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Evaluation of potential sources and transport mechanisms of fecal indicator bacteria to beach water, Murphy Park Beach, Door County, Wisconsin

Scientific Investigations Report 2012-5190

Prepared in collaboration with the Door County Soil and Water Conservation Department and University of Wisconsin-Oshkosh
By:
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Abstract

Fecal Indicator Bacteria (FIB) concentrations in beach water have been used for many years as a criterion for closing beaches due to potential health concerns. Yet, current understanding of sources and transport mechanisms that drive FIB occurrence remains insufficient for accurate prediction of closures at many beaches. Murphy Park Beach, a relatively pristine beach on Green Bay in Door County, Wis., was selected for a study to evaluate FIB sources and transport mechanisms. Although the relatively pristine nature of the beach yielded no detection of pathogenic bacterial genes and relatively low FIB concentrations during the study period compared with other Great Lakes Beaches, its selection limited the number of confounding FIB sources and associated transport mechanisms. The primary sources of FIB appear to be internal to the beach rather than external sources such as rivers, storm sewer outfalls, and industrial discharges. Three potential FIB sources were identified: sand, swash-zone groundwater, and Cladophora mats. Modest correlations between FIB concentrations in these potential source reservoirs and FIB concentrations at the beach from the same day illustrate the importance of understanding transport mechanisms between FIB sources and the water column. One likely mechanism for transport and dispersion of FIB from sand and Cladophora sources appears to be agitation of Cladophora mats and erosion of beach sand due to storm activity, as inferred from storm indicators including turbidity, wave height, current speed, wind speed, sky visibility, 24-hour precipitation, and suspended particulate concentration. FIB concentrations in beach water had a statistically significant relation (p-value ‹0.05) with the magnitude of these storm indicators. In addition, transport of FIB in swash-zone groundwater into beach water appears to be driven by groundwater recharge associated with multiday precipitation and corresponding increased swash-zone groundwater discharge at the beach, as indicated by an increase in the specific conductance of beach water. Understanding the dynamics of FIB sources (sand, swash-zone groundwater, and Cladophora) and transport mechanisms (dispersion and erosion from storm energy, and swash-zone groundwater discharge) is important for improving predictions of potential health risks from FIB in beach water.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Evaluation of potential sources and transport mechanisms of fecal indicator bacteria to beach water, Murphy Park Beach, Door County, Wisconsin
Series title:
Scientific Investigations Report
Series number:
2012-5190
Year Published:
2013
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Wisconsin Water Science Center
Description:
vi, 29 p.
Country:
United States
State:
Wisconsin
County:
Door
Other Geospatial:
Murphy Park Beach
Online Only (Y/N):
Y
Additional Online Files(Y/N):
N