By Cheryl A. Silcox, Bret A. Robinson, and Timothy C. Willoughby
Abstract
Water samples collected from 58 surface- water sites in the Kankakee and Lower Wabash River Watersheds from June through September 1999 were analyzed for concentrations of Escherichia coli bacteria. Each site was sampled five times in a 30-day period. Twenty-nine sites were sampled during June and July, and 29 different sites were sampled during August and September. A five-sample geometric mean of concentrations was computed for each site. Concentrations of Escherichia coli (E. coli) in 126 of the 289 samples exceeded the State of Indiana single-sample standard of 235 colonies per 100 milliliters for waters used for recreation. Concentrations in samples from 38 of the 58 sites exceeded the State of Indiana standard for a five-sample geometric mean of 125 colonies per 100 milliliters for waters used for recreation. Ten of the 58 sites were at or near U.S. Geological Survey streamflow-gaging stations. Based on records from the streamflow-gaging stations, 18 percent of the samples collected at these sites were collected at streamflows above the median daily discharge for each station. E. coli concentrations and turbidity measurements collected during 1999 were analyzed in concert with similar concentration and turbidity data collected in 1998 at streams within the Upper Wabash River Watershed in Indiana to investigate the relation between concentrations of bacteria and turbidity. The analysis indicated a statistically significant correlation between concentrations of E. coli and turbidity. If the turbidity was greater than 83 nephelometric turbidity units, the E. coli concentration always exceeded the single-sample standard. If, however, the turbidity was less than 83 nephelometric turbidity units, concentrations of E. coli were not always below the single-sample standard. Introduction The presence of E. coli in water is direct evidence of the presence of fecal contamination from warm-blooded animals and indicates the possible presence of pathogens (Myers and Sylvester, 1997). E. coli is one of the two preferred indicator bacteria used by the U.S. Environmental Protection Agency (USEPA) to determine the suit-ability of surface waters for recreational use. The water-quality standards for E. coli in recreational waters in Indiana require the concentration of E. coli to be less than the single-sample standard of 235 colonies per 100 mL (milliliters) and less than the geometric mean of 125 colonies per 100 mL computed from five samples collected within a 30-day period (Oddi, 1995).
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