Variability of Escherichia coli Concentrations in Rivers during Base-Flow Conditions in NZ

We compared the variability of E. coli concentrations in baseflow of 3 different-sized rivers in both summer and winter at the time scales of minutes, hours, and days, to variability from laboratory replication of the measurement methods. Estimates of variability, analysed using the coefficient of variation (CV), were approximately 32% and 60% at hourly and daily time scales. There is strong evidence that both time scale (p < 0.001) and river (p < 0.001) significantly affect the variation in E. coli concentrations. This variability should be considered when interpreting the results from a one-off grab sample used to compare against water quality standards or for calibrating models.