Microbial Fecal Indicator Concentrations in Water and Their Correlation to Environmental Parameters in Nine Geographically Diverse Estuaries

Abstract

Fecal contamination of coastal recreational water is a public health concern, which coastal managers monitor using fecal indicator bacteria (FIB). In this study, 20 stations in nine United States (US) estuaries were monitored over three years for FIB (enterococci, fecal coliforms, Escherichia coli, and Clostridium perfringens) and fecal indicator virus (F+ coliphage and somatic coliphage) concentrations in water. Fecal indicator concentrations were significantly correlated with some environmental variables (rainfall, water temperature, salinity, and sample collection time) across all estuaries. Multilinear models utilizing environmental parameters predicted anywhere from 69% (C. perfringens) to 19% (F+ coliphages) of fecal indicator variability. Coliphage equivalence to US Environmental Protection Agency marine water enterococci criteria was estimated with 95% confidence intervals, though these findings should be interpreted with caution because enterococci densities were weakly positively correlated to coliphage densities (R=0.435 somatic coliphages, R=0.367 F+ coliphages). In a comparison of coliphage methods, enrichment (EPA Method 1601) outperformed single agar layer (EPA Method 1602) and membrane filtration. In summary, the relationships among coliphage methods, between fecal indicators, and their interactions with environmental variables represent findings from a geographically diverse set of US estuaries with different fecal waste sources and loads, which suggests these findings are highly generalizable.