U.S. Department of the Interior

U.S. Geological Survey

Prepared in collaboration with the Door County Soil and Water Conservation Department and 

University of Wisconsin–Oshkosh 

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
Cover images:

Upper left: Murphy Park Beach looking north, August 7, 2008. (Photograph by Charles Dunning, U.S. Geological Survey 

(USGS))

Upper right: Murphy Park Beach looking south, August 7, 2008. (Photograph by Charles Dunning, USGS)

Lower left: Murphy Park Beach looking east from the pier, July 23, 2008. (Photograph by Charles Dunning, USGS)

Lower right: Suspended particulate sampling equipment used at Murphy Park Beach. Photograph is from the beach looking 

west, August 25, 2009. (Photograph by Jason Smith, USGS)
Evaluation of Potential Sources and 

Transport Mechanisms of Fecal Indicator 

Bacteria to Beach Water, Murphy Park 

Beach, Door County, Wisconsin

By Paul F. Juckem, Steven R. Corsi, Colleen McDermott, Gregory Kleinheinz, 

Lisa R. Fogarty, Sheridan K. Haack, and Heather E. Johnson

Prepared in collaboration with the Door County Soil and Water Conservation 

Department and University of Wisconsin–Oshkosh

Scientific Investigations Report 2012–5190

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Juckem, P.F., Corsi, S.R., McDermott, Colleen, Kleinheinz, Gregory, Fogarty, L.R., Haack, S.K., and Johnson, H.E., 2013, 

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

Beach, Door County, Wisconsin: U.S. Geological Survey Scientific Investigations Report 2012–5190, 29 p. 
iii

Acknowledgments

Local Project Coordinators

Amanda Surfus, Door County Soil and Water Conservation Department, Sturgeon Bay, Wis.

William Schuster, Door County Soil and Water Conservation Department, Sturgeon Bay, Wis.

Data Collection and Analysis

Nathan Frohn, UW-Oshkosh, collected all of the fecal indicator bacteria samples, except 

particulate-associated samples, and ancillary data in 2009.

Austin Baldwin and Jason Smith, U.S. Geological Survey, Middleton, Wis., collected particulateassociated fecal indicator bacteria samples.

The National Oceanic and Atmospheric Administration, Great Lakes Environmental Research 

Laboratory, Ann Arbor, Mich., supplied results from the Great Lakes Coastal Forecasting System. 

Publishing Support

Laura Nelson, Office Assistant, U.S. Geological Survey Wisconsin Water Science Center, 

Middleton, Wis.

Michelle Greenwood, Reports Specialist, U.S. Geological Survey Wisconsin Water Science 

Center, Middleton, Wis.

Bonnie Stich, Editor, U.S. Geological Survey Science Publishing Network, Louisville, Ky.

Technical Reviewers

Robert Waschbush, U.S. Geological Survey, Wisconsin Water Science Center, Middleton, Wis.

Marlene Noble, U.S. Geological Survey, Pacific Southwest Area, Menlo Park, Calif.

Editorial Reviewer

Elizabeth Ciganovich, Technical Writer-Editor, U.S. Geological Survey Science Publishing 

Network, Madison, Wis.

Approving Official

Kevin Breen, Bureau Approving Official, U.S. Geological Survey Office of Science Quality and 

Integrity, New Cumberland, Pa. 
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Murphy Park Beach and its Watershed............................................................................................2

Study Methods and Sampling Sites............................................................................................................5

Sampling Sites.......................................................................................................................................5

Sampling Schedule...............................................................................................................................5

Lake Water Sampling ...........................................................................................................................7

Groundwater Sampling........................................................................................................................7

Suspended Particulates in Lake Water.............................................................................................7

Sand Sampling.......................................................................................................................................7

Cladophora Sampling...........................................................................................................................7

Ancillary Data........................................................................................................................................8

Pathogens ..............................................................................................................................................8

Multivariate Statistical Analysis ........................................................................................................9

FIB Concentrations at Potential Source Reservoirs ..............................................................................10

FIB in Lake Water................................................................................................................................10

FIB in Groundwater.............................................................................................................................14

FIB Associated with Suspended Particulates in Lake Water......................................................16

FIB in Beach Sand ..............................................................................................................................16

FIB Associated with Cladophora Mats ...........................................................................................16

Pathogen Detection in Lake Water and Groundwater ..........................................................................16

Multivariate Analysis of Escherichia coli (E. coli) Concentrations .....................................................20

Potential Transport Mechanisms for FIB.................................................................................................22

Transport of FIB through Long-Shore Currents .............................................................................22

Transport of FIB from Swash-Zone Groundwater.........................................................................22

Transport of FIB from Sand and Cladophora due to Storm Activity ...........................................24

Summary........................................................................................................................................................28

References Cited..........................................................................................................................................28

Figures

1. Map showing the location of Murphy Park Beach and watershed in 

Door County, Wisconsin ..............................................................................................................3

2. Maps showing the locations of data-collection sites at Murphy Park Beach, 

2008–9 .............................................................................................................................................4

3. Boxplots of A, E. coli and B, enterococci concentrations in lake water and 

ratios of C, E. coli and D, enterococci for lake water sites at Murphy Park 

Beach, 2008–9 .............................................................................................................................11
v

4. Graphs showing time series of A, E. coli and B, enterococci concentrations 

in lake water at Murphy Park Beach, 2008–9 ........................................................................14

5. Boxplots of A, E. coli and B, enterococci concentrations and ratios of 

C, E. coli and D, enterococci in groundwater for piezometer (PZ) sites at 

Murphy Park Beach, 2008–9 .....................................................................................................15

6. Boxplots of A, E. coli and B, enterococci concentrations and ratios of 

C, E. coli and D, enterococci in samples for suspended particulates at 

Murphy Park Beach, 2009 .........................................................................................................17

7. Boxplots of A, E. coli and B, enterococci concentrations in sand at 

Murphy Park Beach, 2009 .........................................................................................................18

8. Boxplots of A, E. coli and B, enterococci concentrations and ratios of 

C, E. coli and D, enterococci in water within and adjacent to Cladophora

mats and in beach water at Murphy Park Beach, 2009 .......................................................19

9. Boxplot of E. coli concentration in beach water at Murphy Park Beach, 2009, 

grouped by specific conductance and wave height ............................................................21

10. Rose diagram showing E. coli and enterococci concentrations with respect 

to A, lake water current direction and B, wind direction at the time of lake 

water-sample collection at the beach water site at Murphy Park Beach, 2009..............23

11. Schematic cross section showing groundwater recharge and discharge as 

a mechanism for transporting fecal indicator bacteria from the swash-zone 

groundwater reservoir into the lake water column..............................................................24

12. Graphs showing A, E. coli and B, enterococci concentrations in beach water 

and in water samples collected within and adjacent to Cladophora mats at 

Murphy Park Beach, 2009 .........................................................................................................26

13. Graphs showing E. coli concentrations associated with relative abundance of 

Cladophora at the time of sampling A, for the 2008–9 study period and for 2009 

categorized by B, wave height, C, turbidity, D, current speed, and E, wind speed 

at the beach water site, Murphy Park Beach........................................................................27

Tables

1. Dates, locations, and types of environmental samples collected at 

Murphy Park Beach, 2008–9.......................................................................................................6

2. Growth medium and enrichment parameters for target pathogenic bacteria...................8

3. Positive controls and detection limits for polymerase chain reaction (PCR) assays .......9

4. Variables used in multivariate regression for E. coli concentrations at 

Murphy Park Beach, July–September 2009.............................................................................9

5. Fecal indicator bacteria concentrations in samples from the lake water 

sampling sites and current directions at the three lake water sampling sites 

at Murphy Park Beach, 2008–9.................................................................................................12
vi

Conversion Factors, Abbreviations, and Abbreviated WaterQuality Units

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 3,785 milliliter (mL)

gallon (gal) 3,785,000 microliter (μL)

Flow rate

mile per hour (mi/h) 1.609 kilometer per hour (km/h) 

Mass

ounce, avoirdupois (oz) 28.35 gram (g)

ounce, avoirdupois (oz) 28,350,000,000 nanogram (g)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Turbidity is given in Nephelometric Turbidity Units (NTU).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Concentrations of Fecal Indicator Bacteria (FIB) from grab samples of water are given as most 

probable number per 100 milliliters of water (MPN/100mL).

Concentrations of FIB from sand samples are given as most probable number per gram of dry 

sand (MPN/g).
Evaluation of Potential Sources and Transport 

Mechanisms of Fecal Indicator Bacteria to Beach Water, 

Murphy Park Beach, Door County, Wisconsin

By Paul F. Juckem,1 Steven R. Corsi,1 Colleen McDermott,2 Gregory Kleinheinz,2 Lisa R. Fogarty,1 

Sheridan K. Haack, and Heather E. Johnson 1 1

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. 

Introduction

Fecal indicator bacteria (FIB) monitoring results are 

often used to assess water quality at recreational beaches for 

protection of human health. The choice of Escherichia coli

(E. coli) for freshwater assessment was based on epidemiological studies that have identified an association of E. coli with 

gastrointestinal illness (Dufour, 1984). Current water-quality 

criteria for fresh recreational waters are based on this information. More recently, epidemiological research has identified a 

relation of gastrointestinal illness to enterococci as measured 

using quantitative polymerase chain reaction (PCR) techniques 

(Wade and others, 2006). Additional research has also identified increased risk for skin illnesses with increased concentrations of enterococci (Fleisher and others, 2010). 

FIB in recreational waters can originate from many 

sources. Some of the primary sources include streams and 

storm sewers that discharge point and nonpoint contamination 

near beaches, overland runoff, fecal matter from birds, groundwater discharges, beach sand, algae such as Cladophora

(Byappanahalli and others, 2003; Englebert and others, 2008; 

Vanden Heuvel and others, 2010), wastewater effluents, and 

resuspension from lake sediments and the swash zone (Lee 

and others, 2006). At beaches that have periodic contamination where a dominant source is not obvious, a comprehensive 

approach is warranted to understand influences on the water 

quality. 

____________

1

U.S. Geological Survey.

2

University of Wisconsin–Oshkosh.
2 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Door County, Wis. is a unique setting in the Great Lakes 

region from a geographic, geologic, social, and economic 

standpoint. Door County is located on a peninsula between 

Green Bay and Lake Michigan and has many public beaches. 

A large portion of the economy is based on tourism, and recreational beaches are an important attraction for tourists in Door 

County. The subsurface geology is dominated by fractured 

carbonate rock aquifers that have a high horizontal to vertical anisotropy and low bulk porosity, which results in rapid 

horizontal transport of water through the shallow groundwater 

system (Sherrill, 1978). 

Frank Murphy Park Beach in Door County (Murphy 

Park Beach) was chosen for this study by the U.S. Geological 

Survey, in collaboration with the Door County Soil and Water 

Conservation Department and University of Wisconsin–Oshkosh, because it (1) is a relatively pristine beach compared 

with other Great Lakes beaches that have been intensively 

studied, but it also has experienced periodic FIB exceedances 

during the summer, (2) has a relatively well-defined extent, 

(3) does not have a substantial surface water tributary nearby, 

and (4) experiences relatively large groundwater discharge 

along the beach during the spring, which at times seeps to the 

land surface on the beach and drains into the swimming area. 

The groundwater typically has relatively low concentrations 

of FIB and only periodically has elevated concentrations of 

E. coli; 5 percent of E. coli samples had greater than 235 most 

probable number per 100 milliliters of water (MPN/100mL) 

from 2003 to 2007 (Door County Soil and Water Conservation 

Department, 2008).

Several research efforts have evaluated Murphy Park 

Beach for factors associated with potential FIB contamination. Rainfall has been shown to have short-term effects on 

E. coli concentrations, which are significant 3 hours (hr) after 

rainfall, but not after 8 hr (Kleinheinz and others, 2009). 

Bird waste was shown to influence E. coli concentration on 

the day following deposition (Kleinheinz, McDermott, and 

Chomeau, 2006). Water samples collected within and outside 

of Cladophora mats revealed that the average concentrations 

of E. coli were greatest within the mats and that concentrations 

decreased with distance from the mat up to 33 feet (ft) (Englebert and others, 2008). In addition, sand has been identified 

as a source of E. coli contamination in nearby beaches, and 

swash zone sand typically has greater E. coli concentrations 

than upshore sand (Zehms and others, 2008). 

Purpose and Scope

This report describes the methods and results of an 

evaluation of multiple potential influences of FIB occurrence, 

including sources and transport mechanisms to the water 

column, at a relatively pristine beach on the shore of Green 

Bay in Door County, Wis. Pathogenic bacteria occurrence was 

also evaluated as part of this study, but sources and transport 

mechanisms for pathogens were not evaluated because no 

pathogenic genes were detected. The field investigation 

for the study described in this report included surface and 

groundwater sampling during August–September 2008 and 

July–August 2009.

Murphy Park Beach and its Watershed

Murphy Park Beach is located in a small embayment 

on the eastern side of Green Bay (the western shore of Door 

County), 50 miles (mi) north of the City of Green Bay (fig. 1) 

and 12 mi north of the City of Sturgeon Bay. Door County is 

entirely within the Door Peninsula, which begins in northern 

Brown and Kewaunee Counties to the south. A pier extends 

approximately 400 feet (ft) into the bay on the northern edge 

of the beach and forms a northern boundary for the beach 

study area. The beach extends approximately 1,000 ft to the 

south of the pier to a boat launch and the northern edge of 

Horseshoe Point, which forms the southern boundary for the 

embayment that encompasses Murphy Park Beach. The beach 

at Murphy Park forms the eastern boundary of the study site 

(fig. 2).

The Murphy Park Beach watershed covers approximately 

140 acres and includes park land, undeveloped woodland, part 

of a golf course, and several private residences. The watershed 

is underlain by dolomite bedrock of Silurian age that forms a 

steep ridge, known as the Niagara Escarpment, and a plateau 

in the eastern part of the watershed. Groundwater flow is 

generally from southeast to northwest along the western side 

of the Door Peninsula through fractures in the carbonate rocks 

(Sherrill, 1978). During the spring, groundwater seepage is 

visible along the beach; no seepage was observed during the 

study periods of August–September 2008 and July–August 

2009, although groundwater is expected to discharge below 

shallow beach water year-round. A concrete-lined pit toilet 

exists on the park premises, but no subterranean or surface wastewater discharges occur within Murphy Park. An 

ephemeral stream channel runs through the center of Murphy 

Park, south of the primary swimming area, but flow was not 

observed in this channel during the summer study periods 

and is therefore not shown in figures 1 or 2. A small perennial 

stream enters Horseshoe Bay between Horseshoe Point and 

the boat launch, approximately 800 ft south of the beach area, 

and was considered to be outside of the study area that was 

defined as being bounded along the south edge by the boat 

launch sampling site.
Introduction 3

87°20'30" 87°20'0" 87°19'30"

45°1'

45°0'30"

45°

Perennial streams and lakes

Murphy Park Beach watershed

EXPLANATION

Base map compiled and modified from digital data sources. 

Aerial photography from U.S. Department of Agriculture (2008).

Pier

Horseshoe Point

Boat launch

Door

County

Murphy Park

Beach

Green

Bay

0 0.2 0.4 MILE

0 0.2 0.4 KILOMETER

Figure 1. Location of Murphy Park Beach and watershed in Door County, Wisconsin.
4 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

!(

!(

!(

#*

#*#*

#*#*

Pier

Beach

Boat launch

EXPLANATION

#* Groundwater sampling sites

!( Lake water sampling sites

Sand and Cladophora sampling area

FEET

METERS

Base maps compiled and modified from digital data sources. 

Aerial photography from U.S. Dept. of Agriculture (2008).

!(

#*

#*#*#*#*

Beach

#*#*

0 40 80 160

0 20 40 10

0 130 260 520 FEET

0 40 80 160 METERS

Figure 2. Locations of data-collection sites at Murphy Park Beach, 2008–9.
Study Methods and Sampling Sites 5

Study Methods and Sampling Sites

U.S. Geological Survey (USGS) and University of 

Wisconsin-Oshkosh personnel collected samples for quantitative analysis of the fecal indicator bacteria E. coli and 

enterococci, analysis of the presence or absence of a suite of 

pathogenic bacteria, concentrations of suspended particulates 

in lake water, and analysis of a suite of basic water-chemistry 

characteristics at sites in Murphy Park. Basic water chemistry 

included cations, water temperature, pH, specific conductance, 

turbidity, and acid neutralizing capacity. Sample collection 

and analysis for E. coli, enterococci, and pathogens followed 

the methods described by Zehms and others (2008), Englebert 

and others (2008), and Eaton and others (2005). E. coli and

enterococci concentrations were expressed as most probable 

number per 100ml of water (MPN/100mL) or as most probable number per gram of dry sand (MPN/g). Pathogen presence 

was tested using PCR assays for signature genes of selected 

bacterial pathogens. Samples for analysis of basic water 

chemistry and suspended particulates were collected using the 

grab method, preserved, and then shipped to the Wisconsin 

State Laboratory of Hygiene. Preservation included acidification of cations with nitric acid to a pH less than 2 and chilling 

of all samples to approximately 4 degrees Celsius (°C). All 

samples were unfiltered, except the filtered lake water samples 

as described below.

Sampling Sites 

Sampling sites (fig. 2) were selected to evaluate sources 

and transport mechanisms of FIB and pathogens to beach 

water at Murphy Park Beach. The beach water site was considered the primary focus of the study, because FIB exceedances 

there trigger beach closure. Thus, the other sampling sites 

represented potential FIB and pathogen sources or transport 

pathways to the beach water. Sites evaluated for this study are 

shown in figure 2 and included the site and sample types listed 

below.

1. Lake water. The water of Green Bay could transport 

FIB and pathogens to the beach water via currents. 

Lake water sampling sites adjacent to the beach site 

included the pier and boat launch. Sampling at these 

sites captured FIB and pathogens potentially available for transport into the beach water column via 

currents. The beach water site is also included as 

a lake water sampling site in sections of the report 

describing sampling and laboratory methods and 

sample collection schedules.

2. Groundwater. Shallow groundwater is a potential 

source or transport mechanism, or both, of microbiological contaminants (Alexander and others, 2008) to 

the beach water column. Groundwater sampling sites 

included several shallow piezometers, or wells, at 

varying distances from the shoreline and a deep well 

about 150 ft from the shoreline that provides drinking 

water. Piezometers were categorized as being near

(typically less than 5 ft from shore), middle (typically 

5–15 ft from shore), or far from the shoreline (typically greater than 100 ft from shore).

3. Suspended particulates. Filters were used to capture 

FIB and pathogens in lake water associated with 

suspended particulates larger than 63 microns (fine 

sand), between 63 and 1 micron (silt), and clay, 

colloids, or free-floating organisms smaller than 1 

micron (filtrate). Samples for FIB associated with 

particulates were collected at the beach water and 

boat launch sites and are referred to as 63 micron, 

1 micron, or filtrate.

4. Sand. Beach sand has been found to harbor high levels 

of FIB and represented a potential source of FIB and 

pathogens to beach water. Sand cores were collected 

representing upshore, swash-zone, and submerged

sand.

5. Cladophora. Water within and adjacent to Cladophora

mats was sampled to evaluate the potential for 

Cladophora mats to act as sources of FIB and pathogens to beach water at Murphy Park Beach. Samples 

were categorized as either interior or exterior of a 

Cladophora mat, and are referred to as either within

or adjacent to a mat.

Sampling Schedule

Surface-water samples were collected into sterile 

120-milliliter (mL) plastic bottles 4 days per week at the beach 

site and 4 consecutive days every other week at the pier and 

boat launch sites. Groundwater samples, sand cores, and water 

samples associated with Cladophora were collected every 

other week and corresponded with the weeks when samples 

were collected at the pier and boat launch sites. Sampling for 

FIB associated with suspended particulates was targeted for 

periods of increased storm activity but always coincided with 

a sample from the beach. Sample collection was typically 

completed during the morning to minimize potential effects 

of FIB reduction due to solar radiation. Although this was 

not always possible, analyses of samples collected from the 

lake water sampling sites showed no statistically significant 

relation with time of day that a sample was collected. Table 1 

summarizes which constituents were sampled at each site 

during 2008 and 2009. Sampling in 2008 focused on FIB in 

lake water at the beach and pier and in groundwater. Sampling in 2009 included collection of samples for analysis for 

pathogens, as well as samples of lake water at the boat launch 

sampling site, particulates, sand cores, and water sampling 

within and adjacent to Cladophora mats.
6 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Table 1. Dates, locations, and types of environmental samples collected at Murphy Park Beach, 2008–9.—Continued

[Dates are indicated by numerals for the month, day, and year. E, Escherichia coli; C, enterococci; W, water chemistry; A, ancillary data including: wave 

height, bather and avian counts (beach only), current direction and speed, turbidity, water temperature, specific conductance, and pH; P, pathogen analysis; 

--, no data. Sand samples included collection of three cores of submerged, swash zone, and upshore sand at the beach]

Date Water-sample locations and types

Filtered sediment and 

water-sample locations 

and types Sand Cladophora

mats

Beach Pier Boat launch Piezometers Beach Boat launch

2008

8/11/2008 E, C, W E, C, W -- E, C, W -- -- -- --

8/12/2008 E, C, W E, C, W -- -- -- -- -- --

8/13/2008 E, C, W E, C, W -- -- -- -- -- --

8/14/2008 E, C, W E, C, W -- -- -- -- -- --

8/18/2008 E, C, W E, C, W -- -- -- -- -- --

8/19/2008 E, C, W E, C, W -- -- -- -- -- --

8/20/2008 E, C, W E, C, W -- -- -- -- -- --

8/21/2008 E, C, W E, C, W -- -- -- -- -- --

8/24/2008 E, C, W E, C, W -- -- -- -- -- --

8/25/2008 E, C, W E, C, W -- -- -- -- -- --

8/26/2008 E, C, W E, C, W -- E, C, W -- -- -- --

8/27/2008 E, C, W E, C, W -- -- -- -- -- --

9/3/2008 E, C, W E, C, W -- E, C, W -- -- -- --

9/4/2008 E, C, W E, C, W -- -- -- -- -- --

9/11/2008 E, C, W E, C, W -- E, C, W -- -- -- --

2009

7/9/2009 E, C, W, A E, C, W, A E, C, W, A E, C, W -- -- -- --

7/10/2009 -- -- -- -- -- -- E, C E, C

7/13/2009 E, C, A -- -- -- -- -- -- --

7/14/2009 E, C, A -- -- -- -- -- -- --

7/15/2009 E, C, A -- -- -- -- -- -- --

7/16/2009 E, C, A -- -- -- -- -- -- --

7/20/2009 E, C, A E, C, A E, C, A E, C -- -- -- --

7/21/2009 E, C, A E, C, A E, C, A E, C -- -- E, C E, C

7/22/2009 E, C, W, A E, C, W, A E, C, W, A E, C, W -- -- E, C E, C

7/23/2009 E, C, A E, C, A E, C, A E, C -- -- -- --

7/27/2009 E, C, A -- -- -- E, C -- -- --

7/28/2009 E, C, A -- -- -- E, C E, C -- --

7/29/2009 E, C, A -- -- -- -- -- -- --

7/30/2009 E, C, A -- -- -- -- -- -- --

8/1/2009 E, C, W, A E, C, W, A E, C, W, A E, C, W -- -- E, C E, C

8/3/2009 E, C, A E, C, A E, C, A E -- -- -- --

8/5/2009 E, C, A, P E, C, A, P E, C, A, P E, C, P -- -- E, C E, C

8/6/2009 E, C, A, P E, C, A, P E, C, A, P E, C, P -- -- -- --

8/10/2009 E, C, A -- -- -- -- -- -- --

8/11/2009 E, C, A -- -- -- -- -- -- --

8/12/2009 E, C, A -- -- -- -- -- -- --

8/13/2009 E, C, A -- -- -- -- -- -- --
Study Methods and Sampling Sites 7

Table 1. Dates, locations, and types of environmental samples collected at Murphy Park Beach, 2008– 9.—Continued

[Dates are indicated by numerals for the month, day, and year. E, Escherichia coli; C, enterococci; W, water chemistry; A, ancillary data including: wave 

height, bather and avian counts (beach only), current direction and speed, turbidity, water temperature, specific conductance, and pH; P, pathogen analysis; 

--, no data. Sand samples included collection of three cores of submerged, swash zone, and upshore sand at the beach]

2009—continued

8/17/2009 E, C, A, P E, C, A, P E, C, A, P E, C, P -- -- -- --

8/18/2009 E, C, W, A, P E, C, W, A, P E, C, W, A, P E, C, W, P -- -- E, C E, C

8/19/2009 E, C, A, P E, C, A, P E, C, A, P E, C, P -- -- -- --

8/20/2009 E, C, A, P E, C, A, P E, C, A, P E, C, P E, C E, C E, C E, C

8/24/2009 E, C, A, P E, C, A, P E, C, A, P -- -- -- -- --

8/25/2009 E, C, A, P E, C, A, P E, C, A, P -- E, C E, C -- --

8/26/2009 E, C, A, P E, C, A, P E, C, A, P -- -- -- -- --

Lake Water Sampling

Samples from the lake water sampling sites were collected using a grab-sampling technique at about 1.0 ft below 

the surface in water with a depth of about 2 ft, except at the 

pier, where the water depth was approximately 6 ft. Samples 

were collected at the end of the pier and at the boat launch 

in 2009 in an effort to evaluate potential transport of FIB 

into the beach area. A stream enters Horseshoe Bay between 

Horseshoe Point and the boat launch. Because the boat launch 

is between Murphy Park Beach and the stream, the samples 

collected at the boat launch were expected to integrate water 

from the stream and from long-shore currents flowing northeast along the eastern shoreline between Horseshoe Point and 

the beach. Thus, the intention was to characterize potential 

transport of FIB into the beach area from external sources by 

collecting samples at the pier and boat launch sites.

Groundwater Sampling

Groundwater samples were collected by first evacuating 

approximately 3 liters (L) (approximately four well volumes) 

of well water at a moderate pumping rate by use of a peristaltic pump and high-density polyethylene tubing, followed by 

sample collection with the same system. Groundwater samples 

from a public drinking water well were collected by first 

evacuating approximately 5 L of water (less than one well volume) at a moderate rate by use of a hand pump prior to sample 

collection directly from the well spigot. 

Suspended Particulates in Lake Water

Samples for FIB associated with suspended particulates 

were collected through direct sampling in the field. Specifically, lake water was pumped through a series of nylon filters 

with pore openings of 63 microns and 1 micron for approximately 1 hr until either the 63-micron or 1-micron filter 

appeared caked with material. The suspended particulates 

collected on the filters and the filters themselves were placed 

in sterile jars and transported to the lab, where the filters and 

particulates were rinsed with deionized water. FIB concentrations from this rinse water were reported as MPN/mL of 

rinse water, which were then normalized by the total amount 

of water pumped through the filters and finally converted to 

MPN/100mL of pumped water. Filtrate water was also collected and analyzed for FIB. 

Sand Sampling

E. coli and enterococci from sand cores were collected using the methods of Zehms and others (2008), which 

included collecting three sand cores in each of three beach 

sand environments: upshore, swash zone, and submerged. 

Submerged sand cores were collected at approximately 2-ft 

water depth, swash-zone sand was collected where wave 

action maintained high moisture in the beach sand, and 

upshore sand was collected beyond the area of wave action, 

10–20 ft away from the shoreline. In the lab, the sand was 

washed with deionized water, and this filtrate was analyzed 

for E. coli and enterococci by the defined substrate methods 

Colilert® and Enterolert®, and the results were expressed in 

units of MPN/100mL. Finally, the sand was dried and each 

MPN/100mL result was converted to MPN/g of dry sand.

Cladophora Sampling 

Water samples in and adjacent to Cladophora mats were 

collected using the methods of Englebert and others (2008), 

with multiple water samples collected within Cladophora

mats and at multiple distances away from the Cladophora mat. 

Visual estimates of relative Cladophora abundance were also 

made during each sampling event.
8 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Ancillary Data 

Ancillary data were collected at the time of sample 

collection at each of the three lake water sampling sites and 

included: wave height, water temperature, current direction 

and speed, bather and bird counts, turbidity, specific conductance, and pH. Ancillary data were collected using the same 

protocols as Zehms and others (2008). Continuous data were 

also recorded at the base of a buoy located in approximately 

6 ft of water and approximately 50 ft south of the pier, and 

additional continuous data were recorded at an onshore 

companion site during the summer of 2009. Continuous data 

included water level, turbidity, specific conductance, precipitation, and solar radiation.

Pathogens

Pathogen samples were collected for lake water and 

groundwater sampling sites starting on Aug. 5, 2009 (table 1). 

Samples were processed by the USGS Michigan Water Science Center Microbiology Laboratory within 48 hr from the 

time of sampling. Immediately upon arrival at the lab, samples 

were unpacked and an identification number was assigned to 

each sample for tracking the sample. 

The targeted bacterial pathogens were human-pathogenic 

enterococci, Shigella sonnei, Shiga toxin-producing E. coli

(STEC), Salmonella species, and Campylobacter jejuni and 

coli. Growth media and enrichment parameters for each target 

organism are shown in table 2. Solid (agar) media for the 

enrichment for E. coli/Shigella (mFC medium) and enterococci (mEI medium) were prepared according the manufacturer’s instructions. Membrane filtration was done according 

to standard procedures (Eaton and others, 2005; U.S. Environmental Protection Agency, 2000). Selective enrichments for 

Campylobacter and Salmonella were done by inoculating the 

appropriate broth (table 2) with a filter containing the filtrate 

from 100 mL of sample water. Observations were enumerated 

from the agar plates, if appropriate, and broth enrichments. 

Membrane filters with subsequent growth were frozen directly 

at −20°C until further analysis. For broth cultures, following 

agitation for 15 minutes, membrane filters were aseptically 

removed and the broth centrifuged to form a pellet. Supernatant was decanted and the pellet was resuspended in 1 mL of 

20 percent glycerol prepared in one-half strength Phosphate 

Buffered Solution. Glycerol preparations were stored at −70°C 

until deoxyribonucleic acid (DNA) extraction, which took 

place up to 2 years later. For DNA extraction, filters cut into 

eighths, or pellets from broth cultures, were thawed at room 

temperature, and DNA was then extracted from all samples 

using the alkaline polyethylene glycol method of Chomczynski and Rymaszewski (2006). Extracted DNA was stored 

at −20°C, and was analyzed within 1 week of extraction. All 

equipment used in filtering was cleaned and sterilized daily 

and checked prior to each use. A laboratory blank was run 

daily by filtering Phosphate Buffered Solution through a filter 

cup onto a filter for each medium prior to testing, and a laboratory replicate was run weekly.

STEC E. coli and pathogenic enterococci were detected 

using previously published methods (Duris and others, 2009; 

Haack and others, 2009). Shigella sonnei was detected using 

modifications of the procedure of Islam and others (1993). 

Campylobacter jejuni and C. coli were detected using modifications of the methods of Inglis and Kalischuk (2003). Salmonella and pathogenic Salmonella species were detected using 

modifications of the methods of Chiu and Ou (1996). Standard 

quality assurance and control procedures were followed for all 

PCR reactions (U.S. Environmental Protection Agency, 2004). 

Detection limits for all PCR reactions were determined using 

serial dilution of DNA from control organisms (table 3). For 

approximately every 20 samples of any given PCR reaction, 

PCR-positive controls and PCR-negative controls (no template 

reactions) were included. Environmental matrix issues were 

minimized in these methods by analyzing DNA extracted from 

pre-enriched cultures. All PCR assays were performed using 

1 microliter (1–100 nanograms) of template DNA. Prior studies indicate a range of detection limits of 20–200 cells for the 

various reactions (Haack and others, 2009).

Table 2. Growth medium and enrichment parameters for target pathogenic bacteria.

[mL, milliliters; ±, plus or minus; °C, degrees Celsius]

Target organism Growth medium Purpose

Volume 

filtered, 

in mL

Incubation temperature Reference

Enterococci mEI Enrichment 100 41.5°C ± 1.0°C for 22–24 hours U.S. Environmental Protection 

Agency (2006)

Shigella mFC Enrichment 100 44°C ± 1.0°C for 22–24 hours Eaton and others (2005)

Escherichia coli mFC Enrichment 100 44°C ± 1.0°C for 22–24 hours Eaton and others (2005)

Salmonella Rappaport-Vassiliadis 

R10 broth

Enrichment 100 37°C ± 1.0°C for 22–24 hours Vassiliadis and others (1978)

Campylobacter Bolton broth Enrichment 100 37°C ± 1.0°C for 4 hours

41.5°C ± 1.0°C for 48 hours

Baylis and others (200)
Study Methods and Sampling Sites 9

Table 3. Positive controls and detection limits for polymerase chain reaction (PCR) assays.

[ng/μL, nanograms per microliter; E. coli, Escherichia coli]

Target organism Gene targets Band size Positive control Detection limit,

in ng/μL

Enterococci esp 954 Enterococcus faecium E53 0.0001

Shigella sonnei ipaH 620 ATCC 9290 .0008

Escherichia coli eaeA

stx1

stx2

E. coli 16S rDNA

rfb0157

890

779

614

544

420

ATC35150

ATC35150

ATC35150

ATC35150

ATC35150

.01

.01

.01

.01

.0001

Salmonella spvC

invA

571

244

Salmonella typhimurium ATCC 14028

Salmonella typhimurium ATCC 14028

.0025

.0025

Campylobacter jejuni and coli 16S rDNA 857 Campylobacter jejuni ATCC 29428 .001

Multivariate Statistical Analysis

E. coli concentrations from samples collected in 2009 

and 202 possible explanatory variables measured in 2009 were 

used in a multivariate analysis to explore potential statistical relations and evaluate which variables explain the most 

variability in E. coli concentrations for this period of study 

(table 4). These variables included data collected directly 

for this study, data gathered from nearby National Weather 

Service stations, and modeling results from the Great Lakes 

Forecasting System (Schwab and Bedford, 1999). Daily data 

collected at the beach and daily variables collected by the 

National Weather Service were used directly. For all other 

variables, data or modeling results were available on a finer 

time scale of less than 1 day (1, 2, 3, 6, and 12 hr). For these 

subdaily variables, the value from the nearest previous measurement as well as a number of chosen temporal summations, 

mean, maximum, and median values were used in multivariate 

analysis (table 4). 

Table 4. Variables used in multivariate regression for Escherichia coli (E. coli) concentrations at Murphy Park Beach, 

July–September 2009.

[UW, University of Wisconsin; USGS, U.S. Geological Survey; min, minute; hr, hour; NWS, National Weather Service; Wis., Wisconsin; NOAA, National 

Oceanic and Atmospheric Administration]

Data type Location Source Time frequency 

of raw data Variables used in analysis

Manual data collection 

at beach

Murphy Park Beach UW–Oshkosh/USGS 1 per day Raw data.

Continuous monitoring 

at beach

Murphy Park Beach USGS 5 min Rainfall: summation of 0.5-, 1-, 2-, 3-, 

5-, and 10-day rainfall.

Solar radiation: nearest previous 

measurement and mean, maximum, 

and median of past 12, 24, 48, 96, 144, 

and 192 hrs.

Turbidity, specific conductance, water 

temperature: nearest previous 

measurement and mean and maximum 

of past 1, 2, 3, 6, 12, and 24 hrs.

NWS stations Sturgeon Bay, Wis.; 

Sister Bay, Wis.; 

Chambers Island, Wis. 

NWS 1 per day Raw data.

Continuous radar 

rainfall

Modeled results NWS 1 hr Rainfall: summation of 0.5, 1, 2, 3, 4, 5, 

and every 2 days from 6 – 40 days.

Great Lakes 

Forecasting System

Modeled results NOAA 1 hr Lake-surface elevation, surface and 

depth-integrated water velocity 

(perpendicular and parallel to beach), 

wave height, wave direction: mean and 

maximum of past 1–24 hrs.
10 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Four levels of statistical analysis were used to explore 

this data. All analyses were conducted using R statistical software (R Development Core Team, 2011). The four levels of 

analyses were performed as follows.

1. Subdaily time series variable selection. For each 

variable that was available on a subdaily basis, all 

temporal summation variables derived from that 

physical variable and, as appropriate, the log transformations were used to generate Pearson correlation 

coefficients with E. coli concentration. The temporal 

summation variable with the highest Pearson correlation coefficient for each physical variable was 

chosen for subsequent analyses. 

2. Recursive partitioning analysis. All daily measurements as well as the subdaily variables that 

were chosen in level 1 were used in a recursive 

partitioning analysis also referred to as classification and regression tree, to explore relations between 

E. coli concentrations and predictor variables. 

Recursive partitioning analysis provides an option 

for exploring complex data relations with nonlinear 

structure and variable interactions by successively 

splitting the data into increasingly homogeneous 

subsets. Stopping rules are used to reach final 

splitting points or “terminal nodes.” The recursive 

partitioning process results in a flow chart or “tree” 

that splits data based on a set of rules. Recursive 

partitioning analyses are particularly well suited for 

use with complex ecological data (De’Ath and Fabricius. 2000). This analysis was conducted independently two times, once for those variables that were 

available on a daily time interval and a second time 

for derivatives of the subdaily time series variables 

that were computed to match the daily sample times 

(table 4). The variables that proved to be somewhat 

influential were carried forward for subsequent 

level 3 and 4 analyses. These variables included the 

first three split variables as well as close competitor 

variables, which would provide a valuable split if the 

chosen split variable were not present, and close surrogate variables, which would provide a split similar 

to the chosen split variable. 

3. Multiple ordinary least squared linear regression

used all possible four variable combinations from 

those variables surviving level 1 and 2 analyses, 

which is referred to as “all subsets regression.” 

4. Stepwise regression used the resulting variables 

from level 3 analysis along with the three most 

influential variables in both of the level 2 recursive 

partitioning analyses. It was necessary to reduce the 

variables from the original 202 for stepwise regression analysis due to the limitations of ordinary least 

squared regression and to avoid overfitting of the 

final regression model.

The first three levels were used to aid with variable selection for the fourth level. Results from the second and fourth 

levels were used to draw final conclusions on potential influential variables identified from this multivariate analysis.

FIB Concentrations at Potential Source 

Reservoirs

FIB in Lake Water

FIB concentrations in water samples collected at the boat 

launch for only 2009 and the pier for 2008 and 2009 combined 

were compared with results from beach water to evaluate 

potential sources for transport of FIB to the beach area (fig. 3, 

table 5). Daily FIB concentrations at the boat launch and the 

pier were directly compared to FIB concentrations in beach 

water by normalizing concentrations at the boat launch and the 

pier with concentrations in beach water (fig. 3C and D). This 

type of direct comparison by normalizing with FIB concentrations in beach water from the same day was performed for 

all potential aquatic source locations, including groundwater, 

suspended particulates, and Cladophora-associated water. 

E. coli concentrations in water at the beach were generally 

higher than those in water at either the boat launch or the pier, 

except on a few dates when E. coli concentrations at the boat 

launch (July 23 and Aug. 26, 2009) and E. coli at the pier 

(Aug. 3, 24, and 26, 2009) exceeded those measured at the 

beach (fig. 4A, table 5). Concentrations of enterococci in beach 

water were higher than those at the pier and boat launch sites, 

except on a few occasions at the boat launch (July 23 and 

Aug. 5, 2009) and at the pier (Aug. 24 and Sept. 11, 2008, and 

Aug. 19 and Sept. 17, 2009). Aside from the E. coli measured 

at the boat launch on July 23, 2009, the E. coli concentrations at the boat launch and the pier were always less than the 

U.S. Environmental Protection Agency water-quality criterion 

of 235 MPN/100mL.
FIB Concentrations at Potential Source Reservoirs 11

E. coli, in most probable number 

per 100 milliliters of water

Enterococci, in most probable number 

per 100 milliliters of water

Beach water

Boat launch

Pier

1

5

10

50

100

500

1,000

(42)

(16)

(30)

o

o

o

o

o

o

xx

x

Beach water

Boat launch

Pier

1

5

10

50

100

500

1,000

5,000 5,000 (31)

(13)

(26)

o

o

o

o

o

o

o

o

x

x x

E. coli ratio 

Boat lanch / Beach

Pier / Beach

0.001

0.01

0.1

1

10

100

1,000

(16)

(30)

o

o o

x

Enterococci ratio 

Boat lanch / Beach

Pier / Beach

0.001

0.01

0.1

1

10

100

1,000

(13)

(27)

o

o

o

ox

A B

C

EXPLANATION

Number of points

o

x

Severe outlier

Moderate outlier

Adjacent value

75th Percentile

25th Percentile

Median

D

(25)

Figure 3. Boxplots of A, Escherichia coli (E. coli) and B, enterococci concentrations in lake water and ratios of C, E. coli

and D, enterococci for lake water sites at Murphy Park Beach, 2008–9.
Table 5. Fecal indicator bacteria concentrations in samples from the lake water sampling sites and current directions at the three lake water samplMurphy Park Beach, 2008–9.—Continued [Dates are indicated by numerals for the month, day, and year. E. coli, Escherichia coli; MPN/100mL, most probable number per 100 milliliters; --, no data] Date Beach Boat launch Pier E. coli (MPN/100mL) Enterococci (MPN/100mL) Current direction (degrees from north) E. coli (MPN/100mL) Enterococci (MPN/100mL) Current direction (degrees from north) E. coli (MPN/100mL) Enterococci (MPN/100mL) 

8/11/2008 206 328 -- -- -- -- 6 6 8/12/2008 28 10 -- -- -- -- 2 1 8/13/2008 75 20 -- -- -- -- 4 1 8/14/2008 91 40 -- -- -- -- 5 2 8/18/2008 39 13 -- -- -- -- 3 5 8/19/2008 127 184 -- -- -- -- 16 13 8/20/2008 4 3 -- -- -- -- 1 2 8/21/2008 3 6 -- -- -- -- 1 2 8/24/2008 13 2 -- -- -- -- 15 792 8/25/2008 2 2 -- -- -- -- 1 1 8/26/2008 6 37 -- -- -- -- 1 2 9/3/2008 1 1 -- -- -- -- 1 1 9/4/2008 1 2 -- -- -- -- 1 2 9/11/2008 11 14 -- -- -- -- 3 16 7/9/2009 5 81 360 1 24 360 1 10 7/13/2009 6 3 95 -- -- -- -- -- 7/14/2009 1 1 95 -- -- -- -- -- 7/15/2009 60 2,420 90 -- -- -- -- -- 7/16/2009 12 46 90 -- -- -- -- -- 7/20/2009 17 9 360 1 2 345 1 1 7/21/2009 1 1 270 1 1 270 1 1 7/22/2009 56 66 245 1 1 190 19 1 7/23/2009 7 9 90 548 47 190 1 1 7/27/2009 2 -- 45 -- -- -- -- -- 7/28/2009 2 -- 90 -- -- -- -- -- 7/29/2009 2 -- 90 -- -- -- -- -- 7/30/2009 84 -- 90 -- -- -- -- -- 
Table 5. Fecal indicator bacteria concentrations in samples from the lake water sampling sites and current directions at the three lake water samplMurphy Park Beach, 2008–9.—Continued[Dates are indicated by numerals for the month, day, and year. E. coli, Escherichia coli; MPN/100mL, most probable number per 100 milliliters; --, no data]

Beach Boat launch Pier

Date E. coli 

(MPN/100mL)

Enterococci 

(MPN/100mL)

Current 

direction 

(degrees 

from north)

E. coli 

(MPN/100mL)

Enterococci 

(MPN/100mL)

Current 

direction 

(degrees 

from north)

E. coli 

(MPN/100mL)

Enterococci 

(MPN/100mL)

8/1/20098/3/20098/5/20098/6/20098/10/20098/11/20098/12/20098/13/20098/17/20098/18/20098/19/20098/20/20098/24/20098/25/20098/26/2009

195

84

210

487541

125

15

1,203

4

199

5

2342

435

22

1

727

--------

10

2,420

3

133

------

45459045

270125360

904590904590

210

90

5229

--------

13

31

64

11

194

3191

--------

171

66

------

45459045--------9090904590

180

90

3712

14

--------

9

20

3415

117

13

51

86

--------

25321013

------
14 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

EXPLANATION

0

500

1,000

1,500

2,000

2,500

2009

0

500

1,000

1,500

2,000

2,500

2008

0

200

400

600

800

1,000

1,200

1,400

2009

0

200

400

600

800

1,000

1,200

1,400

2008

July 1 July 21 Aug. 10 Aug. 30

July 1 July 21 Aug. 10 Aug. 30

July 1 July 21 Aug. 10 Aug. 30

July 1 July 21 Aug. 10 Aug. 30

E. coli, in most probable number 

per 100 milliliters of water

E. coli, in most probable number 

per 100 milliliters of water

Enterococci, in most probable number 

per 100 milliliters of water

Enterococci, in most probable number 

per 100 milliliters of water

A

B

Beach

Boat launch

Pier

Figure 4. Time series of A, Escherichia coli (E. coli) and B, enterococci concentrations in lake water at Murphy Park 

Beach, 2008–9.

FIB in Groundwater

All groundwater data from 2008 and 2009 were grouped 

into relative piezometer location descriptions as near, middle, 

and far from shore (fig. 5). This approach was used because 

the shoreline eroded approximately 15 ft between August 2008 

and August 2009, and shallow piezometers that had originally 

been installed in the swash zone had to be removed and reinstalled farther upshore. Following installation, the piezometers 

were purged until at least 8 L of water had been removed from 

the well casing and surrounding aquifer; the typical installation resulted in 0.8 L of water stored within the piezometer 

itself. In addition to the groundwater purging, any samples 

with unusually high FIB concentrations that were suspected of 

being associated with the installation process were removed 

from the analysis. Such samples were limited to the first round 

of sampling following piezometer reinstallation and were 

expected to be caused by mixing and agitation of the native 

sand surrounding the piezometer.

The nearshore piezometers typically had the highest FIB 

concentrations of all piezometers and in some instances had 

higher FIB concentrations than the beach water (50 percent 

of E. coli samples, fig. 5C); however, the median and interquartile range in FIB concentrations in groundwater decreased 

rapidly with distance from the shore (fig. 5A and B). This 

suggests that regional groundwater, or the groundwater originating hundreds of feet to a few miles inland, is likely not a 

major source of FIB to the beach water, although swash-zone

groundwater may be a substantial source of FIB to beach 

water. Because regional groundwater does not appear to be a 

source of FIB to swash-zone groundwater, FIB in the wells 

nearest the lake (in the swash zone) likely originated from FIB 

in beach water or was washed off of sand or organic material 

on the shore. This process would occur as wave action spreads 

water inland over the shore and the water infiltrates into the 

soil, at which point the water and associated FIB mix with 

groundwater in the swash zone. This swash-zone groundwater is expected to discharge into the beach water following 

groundwater recharge events.
FIB Concentrations at Potential Source Reservoirs 15

E. coli, in most probable number 

per 100 milliliters of water

Enterococci, in most probable number 

per 100 milliliters of water

Far PZ

Middle PZ

Near PZ

Beach water

1

5

10

50

100

500

1,000

5,000

(16) (11)

(17)

(17)

o

o

o

o x

x

Far PZ

Middle PZ

Near PZ

Beach water

1

5

10

50

100

500

1,000

5,000

(15)

(11) (17)

(17)

o

o

o

o

o

o o

o

o

x x

E. coli ratio

Far PZ / Beach

Middle PZ / Beach

Near PZ / Beach

0.001

0.01

0.1

1

10

100

1,000

(16) (11)

(17)

o

oo

o

o

o

Enterococci ratio 

Far PZ / Beach

Middle PZ / Beach

Near PZ / Beach

0.001

0.01

0.1

1

10

100

1,000

(15)

(11)

(17)

o

o

o

o o

o

o

A B

EXPLANATION

(25) Number of points

o

x

Severe outlier

Moderate outlier

Adjacent value

75th Percentile

Median

25th Percentile

C D

Figure 5. Boxplots of A, Escherichia coli (E. coli) and B, enterococci concentrations and ratios of C, E. coli

and D, enterococci in groundwater for piezometer (PZ) sites at Murphy Park Beach, 2008–9. Far, Middle, and 

Near descriptors indicated the relative distance from the shoreline, respectively. 
16 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

FIB Associated with Suspended Particulates in 

Lake Water

FIB concentrations generally increased from the lowest 

concentrations in samples associated with suspended particulates larger than 63 microns, to larger concentrations in 

samples associated with suspended particulates larger than 

1 micron, to the highest concentrations in the filtrate (fig. 6). 

The increasing FIB concentration with decreasing filter pore 

size suggests that fewer FIB are associated with coarsegrained suspended particulates (sand) than with fine-grained 

particulates. In general, it appears more FIB are present either 

as free-floating bacteria or attached to particles smaller than 

1 micron than are attached to larger suspended particulates. 

This finding suggests that potential high FIB concentrations 

released from eroded beach sand may be dispersing directly to 

the water column rather than settling out with sediment. Similarly, this finding suggests that submerged sand would be an 

unlikely source of FIB to the water column, because it appears 

that FIB are not strongly bound to sand-sized particulates (see 

“FIB in Beach Sand” below). In general, the sum of total FIB 

concentration from each filter pore-size category was similar 

to that measured from the corresponding grab sample of beach 

water. Still, summations for several samples produced concentrations that were larger or smaller than the grab sample by 

more than an order of magnitude, highlighting the uncertainties associated with this analysis.

FIB in Beach Sand

Similar to previous findings from this region of Lake 

Michigan (Zehms and others, 2008), FIB concentrations associated with sand samples at Murphy Park Beach were higher 

in swash and upshore areas of the beach than in submerged 

sand samples (fig. 7). Moreover, variability in FIB concentrations was higher in the swash and upshore samples than in the 

submerged sand samples.

FIB Associated with Cladophora Mats

Similar to previous findings (Englebert and others, 2008; 

Vanden Heuvel and others, 2010), FIB concentrations in water 

near Cladophora mats at Murphy Park Beach span a large 

range of more than three orders of magnitude and decrease 

with distance from Cladophora mats (fig. 8). In general, FIB 

concentrations were highest in water samples collected within 

Cladophora mats, with medians of 471 MPN/100mL for 

E. coli and 794 MPN/100mL for enterococci; intermediate in 

water samples adjacent to Cladophora mats, with medians of 

136 MPN/100mL for E. coli and 529 MPN/100mL for enterococci; and lowest in water samples from the standard beach 

water sampling location, with medians of 125 MPN/100mL 

for E. coli and 99 for and enterococci. Differences in the mean 

concentrations among these locations were not statistically 

significant due to the small sample size.

Pathogen Detection in Lake Water and 

Groundwater

No genes indicating the presence of E. coli O157 

(rfbO157), Campylobacter jejuni or coli, or pathogenic Salmonella, Shigella, or Enterococcus were detected in lake water 

or groundwater. Of the three genes indicating potential STEC, 

only the eaeA gene was detected, and that only in 8 of the 44 

samples tested. The eaeA gene encodes the ability to attach to 

intestinal cells and is considered a fundamental virulence factor for several types of pathogenic E. coli, although multiple 

subtypes of this gene are associated with varying disease 

outcomes (Trabulsi and others, 2002). In the United States, 

the eaeA gene is not typically considered a primary indicator 

of pathogenic E. coli in the absence of other virulence genes, 

such as the Shiga toxin genes. 

The lack of detection of pathogen genes in these samples 

could simply be a reflection of the quality of the water at this 

site. As noted previously, however, samples were preserved 

for an extended period before DNA extraction. Although we 

cannot determine whether this preservation period compromised the ability to detect pathogen genes, the E. coli 16S 

rDNA gene was detected in every sample where it would be 

expected, based on E. coli counts conducted at the site on the 

day of sampling. Thus, analysis of this internal control gene 

did not appear to be compromised by extended storage.
Pathogen Detection in Lake Water and Groundwater 17

63 micron

1 micron

Filtrate

Unfiltered water

0.01

0.1

1

10

100

(11) (11)

(19)

(6)

o

o

o

o

o

63 micron

1 micron

Filtrate

Unfiltered water

0.01

0.1

1

10

100

(11)

(11)

(19)

(2)

o

o

o

o

o

o

E. coli ratio 

63 micron / 

Unfiltered water

1 micron /

 Unfiltered water

Filtrate /

Unfiltered water

0.00001

0.0001

0.001

0.01

0.1

1

10

(10) (10)

(18)

o

o

Enterococci ratio 

(4)

(4)

(8)

63 micron /

Unfiltered water

1 micron /

Unfiltered water

Filtrate /

Unfiltered water

0.00001

0.0001

0.001

0.01

0.1

1

10

A B

EXPLANATION

(25) Number of points

o

x

Severe outlier

Moderate outlier

Adjacent value

75th Percentile

Median

25th Percentile

C D

E. coli, in most probable number 

per 100 milliliters of water

Enterococci, in most probable number 

per 100 milliliters of water

Figure 6. Boxplots of A, Escherichia coli (E. coli) and B, enterococci concentrations and ratios of C, E. coli and 

D, enterococci in samples for suspended particulates at Murphy Park Beach, 2009. 
18 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

A B E. coli, in most probable number per gram Enterococci, in most probable number per gram

EXPLANATION

(25) Number of points

o

x

Severe outlier

Moderate outlier

Adjacent value

75th Percentile

Median

25th Percentile

Submerged

Swash

Upshore

1

10

100

1,000

10,000

(21)

(20) (21)

o

o

o

o

o

o

o

oo

Submerged

Swash

Upshore

1

5

10

50

100

500

1,000

5,000

(20)

(20)

(21)

o

o

o

o

o

o

x

Figure 7. Boxplots of A, Escherichia coli (E. coli) and B, enterococci concentrations in sand at Murphy Park Beach, 2009.
Pathogen Detection in Lake Water and Groundwater 19

A B

E. coli, in most probable number 

per 100 milliliters of water

Enterococci, in most probable number 

per 100 milliliters of water

EXPLANATION

(25) Number of points

o

x

Severe outlier

Moderate outlier

Adjacent value

75th Percentile

Median

25th Percentile

Within mat

Adjacent to mat

Beach water

(7) (7) (6)

o

1

5

10

50

100

500

1,000

5,000

1

5

10

50

100

500

1,000

5,000

(7) (7) (6) o Within mat Adjacent to mat Beach water

E. coli ratio 

Within mat/

Beach water

Adjacent to mat/

Beach water

0.01

0.1

1

10

100

1,000

(6)

(6)

x

Enterococci ratio 

(6)

(6)

o

x

Within mat/

Beach water

Adjacent to mat/

Beach water

0.01

0.1

1

10

100

1,000

C D

Figure 8. Boxplots of A, Escherichia coli (E. coli) and B, enterococci concentrations and ratios of C, E. coli and 

D, enterococci in water within and adjacent to Cladophora mats and in beach water at Murphy Park Beach, 2009.
20 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Multivariate Analysis of E. coli

Concentrations

Results of recursive partitioning routines (level 2 analysis) using variables from the level 1 correlation analysis are 

as follows. The first three split variables for the two recursive 

partitioning analyses included hourly mean specific conductance, 10-day radar rainfall, maximum 12-hr turbidity, visibility in Sturgeon Bay, Wis., and specific conductance and wave 

height measured at the time of sample collection. Competitor 

and surrogate variables included the 96-hr median of 5-minute 

maximum solar radiation values, mean 6-hr wave height, maximum 12-hr wave height, and mean 6-hr current parallel to the 

beach. Results of the all-subsets regression (level 3 analysis) 

indicated that four influential variables in explaining E. coli

concentration were hourly mean specific conductance, turbidity measured at the time of sample collection, the most recent 

wind speed value from the Great Lakes Forecasting System, 

and wind speed at Sturgeon Bay. By use of results from levels 

2 and 3, stepwise regression (level 4 analysis) indicated that 

the most influential variables were hourly mean specific 

conductance, maximum 12-hr turbidity, the most recent wind 

speed value from the Great Lakes Forecasting System, and 

visibility at Sturgeon Bay, Wis. 

On the basis of this multivariate analysis, variables 

that appeared influential or related to E. coli concentration 

included variables indicative of storm activity (turbidity, wave 

height, wind speed, rainfall), exposure to sunlight (solar radiation and visibility), and specific conductance. Although all of 

these variables could conceivably influence E. coli in a setting 

such as Murphy Beach Park, the number of observations is not 

sufficient to find strong statistical relations with any individual 

variables except specific conductance. Specific conductance 

is the first split variable in both recursive partitioning analyses and the most significant variable in the stepwise regression. Specifically, the recursive partitioning routines (level 2 

analyses) indicate that higher E. coli concentrations are correlated with specific conductance concentrations higher than 

287.6 microsiemens per centimeter (μS/cm).

Variation in specific conductance can indicate influences 

from different water sources. Rain water, overland flow, and 

groundwater are expected to have different specific conductance values than waters of Green Bay and Murphy Park 

Beach. Rainfall would have lower specific conductance than 

lake water. Overland flow could have a large range in specific 

conductance depending upon the residence time and source, 

because quick, overland flow would have low values and 

large rivers or piped storm outflows could have high values. 

Groundwater would have substantially higher specific conductance than lake water; the average specific conductance of 

all groundwater samples during the study period was 700 μS/

cm. Specific conductance in lake water was measured by the 

continuous sensor at Murphy Park Beach in 2009 and ranged 

over a very small interval of 283–292 μS/cm. This small range 

in values indicates that large surface-water discharges in the 

Murphy Park Beach area likely were not an influence, in contrast to very high specific conductance values that have been 

observed at other Great Lakes beaches near large river or pipe 

outfalls (Francy and others, 2005). If rainfall influenced specific conductance, it would have had a diluting effect and been 

nearly immediate during and after the rainfall period, and this 

effect was not observed. If groundwater influenced specific 

conductance, there could conceivably be a substantial lag time 

from rainfall periods to increased groundwater discharge to 

the beach area due to the aquifer diffusivity, which is the ratio 

of transmissivity to storativity (Bredehoeft, 2011). To explore 

this possibility, a series of different rainfall summations from 

0.5 to 40 days were used to predict daily average specific conductance as measured by the continuous sensor for the period 

of study in 2009; an autoregressive integrated moving average (ARIMA) time-series modeling approach was used for 

this analysis. Autoregressive integrated moving averaging is a 

class of stochastic models that is commonly applied to timeseries data to account for autocorrelation and temporal trends 

(nonstationarity) of the time series. The optimal relation, as 

measured by maximum log-likelihood, was found using a 

20-day summation of rainfall, with local maxima of the loglikelihood values at 8- and 12-day rainfall summations. In all 

three of these cases, an autoregressive term of one, a differencing term of one (the “integration” term), and a moving average 

term of zero (no moving average) were optimal. The resulting 

model for 20-day rainfall had an R2 of 0.92. 

An 8-, 12-, or 20-day time lag for the relation of rainfall to specific conductance suggests a possible influence of 

groundwater discharge during this study. The time lag is due to 

the aquifer diffusivity, which dampens and delays the propagation of a change in hydraulic gradient (due to recharge) 

through the aquifer (Bredehoeft, 2011). Propagation of a 

relatively distinct recharge event, albeit lagged by 8–20 days, 

through fracture conduits in the carbonate aquifers of Door 

County is reasonable given the high bulk transmissivity of the 

aquifer and the low storage properties of conduit flow in Door 

County (K.R. Bradbury, Wisconsin Geological and Natural 

History Survey, oral commun.). 

The recursive partitioning split (level 2 analysis) of 

samples with specific conductance greater than 287.6 μS/

cm was examined further using the remaining explanatory 

variables that were identified during the multivariate analysis, 

which were variables used in levels 3 and 4. A threshold of 1 ft 

for 12-hr maximum wave height was identified as a secondary partitioning split for the subset of FIB samples that also 

had specific conductance values greater than 287.6 μS/cm. 

Indeed, all five E. coli samples with concentrations greater 

than 100 MPN/100mL are in the category with relatively high 

specific conductance and high wave height (fig. 9). Although 

this type of “decision tree” is not necessarily predictive of 

future conditions, it serves to provide valuable information 

about the mechanisms that influence water quality at Murphy 

Beach Park.
Multivariate Analysis of E. coli Concentrations 21

E. coli concentration, in most probable number 

per 100 milliliters of water

EXPLANATION

(25) Number of points

o

x

Severe outlier

Moderate outlier

Adjacent value

75th Percentile

Median

25th Percentile

1

5

10

50

100

500

1,000

(15) (4) (7)

oo

o

o

Specific conductance less than 

287.6 microsiemens per centimeter

Specific conductance greater than 

287.6 microsiemens per centimeter and 

wave height less than 1 foot

Specific conductance greater than 

287.6 microsiemens per centimeter and 

wave height greater than 1 foot

Figure 9. Escherichia coli (E. coli ) concentration in beach water at Murphy Park Beach, grouped by specific 

conductance and wave height, 2009.
22 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Potential Transport Mechanisms for 

FIB

Transport of FIB through Long-Shore Currents

Because FIB concentrations were typically higher at the 

beach site than at the pier and boat launch sites, which border 

the beach to the northwest and south, external loading of FIB 

to the beach via lake water currents does not appear likely. 

Similarly, Kleinheinz, McDermott, Leewis, and Englebert 

(2006) found little indication of FIB conveyance along the 

periphery of beaches. Nonetheless, although FIB loading from 

lake water beyond the immediate swimming area is likely 

small, such FIB transport cannot be categorically ruled out. 

An evaluation of water current direction on days with high 

FIB concentrations outside of the beach in 2009 was used to 

further evaluate external loading of FIB to the beach; current 

direction data were not collected in 2008.

Water current direction information collected at the time 

of water-sample collection at all three lake water sampling 

sites indicates that on the day in 2009 with the highest FIB 

concentration outside of the beach—when the E. coli concentration was 548 MPN/100mL at the boat launch on July 23, 

2009—the current direction at the boat launch and pier was 

toward the south (190 degrees from north) and, thus, was flowing away from the recreational beach area. On all other days 

in 2009 when FIB concentrations at the pier or boat launch 

exceeded those at the beach (as noted in “FIB in Lake Water” 

above and table 5), current direction at the boat launch was 

easterly (90 degrees from north and toward shore) and northeasterly at the pier (45 degrees from north). Current direction 

at the beach was easterly (toward shore) on July 23, 2009, 

and either easterly or northeasterly on the other dates when 

external FIB concentrations exceeded FIB concentrations in 

beach water. The portion of the shoreline where Cladophora

samples were collected (fig. 2) is angled at about 16 degrees 

east of north. These current direction data imply that some 

water can circulate within the beach area, as must be the case 

when current direction at the beach is directed toward the 

beach, and that some lake water transport to the beach area is 

possible—though there is little evidence to suggest that lake 

water transport is a primary source of FIB to the beach. At 

the beach, the highest FIB concentrations were evident when 

the current was directed generally northeasterly or easterly 

(fig. 10A). These patterns could imply importation of FIB 

from Green Bay waters, or, more likely, increased erosion 

of beach sand due solely to waves, or to the accumulation of 

Cladophora mats along the beach shoreline where they can be 

trapped by the pier, or to a combination of beach sand erosion 

and Cladophora mats. 

Wind directions from the nearest model grid point, provided by the National Oceanic and Atmospheric Administration Great Lakes Forecasting System (Schwab and Bedford, 

1999), show that FIB concentrations were highest when wind 

was coming from the south to southwest (fig. 10B). This relation, though not statistically significant, may be associated 

with possible north-to-northeasterly oriented wave motion or 

from trapping of Cladophora mats along the beach and pier.

Transport of FIB from Swash-Zone Groundwater

Groundwater discharge is another possible mechanism 

for transporting FIB from swash-zone and upshore sand to 

beach water (figs. 5 and 11). Indeed, one of the strongest correlations with FIB concentrations in lake water at the beach 

site is the specific conductance of the lake water, which is 

expected to be influenced by groundwater discharge (see 

“Multivariate Analysis”). Moreover, the specific conductance 

in lake water measured in 2009 is highly correlated with 

weekly to multiweek precipitation levels (rho >0.8 between 

specific conductance and 12-day total rainfall), which may be 

an indicator of groundwater recharge and subsequent groundwater discharge. The influence of enhanced groundwater 

discharge on specific conductance can be extended to FIB

transport as well. FIB contamination at the beach does not 

appear to come from the regional groundwater due to the lack 

of FIB in piezometers far from the beach, as described above 

in “Fecal Indicator Bacteria in groundwater.” Instead, the 

relatively higher FIB concentrations in swash-zone groundwater suggest that increases in the groundwater gradient directed 

toward the lake (Sherrill, 1978) would induce transport of 

FIB in swash-zone groundwater into the beach water column. 

That is, FIB loading into swash-zone groundwater is likely 

from waves or precipitation washing FIB through the beach 

sand into the swash-zone groundwater reservoir. Following a 

regional groundwater recharge event, the hydraulic gradient at 

the shoreline rises, increasing the rate of swash-zone groundwater discharge, and FIB and ions associated with specific 

conductance, into the beach water. This idea is shown conceptually in figure 11.

The significance of FIB loading to beach water from 

swash-zone groundwater is difficult to evaluate and may not 

be fully characterized by comparing daily FIB concentrations 

in lake water and groundwater (fig. 5C and D). Nonetheless, future studies may benefit from a dense well network 

and monitoring protocols to evaluate transient gradients and 

flow paths toward or away from the shoreline and the use of 

seepage meters that allow for direct sampling of discharging 

swash-zone groundwater.
Potential Transport Mechanisms for FIB 23

A

B

EXPLANATION

E. Coli

Enterococci

Approximate orientation of the beach shoreline at Murphy Park Beach, 

with arrows pointing towards shore

30°

60°

120°

210° 150°

240°

300°

330°

N

W E

S

30°

60°

120°

210° 150°

240°

300°

330°

N

S

W E

10,000 100 10 10,000 1,000 100 10 10 100 1,000 10,000 1,000 10,000

10,000 1,000 100 10 10 100 1,000 10,000

Figure 10. Rose diagram showing Escherichia coli (E. coli) and enterococci concentrations with respect to A, lake water 

current direction and B, wind direction at the time of lake water-sample collection at the beach water site at Murphy Park 

Beach, 2009.
24 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Carbonate aquifer 

and water table

Fractures

Fecal indicator bacteria in 

swash-zone groundwater

Precipitation and groundwater recharge

EXPLANATION

Beach water

Specific conductance ~285 μS/cm

Groundwater

Specific conductance ~700 μS/cm

Increased hydraulic gradient at the beach 

following recharge event induces discharge 

of swash-zone groundwater

Figure 11. Schematic cross section showing groundwater recharge and discharge as a mechanism for transporting fecal 

indicator bacteria from the swash-zone groundwater reservoir into the lake water column.

Transport of FIB from Sand and Cladophora due 

to Storm Activity

Previous work by Zehms and others (2008), Englebert 

and others (2008), and Vanden Heuvel and others (2010) 

suggests that sand and Cladophora provide favorable environments for FIB growth or accumulation and may be a source 

of FIB to beach water. Thus, relations were evaluated to gain 

insight into potential FIB transport pathways among beach 

sand, Cladophora, and beach water. The relatively high FIB 

concentrations in swash-zone and upshore sand samples 

(fig. 7) and water samples associated with Cladophora mats 

(fig. 8) suggest that sand, or Cladophora, or both could be a 

direct source of FIB to beach water when combined with a 

transport mechanism.

Erosion of beach sand with direct dispersal of FIB associated with sand into the water column due to storm activity is 

a possible mechanism for direct transfer of FIB in swash-zone 

sand to beach water. Indeed, as noted earlier, approximately 

15 ft of landward migration of the shoreline owing to erosion was observed at Murphy Park Beach between September 2008 and August 2009. Moreover, FIB concentrations in 

beach water showed statistically significant (p-value <0.05) 

associations with water turbidity, wave height, current speed, 

wind speed, sky visibility, 24-hr precipitation, and suspended 

particulate concentrations. All of these ancillary metrics are 

indicators of storm activity that could affect beach erosion 

rates. These results do not constitute a direct relation between 

FIB concentrations in beach water and erosion of beach sand, 

but suggest that future work on this transport mechanism 

would benefit from incorporating more direct metrics of erosion and storm activity.
Potential Transport Mechanisms for FIB 25

Likewise, FIB concentrations associated with 

Cladophora mats at Murphy Park Beach are correlated with 

FIB concentrations in beach water (rho = 0.8 for E. coli

and enterococci), but lack statistical significance due to the 

small sample set. This relation is evident in time series plots 

(fig. 12), in which FIB concentrations in beach water appear 

to generally follow the pattern of FIB concentrations associated with Cladophora. This pattern is not as obvious for 

the last day that Cladophora-associated water was sampled, 

Aug. 20, 2009. The moderate beach water FIB concentrations 

of 199 MPN/100mL E. coli and 133 MPN/100mL enterococci 

on this day, compared with large concentrations on Aug. 18, 

2009, of 1203 and 2420 MPN/100mL, may indicate that active 

dispersion and transport of FIB associated with Cladophora

into the water column is required to produce correspondingly high FIB concentrations in beach water. Ancillary data 

on Aug. 18, 2009, indicate more turbulent conditions at the 

beach than on Aug. 20, 2009. For example, storm indicators, 

such as wave height, turbidity, current speed, wind speed, 

and suspended particulate concentrations were all substantially higher on Aug. 18, 2009, than on Aug. 20, 2009. That 

is, Aug. 18, 2009, had large storms, high FIB concentrations 

in Cladophora mats, and a high FIB concentration at the 

beach water sampling site. Two days later, on Aug. 20, 2009, 

Cladophora-associated water still had high FIB concentrations, but there was little storm activity and the beach water 

sample had a substantially reduced FIB concentration.

Visual evaluations of the relative amount of Cladophora

present at the beach at the time of beach water sample collection illustrate that higher amounts of Cladophora appear 

generally associated with higher FIB concentrations in beach 

water (fig. 13A). The pattern does not appear to hold, however, 

for samples taken during periods with the greatest amount of 

visible Cladophora. Although this exception may appear to 

contradict a relation of Cladophora to higher concentrations 

of FIB in beach water, it may instead indicate a lack of storm 

activity during periods with high Cladophora abundance as 

estimated visually. That is, it seems reasonable to infer that a 

visual evaluation of the amount of Cladophora at a beach is 

likely to be biased by the number of large mats, which “catch” 

a person’s eye, as opposed to the number of small and dispersed mats, even if the total Cladophora biomass were the 

same. Large mats of Cladophora are likely to be dispersed 

during periods of storm activity when wave and wind energy 

can also transport FIB into the larger beach water area. Indeed, 

evaluating FIB concentrations in the context of storm indexes 

suggests that E. coli concentrations are generally higher when 

Cladophora occurrence is moderate and storm indices (wave 

height, turbidity, current speed, wind speed) are relatively 

high, compared with other periods (fig. 13B–E). These relations suggest that Cladophora may be an internal source 

of FIB to Murphy Park Beach water during times of storm 

activity, although perturbation of the mats by bathers could 

disperse FIB to the water column immediately adjacent to the 

Cladophora mats.
26 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin E. coli, in most probable number per 100 milliliters of water

0

500

1,000

1,500

2,000

2,500

3,000

A

B

0

500

1,000

1,500

2,000

2,500

3,000

July 16 July 21 July 26 July 31 Aug. 5 Aug. 10 Aug. 15 Aug. 20 Aug. 25

July 16 July 21 July 26 July 31 Aug. 5 Aug. 10 Aug. 15 Aug. 20 Aug. 25

Enterococci, in most probable number 

per 100 milliliters of water

Within mat

Adjacent to mat

Beach water

EXPLANATION

Figure 12. Graphs showing A, Escherichia coli (E. coli) and B, enterococci concentrations in beach water and in water 

samples collected within and adjacent to Cladophora mats at Murphy Park Beach, 2009.
Potential Transport Mechanisms for FIB 27

E. coli, in most probable number 

per 100 milliliters of water

E. coli, in most probable number 

per 100 milliliters of water

E. coli, in most probable number 

per 100 milliliters of water

E. coli, in most probable number 

per 100 milliliters of water

E. coli, in most probable number 

per 100 milliliters of water

1

10

100

1,000

10,000

Wind speed less than 5 miles per hour

Wind speed greater than 5 miles per hour

None Minimal Moderate High

1

10

100

1,000

10,000

Current speed less than .5 miles per hour

Current speed greater than .5 miles per hour

None Minimal Moderate High

1

10

100

1,000

10,000

Nephelometric Turbidity Units less than 20

Nephelometric Turbidity Units greather than 20

None Minimal Moderate High

1

10

100

1,000

10,000

Measured wave height less than 1 foot

Relative abundance of Cladophora Relative abundance of Cladophora

Relative abundance of Cladophora Relative abundance of Cladophora

Relative abundance of Cladophora

Measured wave height greater than 1 foot

None Minimal Moderate High

1

10

100

1,000

10,000

None Minimal Moderate High

A B

C D

E

Figure 13. Escherichia coli (E. coli) concentrations associated with relative abundance of Cladophora at the time of 

sampling A, for the 2008–9 study period and for 2009 categorized by B, wave height, C, turbidity, D, current speed, and 

E, wind speed at the beach water site, Murphy Park Beach.
28 Evaluation of Potential Sources and Transport Mechanisms of Fecal Indicator Bacteria, Murphy Park Beach, Wisconsin

Summary

Several potential sources of fecal indicator bacteria (FIB) 

to beach water at Murphy Park Beach in Door County, Wis., 

were evaluated by the U.S. Geological Survey, in collaboration with the Door County Soil and Water Conservation 

Department and the University of Wisconsin–Oshkosh. Primary sources of FIB appear to be internal to the beach rather 

than external FIB sources such as rivers, sewer outfalls, and 

industrial discharges, which are common FIB sources at other 

Great Lakes beaches. Three likely sources of FIB to the water 

column are FIB associated with sand, swash-zone groundwater, and Cladophora mats. The modest correlations between 

FIB concentrations in these potential source reservoirs and 

FIB concentrations at the beach water sampling site illustrate 

the importance of evaluating transport mechanisms between 

the sources and the water column. Likely mechanisms for 

transport and dispersion appear to include (1) increased discharge of swash-zone groundwater due to regional groundwater recharge and increased hydraulic gradients, and (2) erosion 

of sand or agitation of Cladophora mats, or both, due to storm 

activity, as interpreted from storm indicators such as 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 with these storm indicators. Because there is relatively 

little apparent external loading of FIB to this beach, understanding the dynamic interactions between sources of FIB 

from sand, swash-zone groundwater, and Cladophora with 

groundwater and storm transport mechanisms is important for 

improved predictions of beach closure due to FIB in beach 

water. 

References Cited

Alexander, E.C., Green, J.A., Alexander, S.C., 2008, Plum 

Bottom closed depression groundwater trace final report: 

Door County Soil and Water Conservation Department, 

13 p., accessed on July 13, 2011, at http://map.co.door.

wi.us/swcd/Plum%20Bottom%20Groundwater%20

Trace%20Final%20Report%20Jan%202008.pdf.

Baylis, C.L., MacPhee, S., Martin, K.W., Humphrey, T.J., 

Betts, R.P., 2000, Comparison of three enrichment media 

for the isolation of Campylobacter spp. from foods: Journal 

of Applied Microbiology, v. 89, p. 884–891.

Bredehoeft, J.D., 2011, Monitoring regional groundwater 

extraction—The problem: Ground Water, v. 49, no. 6, 

p. 808–814.

Byappanahalli, M.N., Shively, D.A., Nevers, M.B., Sadowsky, 

M.J., and Whitman, R.L., 2003, Growth and survival of 

Escherichia coli and enterococci populations in the macroalga Cladophora (Chlorophyta): FEMS Microbiology Ecology, v. 46, no. 2, p. 203–211.

Chiu, C., and Ou, J.T., 1996, Rapid identification of Salmonella serovars in feces by specific detection in virulence 

genes, invA and spvC, by an enrichment broth culture-multiplex PCR combination assay: Journal of Clinical Microbiology, v. 34, p. 2619–2622.

Chomczynski, P., and Rymaszewski, M., 2006, Alkaline polyethylene glycol-based method for direct PCR from bacteria, 

eukaryotic tissue samples, and whole blood: BioTechniques, 

v. 40, p. 454–458. 

De’Ath, G., and Fabricius, K.E., 2000, Classification and 

regression trees—A powerful yet simple technique for ecological data analysis: Ecology, v. 81, no. 11, p. 3178–3192.

Door County Soil and Water Conservation Department, 

2008, Door County beach contamination source identification final report 2006–2007: 93 p., accessed on Sept. 15, 

2011, at http://map.co.door.wi.us/swcd/Beach%20

Contamination%20Source%20Identification%20Final%20 

Report.pdf.

Dufour, A.P., 1984, Health effects criteria for fresh recreational waters: U.S. Environmental Protection Agency, 

EPA–600/I–84–004, 33 p.

Duris, J.W., Haack, S.K., and Fogarty, L.R., 2009, Gene and 

antigen markers of Shiga toxin-producing E. coli from 

Michigan and Indiana river water—Occurrence and relation 

to recreational water quality criteria: Journal of Environmental Quality, v. 38, p. 1878–1886.

Eaton, A.D., Clesceri, L.S., Rice, E.W., and Greenberg, A.E., 

eds., 2005, Standard methods for the examination of water 

and wastewater (21st ed.): Washington D.C., American Public Health Association, American Water Works Association , 

and Water Pollution Control Federation, p. 9–1 to 9–125. 

Englebert, E.T., McDermott, C.M., and Kleinheinz, G.T., 

2008, Effects of the nuisance algae, Cladophora, on Escherichia coli at recreational beaches in Wisconsin: Science of 

the Total Environment, v. 404, no. 1, p. 10–17.

Fleisher, J.M., Flemming, L.E., Solo-Gabriele, H.M., Kish, 

J.K., Sinigalliano, C.D., Plano, L., Elmir, S.M., Wang, J.D., 

Withum, K., Hibata, T., Gidley, M.L., Abdelzaher, A., He, 

G., Ortega, C., Zhu, X., Wright, M., Hollenbeck, J., and 

Backer, L.C., 2010, The BEACHES study—Health effects 

and exposures from non-point source microbial contaminants in subtropical recreational marine waters: International Journal of Epidemiology, v. 39, p. 1291–1298.
References Cited 29

Francy, D.S., Struffolino, P., Brady, A.M.G., and Dwyer, 

D.F., 2005, A spatial, multivariable approach for identifying proximate sources of Escherichia coli to Maumee Bay, 

Lake Erie, Ohio: U.S. Geological Survey Open-File Report 

2005–1386, 20 p.

Haack, S.K., Duris, J.W., Fogarty, L.R., Kolpin, D.W., Focazio,M.J., Furlong, E.T., and Meyer, M.T., 2009, Comparing 

wastewater chemicals, indicator bacteria concentrations, 

and bacterial pathogen genes as fecal pollution indicators: 

Journal of Environmental Quality, v. 38, p. 248–258.

Inglis, G.D. and Kalischuk, L.D., 2003, Use of PCR for 

direct detection of Campylobacter species in bovine feces: 

Applied and Environmental Microbiology, v. 69, p. 3435–

3447.

Islam, M.S., Hasan, M.K., Miah, M.A., Sur, G.C., Felsenstein, 

A., Venkatesan, M., Sack, R.B., and Albert, M.J., 1993, Use 

of the polymerase chain reaction and fluorescent-antibody 

methods for detection of viable but nonculturable Shigella 

dysenteriae type 1 in laboratory microcosms: Applied and 

Environmental Microbiology, v. 59, p. 536–540.

Kleinheinz, G.T., McDermott, C.M., Hughes, S., Brown, A., 

2009, Effects of rainfall on E. coli concentrations at Door 

County, Wisconsin beaches: International Journal of Microbiology, v. 2009, article ID 876050, 9 p., accessed at http://

dx.doi.org/10.1155/2009/876050.

Kleinheinz, G.T., McDermott, C.M., and Chomeau, V., 2006, 

Evaluation of avian waste and bird counts as predicators of 

Escherichia coli contamination at Door County, Wisconsin 

beaches: Journal of Great Lakes Research, v. 32, p. 117–

123.

Kleinheinz, G.T., McDermott, C.M., Leewis, M.C., and Englebert, E., 2006, Influence of sampling depth on Escherichia 

coli concentrations in beach monitoring: Water Research, 

v. 40, p. 3831–3837.

Lee, C.M., Lin, T.Y., Lin, C., Kohbodi, G.A., Bhatt, A., 

Lee, R., and Jay, J.A., 2006, Persistence of fecal indicator bacteria in Santa Monica Bay beach sediments: Water 

Research, v. 40, p. 2593–2602.

R Development Core Team, 2011, R—A language and environment for statistical computing, accessed on Sept. 15, 

2011, at http://cran.r-project.org/manuals.html.

Schwab, D.J., and Bedford, K.W., 1999, The Great Lakes 

Forecasting System, in Mooers, C.N.K., ed., Coastal ocean 

prediction, coastal and estuarine studies: Washington, D.C., 

American Geophysical Union, v. 56, p. 157–173.

Sherrill, M.G., 1978, Geology and ground water in Door 

County, Wisconsin, with emphasis on contamination potential in the Silurian dolomite: U.S. Geological Survey WaterSupply Paper 2047, 43 p.

Trabulsi, L.R., Keller, R., and Gomes, T.A.T, 2002, Typical 

and atypical enteropathogenic Escherichia coli: Emerging 

Infectious Diseases, v. 8, p. 508–512.

U.S. Department of Agriculture, 2008, National Agriculture 

Imagery Program (NAIP) Information Sheet, accessed on 

August 23, 2011, at http://www.fsa.usda.gov/Internet/FSA_

File/naip_2007_infosheetpdf.pdf.

U.S. Environmental Protection Agency, 2000, Improved 

enumeration methods for recreational water quality indicators—Enterococci and Escherichia coli: EPA 821–R–97–

004, 53 p.

U.S. Environmental Protection Agency, 2004, Quality assurance/quality control guidance for laboratories performing 

PCR analysis on environmental samples: EPA 815–B–04–

001, 57 p.

U.S. Environmental Protection Agency, 2006, Method 1600—

Enterococci in water by membrane filtration using membrane-Enterococcus Indoxyl-b-D-Glucoside agar (mEI): 

Washington, D.C., EPA/821/R-06/009, 42 p.

Vanden Heuvel, A., McDermott, C., Pillsbury, R., Sandrin, T., 

Kinzelman, J., Ferguson, J., Sadowsky, M., Byappanahalli, 

M., Whitman, R., and Kleinheinz, G.T., 2010, The green 

alga, Cladophora, promotes Escherichia coli growth and 

contamination of recreational waters in Lake Michigan: 

Journal of Environmental Quality, v. 39, no. 1, p. 333–344.

Vassiliadis, P., Trichopoulos, D., Kalandidi, A., and Xirouchaki, E., 1978, Isolation of salmonellae from sewage 

with a new procedure of enrichment: Journal of Applied 

Bacteriology, v. 44, p. 233–239. 

Wade, T.J., Calderon, R.L., Sams, E., Beach, M., Brenner, 

K.P., Williams, A.H., and Dufour, A.P., 2006, Rapidly measured indicators of recreational water quality are predictive 

of swimming-associated gastrointestinal illness: Environmental Health Perspectives, v. 114, no. 1, p. 24–28.

Zehms, T.T., McDermott, C.M., and Kleinheinz, G.T., 2008, 

Microbial concentrations in sand and their effect on beach 

water in Door County, Wisconsin: Journal of Great Lakes 

Research, v. 34, p. 524–534.


Juckem and others—Evaluation of Sources and Transport Mechanisms of FIB to Beach Water, Murphy Park Beach, Wisconsin —Scientific Investigations Report 2012–5190