Transfer of Escherichia coli to water from drained and undrained grassland after grazing

The aim of this study was to determine the load of Escherichia coli transferred via drainage waters from drained and undrained pasture following a grazing period. Higher concentrations (ranging between 10(4) and 10(3) colony forming units [CFU] g(-1)) of E. coli persisted in soil for up to 60 d beyond the point where cattle were removed from the plots, but these eventually declined in the early months of spring to concentrations less than 10(2) CFU g(-1). The decline reflects the combined effect of cell depletion from the soil store through both wash-out and die-off of E. coli. No difference (P > 0.05) was observed in E. coli loads exported from drained and undrained plots. Similarly, no difference (P > 0.05) was observed in E. coli concentrations in drainage waters of mole drain flow and overland plus subsurface interflow. Intermittent periods of elevated discharge associated with storm events mobilized E. coli at higher concentrations (e.g., in excess of 400 CFU mL(-1)) than observed during low flow conditions (often < 25 CFU mL(-1)). The combination of high discharge and cell concentrations resulted in the export of E. coli loads from drained and undrained plots exceeding 10(6) CFU L-1 s(-1). The results highlight the potential for drained land to export E. coli loads comparable with those transferred from undrained pasture.