E. coli in PA streams as affected by climate forcing

Authors: HONG, EUNMI - Orise Fellow; Pachepsky, Yakov; PARK, YONGEUN - Us Forest Service (FS); Shelton, Daniel

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/7/2016
Publication Date: 7/16/2016
Citation: Hong, E., Pachepsky, Y.A., Park, Y., Shelton, D.R. 2016. E. coli in PA streams as affected by climate forcing. In:ASABE Annual International Meeting, Orlando, FL on July 17-20, 2016. p.162462928.

Interpretive Summary: Knowledge about microbial quality of irrigation waters currently is extremely scarce. For this reason, US FDA rules on irrigation water require first testing the irrigation water source and accumulating 20 samples to decide whether and how this water can be used in produce irrigation. The objective of this work was to evaluate the effect of the interannual weather variability on the microbial water quality assessment results. Using a 90-year time series of weather data in the Southern Pennsylvania and Soil and Water assessment Tool model, we simulated microbial water quality in the second-order Cove Mountain perennial creek, and randomly sampled simulated water time series. We found that weather conditions of a specific year may strongly affect the microbial water quality evaluation, but the long-term assessment of microbial water quality may be quite different from the evaluation based on short-term observations. Results of this work can be useful for industry and consultants in that they show the opportunity of using modeling to design and assess monitoring of microbial water quality for irrigation purposes.

Technical Abstract: Each year, more than 9 million foodborne illnesses are estimated to be caused by major pathogens. More than 70% of the cropland for vegetables is irrigation water may contain pathogens or potential bacteria that affect human health. The FDA (Food and Drug Administration) has issued regulations mandated by the Food Safety Modernization Act that include microbial water quality standards for irrigation water based on E. coli concentration. However, there is no comprehensive explanation of where, how or when water samples have to be taken. To develop the optimal monitoring guidelines, it is necessary to discover, evaluate and integrate the knowledge affecting microbial quality of irrigation water using watershed model. In this study, the modified SWAT (Soil and Water Assessment Tool) model was applied to estimate E. coli concentration on the stream in the Little Cove Creek Watershed in Pennsylvania with forestry and dairy pasture land use using the 90-year meteorological data since 1923. The geometric mean of daily simulation results for 90 years during growing periods is 141 CFU of E. coli in 100ml water with exceedance rate for FDA regulation is about 59%. We also sampled simulated time series of daily E. coli concentrations. Random subsets of 20 samples per year were taken 100 times. The geometric mean of samples was 153 CFU of E. coli in 100 ml with the 82% rate of exceeding regulatory thresholds. Improvements in simulations of bacteria fate and transport during base flow appear to be needed. This study shows opportunities of using fate and transport modeling to approach existing needs in microbial water quality monitoring design.