Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Abstract Only
Publication Acceptance Date: 1/31/2008
Publication Date: 4/1/2008
Citation: Shelton, D.R., Karns, J.S., Sadeghi, A.M., Coppock, C.R., Pachepsky, Y.A. 2008. Evaluation of Microbial Water Quality Indicators in a Forested/Agricultural Watershed. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE). Online: http://asae.frymulti.com/abstract.asp?aid=24306&t=1. Interpretive Summary:
Technical Abstract: Many countries are interested in assessing and improving surface water quality, including decreasing risks to public health from water-borne pathogens. Indicators of fecal contamination such as Escherichia coli are commonly utilized to assess water quality. However, the relationship between indicators and pathogens, and their population dynamics in watersheds are poorly understood. We undertook this monitoring study in a small rural watershed with inputs from wildlife and grazing cattle to evaluate fluctuations in E. coli populations and to assess the use of virulence factors typically associated with pathogenic E. coli as indicators of water quality. Generic E. coli concentrations were substantially higher in agricultural than in forested sites indicative of the much higher fecal inputs from cattle vs. wildlife. High E. coli concentrations found in sediments suggest that these may be relatively stable habitats for E. coli growth/survival and be responsible for some portion of the downstream contamination. A general decrease was observed in E. coli concentrations from summer through fall/winter. This decrease was partially due to decreased wildlife activity and cattle densities. However, an additional factor was likely “flushing” of sediment-borne E. coli caused by high discharge levels (due to high rainfall) beginning in late fall. Virulence factors associated with pathogenic E. coli (O157 serogroup, eae gene, and stx1/2 genes) were prevalent throughout the watershed. However, no definitive conclusions could be drawn regarding the presence/absence of specific pathogenic E. coli strains due to the distribution of virulence factors among other bacteria. No correlation was observed between concentrations of generic E. coli and the eae gene at agricultural sites, suggesting that E. coli data cannot be used to predict the risk of pathogen exposure. Our results illustrate the difficulty in interpreting microbial data and in predicting public health risks.