The Influence of Precipitation and Vessel Traffic on the Distribution of Fecal Indicator Bacteria and qPCR Source Tracking Markers Across Coastal Groundwater and Surface Water in Brazoria County, Texas.

AIMS: This study aimed to assess the spatial and categorical variability of fecal contamination across well, pore, and surface waters along the Brazoria County Texas coastline, and to identify environmental and anthropogenic drivers influencing microbial distributions using fecal indicator bacteria (FIB) and microbial source tacking (MST) approaches. METHODS AND RESULTS: A total of 398 water samples were collected from 18 sites between July 2023 and June 2024. Culture-based Enterococcus enumeration and qPCR-based MST markers targeting avian (GFD), canine (DG3), environmental Enterococcus (Entero1a), and human-associated (HF183 & HumanmtND5) sources were analyzed alongside physicochemical parameters, environmental and anthropogenic data. Enterococcus concentrations ranged from <1 to >2419.6 MPN/100mL, with surface waters showing significantly higher contamination than well and pore waters (p < 0.05). Entero1a and GFD were detected in all samples, indicating dominant environmental and avian contributions, while human associated markers were spatially concentrated near the Houston Freeport channel. Correlation and principal component analysis revealed compartment-specific microbial dynamics and demonstrated that precipitation and vessel activity significantly influenced microbial variability in surface waters. CONCLUSIONS: Fecal contamination was strongly structured by hydrological compartment, environmental conditions, and proximity to anthropogenic activity. The combined use of culture-based Enterococcus FIB and qPCR MST markers enhance both quantification and source identification across interconnected water systems.