Analysis of E. coli and enterococci concentrations patterns in a Pennsylvania creek using empirical orthogonal functions

Authors: JEON, DONGJIN - U.S. DEPARTMENT OF AGRICULTURE (USDA); Pachepsky, Yakov; HARRIGER, DANA - WILSON COLLEGE; PICARD, RACHAEL - WILSON COLLEGE; COPPOCK, CARY; WELLS, EDWARD - WILSON COLLEGE; HONG, EUNMI - KANGWON NATIONAL UNIVERSITY

Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2019
Publication Date: 9/12/2019
Citation: Jeon, D., Pachepsky, Y.A., Harriger, D., Picard, R., Coppock, C.R., Wells, E., Hong, E. 2019. Analysis of E. coli and enterococci concentrations patterns in a Pennsylvania creek using empirical orthogonal functions. Environmental Quality. https://doi.org/10.2134/jeq2019.05.0191.
DOI: https://doi.org/10.2134/jeq2019.05.0191

Interpretive Summary: Presence of pathogenic microorganisms in irrigation water is threatening human health. Generic Escherichia coli (E. coli) and enterococci are generally used as indicator microorganisms to estimate microbial water quality in irrigation water sources. These organisms are monitored. We hypothesized that there are one or more spatial patterns of both microbial concentrations along the creek that do not change with time. analysis of three years of data for the Conococheague creek, PA, showed that such patterns exist and that the most influential one reflects the distribution of the land use along the creek. Less influential were patterns that could be attributed to tributaries and braided reaches effects. Results of this work can be useful for water quality evaluation and management in that they indicate the possibility of using small number of monitoring locations to assess the microbial quality of irrigation water.

Technical Abstract: Assessing microbial quality of irrigation water is important to prevent foodborne illnesses caused by fresh produce contamination. Generic Escherichia coli (E. coli) and enterococci are commonly used to evaluate the microbial water quality. Understanding of factors which cause the creation of spatial distribution of the microbial concentrations facilitates effective monitoring strategies. These factors can create more than one spatial pattern of the fecal indicator bacteria concentrations. The objective of this study was to see if temporally stable patterns are present in time series of the fecal indicator bacteria concentrations at the baseflow in a Pennsylvania creek. Microbial concentrations were measured weekly at five locations along the creek Conococheague creek in Pennsylvania during three years. Empirical orthogonal functions (EOFs) have been applied to detect temporally stable spatial pattern. The highest bacteria concentrations were found in the urbanized area; the concentrations were relatively lower in the agricultural and spatially urbanized area regardless of different observation years. The most significant spatial pattern of both bacteria was followed the change of land use; 74.6% and 68.6 were explained by the first EOF for E. coli and enterococci, respectively. Much less variability (19.6 and 17%) was explained by the EOF that possible tributary and braided sections of the creek. A good approximation of the average logarithms of concentrations across the studied reach was provided by logarithms of concentrations at the sampling location where the first EOF was close to zero. We confirmed that EOF analysis can uncover the significant multiple temporally stable spatial patterns for the fecal indicator bacteria concentration along the creek in presence of multiple land use.