Hydrological and anthropogenic associations with fecal contamination in coastal pore and surface waters: a one-year FIB and MST study of the Brazoria County, Texas coast.

Coastal recreational waters face increasing fecal contamination from poorly defined sources, yet most monitoring relies on fecal indicator bacteria (FIB) that cannot identify pollution origins. This study evaluated microbial water quality at 12 sites (six pore water, six surface water) along the Brazoria County, Texas coastline from July 2024 to June 2025, combining culturable enterococci with a general fecal marker (Entero1a) and two human-associated markers (HF183 and HumanmtND5), and integrating physicochemical parameters, precipitation, and Houston Freeport vessel-arrival data. Culturable enterococci were detected in 94% of pore and 100% of surface samples, with significantly higher concentrations in surface waters. Using the 104 MPN/100 mL marine recreational criterion as a reference benchmark, 58.1% of surface water samples exceeded this value compared with 10.4% of pore water samples. Marker concentrations differed significantly between water categories for all three assays. Among sites, pore waters showed no significant differences for any microbial parameter, whereas surface sites differed significantly in culturable enterococci and Entero1a, driven by elevated concentrations at S12 and S14.Spearman correlations among culturable enterococci, the three qPCR markers, physicochemical parameters and nitrogen species were stronger and more frequent in surface waters than pore waters. Principal component analysis placed 24-h and 7-day cumulative rainfall on the same component axes as the human-associated HF183 marker in both compartments, and vessel arrivals loaded together with HF183 and HumanmtND5 at surface sites nearest the Houston Freeport channel. Non-metric multidimensional scaling produced weak and largely non-significant ordination structure, indicating that the measured environmental conditions were relatively homogeneous across sites. Collectively, surface waters exhibited episodic microbial responses that co-varied with rainfall and vessel activity, whereas both compartments showed weak multivariate structure. Because the marker panel did not include non-human host-associated assays, these findings identify human-associated and hydrologically mediated pathways as detectable contributors rather than as the dominant sources of the observed contamination, and underscore the need for intensified, source-targeted coastal monitoring.