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Volume 57, Issue 1 p. 362-381
Article
Free Access

Nearshore hydrodynamics as loading and forcing factors for Escherichia coli contamination at an embayed beach

Zhongfu Ge

Corresponding Author

Zhongfu Ge

U.S. Geological Survey, Great Lakes Science Center, Lake Michigan Ecological Research Station, Porter, Indiana

Corresponding author: [email protected]Search for more papers by this author
Richard L. Whitman

Richard L. Whitman

U.S. Geological Survey, Great Lakes Science Center, Lake Michigan Ecological Research Station, Porter, Indiana

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Meredith B. Nevers

Meredith B. Nevers

U.S. Geological Survey, Great Lakes Science Center, Lake Michigan Ecological Research Station, Porter, Indiana

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Mantha S. Phanikumar

Mantha S. Phanikumar

Department of Civil and Environmental Engineering, Michigan State University, East Lansing, Michigan

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Muruleedhara N. Byappanahalli

Muruleedhara N. Byappanahalli

U.S. Geological Survey, Great Lakes Science Center, Lake Michigan Ecological Research Station, Porter, Indiana

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First published: 16 January 2012
Citations: 45

Abstract

Numerical simulations of the transport and fate of Escherichia coli were conducted at Chicago's 63rd Street Beach, an embayed beach that had the highest mean E. coli concentration among 23 similar Lake Michigan beaches during summer months of 2000–2005, in order to find the cause for the high bacterial contamination. The numerical model was based on the transport of E. coli by current circulation patterns in the embayment driven by longshore main currents and the loss of E. coli in the water column, taking settling as well as bacterial dark- and solar-related decay into account. Two E. coli loading scenarios were considered: one from the open boundary north of the embayment and the other from the shallow water near the beachfront. Simulations showed that the embayed beach behaves as a sink for E. coli in that it generally receives E. coli more efficiently than it releases them. This is a result of the significantly different hydrodynamic forcing factors between the inside of the embayment and the main coastal flow outside. The settled E. coli inside the embayment can be a potential source of contamination during subsequent sediment resuspension events, suggesting that deposition-resuspension cycles of E. coli have resulted in excessive bacterial contamination of beach water. A further hypothetical case with a breakwater shortened to half its original length, which was anticipated to enhance the current circulation in the embayment, showed a reduction in E. coli concentrations of nearly 20%.