Effects of Fecal Source Input, Environmental Conditions, and Environmental Sources on Enterococci Concentrations in a Coastal Ecosystem

Fecal pollution at coastal beaches in the Northeast, USA requires management efforts to address public health and economic concerns. Concentrations of fecal-borne bacteria are influenced by different fecal sources, environmental conditions, and ecosystem reservoirs, making their public health significance convoluted. In this study, we sought to delineate the influences of these factors on enterococci concentrations in southern Maine coastal recreational waters. Weekly water samples and water quality measurements were conducted at freshwater, estuarine, and marine beach sites from June through September 2016. Samples were analyzed for total and particle-associated enterococci concentrations, total suspended solids, and microbial source tracking markers for multiple sources. Water, soil, sediment, and marine sediment samples were also subjected to 16S rRNA sequencing and SourceTracker analysis to determine the influence from these environmental reservoirs on water sample microbial communities. Enterococci and particle-associated enterococci concentrations were elevated in freshwater, but suspended solids concentrations were relatively similar. Mammal fecal contamination was significantly elevated in the estuary, with human and bird fecal contaminant levels similar between sites. A partial least squares regression model indicated particle-associated enterococci and mammal marker concentrations had the most significant positive relationships with enterococci concentrations across marine, estuary, and freshwater environments. Freshwater microbial communities were significantly influenced by underlying sediment while estuarine/marine beach communities were influenced by freshwater, high tide height, and estuarine sediment. We found elevated enterococci levels are reflective of a combination of increased fecal source input, environmental sources, and environmental conditions, highlighting the need for encompassing MST approaches for managing water quality issues. IMPORTANCE Enterococci have long been the federal standard in determining water quality at estuarine and marine environments. Although enterococci are highly abundant in the fecal tracts of many animals they are not exclusive to that environment and can persist and grow outside of fecal tracts. This presents a management problem for areas that are largely impaired by non-point source contamination, as fecal sources might not be the root cause of contamination. This study employed different microbial source tracking methods to delineate influences from fecal source input, environmental sources, and environmental conditions to determine which combination of variables are influencing enterococci concentrations in recreational waters at a historically impaired coastal town. Results showed that fecal source input, environmental sources and conditions all play a role in influencing enterococci concentrations. This highlights the need to include an encompassing microbial source tracking approach to assess the effects of all important variables on enterococci concentrations.