GENETIC DIVERSITY OF ESCHERICHIA COLI IN SOILS AND SEDIMENTS OF AN AGRICULTURAL WATERSHED AND THEIR SPATIOTEMPORAL INFLUENCES ON WATER QUALITY

Abstract

In a series of field and watershed scale studies, the genetic diversity of Escherichia coli in secondary habitats (e.g. soils and sediments) of an agricultural watershed was assessed in order to examine the dynamics of E. coli inhabiting these matrices and to determine their contribution to waterborne populations. Using replicated field plots, persistent subpopulations of E. coli were observed to be significantly affected by hillslope position due to inherent differences in soil texture and moisture content. The dynamics of E. coli populating tile drainage effluent in a working cultivated field were monitored and it was observed that putatively naturalized E. coli dominated the effluent after approximately 55 days following manure amendments. The contribution of tile drainage effluents to the waterborne E. coli population in an adjacent stream was exponentially related to tile discharge rates, regardless of whether the effluent was populated by manure-associated or naturalized E. coli strains. Streambed E. coli populations differed according to stream geomorphological features, with strains responding to sediment texture and water velocity distributions among the features. In a temporal study of sediment E. coli, population turnover was observed to be affected by sediment redistribution in highenergy stream reaches and was stabilized by immigration from adjacent catchment sources in low-energy stream reaches. Reach-specific connectivity between sediment and waterborne E. coli populations was observed in this watershed. Reach- and catchmentscale hyporheic processes are speculated to be occurring, which may be in part influenced by strain-dependent attachment behaviour of E. coli strains in disjoint stream reaches influenced by different catchment sources of E. coli. The attachment of waterborne E. coli to suspended particles was observed to be associated with land use, water quality and suspended particle variables. The relationship of land use type to particle attachment reinforces the hypothesis that strain-specificity in attachment behaviour can affect the transport of E. coli in fluvial systems. This work provides evidence that putatively naturalized strains in cultivated fields can contribute a large part to waterborne E. coli, and that reach-specific hydrological factors need to be considered when relating sediment- to waterborne E. coli in fluvial systems.