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| Ohio Water Science Center |
U.S. Geological Survey, Scientific Investigations Report 2006-5298
By Donna S. Francy, Erin E. Bertke, Dennis P. Finnegan, Christopher M. Kephart, Rodney A. Sheets, John Rhoades, and Lester Stumpe
In Cooperation with the Northeast Ohio Regional Sewer District and Ohio Water Development Authority
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Source-tracking tools were used to identify potential sources of fecal contamination at two Lake Erie bathing beaches: an urban beach (Edgewater in Cleveland, Ohio) and a beach in a small city (Lakeshore in Ashtabula, Ohio). These tools included identifying spatial patterns of Escherichia coli (E. coli) concentrations in each area, determining weather patterns that caused elevated E. coli, and applying microbial source tracking (MST) techniques to specific sites. Three MST methods were used during this study: multiple antibiotic resistance (MAR) indexing of E. coli isolates and the presence of human-specific genetic markers within two types of bacteria, the genus Bacteroides and the species Enterococcus faecium.
At Edgewater, sampling for E. coli was done during 2003–05 at bathing-area sites, at nearshore lake sites, and in shallow ground water in foreshore and backshore areas. Spatial sampling at nearshore lake sites showed that fecal contamination was most likely of local origin; E. coli concentrations near the mouths of rivers and outfalls remote to the beach were elevated (greater than 235 colony-forming units per 100 milliliters (CFU/100 mL)) but decreased along transport pathways to the beach. In addition, E. coli concentrations were generally highest in bathing-area samples collected at 1- and 2-foot water depths, midrange at 3-foot depths, and lowest in nearshore lake samples typically collected 150 feet from the shoreline. Elevated E. coli concentrations at bathing-area sites were generally associated with increased wave heights and rainfall, but not always. E. coli concentrations were often elevated in shallow ground-water samples, especially in samples collected less than 10 feet from the edge of water (near foreshore area). The interaction of shallow ground water and waves may be a mechanism of E. coli storage and accumulation in foreshore sands. Infiltration of bird feces through sand with surface water from rainfall and high waves may be concentrating E. coli in shallow ground water in foreshore and backshore sands.
At Lakeshore, sampling for E. coli was done at bathing-area, nearshore lake, and parking-lot sites during 2004–05. Low concentrations of E. coli at nearshore lake sites furthest from the shoreline indicated that fecal contamination was most likely of local origin. High concentrations of E. coli in water and bed sediments at several nearshore lake sites showed that contamination was emanating from several points along the shoreline during wet and dry weather, including the boat ramp, an area near the pond drainage, and parking-lot sediments. Physical evidence confirmed that runoff from the parking lot leads to degradation of water quality at the beach.
MST samples were collected to help interpret spatial findings and determine whether sources of fecal contamination were from wastewater or bird feces and if a human-specific marker was present. MAR indices were useful in distinguishing between bird feces and wastewater sources because they were about 10 times higher in the latter. The results from MAR indices agreed with results from the two human-specific markers in some but not all of the samples tested. Bacteroides and enterococci human-specific markers were found on one day at Edgewater and two days at Lakeshore. On three days at Edgewater and two days at Lakeshore, the MAR index indicated a mixed source, but neither marker was found in bathing-water samples; this may be because bacterial indicator concentrations were too low to detect a marker.
Multiple tools are needed to help identify sources of fecal contamination at coastal beaches. Spatial sampling identified patterns in E. coli concentrations and yielded information on the physical pathways of contamination. MST methods provided information on whether the source was likely of human or nonhuman origin only; however, MST did not provide information on the pathways of contamination.
Abstract
Introduction
Study Areas
Edgewater
Lakeshore
Methods
Sampling Frequencies and Locations
Spatial Sampling at Edgewater
Spatial Sampling at Lakeshore
Samples for Microbial Source Tracking
Sample-Collection Methods
Laboratory Methods
Escherichia coli
Multiple Antibiotic Resistance Indices of Escherichia coli Isolates
Bacteroides Marker
Enterococcus faecium Marker
Quality Assurance and Quality Control
Data Analysis and Statistics
Spatial Distributions of Escherichia coli
Edgewater
Nearshore Lake
Bathing Area
Shallow Ground Water
Lakeshore
Sediments
Nearshore Lake and Bathing Areas
Multiple Antibiotic Resistance Indices of Escherichia coli Isolates and Presence of Human Markers
Discussion and Conclusions
Edgewater
Lakeshore
Using a Multiple-Method Approach to Source Tracking
Summary
Acknowledgments
References Cited
1. Maps showing location of Edgewater, Cleveland, Ohio: nearshore lake sampling sites and bathing-area and shallow ground-water sampling sites, 2003–2005.
2. Map showing location of Lakeshore, Ashtabula, Ohio, and bathing-area, nearshore lake, and parking-lot sampling sites, 2004 and 2005.
3. Photographs showing temporary piezometers with 0.5-foot-long screens, installed at depths ranging from approximately 0.5 to 3.0 feet, at various intervals from the edge of water.
4. Photograph showing multiple antibiotic resistance testing on Luria-Bertani agar plates containing no antibiotic and one antibiotic.
5.-10. Graphs showing:
5. Distribution of Escherichia coli concentrations at nearshore lake sampling sites in and around Edgewater, Cleveland, Ohio, 2003 and 2004, on 10 dry and 9 wet days.
6. Average concentrations of Escherichia coli at Main and Middle Beach bathing-area sites, Edgewater, Cleveland, Ohio, 2005.
7. Land surface, water levels, and Escherichia coli concentrations in shallow ground water and lake water at the east sampling location at Edgewater, Cleveland, Ohio, 2004, in June, and July.
8. Land surface, water levels, and Escherichia coli concentrations in shallow ground water and lake water at the west sampling location at Edgewater, Cleveland, Ohio, 2005, in June and July.
9. Escherichia coli concentrations in shallow ground water and lake water at the west sampling location, Edgewater, Cleveland, Ohio, 2005, associated with distance to edge of water and Rd-1, lake level, wave height, and the water level in the piezometer 6 feet inland.
10. Concentrations of Escherichia coli in water collected at nearshore and bathing-water sites at Lakeshore, Ashtabula, Ohio, on three days in 2004.
11. Photograph showing stormwater runoff from a pipe draining the parking lot to the beach at Lakeshore, Ashtabula, Ohio, July 12, 2004.
12. Graph showing average concentrations of Escherichia coli at nearshore lake sites, Lakeshore, Ashtabula, Ohio, 2005.
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Suggested Citation:
Francy, D.S., Bertke, E.E., Finnegan, D.P., Kephart, C.M., Sheets, R.A., Rhoades, John, and Stumpe, Lester,
2006, Use of Spatial Sampling and
Microbial Source-Tracking Tools for Understanding Fecal Contamination at Two Lake Erie Beaches: U.S. Geological Survey Scientific Investigations
Report 2006-5298, 29 p.
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