Escherichia coli and fecal coliform export rates in two agricultural watersheds of the U.S. Midwest

• Published in: Proceedings of the Indiana Academy of Science Vol. 118; no. 1; pp. 13 - 21
• Main Authors: Vidon, P, Campbell, M.A, Soyeux, E
• Format: Journal Article
• Language: English
• Published: Indiana Academy of Science 09.07.2009
• Subjects: Distribution; Enterobacter; Enterobacteriaceae; Escherichia coli; Freshwater; Methods; Watershed management; United States; USA, Indiana
• ISSN: 0073-6767; 2380-7717

The development of sound regulatory standards for fecal bacterial contamination in streams requires the determination of bacterial export rates at the watershed scale. This study reports Escherichia coli (E. coli) and fecal coliform bacteria export rate dynamics for two agricultural watersheds in till landscapes of the U.S. midwest. Bacteria concentrations in streams were lowest during the December-February period and were not significantly correlated (P > 0.05) to discharge, suggesting that discharge was not a good indicator of bacteria concentration in the study watersheds. Annual E. coli and fecal coliform export rates were similar between watersheds and varied between 4.60 x 10 super(+12) MPN/km super(2)/yr and 6.56 x 10 super(+12) MPN/km super(2)/yr for E. coli and between 2.56 x 10 super(+14) MPN/km super(2)/yr and 3.33 x 10 super(+14) MPN/km super(2)/yr for fecal coliform (MPN = most probable number). Although discharge was poorly correlated to bacteria concentration, annual E. coli and fecal coliform exports were dominated by a few precipitation events during which high flow and high bacteria concentrations occurred simultaneously. In both watersheds, 90% and 50% of annual E. coli exports occurred in approximately 16% and 2% of the time, respectively. Similarly, 90% and 50% of annual fecal coliform exports occurred in approximately 18% and 2-2.5% of the time in both watersheds. Considering the importance of some high flow events on annual bacterial export, we propose that management efforts should be focused on best management practices capable of efficiently controlling bacterial transport to streams during storms. Although high bacteria concentrations can occur at baseflow, bacteria loadings at baseflow are small and have limited impact on annual bacterial export rates at the watershed scale.