Temporal stability of E. coli and Enterococci Concentrations in a Pennsylvania creek

Authors: JEON, DONG JIN - Gwangju Institute Of Science And Technology; Pachepsky, Yakov; Coppock, Cary; HARRIGER, DANA - Wilson College; PICARD, RACHAEL - Wilson College; WELLS, EDWARD - Wilson College

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2019
Publication Date: 11/11/2019
Citation: Jeon, D., Pachepsky, Y.A., Coppock, C.R., Harriger, D., Picard, R., Wells, E. 2019. Temporal stability of E. coli and Enterococci Concentrations in a Pennsylvania creek. Journal of Hydrology. https://doi.org/10.1007/s11356-019-07030-9.
DOI: https://doi.org/10.1007/s11356-019-07030-9

Interpretive Summary: Microbial water quality for irrigation is a substantial factor of produce contamination. Design of microbial water quality monitoring is complicated by the considerable spatial and temporal variability of the Escherichia coli and Enterococci concentration in freshwater sources including creeks. We hypothesized that there is a stable spatial pattern in E. coli and enterococci concentrations along creeks, and there are locations where the bacterial concentrations are consistently larger than average concentration across the creek. We examined this hypothesis by performing statistical analysis of bacteria concentrations along the reach of the Conococheague creek, PA, observed weekly for three years at baseflow. Persistent in time locations with relatively high and relatively low concentrations existed. The highest concentrations were found at urbanized area, the lowest concentrations were found at forested area, and average concentrations were found at agricultural and sparsely urbanized area. Results of this study will help in selecting the representative microbial quality monitoring locations to estimate the geometric mean concentrations across the creek reach for irrigation management purposes.

Technical Abstract: Microbial quality of irrigation waters is a substantial food safety factor. Bacteria Escherichia coli (E. coli) and enterococci are used as indicators of the microbial water quality. Analysis of temporally stable patterns facilitates effective monitoring strategis in hydrology. The objective of this study was to analyze spatiotemporal variation and temporal stability of E. coli and enterococci concentrations along a intensively monitored creek. Concentrations both bacteria awere measured at five water monitoring locations along the creek in Pennsylvania weekly during three years across 20 km-long reach. The temporal stability was assessed using mean relative differences of logarithms of bacterial concentration and Spearman rank correlation coefficients. Logarithms of bacterial concentrations had sine dependence on time and correlated significantly with temperature at all locations. Both bacteria exhibited temporal stability of concentrations. Two locations in urbanized area tended to have logarithms of concentrations higher than average across the observation reach, one locations in forested area had mostly lower concentrations than average, and two locations in agricultural and sparcely urbanized area had these values close to the average. The temporal stability was more pronounced in cold seasons than in warm seasons. The Spearman rank correlations between observations on consecutive dates showed mostly moderate to very strong relationships. Existence of the temporal stability of bacterial concentrations in creek can help to find the locations that inform about the average logarithm or the geometric maan concentrations along the whole observation reach.