A Comparison of Escherichia Coli Levels in the Chattahoochee River Between Drought and Non-drought Years
Dalman, Nancy Eufemia
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The Chattahoochee River in northeastern Georgia is a popular summer recreational site. The section of the river that flows through the city of Helen, about eighty miles northeast of Atlanta, is visited by thousands of swimmers and “tubers” each year. Studies have been conducted in drought and non-drought years on Escherichia coli levels in the water before and after peak recreational use. Recreational river use may lead to increased levels of bacteria suspended in the water due to sediment disruption and subsequent dispersal of bacteria contained in the soil. Water samples were taken from five recreational sites in town and five secluded, nonrecreational sites in the Chattahoochee National Forest. Samples were collected on days known to have the highest volume of recreational users, from late June to mid- September. Sites were sampled in the morning and evening, before and after peak recreational use, respectively. E. coli levels were quantified using the Colilert® Quanti – tray® 2000 system (IDEXX), and the results from 2009 (a non-drought year) were compared with those from 2007 (a drought year). E. coli levels were significantly higher at recreational sites than nonrecreational sites for both years. Though 2009 sampling exhibited higher E. coli levels than 2007 overall, 2009 sites showed no significant difference between morning and evening samples. In 2007, however, E. coli levels were higher after peak recreational use. Furthermore, evening sampling at recreational sites revealed a correlation between suspended sediments and water-borne E. coli levels in 2007, but not in 2009. This dissimilarity between drought and non-drought years suggests that sediment bacteria, in drought years, are more dispersed in the water due to the lower water volume, and increased disruption of the sediment. These results indicate that users of the Chattahoochee River are exposed to higher water-borne E. coli levels during the summers of drought years.