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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 119-122 in Total Maximum Daily Load (TMDL) Environmental Regulations–II Proceedings of the 8-12 November 2003 Conference (Albuquerque, New Mexico USA), Publication Date 8 November 2003.  .(doi:10.13031/2013.15546)
Authors:   D.S. Fisher and A.L. Dillard
Keywords:   animal wastes, bacteria, fecal coliform, lakes, microbial, ponds, water quality

The Upper Oconee watershed of Georgia is typical of the Piedmont and water quality is a key issue in the urbanization of this historically agricultural region. Fecal indicators may be found in higher numbers than regulatory targets and agricultural non-point sources are sometimes implicated. We enumerated E. coli and enterococci bacteria at 18 sites for 3 years (2200 observations) within the Upper Oconee watershed of Georgia in the Southern Piedmont of the USA. Contributing areas ranged from 1,500 to 40,000 ha. Even though both E. coli and enterococci are both used as fecal indicator organisms they were not highly correlated. High numbers of enterococci relative to E. coli may indicate wildlife sources. Cumulative distributions provided a means of comparing various regulatory threshold levels and the percentage of observations below the threshold. With the E. coli data pooled, approximately 25% of the samples were below 200 MPN/100 ml, approximately 68% were below 550 MPN/100 ml, and at 1000 MPN/100 ml only 82% of the samples had lower estimates. With the enterococci data, 38% of the samples were below 200 MPN/100 ml, 72% were below 550 MPN/100 ml, and approximately 82% of the samples were below 1000 MPN/100 ml. The two assays had similar distributions but enterococci numbers were more frequently (38% vs. 25%) below an MPN of 200 /100ml than E. coli. Both assays indicate contamination but lack of correlation may be related to source and viability in the watershed.

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