Increasing salinity in developed watersheds can result from changes in the concentration of different ions. Our understanding of the sources and relationships between cation concentrations and microbial communities remains poorly developed. These relationships could help serve as indicators of surface water pollution and changing watershed processes. The objective of this study was to examine the relationship between water chemistry and microbial water quality indicators. We collected weekly grab samples from nine small watersheds in Southwest Virginia. Samples were measured for standard physical and chemical properties: dissolved oxygen, temperature, specific conductance, pH, calcium, magnesium, potassium, chloride, fluoride, sulfate, nitrogen species, phosphorus, and dissolved organic carbon. In addition, three types of microbial fecal indicators were measured: total coliforms, E. coli, and HF183:a human specific genomic marker.
The relationships within and between water chemistry and water quality indicators in these watersheds are complex. Surprisingly, concentrations of traditional biogeochemical elements (N, P, C) were less strongly related to water quality indicators than were Ca, Mg, Na in watersheds. Calcium and magnesium were strongly correlated with total coliforms, r2 = 0.88 and r2 = 0.86 respectively. While potassium is very strongly related to E. coli (r2 = 0.96). Currently, we cannot reasonably explain these relationships by the land use composition or common sources within the landscape. Human specific fecal indicators were not well correlated with other microbial water quality indicators, and yet found ubiquitously across the developed watersheds and most strongly correlated with sodium concentrations (r2 = 0.84). The results suggest that 1) wastewater via subsurface flowpaths may more broadly impact surface water chemistry and quality than expected, and 2) that cation chemistry may influence the microbial community and serve as a background mediator of watershed biogeochemical cycling in cities.