The effect of wind speed and direction on the distribution of sewage-associated bacteria

A study of the relationship between wind and the distribution of sewage-ass ociated bacteria was undertaken at a location where the sewage was discharg ed into the sea adjacent to the mouth of a river. The numbers of presumptiv e Escherichia roll cr ere determined in 149 sea-water samples taken from th ree locations at distances of 1.9, 2.4 and 4.3 km from the outfall. On each sampling occasion, data on the wind speed and direction in the 3 h prior t o collection of the samples were also collected. Analysis of these data dem onstrated a significant role for wind speed and direction. With respect to wind direction, the numbers of presumptive E. coli present in a sample were significantly higher when the sample site lay downwind of the outfall. Win d speed was shown to have an influence on the numbers of presumptive E. col i only when the sample site was downwind of the outfall. In an analysis of 61 samples, an inverse correlation (r(2) = 0.73) between salinity and log p resumptive E. coli numbers was demonstrated. These data demonstrate that wi nd speed and direction at the rimu of sampling significantly influence the numbers of presumptive E. coli detected in any sea-water sample. It is argu ed that failure to pay sufficient attention to these parameters in the desi gn of monitoring programmes may result in the generation of data that could provide a seriously distorted picture of the microbiological status of a w ater body.