Occurrence and Origin of Escherichia coli in Water and Sediments at Two Public Swimming Beaches at Lake of the Ozarks State Park, Camden County, Missouri, 2011–13

Abstract

In the past several years, the Missouri Department of Natural Resources has closed two popular public beaches, Grand Glaize Beach and Public Beach 1, at Lake of the Ozarks State Park in Osage Beach, Missouri when monitoring results exceeded the established Escherichia coli (E. coli) standard. As a result of the beach closures, the U.S. Geological Survey and Missouri University of Science and Technology, in cooperation with the Missouri Department of Natural Resources, led an investigation into the occurrence and origins of E. coli at Grand Glaize Beach and Public Beach 1. The study included the collection of more than 1,300 water, sediment, and fecal source samples between August 2011 and February 2013 from the two beaches and vicinity. Spatial and temporal patterns of E. coli concentrations in water and sediments combined with measurements of environmental variables, beach-use patterns, and Missouri Department of Natural Resources water-tracing results were used to identify possible sources of E. coli contamination at the two beaches and to corroborate microbial source tracking (MST) sampling efforts.

Results from a 2011 reconnaissance sampling indicate that water samples from Grand Glaize Beach cove contained significantly larger E. coli concentrations than adjacent coves and were largest at sites at the upper end of Grand Glaize Beach cove, indicating a probable local source of E. coli contamination within the upper end of the cove. Results from an intensive sampling effort during 2012 indicated that E. coli concentrations in water samples at Grand Glaize Beach cove were significantly larger in ankle-deep water than waist-deep water, trended downward during the recreational season, significantly increased with an increase in the total number of bathers at the beach, and were largest during the middle of the day. Concentrations of E. coli in nearshore sediment (sediment near the shoreline) at Grand Glaize Beach were significantly larger in foreshore samples (samples collected above the shoreline) than in samples collected in ankle-deep water below the shoreline, significantly larger in the left and middle areas of the beach than the right area, and substantially larger than similar studies at E. coli- contaminated beaches on Lake Erie in Ohio. Concentrations of E. coli in the water column also were significantly larger after resuspension of sediments.

Results of MST indicate a predominance of waterfowl-associated markers in nearshore sediments at Grand Glaize Beach consistent with frequent observations of goose and vulture fecal matter in sediment, especially on the left and middle areas of the beach. The combination of spatial and temporal sampling and MST indicate that an important source of E. coli contamination at Grand Glaize Beach during 2012 was E. coli released into the water column by bathers resuspending E. coli-contaminated sediments, especially during high-use days early in the recreational season.

First posted March 3, 2014