Sources, drivers, and impacts of fecal pollution in coastal Texas

Fecal pollution in marine environments is a leading cause of water impairment in the United States. Millions of waterborne infections occur annually as a result of this pollution, contributing to a multibillion-dollar economic burden. The purpose of this dissertation was to investigate the sources, drivers, and impacts of fecal pollution in the northwestern Gulf of Mexico. This was accomplished by conducting targeted water quality studies in Corpus Christi Bay and Little Bay, Texas, followed by a comprehensive, long-term study of water quality across coastal Texas. Water quality was assessed through a combination of the following methods: quantification of enterococci, measurement of three host-associated fecal markers, characterization of antimicrobial resistance profiles in Enterococcus isolates, and analysis of the microbial community composition. Overall, in each of the three independent studies, enterococci frequently exceeded the United States Environmental Protection Agency (USEPA) beach action value. Rainfall often acted as a driver of enterococci, particularly in Corpus Christi Bay, where the mean enterococci concentration after rainfall was nearly 40 times higher than the USEPA beach action value. However, rainfall did not influence the levels of enterococci in Little Bay; rather, enterococci concentrations decreased along the estuarine ecocline, with the highest concentrations detected downstream of a local wastewater treatment plant (WWTP). Regardless of location (i.e., Corpus Christi Bay or Little Bay), enterococci were not correlated with human, canine, or gull fecal pollution markers. In Corpus Christi, elevated levels of the human fecal marker were detected throughout the study, although the concentration of this marker decreased after rainfall, likely due to a dilution effect from rainfall-induced freshwater inflows. In contrast, rainfall acted as a significant driver of human fecal waste in Little Bay. In addition to influencing fecal bacteria levels, rainfall also acted as a pulse disturbance and altered the microbial diversity in both systems. In terms of long-term water quality trends, enterococci were significantly correlated with population size and sea level throughout coastal Texas. The strongest associations were observed in counties that are currently experiencing rapid population growth and are acutely vulnerable to future sea level rise. Taken together, these findings highlight the dynamic nature of water quality and demonstrate the need for independent and location-specific water quality analyses throughout coastal Texas. Given current and projected rates of population growth and sea level rise, efforts to mitigate and manage coastal water quality should be directed towards the most vulnerable locations, including Harris, Matagorda, and Brazoria Counties. Further, given the lack of correlation between enterococci and human fecal pollution, future water quality assessments should incorporate additional indicators, such as molecular markers of human-associated fecal pollution and assessments of microbial community composition.