Elucidating the effects of land cover and usage on background E. coli sources in edge-of-field runoff

Authors: GREGORY, L - Texas Water Resources Institute; Harmel, Daren; KARTHIKEYAN, R - Texas A&M University; WAGNER, K - Oklahoma State University; GENTRY, T - Texas A&M University; AITKENHEAD-PETERSON, J - Texas A&M University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Bacteria contamination in surface waters is a universal issue that signifies increased risks to human health from fecal loading. Nonpoint source fecal deposition is responsible for a portion of these loads; however, land use and land cover can alter the overall effect they have on instream water quality. Human influences often enhance this effect through animal use modification, but the same has been observed in areas managed to exclude non-natural sources of bacteria. Understanding the extent of bacteria loading, transport, and distribution in watersheds is critical for reducing these risks and improving watershed based bacteria fate and transport model predictions. This study evaluated bacteria occurrence, movement and distribution by monitoring soil and runoff from small ungrazed, upland watersheds under native prairie, managed hay pasture, and cultivated cropland uses and land covers. Significant differences in bacteria concentrations and loads in runoff and soil were identified despite the lack of significant differences in runoff volume between watersheds. This suggests that in areas with only natural bacteria sources, land use and land cover can result in significantly different pollutant load transport offsite during runoff events. However, results were contrary to similar works due to abnormally wet conditions during the study demonstrating inherent variability in this type of data. Soil derived bacteria loads were found to be significantly less than runoff bacteria loads suggesting that recent fecal deposition supplies the dominant proportion of bacteria loading in surface runoff. Further, study results demonstrate that bacteria loads in watersheds with only natural fecal sources (wildlife) can contribute substantial bacteria quantities to downstream waters during runoff events.

Technical Abstract: Escherichia coli (E. coli) contamination in surface waters is a universal issue that signifies potentially increased risks to human health from fecal loading. Nonpoint source fecal deposition is responsible for a portion of these loads; however, land use and land cover can alter the overall effect they have on instream water quality. Human influences often enhance this effect through animal use modification, but the same has been observed in areas managed to exclude non-natural sources of E. coli. Understanding the extent of E. coli loading, transport, and distribution in watersheds is critical for reducing these risks and improving watershed based bacteria fate and transport modeling capabilities. This study evaluated E. coli occurrence, movement and distribution by monitoring soil and runoff from small ungrazed, upland watersheds under native prairie, managed hay pasture, and cultivated cropland uses and land covers. Significant differences in E. coli concentrations and loads in runoff and soil were identified despite the lack of significant differences in runoff volume between watersheds. This suggests that in areas with only natural E. coli sources, land use and land cover can result in significantly different pollutant load transport offsite during runoff events. However, results were contrary to similar works due to abnormally wet conditions during the study demonstrating inherent variability in this type of data. Soil derived E. coli loads were found to be significantly less than runoff E. coli loads suggesting that recent fecal deposition supplies the dominant proportion of E. coli loading in surface runoff. Further, study results demonstrate that E. coli loads in watersheds with only natural fecal sources (wildlife) can contribute substantial E. coli quantities to downstream waters during runoff events.