On the potential for reconstructed wetlands to remediate fecal coliform loading in an agricultural watershed

Grand Lake St Marys (GLSM) is one of the most hypereutrophic lakes in North America and was officially declared distressed in 2011 as a result of excess nutrient runoff from primarily agricultural cropland and livestock facilities. Concurrently, the watershed has also struggled with excessive fecal coliform loads most evident by the routine public warnings regarding colony counts in GLSM. This study evaluated in stream trends and the potential for reconstructed wetlands along Coldwater Creek to reduce coliforms in the watershed. Non-Escherichia coli coliforms in Coldwater Creek showed a seasonal pattern, with a winter low coincident with the distressed watershed winter ban on manure application. E. coli coliform loads did not show the same seasonal pattern, but may have been offset by wildlife fecal inputs. When water flowed into the wetland, concentrations of total coliforms were reduced by 40%, mainly driven by residence time. When the wetland was a net sink, it reduced E. coli by 71% and non-E. coli coliforms by 51%. Unfortunately, it also served as a source for total coliforms 4 weeks of the year. Treating all tributaries into GLSM would require the equivalent of ~ 20× the current wetland area in the watershed.