Persistence and Microbial Source Tracking of Escherichia coli at a Swimming Beach at Lake of the Ozarks State Park, Missouri

The Missouri Department of Natural Resources (MDNR) has closed or posted advisories at public beaches at Lake of the Ozarks State Park in Missouri because of Escherichia coli (E.coli) concentration exceedances in recent years. Spatial and temporal patterns of E.coli concentrations, microbial source tracking, novel sampling techniques, and beach-use patterns were studied during the 2012 recreational season to identify possible sources, origins, and occurrence of E.coli contamination at Grand Glaize Beach (GGB). Results indicate an important source of E.coli contamination at GGB was E.coli released into the water column by bathers resuspending avian-contaminated sediments, especially during high-use days early in the recreational season. Escherichia coli concentrations in water, sediment, and resuspended sediment samples all decreased throughout the recreational season likely because of decreasing lake levels resulting in sampling locations receding away from the initial spring shoreline as well as natural decay and physical transport out of the cove. Weekly MDNR beach monitoring, based solely on E.coli concentrations, at GGB during this study inaccurately predicted E.coli exceedances, especially on weekends and holidays. Interestingly, E.coli of human origin were measured at concentrations indicative of raw sewage in runoff from an excavation of a nearby abandoned septic tank that had not been used for nearly two years.