water quality criteria, indicating a low risk to potential recreators. The MST results generally corroborated these findings, except for one water sample where the combined HF183 and LeeSeaGull marker concentrations were above the recommended risk-based threshold. These results highlight the complex relationship between enterococci and mixed sources of fecal pollution in marine environments, thereby emphasizing the need for holistic water quality monitoring that prioritizes microbial source tracking in addition to traditional fecal indicator bacteria measurements.