Recreational water quality response to a filtering barrier at a Great Lakes beach

Recent research has sought to determine the off- or onshore origin of fecal indicator bacteria (FIB) in order to improve local recreational water quality. In an effort to reduce offshore contamination, a filtering barrier (FB) was installed at Calumet Beach, Lake Michigan, Chicago, IL. A horseshoe-shaped curtain (146 m long, 0.18 mm apparent opening size, 1.5-1.6 m deepest point) was designed to exclude FIB containing or promoting debris and thus reduce the number of swimming advisories during the examination period of July through September 2012. Mean water Escherichia coli concentrations were significantly lower at southern transects (S; outside FB) than at transects within the FB (WN) and at northern transects (N; outside FB) (1.45 log (MPN)/100 ml vs. 1.74 and 1.72, respectively, p < 0.05, n = 234). Turbidity was significantly higher at the WN transects (p < 0.001, n = 233), but it tended to increase throughout the sampling season within and outside the FB. E. coli in adjacent foreshore sand was significantly lower at the WN transects. A combination of factors might explain higher E. coli and turbidity within the FB including increased sediment resuspension, trapped algae, shallowing within the FB, and large lake hydrodynamic processes. This remediation approach may find better use in a different hydrodynamic setting, but the results of this experiment provide insight on sources of contamination and nearshore dynamics that may direct future beach management strategies.