Water Quality Dynamics in Response to Rainfall along an Estuarine Ecocline

Stormwater runoff is an important nonpoint source of fecal pollution in coastal environments. In anticipation of future coastal urbanization and altered weather patterns, it is increasingly important to understand the impact of rainfall; therefore, the purpose of this study was to determine how rainfall impacts water quality along an estuarine ecocline in the northwestern Gulf of Mexico (GOM). Decreasing levels of enterococci were detected along the ecocline from land to sea, with the highest concentrations measured immediately downstream of a wastewater treatment plant (WWTP). Human-, canine-, and gull-associated markers were detected consistently throughout the study, but they were not correlated with enterococci and they did not experience a significant trend along the ecocline. Antecedent rainfall was associated with significant changes in bacterial community structure and increased human marker concentrations. These results question the utility of enterococci as a fecal pollution indicator in the northwestern GOM and suggest that increased rainfall frequency or intensity could negatively impact water quality in this region. Taken together, these results clearly demonstrate the need for a data-based approach to water quality management that incorporates modern water quality indicators such as host-associated markers and microbial community composition.