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

초록

Assessing microbial quality of irrigation water is important to prevent foodborne illnesses caused by fresh produce contamination. Generic Escherichia coli and enterococci are commonly used to evaluate the microbial water quality. The objective of this study was to see if patterns in spatial distributions of the fecal indicator bacteria concentrations along a creek at baseflow that are preserved over time can be detected. Such patterns are commonly referred to as temporally stable patterns. Microbial concentrations were measured along the Conococheague Creek in Pennsylvania during 3 yr on weeks when the creek was at base flow. The upstream sampling location was at the outlet of the forested subwatershed, next two locations were in agricultural area dominated by crops and pastures, and another two were in urbanized areas. Empirical orthogonal functions (EOFs) have been applied to detect a temporally stable spatial pattern. 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 impacts of 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 the presence of multiple land uses. © 2019 The Author(s).