Stream channel properties and their effect on the release of Escherichia coli from bottom sediment

Escherichia coli (E. coli) is the standard fecal indicator bacteria used to monitor water quality in rivers, particularly around recreational areas. Recent research indicates that while agricultural and urban wastewater runoff remains the dominant source of E. coli to rivers, there is growing evidence to suggest that the disturbance-induced resuspension of E. coli from bottom sediments contributes significantly to microbial contaminant levels in the water column. This research was focused on the question, “How does the resuspension of E. coli from bottom sediments contribute to the overall microbiological impairment of the Rivanna River and its tributaries?” Sediment cores were collected from 14 sites throughout the Rivanna watershed in Central Virginia and analyzed for their E. coli concentration, organic matter content, and particle size. Linear regressions were used to identify any significant relationship between E. coli concentrations in the water column, derived from existing data gathered by the Rivanna Conservation Alliance between 2018 and 2022, and sediment E. coli concentrations. Relationships between stream channel properties and subwatershed land use with the observed water column and sediment E. coli concentrations were also explored. A significant finding of this study was the relationship between sediment E. coli concentrations and water column concentrations at a turbidity level of 5 NTU (p=0.025), indicating a potential link between E. coli supply in sediment and E. coli transport during periods of high flow. Sediment E. coli concentrations were not significantly related to any of the factors considered, although it was concluded that texture is more predictive of microbial levels than subwatershed land use practices. This study offers insight into the physical mechanisms affecting the persistence and prevalence of E. coli in recreational areas, thereby improving public health initiatives aimed at identifying sources of water quality impairment.