Spatiotemporal trends of Escherichia coli levels and their influences vary among ponds in the coastal plain of Georgia

Abstract

Quantification of Escherichia coli in water is commonly used to understand a surface source's suitability for produce irrigation. Location, season, and physicochemical water quality impact the levels of E. coli in irrigation ponds. Water samples were collected periodically at three ponds in Southeast Georgia along a sampling grid from July 2021 through September 2023 and quantified for E. coli with simultaneous collection of relevant water physicochemical parameters. Mean relative differences (MRDs) were calculated for each collection point to determine differences in E. coli levels across sampling locations. E. coli levels varied significantly across sampling area (perimeter, surface, and subsurface) at each pond. The log most probable number E. coli 100 mL⁻¹ (EC MRD) values ranged from −0.25 to 0.33 in Pond 1, −1.5 to 0.65 in Pond 2, and −1.25 to 0.65 in Pond 3. In Pond 1, EC MRD correlated positively with chlorophyll and turbidity, and negatively with dissolved organic matter, dissolved oxygen (DO), specific conductance, and pH MRDs. In Pond 2, the MRD of E. coli correlated with the MRDs of chlorophyll, DO, phycocyanin, pH, and temperature. In Pond 3, E. coli MRD correlated positively with nitrate MRD. This work showed MRD analysis may reveal stable patterns of E. coli and the physicochemical factors that impact these levels in ponds, though no universal covariates were identified that could estimate E. coli levels. These findings may provide context for water quality managers wishing to augment measurements of E. coli with other factors, or better represent variable E. coli levels with MRD.