Spatial and temporal dynamics of E. coli in streamwater, sediments and rock biofilm

Most studies address the dynamics of Escherichia coli (E. coli) in streamwater during storms, while baseflow conditions in streambed environments have received less attention. Specifically, few explored how E. coli is distributed across biofilms and sediment size fractions. Thus, the objective of this study was to quantify the distribution of E. coli in streamwater, biofilm, and sediment fractions, and to determine how these niches influence spatiotemporal variations in E. coli concentration in a highland Mediterranean stream. E. coli dynamics across streamwater, rock biofilms, and size-fractionated sediments (<75, 75–300, and 300–2000 μm) were measured over 12 months across five sites along the Meshushim Stream, Israel. E. coli concentrations in streamwater ranged between 1 and 1.4 × 10 4 MPN 100 ml −1 . E. coli concentration increased significantly during the warm season (May-September) and was significantly correlated with temperature and, to a lesser extent, with total suspended solids. While streamwater E. coli concentrations fluctuated seasonally, the concentrations of E. coli associated with biofilms (250–1.4 × 10 5 MPN m −2 ) and sediment (40–5.4 × 10 3 MPN g −1 SDW) reservoirs did not have a temporal trend. E. coli was found attached to the finest sediment fractions, yielding concentrations that are 50 times higher than those in the coarsest material. These findings suggest that fine sediments serve as an important habitat for E. coli under both high-flow and baseflow conditions. During high flows, E. coli is often transported bound to particles that resuspend in the water, whereas during baseflow, fine-sediment reservoirs may influence stream-water dynamics even without substantial resuspension.