Assessing Relationships Between Water Quality, Precipitation, Land Cover and Stormwater Conveyance Type Across a Range of Sub-Watersheds in the Southeastern Coastal Zone

The expansion of urban land use/cover along the coast may degrade water quality by introducing a plethora of pollutants and pathogens that negatively impact human and ecological health. It is hypothesized that anthropogenic contaminants associated with stormwater runoff increase with increasing urban density and vary with the timing and magnitude of rainfall. In this study, we examined land use/cover change and relationships between Escherichia coli (E. coli), turbidity, nutrients, and the timing and magnitude of rainfall in two different types of stormwater conveyances (ditches and ponds) within Murrells Inlet, SC during the summer of 2023. Our results indicate there has been a 12.5% increase in impervious surface coverage from 1996-2016 in the Murrells Inlet study area. Levels of E. coli generally exceeded state regulatory standards, with ponds having significantly lower E. coli and phosphorus and significantly higher nitrogen concentrations than ditch sites (p < 0.001), supporting the efficacy of ponds in retaining particle associated pollutants. Percent impervious surface relationships with E. coli and nutrient concentrations were more complicated and differed between pond and ditch sites. There were no large-scale patterns between precipitation timing and magnitude with water quality indicators. However, event scale measurements suggest that precipitation contributes to poor water quality in ditch sites. These results underscore the need for targeted best management practices to mitigate further water quality degradation in Murrells Inlet, emphasizing the importance of controlling impervious surface expansion and improving stormwater management systems.