Temporal variability of Escherichia coli concentrations in surface and subsurface water systems impacted by agricultural activities

Escherichia coli (E. coli) concentrations are known to be temporally variable between consecutive water samples. Temporal variability of E. coli was studied by monitoring E. coli concentrations from two subsurface drainage systems (383 samples) and two surface water systems (825 samples). Two methods of bacterial analysis were used (Membrane filtration (MF) and Most Probable Numbers (MPN)). The MF E. coli concentrations were consistently higher than the MPN data at concentrations < 50 CFU 100 mL-1. Therefore, the remaining samples (968) were analyzed using only the MF technique. Extreme variability was present and measured by the coefficient of variation (CV). E. coli concentrations frequently exceeded Canadian guidelines (200 E. coli CFU 100 mL-1). E. coli decay constants (k) were determined and used to predict E. coli concentrations. Predicting E. coli concentrations that are temporally variable is difficult, as the concentrations do not always follow an exponential decrease.