Annual Precipitation and Discharge Drive Increases in Escherichia Coli Concentrations in an Urban Stream

Abstract

Determining climate change influences on E. coli dynamics in urban aquatic systems and predicting future E. coli changes are important to regulate water quality. In this study, data from 6985 measurements of E. coli from 1999-2019 in the Indianapolis, Indiana (USA) urban waterway Pleasant Run were analyzed by Mann-Kendall and multiple linear regression to examine long term trends in E. coli concentrations and loads, and to project E. coli concentrations under future climate change scenarios. E. coli concentrations and loads monotonically increased over the last two decades, with E. coli concentrations increasing from 111 MPN/100 mL in 1999 to 911 MPN/100 mL in 2019. E. coli loads increased from 5×10 12 MPN/year to 90×10 12 MPN/year over the same period. E. coli showed peak concentration in summer, and significantly higher concentration in sites with Combined Sewer Outfalls relative to those without. Precipitation had both direct and indirect impacts on E. coli concentrations, meditated by stream discharge. Multiple linear regression results showed annual precipitation and discharge accounted for 60% of E. coli concentration variations. Based on the observed precipitation-discharge- E. coli concentration relationship, the projection results showed that, in the highest emission RCP 8.5 climate scenario, E. coli concentrations in 2020s, 2050s, and 2080s will be 1350 MPN/100mL, 1386 MPN/100mL, and 1443 MPN/100mL, respectively.