Exploring Seasonality in Escherichia coli and Fecal Coliform Ratios in Urban Watersheds

As regulators in the United States develop plans to mitigate microbial pollution via the design of total maximum daily load (TMDL) plans, historical data sets are often used to establish existing conditions for watersheds. Due to the revision of guidance recommending Escherichia coli (E. coli) as the preferred target indicator species in surface-water quality-monitoring programs, historical fecal-coliform concentration data are often used to estimate E. coli concentrations and loadings. Data from Raleigh and Durham, North Carolina, suggest the ratio of E. coli to fecal coliform (EC/FC) varies significantly by season throughout the year (p<0.05). These seasonal differences are not accounted for in most translator equations, which assume a single linear relationship between E. coli and fecal coliform regardless of season. These observations imply that seasonal translator equations may more accurately reflect the relationship between fecal coliforms and E. coli, and would thus result in the development of more accurate and effective TMDL plans.