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Microbial Concentrations in Sand and their Effect on Beach Water in Door County, Wisconsin
J. Great Lakes Res. 34:524–534 Internat. Assoc. Great Lakes Res., 2008
Microbial Concentrations in Sand and their Effect on Beach Water in Door County, Wisconsin Tabitha T. Zehms, Colleen M. McDermott, and Gregory T. Kleinheinz* Department of Biology and Microbiology University of Wisconsin—Oshkosh 800 Algoma Boulevard Oshkosh, Wisconsin 54901 ABSTRACT. The seasonal variations and patterns of Escherichia coli in Wisconsin’s coastal waters have been closely studied in recent years due to increased beach monitoring activities. Patterns of distribution of the indicator organism, E. coli, in the sand at these beaches are now being investigated as a source of E. coli to adjacent beach water. This project investigates the concentrations of E. coli in beach sand, and the relationship between these sand-microbe concentrations and concentrations of microbes in the corresponding beach water. Weekly sampling of upshore, swash, and submerged sand at six beaches provided numbers of the indicator bacteria in each beach’s sand substrate for two consecutive summers. Overall concentrations of E. coli were highest in the swash sand of the beach, with the highest numbers seen in the summer months and lowest numbers in the winter months. Each location had very different concentrations of E. coli in the beach sand from 1,800 CFU/100 g to 21,670 CFU/100 g sand. Each location had a very different relationship between the indicator organism found in the beach sand and that found in the beach water. These data suggest that sand may be a reservoir for E. coli at some locations, and another source of contamination that should be considered in beach monitoring programs. However, elevated levels of E. coli in beach sand were not universal and varied greatly from location to location. INDEX WORDS:
E. coli, water quality, sand, beach, Lake Michigan.
Pathogens, or disease-causing microbes, can be found in human and animal waste, and fecal contamination of recreational waters can thus present a health risk to bathers. High concentrations of bacteria from a fecal contamination source could cause severe gastrointestinal illness if swallowed, especially in those that have a high potential for illness, such as the very young and very old or the immunocompromised. Wisconsin has chosen to utilize E. coli as the indicator organism for fecal contamination of its recreational waters, based on strong correlations between swimming-associated gastrointestinal symptoms and E. coli densities (Dufour 1984). The persistence and survival of E. coli in beach water should parallel the persistence and survival of bacterial pathogens in this environment. The greater the survival of indicator organisms in the environment relative to associated pathogens’ survival, however, the less useful they are as an indication of recent fecal contamination. Several studies have been conducted to ascertain the duration of E. coli
INTRODUCTION The year 2006 was the fourth in the implementation of Wisconsin’s large-scale Great Lakes Beach Monitoring and Notification Program. The program works with local health departments to ensure prompt public notification and efficient monitoring, as mandated by the U.S. Environmental Protection Agency (EPA). Door County, WI (a peninsula located between the Bay of Green Bay and Lake Michigan) has over 250 miles of shoreline and accounts for 30 of the 192 beaches that are regularly monitored in the state. Door County relies on tourism for the bulk of its revenue—according to its Chamber of Commerce, Door County is one of the top ten vacation destinations in North America (Door County Visitor Bureau Website 2007). Summer is the busiest time of year for Door County tourism, so beach water quality is vital to keeping visitors healthy, and integral to the sustainability of the region’s economy. *Corresponding
author. E-mail: [email protected]
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Microbial Concentrations in Sand and their Effect on Beach Water persistence in water. Results vary from 6 days to 40 days in microcosms with varying temperatures (Bogosian et al. 1996, Sampson et al. 2006). Cooler temperatures have consistently provided longer time periods of E. coli persistence, an interesting concept considering the very warm temperature of the gastrointestinal tract, where E. coli are naturally found (Brettar and Höfle 1992, Smith et al. 1994, Bogosian et al. 1996, Sampson et al. 2006). While colder temperatures aid in lengthening survival time, warmer temperatures are still tied to higher E. coli concentrations in beach water, particularly as the summer months progress (Whitman and Nevers 2003, Ishii et al. 2007). Temperature is not the only factor that affects E. coli concentrations and their persistence in recreational water. Sunlight exposure decreased E. coli counts exponentially on sunny days at a Lake Michigan swimming beach, with mesocosm experiments providing similar results (Whitman et al. 2004). Nutrient availability, competition and predation, and wind direction are other factors that will impact a bacterium’s survival in the environment at large. Fecal contamination sources, such as wastewater and stormwater outfall pipes, sewage and septic leaks, runoff, avian waste, and Cladophora accumulation, can influence indicator organism populations in recreational waters as well (Byappanahalli et al. 2003, Fogarty et al. 2003, Ishii et al. 2006, Noble et al. 2003, Whitman et al. 2003, Olapade et al. 2006). Recently, the importance of E. coli survival in beach sand has been investigated. Several studies have confirmed the presence of E. coli in sand, as well as sand’s potential as a reservoir for the organism (Ishii et al. 2007, Beversdorf et al. 2007). Summer studies indicate that fecal indicator bacteria are more abundant in sand than in water; in some cases counts are an order of magnitude higher in the sand substrate (Obiri and Jones 1999, Wheeler Alm et al. 2003). Furthermore, the presence of sand helped E. coli survive 10 additional days, for a total of 40 days, in nonsterile lake water in one microcosm study (Sampson et al. 2006). High concentrations of indicator organisms found in the foreshore sand (sand in contact with wave action of water) at the 63rd Street Beach in Chicago, Illinois, prompted replacing that sand with E. coli-free sand for the 2000 swimming season. The E. coli counts were back to the original detected concentrations within 2 weeks (Whitman and Nevers 2003). Indicator organisms were also found to be more persistent in contaminated subtropical sediment than in wastewater or
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dog feces (Anderson et al. 2005). Regular grooming of beaches has been shown to either increase or decrease the E. coli populations in beach sand, depending on the depth of raking (Kinzelman et al. 2004). The presence of E. coli in beach sand represents a possible source of contamination of the recreational water itself. Fecal pollution contaminates not only the water but the environment it travels through to get to the water. Swash zone beach sand constantly endures wave action, and this contact could transfer indicator organisms from the water to the sand, and the sand to the water (Yamahara and Boehm 2006, Beversdorf et al. 2007). When monitored, concentrations of E. coli in beach sand can inform beach managers of potential reservoir loading, and thus, additional sources of contamination that could greatly affect water quality. The overall objective of this study was to investigate the concentrations of E. coli in sand at selected beaches and to investigate the impact that E coli in the sand may have on the E. coli concentrations found in beach water. Specifically, we tested the following hypotheses: 1. E. coli concentrations in sand will differ from season to season with the greatest concentrations occurring in the warmer months of the year. 2. E. coli concentrations in sand will differ based on location at a beach (submerged, swash zone, and upshore), with the greatest concentrations occurring at the swash zone. 3. Concentrations of E. coli in sand, especially in the swash zone, will correlate with E. coli concentrations in adjacent beach water, indicating that sand may act as a source of microbial contamination at beaches. 4. Concentrations of E. coli in sand will correlate best with E. coli concentrations in the next day’s beach water sample to account for a lag necessary to wash E. coli from sand into water. MATERIALS AND METHODS Sand Sample Collection Six beaches were tested weekly throughout the swimming season (n = 12) along both the Green Bay and Lake Michigan sides of the Door County Peninsula: Ephraim Beach, Fish Creek Beach, Sunset Park Beach, Otumba Park Beach, Whitefish Dunes State Park Beach, and Bailey’s Harbor
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FIG. 1. Map of recreational beaches used in this study in Door County, WI and location in Wisconsin and within Lake Michigan. Ridges Beach (Fig. 1). These beaches were selected because they represent a range of shoreline conditions commonly found along the Great Lakes. These conditions included open Great Lakes water shorelines, embayed shorelines, and beach-front shorelines along a man-made canal. Likewise, these beaches ranged from semi-urban to remote parklike locations. The sampling period lasted 12 weeks
(n = 12), from late May to late August, in both 2005 and 2006. Additional samples were taken from each of the selected beaches in November 2005, January 2006, and November 2006. During each sampling event, nine sand samples were taken from each beach using an AMS soil recovery probe (2.25 cm × 30.5 cm, AMC Inc., American Falls, ID, USA) and sterile polybutyrate liners. Samples were col-
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FIG. 2. A sampling schematic of the nine sand samples taken weekly at each beach. UR, UC, and UL refer to the upshore right, center, and left samples, respectively. SR, SC, and SL refer to the swash zone samples, and WR, WC, and WL refer to the submerged sand samples taken. lected to a depth of 6 inches and were taken from the upshore sand (4.6 m away from wave action), the swash sand, and the submerged sand (under 60 cm of water). Three samples spaced 5 meters apart were then taken from each sand zone; this small measurement scale corresponded with the small size of most of the beaches sampled (Fig. 2). Care was taken to avoid sand samples with noticeable amounts of avian waste, Cladophora, or other environmental material that could affect the concentrations of indicator organisms in the sample. When taking the sand samples, the liner was removed from the probe without contaminating the inside of the liner. Caps were placed on both ends of the liner. The capped liners were placed in a cooler containing an ice pack to maintain temperature at 4°C. Samples remained on ice until analysis. Analysis typically occurred within 4 hours of col-
lection. In addition, one 100 mL sterile bottle was filled with swash zone sand from each beach. These samples were used to determine dry weight of sand from each beach. Water Sample Collection Water samples were taken at least once weekly (usually 4–5 times/week to comply with Beach Act monitoring schedules) at the time of the sand sampling for E. coli enumeration. Samples were collected using the methods described in the U.S. EPA Microbiology Methods Manual, the Standard Methods for the Examination of Water and Wastewater #1060 (APHA 1998). Specifically, samples were collected from water with a depth of 61 cm (to be consistent with Wisconsin Department of Natural Resources (WIDNR) guidelines for BEACH Act
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sampling) into sterile, 100 mL polystyrene bottles (IDEXX Corp., Portland, ME). The water samples were taken from the center of the beach, the site in the water that is the midpoint of the length of the defined beach area. Samples were placed into a cooler at 4ºC until they were analyzed. Sand Sample Analysis Laboratory analysis on sand collected with the soil recovery probe was conducted via membrane filtration and U.S. EPA method 1603 using modified mTEC for E.coli (U.S. EPA 2002). Sub sections of sand from the 100 mL bottles were placed in 20 separate aluminum weigh boats, weighed, and placed in a 44°C incubator for 48 hours. The dry weight then was recorded. A sand wet/dry conversion factor was calculated by taking the sum of the dry weight divided by the wet weight for all 20 swash sand samples, and dividing this sum by the total number of samples. This average was used as a conversion factor and multiplied with the Colony Forming Unit per gram (CFU/g) of wet sand, or the number of colonies on the mTEC after 24 hours of incubation. This step allowed all beaches to be normalized with final measurements in CFU/g dry weight. In order to make comparisons with E. coli concentrations in water (expressed as MPN/100 mL), sand E. coli concentrations were then expressed as CFU/100 g sand.
number of paired samples required to maintain the accepted power of 0.9 decreased only slightly, to 493 (data not shown). Due to this high amount of variation within the data, a p-value ≤ 0.10 was considered significant. Since E. coli in beach water was enumerated 4–5 per week, there were data available so the E.coli concentrations in the various sand locations could be statistically compared to the previous, same, and next day’s beach water E.coli concentrations. No statistical comparisons were conducted with data collected outside the swimming season due to very low, or non-detectable, concentrations of microbes. RESULTS AND DISCUSSION E. coli Seasonal Concentrations in Sand The hypothesis that E. coli in beach sand would vary by season was tested by measuring E. coli concentrations during summer months (May–August), in November before freezing had occurred, and in January when beach sand was frozen and snow covered. E. coli concentrations in sand were highest in the summer months, declined in the November samples, and were undetectable in January 2006 (Fig. 3). Because there were so few samples collected in the November and January, statistical differences between these seasons were not calculated.
Water Sample Analysis The defined substrate tests, Colilert™ (IDEXX Corp., Portland, ME), was used to analyze the water samples for E. coli. Incubation and microbial enumeration were conducted following the manufacturer’s recommendations. All water samples were maintained at 4°C until analysis, and all samples were processed within 2 hours of collection in a State of Wisconsin Department of Agriculture Trade and Consumer Protection (DATCP) certified laboratory in Sturgeon Bay, WI (certification #105453). E. coli concentrations were expressed as most probable number/100 mL water (MPN/100 mL). Statistical Analysis All results were performed on log10-transformed data with SPSS (SPSS Inc., Chicago, IL). Power analysis was performed based on paired t-test data and indicated 605 paired samples were necessary to maintain the widely accepted α = 0.05 and α = 0.10. When the alpha value was adjusted to 0.10 the
FIG. 3. E. coli concentrations in sand (CFU/ 100 g) sampled at various times throughout the year. For summer samples (June–August) n = 12. For November samples, n = 1. For January samples, n = 1. Because there was only one sampling in January, statistical differences between means of these time periods could not be determined.
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These results are similar to the observed prevalence of E. coli in other beach sand studies (Whitman and Nevers 2003) and indicates that beach sand in northern latitudes likely is repopulated by E. coli each spring/summer, rather than harbors E. coli from year to year. Comparisons of E. coli Concentrations in Sand at Different Locations within the Beach Our second hypothesis was tested by comparing E. coli concentrations at various locations at each selected beach. Mean E. coli concentrations within each sand zone (upshore, swash, and submerged areas) at each beach were calculated and compared (Figs. 4 and 5 and Table 1). Generally, the highest numbers of E. coli were consistently found in the swash sand, second highest in the upshore sand, and lowest in the submerged sand. (Figs. 4 and 5). Four of the six beaches showed the highest average E. coli in the swash sand in both 2005 and 2006. Bailey’s Harbor had a higher mean E. coli concentration in the upshore sand only in 2006. Whitefish Dunes instead showed the highest mean E. coli in upshore sand in both 2005 and 2006 (Figs. 4 and 5). This is likely due to the increased upshore area of this particular beach and the large populations of gulls that inhabit it. While gulls scavenge at this beach in the swash zone, they often roost for large parts of the day in the upshore area. This beach had the largest waterfowl population of any of the selected beaches (approximately 50 birds/sampling for Whitefish Dunes vs. < 5 birds/sampling for the other beaches) (Kleinheinz et al. 2006). Mean submerged sand E. coli concentration was the lowest of the three sand zones at every beach for both years. Submerged sand E. coli concentrations were 2–32 times less than the swash zone levels in 2005 and 3–73 times less than swash sand levels in 2006 for all beaches studied. Although swash zone sand is more prone to desiccation and the effects of UV irradiation than is submerged sand, perhaps the difference in temperature and frequency of microbial loading account for the large number of E. coli in the swash zone sand (Whitman et al. 2004, Sampson et al. 2006). Paired t-tests of log10-transformed data were used to ascertain whether the general trend described above held true on a weekly basis. Due to the large amount of inherent variance in this type of sampling, significance was set at a p-value ≤ 0.10. All six beaches had significant differences between the submerged sand E. coli concentration averages and
FIG. 4. Differences between mean E. coli concentrations in sand (CFU/100 g) at various locations on beaches (upshore, swash zone, and submerged) for 2005 and 2006 summer seasons. E. coli concentrations in water (MPN/100 mL) also is indicated (triangles), for comparison with sand E. coli concentrations. the swash zone sand E. coli averages (Table 1). Three of the beaches sampled—Fish Creek, Otumba, and Sunset Park—showed the same significant relationships between E. coli concentrations in the various zones of sand sampled, in both years. All three beaches share similar beach characteristics, with relatively narrow and short sandy areas in semi-urban settings. A more urban environment generally has more impervious surfaces and less green space than a rural environment, which could influence the amount of contamination reaching
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FIG. 5. E. coli concentrations in sand (CFU/100 g) at various locations on beaches (upshore, swash zone, and submerged) for 2005 and 2006. E. coli concentrations in water (MPN/100 mL) also is indicated (triangles), for comparison with sand E. coli concentrations.
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TABLE 1. Results of statistically significant (p < 0.1) paired t-test comparisons of E. coli concentrations from various sand locations and beach water at studied beaches. Location Submerged Sand
Comparison vs. swash sand
vs. upshore sand
vs. water
Swash Zone Sand
vs. water
Upshore Sand
vs. swash sand
vs. water
beach areas via rainfall runoff. Urban settings also have storm water outfall pipes and the potential for storm water drain overflows. A two-way ANOVA with log10-transformed averages from each zone each week revealed that beach (p = 0.006) and location (zone within the beach, p < 0.000) were significant determinants of E. coli concentrations (data not shown). The interaction between beach and location was also found to be significant (p = 0.07), suggesting that E. coli populations in beach sand are unique for each beach and for each zone (upshore, swash, or submerged area) within the beach.
Beach Baileys Harbor Ephraim Fish Creek Otumba Sunset Whitefish Dunes Ephraim Fish Creek Otumba Sunset Fish Creek Sunset Whitefish Dunes Fish Creek Bailey’s Harbor Bailey’s Harbor Fish Creek Otumba Sunset Ephraim Fish Creek Otumba Sunset Whitefish Dunes Otumba Whitefish Fish Creek Fish Creek Otumba Sunset Whitefish Dunes Fish Creek Otumba Sunset
Year 2005 2005 2005 2005 2005 2005 2006 2006 2006 2006 2005 2005 2005 2006 2006 2005 2005 2005 2005 2006 2006 2006 2006 2006 2005 2005 2005 2006 2006 2006 2005 2006 2006 2006
p-value 0.012 0.059 0.001 0.023 0.016 0.008 0.038 0.001 0.001 0.008 0.040 0.054 0.008 0.037 0.066 0.085 0.042 0.063 0.036 0.046 0.001 0.012 0.001 0.070 0.021 0.073 0.011 0.024 0.007 0.008 0.073 0.050 0.015 0.006
Correlations between Sand Zone E. coli and Beach Water E. coli Concentrations Our third hypothesis (E. coli concentrations in sand will correlate with E. coli concentrations in beach water) was tested by measuring E. coli concentrations in beach water with a depth of 61 cm, at the center of each beach, and comparing with E. coli concentrations at the various sand locations. Log10-transformed data were analyzed with bivariate two-tailed correlations with the Pearson’s correlation coefficient. Each summer season was analyzed separately, since meteorological factors are very different at each beach from year to year.
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The swash sand E. coli concentrations correlated positively with the water E. coli MPN/100 mL twice, at Whitefish Dunes (p = 0.056) and Sunset Park (p = 0.041) in 2006 (Table 1). On two occasions the upshore sand also had positive correlations with the water levels of E. coli, at Fish Creek in 2005 (p = 0.060) and again at Sunset Park in 2006 (p = 0.008). One positive correlation was noted at Sunset Park in 2006 between the submerged sand and the water E. coli MPN/100 mL (p = 0.034). Perhaps the correlations observed between E. coli concentrations in upshore sand and in water may serve as an indication of high levels of contamination. It is probable that contamination events frequently impact the beach sand and the water at the same time (rainfall runoff, avian waste on the beach and in the water, etc.) and could explain this relationship. The presence of indicator organisms in the swash sand substrate could act as a reservoir for the bacteria to potentially contaminate the water (and vice versa), leading to beach monitoring results that misleadingly indicate repeated fecal contamination. The submerged sand correlated positively with the swash sand at Otumba Park Beach (p = 0.035) and Sunset Park (p = 0.102) in 2006 (Table 1). The submerged sand also correlated positively with the upshore sand E. coli averages for 2 consecutive years at Sunset Park Beach (p = 0.060 and p = 0.096, respectively). One positive correlation was noted between the upshore sand and the swash sand at Sunset Park in 2006 (p = 0.005, Table 1). Sunset Park accounted for seven significant correlations between E. coli sampling sites at this location during this study. This location had the highest concentrations of E. coli in submerged sand and suggests that there are distinct and identifiable patterns unique to this beach. Sunset Park and Otumba Park Beaches were the most urban of the studied locations and both had a positive correlation between the swash sand and the submerged sand. These two beaches accounted for the highest and second highest concentrations of E. coli in the swash sand and submerged sand (Figs. 4 and 5). Significant positive relationships between sand E. coli concentrations and water E. coli concentrations indicate that as sand E. coli concentrations rise, concentrations of E. coli in water also increase. The presence of indicator organisms in the sand substrate could act, then, as a reservoir for the bacteria to potentially contaminate the water (and vice versa), leading to beach monitoring results that misleadingly indicate repeated fecal contamination.
This effect would be exacerbated by wind and wave patterns. Correlations between Sand Zone E. coli and Previous or Following Day Water E. coli Concentrations It also was hypothesized that E. coli concentrations in sand would best correlate with E. coli concentrations in the following day’s water. In order to further investigate this relationship between sand and water concentrations, Log10-transformed E. coli concentrations from upshore, swash, and submerged sand areas of the beach were compared with the next day E. coli water concentration and previous day E. coli water concentration. Bailey’s Harbor had a positive correlation between the swash sand average and the next day E. coli water concentration in 2006 (p = 0.080, r2 = 0.491). This was the only beach with a significant relationship between swash sand and water E. coli concentrations. Three beaches revealed at least one significant relationship between a sand E. coli mean concentration and the previous or next day water concentration of E. coli. Otumba Park Beach upshore sand E. coli concentration averages correlated negatively with the previous day E. coli water concentration (p = 0.059, r2 = 0.632), while at Sunset Park Beach, the upshore sand E. coli concentration correlated positively with the previous day E. coli water concentration in both 2005 (p = 0.072, r2 = 0.348) and 2006 (p = 0.076, r2 = 0.433). Interestingly, Otumba and Sunset Park Beaches are both located on the Sturgeon Bay Canal, are less than 1 km apart, and have identical weather and rainfall patterns. Wind direction and wave height could vary between the two beaches, however, and might help explain how differences between regional beaches can occur. At some beaches the swash zone sand E. coli concentration or the submerged sand E. coli concentration correlates with the next day E. coli water concentration, suggesting that sand may act as a reservoir for this indicator organism. Further study is needed to determine if this observation can be generalized to other beaches. CONCLUSIONS E. coli concentrations in sand were highest in the summer months, lower in the fall, and undetectable in winter. During the summer months, five of the six Door County, WI beaches consistently had the
Microbial Concentrations in Sand and their Effect on Beach Water highest concentrations of E. coli in the swash sand, second highest in the upshore sand, and lowest concentrations in the submerged sand. Regardless of the sand sampling location (upshore, swash, or submerged), E. coli concentrations in sand were different from the concentrations of E. coli detected in water. That does not mean that there is no correlation between the E. coli concentration in the sand and the E. coli concentration in the water—merely that no two areas of the beach had consistently similar E. coli averages. Elevated water and sand concentrations of E. coli can be coupled when a time lag (of 24 hours) is implemented between sampling events, which is consistent with the findings of other investigators (Whitman and Nevers 2003). It appears that sand may contaminate water or water may contaminate sand. Factors such as urban vs. rural setting and avian populations should be considered when determining contamination sources of sand for a particular beach, and each beach should be considered individually. ACKNOWLEDGMENTS Funding for this project was provided by the Wisconsin Coastal Management Program with a grant to the Door County Soil and Water Conservation Department (DCSW). The authors would like to thank William Schuster, Amanda Brown, and Vinni Chomeau from the DCSW, Rhonda Kohlberg from the Door County Health Department, and numerous members of the “Beach Group” at UWOshkosh for their input and assistance with this project. REFERENCES Anderson, K.L., Whitlock, J.E., and Harwood, V.J. 2005. Persistence and differential survival of fecal indicator bacteria in subtropical waters and sediments. Appl. Environ. Microbiol. 71(6):3041–3048. APHA (American Public Health Association). 1998. Standard Methods for Examination of Water and Wastewater, 20th ed. Washington, DC. APHA. Beversdorf, L.J., Bornstein-Forst, S.M., and McLellan, S.L. 2007. The potential for beach sand to serve as a reservoir for Escherichia coli and the physical influences on cell die-off. J. Appl. Microbiol.102 (5):1372–1381. Bogosian, G., Sammons, L.E., Morris, P.J.,O’Neil, J.P., Heitkamp, M.A., and Weber, D.B., 1996. Death of the Escherichia coli K-12 strain W3110 in soil and Water. Appl. Environ. Microbiol. 62: 4114–4120. Brettar, I., and Hölfe, M.G. 1992. Influence of ecosystematic factors on survival of Escherichia coli after
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large-scale release into lake water mesocosms. Appl. Environ. Microbiol. 58:2201–2210. Byappanahalli, M.N., Shively, D., Nevers, M., Sadowsky, M., and Whitman, R. 2003. Growth and survival of Escherichia coli and enterococci populations in the macro-alga Cladophora (Chlorophyta). FEMS Microbiology Ecology 46:203–211. Door County Wisconsin Visitor Bureau Website. 2007. Official Vacation Planner Visitor Guide. Door County Chamber of Commerce. Accessed 12 January 2007. http://www.doorcounty.com/. Dufour, A. 1984. Health Effects Criteria for Fresh Recreational Waters. EPA 600/1-84-100. Cincinnati, Ohio, U.S. Environmental Protection Agency. Fogarty, L.R., Haack, S.K., Wolcott, M.J., and Whitman, R. L. 2003. Abundance and characteristics of the recreational water quality indicator bacteria Escherichia coli and enterococci in gull faeces. J. Appl. Microbiol. 94:865–878. Ishii, S., Yan, T., Shively, D.A., Byappanahalli, M.N., Whitman, R.L., and Sadowsky, M.J. 2006. Cladophora (Chlorophyta) spp. harbor human bacterial pathogens in nearshore water of Lake Michigan. Appl. Environ. Microbiol. 72(7):4545–53. ——— , Hansen, D.L., Hicks, R.E., and Sadowsky, M.J. 2007. Beach sand and sediments are temporal sinks and sources of Escherichia coli in Lake Superior. Environ. Sci. Technol. 41:2203–2209. Kinzelman, J.L., Pond, K., Longmaid, K., and Bagley, R. 2004. The effect of two mechanical beach grooming strategies on Escherichia coli density in beach sand at a southwestern Lake Michigan beach. Aquatic Ecosystem Health & Management 7(3):425–432. Kleinheinz, G.T., McDermott, C.M., and Chomeau, V. 2006. Evaluation of avian waste and bird counts as predictors of Escherischia coli contamination at Door County, WI beaches. J. Great Lakes Res. 32: 117–123. Noble, R.T.,Weisberg, S.B., Leecaster, M.K., McGeen, C.D., Dorsey, J.H., Vainik, P., and Orozco-Borbon, V. 2003. Storm effects on regional beach water quality along the southern California shoreline. J. Water & Health 01.1: 23–31. Obiri, D.K., and Jones, K. 1999. Distribution and seasonality of microbial indicators and Thermophilic campylobacters in two freshwater bathing sites on the River Lune in northwest England. Appl. Environ. Microbiol. 87(6):822–32. Olapade, O.A., Depas, M.M., Jensen, E.T., and McLellan, S.L. 2006. Microbial communities and fecal indicator bacteria associated with Cladophora mats on beach sites along Lake Michigan shores. Appl. Environ. Microbiol. 72(3):1932–1938. Sampson, R. W. Swiatnicki, S.A., Osinga, V.L., Supita, J.L., McDermott, C.M., and Kleinheinz, G.T. 2006. Effects of temperature and sand on E. coli survival in
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a northern lake water microcosm. J. Water & Health. 4(3):389–393. Smith, J.J., Howington, J.P., and McFeters, G.A. 1994. Survival, physiological response, and a recovery of enteric bacteria exposed to a polar marine environment. Appl. Environ. Microbiol. 60:2977–2984. U.S. Environmental Protection Agency (USEPA). 2002. Method 1603: Escherichia coli (E. coli) in water by membrane filtration using modified membrane-thermotolerant Escherichia coli agar (Modified mTEC). EPA-821-R-02-023. Wheeler Alm, E., Burke, J., and Spain, A. 2003. Fecal indicator bacteria are abundant in wet sand at freshwater beaches. Water Res. 37(16):3978–82. Whitman, R.L., and Nevers, M.B. 2003. Foreshore sand as a source of Escherichia coli in nearshore water of a Lake Michigan beach. Appl. Environ. Microbiol. 69(9):5555–5562.
——— , Shively, D.A., Pwlik, H., Nevers, M.B., and Byappanahalli, M. 2003. Occurrence of Escherichia coli and enterococci. In Cladophora (Chlorophyta) in nearshore water and beach sand of Lake Michigan. Appl. Environ. Microbiol. 69(8):4714–4719. ——— , Nevers, M.B., Korinek, G.C., and Byappanahalli, M. 2004. Solar and temporal effects on Escherichia coli concentration at a Lake Michigan swimming beach. Appl. Environ. Microbiol. 70(7):4276–7285. Yamahara, K., and Boehm, A. 2006. Beach sands: A diffuse source of indicator bacteria to California coastal waters. [abstract]. In: National Beaches Conference, Oct 11–13; Niagara Falls, N.Y. p. 35. Submitted: 23 October 2007 Accepted: 2 May 2008 Editorial handling: William C. Sonzogni
Microbial Concentrations in Sand and their Effect on Beach Water in Door County, Wisconsin Tabitha T. Zehms, Colleen M. McDermott, and Gregory T. Kleinheinz* Department of Biology and Microbiology University of Wisconsin—Oshkosh 800 Algoma Boulevard Oshkosh, Wisconsin 54901 ABSTRACT. The seasonal variations and patterns of Escherichia coli in Wisconsin’s coastal waters have been closely studied in recent years due to increased beach monitoring activities. Patterns of distribution of the indicator organism, E. coli, in the sand at these beaches are now being investigated as a source of E. coli to adjacent beach water. This project investigates the concentrations of E. coli in beach sand, and the relationship between these sand-microbe concentrations and concentrations of microbes in the corresponding beach water. Weekly sampling of upshore, swash, and submerged sand at six beaches provided numbers of the indicator bacteria in each beach’s sand substrate for two consecutive summers. Overall concentrations of E. coli were highest in the swash sand of the beach, with the highest numbers seen in the summer months and lowest numbers in the winter months. Each location had very different concentrations of E. coli in the beach sand from 1,800 CFU/100 g to 21,670 CFU/100 g sand. Each location had a very different relationship between the indicator organism found in the beach sand and that found in the beach water. These data suggest that sand may be a reservoir for E. coli at some locations, and another source of contamination that should be considered in beach monitoring programs. However, elevated levels of E. coli in beach sand were not universal and varied greatly from location to location. INDEX WORDS:
E. coli, water quality, sand, beach, Lake Michigan.
Pathogens, or disease-causing microbes, can be found in human and animal waste, and fecal contamination of recreational waters can thus present a health risk to bathers. High concentrations of bacteria from a fecal contamination source could cause severe gastrointestinal illness if swallowed, especially in those that have a high potential for illness, such as the very young and very old or the immunocompromised. Wisconsin has chosen to utilize E. coli as the indicator organism for fecal contamination of its recreational waters, based on strong correlations between swimming-associated gastrointestinal symptoms and E. coli densities (Dufour 1984). The persistence and survival of E. coli in beach water should parallel the persistence and survival of bacterial pathogens in this environment. The greater the survival of indicator organisms in the environment relative to associated pathogens’ survival, however, the less useful they are as an indication of recent fecal contamination. Several studies have been conducted to ascertain the duration of E. coli
INTRODUCTION The year 2006 was the fourth in the implementation of Wisconsin’s large-scale Great Lakes Beach Monitoring and Notification Program. The program works with local health departments to ensure prompt public notification and efficient monitoring, as mandated by the U.S. Environmental Protection Agency (EPA). Door County, WI (a peninsula located between the Bay of Green Bay and Lake Michigan) has over 250 miles of shoreline and accounts for 30 of the 192 beaches that are regularly monitored in the state. Door County relies on tourism for the bulk of its revenue—according to its Chamber of Commerce, Door County is one of the top ten vacation destinations in North America (Door County Visitor Bureau Website 2007). Summer is the busiest time of year for Door County tourism, so beach water quality is vital to keeping visitors healthy, and integral to the sustainability of the region’s economy. *Corresponding
author. E-mail: [email protected]
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Microbial Concentrations in Sand and their Effect on Beach Water persistence in water. Results vary from 6 days to 40 days in microcosms with varying temperatures (Bogosian et al. 1996, Sampson et al. 2006). Cooler temperatures have consistently provided longer time periods of E. coli persistence, an interesting concept considering the very warm temperature of the gastrointestinal tract, where E. coli are naturally found (Brettar and Höfle 1992, Smith et al. 1994, Bogosian et al. 1996, Sampson et al. 2006). While colder temperatures aid in lengthening survival time, warmer temperatures are still tied to higher E. coli concentrations in beach water, particularly as the summer months progress (Whitman and Nevers 2003, Ishii et al. 2007). Temperature is not the only factor that affects E. coli concentrations and their persistence in recreational water. Sunlight exposure decreased E. coli counts exponentially on sunny days at a Lake Michigan swimming beach, with mesocosm experiments providing similar results (Whitman et al. 2004). Nutrient availability, competition and predation, and wind direction are other factors that will impact a bacterium’s survival in the environment at large. Fecal contamination sources, such as wastewater and stormwater outfall pipes, sewage and septic leaks, runoff, avian waste, and Cladophora accumulation, can influence indicator organism populations in recreational waters as well (Byappanahalli et al. 2003, Fogarty et al. 2003, Ishii et al. 2006, Noble et al. 2003, Whitman et al. 2003, Olapade et al. 2006). Recently, the importance of E. coli survival in beach sand has been investigated. Several studies have confirmed the presence of E. coli in sand, as well as sand’s potential as a reservoir for the organism (Ishii et al. 2007, Beversdorf et al. 2007). Summer studies indicate that fecal indicator bacteria are more abundant in sand than in water; in some cases counts are an order of magnitude higher in the sand substrate (Obiri and Jones 1999, Wheeler Alm et al. 2003). Furthermore, the presence of sand helped E. coli survive 10 additional days, for a total of 40 days, in nonsterile lake water in one microcosm study (Sampson et al. 2006). High concentrations of indicator organisms found in the foreshore sand (sand in contact with wave action of water) at the 63rd Street Beach in Chicago, Illinois, prompted replacing that sand with E. coli-free sand for the 2000 swimming season. The E. coli counts were back to the original detected concentrations within 2 weeks (Whitman and Nevers 2003). Indicator organisms were also found to be more persistent in contaminated subtropical sediment than in wastewater or
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dog feces (Anderson et al. 2005). Regular grooming of beaches has been shown to either increase or decrease the E. coli populations in beach sand, depending on the depth of raking (Kinzelman et al. 2004). The presence of E. coli in beach sand represents a possible source of contamination of the recreational water itself. Fecal pollution contaminates not only the water but the environment it travels through to get to the water. Swash zone beach sand constantly endures wave action, and this contact could transfer indicator organisms from the water to the sand, and the sand to the water (Yamahara and Boehm 2006, Beversdorf et al. 2007). When monitored, concentrations of E. coli in beach sand can inform beach managers of potential reservoir loading, and thus, additional sources of contamination that could greatly affect water quality. The overall objective of this study was to investigate the concentrations of E. coli in sand at selected beaches and to investigate the impact that E coli in the sand may have on the E. coli concentrations found in beach water. Specifically, we tested the following hypotheses: 1. E. coli concentrations in sand will differ from season to season with the greatest concentrations occurring in the warmer months of the year. 2. E. coli concentrations in sand will differ based on location at a beach (submerged, swash zone, and upshore), with the greatest concentrations occurring at the swash zone. 3. Concentrations of E. coli in sand, especially in the swash zone, will correlate with E. coli concentrations in adjacent beach water, indicating that sand may act as a source of microbial contamination at beaches. 4. Concentrations of E. coli in sand will correlate best with E. coli concentrations in the next day’s beach water sample to account for a lag necessary to wash E. coli from sand into water. MATERIALS AND METHODS Sand Sample Collection Six beaches were tested weekly throughout the swimming season (n = 12) along both the Green Bay and Lake Michigan sides of the Door County Peninsula: Ephraim Beach, Fish Creek Beach, Sunset Park Beach, Otumba Park Beach, Whitefish Dunes State Park Beach, and Bailey’s Harbor
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FIG. 1. Map of recreational beaches used in this study in Door County, WI and location in Wisconsin and within Lake Michigan. Ridges Beach (Fig. 1). These beaches were selected because they represent a range of shoreline conditions commonly found along the Great Lakes. These conditions included open Great Lakes water shorelines, embayed shorelines, and beach-front shorelines along a man-made canal. Likewise, these beaches ranged from semi-urban to remote parklike locations. The sampling period lasted 12 weeks
(n = 12), from late May to late August, in both 2005 and 2006. Additional samples were taken from each of the selected beaches in November 2005, January 2006, and November 2006. During each sampling event, nine sand samples were taken from each beach using an AMS soil recovery probe (2.25 cm × 30.5 cm, AMC Inc., American Falls, ID, USA) and sterile polybutyrate liners. Samples were col-
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FIG. 2. A sampling schematic of the nine sand samples taken weekly at each beach. UR, UC, and UL refer to the upshore right, center, and left samples, respectively. SR, SC, and SL refer to the swash zone samples, and WR, WC, and WL refer to the submerged sand samples taken. lected to a depth of 6 inches and were taken from the upshore sand (4.6 m away from wave action), the swash sand, and the submerged sand (under 60 cm of water). Three samples spaced 5 meters apart were then taken from each sand zone; this small measurement scale corresponded with the small size of most of the beaches sampled (Fig. 2). Care was taken to avoid sand samples with noticeable amounts of avian waste, Cladophora, or other environmental material that could affect the concentrations of indicator organisms in the sample. When taking the sand samples, the liner was removed from the probe without contaminating the inside of the liner. Caps were placed on both ends of the liner. The capped liners were placed in a cooler containing an ice pack to maintain temperature at 4°C. Samples remained on ice until analysis. Analysis typically occurred within 4 hours of col-
lection. In addition, one 100 mL sterile bottle was filled with swash zone sand from each beach. These samples were used to determine dry weight of sand from each beach. Water Sample Collection Water samples were taken at least once weekly (usually 4–5 times/week to comply with Beach Act monitoring schedules) at the time of the sand sampling for E. coli enumeration. Samples were collected using the methods described in the U.S. EPA Microbiology Methods Manual, the Standard Methods for the Examination of Water and Wastewater #1060 (APHA 1998). Specifically, samples were collected from water with a depth of 61 cm (to be consistent with Wisconsin Department of Natural Resources (WIDNR) guidelines for BEACH Act
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sampling) into sterile, 100 mL polystyrene bottles (IDEXX Corp., Portland, ME). The water samples were taken from the center of the beach, the site in the water that is the midpoint of the length of the defined beach area. Samples were placed into a cooler at 4ºC until they were analyzed. Sand Sample Analysis Laboratory analysis on sand collected with the soil recovery probe was conducted via membrane filtration and U.S. EPA method 1603 using modified mTEC for E.coli (U.S. EPA 2002). Sub sections of sand from the 100 mL bottles were placed in 20 separate aluminum weigh boats, weighed, and placed in a 44°C incubator for 48 hours. The dry weight then was recorded. A sand wet/dry conversion factor was calculated by taking the sum of the dry weight divided by the wet weight for all 20 swash sand samples, and dividing this sum by the total number of samples. This average was used as a conversion factor and multiplied with the Colony Forming Unit per gram (CFU/g) of wet sand, or the number of colonies on the mTEC after 24 hours of incubation. This step allowed all beaches to be normalized with final measurements in CFU/g dry weight. In order to make comparisons with E. coli concentrations in water (expressed as MPN/100 mL), sand E. coli concentrations were then expressed as CFU/100 g sand.
number of paired samples required to maintain the accepted power of 0.9 decreased only slightly, to 493 (data not shown). Due to this high amount of variation within the data, a p-value ≤ 0.10 was considered significant. Since E. coli in beach water was enumerated 4–5 per week, there were data available so the E.coli concentrations in the various sand locations could be statistically compared to the previous, same, and next day’s beach water E.coli concentrations. No statistical comparisons were conducted with data collected outside the swimming season due to very low, or non-detectable, concentrations of microbes. RESULTS AND DISCUSSION E. coli Seasonal Concentrations in Sand The hypothesis that E. coli in beach sand would vary by season was tested by measuring E. coli concentrations during summer months (May–August), in November before freezing had occurred, and in January when beach sand was frozen and snow covered. E. coli concentrations in sand were highest in the summer months, declined in the November samples, and were undetectable in January 2006 (Fig. 3). Because there were so few samples collected in the November and January, statistical differences between these seasons were not calculated.
Water Sample Analysis The defined substrate tests, Colilert™ (IDEXX Corp., Portland, ME), was used to analyze the water samples for E. coli. Incubation and microbial enumeration were conducted following the manufacturer’s recommendations. All water samples were maintained at 4°C until analysis, and all samples were processed within 2 hours of collection in a State of Wisconsin Department of Agriculture Trade and Consumer Protection (DATCP) certified laboratory in Sturgeon Bay, WI (certification #105453). E. coli concentrations were expressed as most probable number/100 mL water (MPN/100 mL). Statistical Analysis All results were performed on log10-transformed data with SPSS (SPSS Inc., Chicago, IL). Power analysis was performed based on paired t-test data and indicated 605 paired samples were necessary to maintain the widely accepted α = 0.05 and α = 0.10. When the alpha value was adjusted to 0.10 the
FIG. 3. E. coli concentrations in sand (CFU/ 100 g) sampled at various times throughout the year. For summer samples (June–August) n = 12. For November samples, n = 1. For January samples, n = 1. Because there was only one sampling in January, statistical differences between means of these time periods could not be determined.
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These results are similar to the observed prevalence of E. coli in other beach sand studies (Whitman and Nevers 2003) and indicates that beach sand in northern latitudes likely is repopulated by E. coli each spring/summer, rather than harbors E. coli from year to year. Comparisons of E. coli Concentrations in Sand at Different Locations within the Beach Our second hypothesis was tested by comparing E. coli concentrations at various locations at each selected beach. Mean E. coli concentrations within each sand zone (upshore, swash, and submerged areas) at each beach were calculated and compared (Figs. 4 and 5 and Table 1). Generally, the highest numbers of E. coli were consistently found in the swash sand, second highest in the upshore sand, and lowest in the submerged sand. (Figs. 4 and 5). Four of the six beaches showed the highest average E. coli in the swash sand in both 2005 and 2006. Bailey’s Harbor had a higher mean E. coli concentration in the upshore sand only in 2006. Whitefish Dunes instead showed the highest mean E. coli in upshore sand in both 2005 and 2006 (Figs. 4 and 5). This is likely due to the increased upshore area of this particular beach and the large populations of gulls that inhabit it. While gulls scavenge at this beach in the swash zone, they often roost for large parts of the day in the upshore area. This beach had the largest waterfowl population of any of the selected beaches (approximately 50 birds/sampling for Whitefish Dunes vs. < 5 birds/sampling for the other beaches) (Kleinheinz et al. 2006). Mean submerged sand E. coli concentration was the lowest of the three sand zones at every beach for both years. Submerged sand E. coli concentrations were 2–32 times less than the swash zone levels in 2005 and 3–73 times less than swash sand levels in 2006 for all beaches studied. Although swash zone sand is more prone to desiccation and the effects of UV irradiation than is submerged sand, perhaps the difference in temperature and frequency of microbial loading account for the large number of E. coli in the swash zone sand (Whitman et al. 2004, Sampson et al. 2006). Paired t-tests of log10-transformed data were used to ascertain whether the general trend described above held true on a weekly basis. Due to the large amount of inherent variance in this type of sampling, significance was set at a p-value ≤ 0.10. All six beaches had significant differences between the submerged sand E. coli concentration averages and
FIG. 4. Differences between mean E. coli concentrations in sand (CFU/100 g) at various locations on beaches (upshore, swash zone, and submerged) for 2005 and 2006 summer seasons. E. coli concentrations in water (MPN/100 mL) also is indicated (triangles), for comparison with sand E. coli concentrations. the swash zone sand E. coli averages (Table 1). Three of the beaches sampled—Fish Creek, Otumba, and Sunset Park—showed the same significant relationships between E. coli concentrations in the various zones of sand sampled, in both years. All three beaches share similar beach characteristics, with relatively narrow and short sandy areas in semi-urban settings. A more urban environment generally has more impervious surfaces and less green space than a rural environment, which could influence the amount of contamination reaching
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FIG. 5. E. coli concentrations in sand (CFU/100 g) at various locations on beaches (upshore, swash zone, and submerged) for 2005 and 2006. E. coli concentrations in water (MPN/100 mL) also is indicated (triangles), for comparison with sand E. coli concentrations.
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TABLE 1. Results of statistically significant (p < 0.1) paired t-test comparisons of E. coli concentrations from various sand locations and beach water at studied beaches. Location Submerged Sand
Comparison vs. swash sand
vs. upshore sand
vs. water
Swash Zone Sand
vs. water
Upshore Sand
vs. swash sand
vs. water
beach areas via rainfall runoff. Urban settings also have storm water outfall pipes and the potential for storm water drain overflows. A two-way ANOVA with log10-transformed averages from each zone each week revealed that beach (p = 0.006) and location (zone within the beach, p < 0.000) were significant determinants of E. coli concentrations (data not shown). The interaction between beach and location was also found to be significant (p = 0.07), suggesting that E. coli populations in beach sand are unique for each beach and for each zone (upshore, swash, or submerged area) within the beach.
Beach Baileys Harbor Ephraim Fish Creek Otumba Sunset Whitefish Dunes Ephraim Fish Creek Otumba Sunset Fish Creek Sunset Whitefish Dunes Fish Creek Bailey’s Harbor Bailey’s Harbor Fish Creek Otumba Sunset Ephraim Fish Creek Otumba Sunset Whitefish Dunes Otumba Whitefish Fish Creek Fish Creek Otumba Sunset Whitefish Dunes Fish Creek Otumba Sunset
Year 2005 2005 2005 2005 2005 2005 2006 2006 2006 2006 2005 2005 2005 2006 2006 2005 2005 2005 2005 2006 2006 2006 2006 2006 2005 2005 2005 2006 2006 2006 2005 2006 2006 2006
p-value 0.012 0.059 0.001 0.023 0.016 0.008 0.038 0.001 0.001 0.008 0.040 0.054 0.008 0.037 0.066 0.085 0.042 0.063 0.036 0.046 0.001 0.012 0.001 0.070 0.021 0.073 0.011 0.024 0.007 0.008 0.073 0.050 0.015 0.006
Correlations between Sand Zone E. coli and Beach Water E. coli Concentrations Our third hypothesis (E. coli concentrations in sand will correlate with E. coli concentrations in beach water) was tested by measuring E. coli concentrations in beach water with a depth of 61 cm, at the center of each beach, and comparing with E. coli concentrations at the various sand locations. Log10-transformed data were analyzed with bivariate two-tailed correlations with the Pearson’s correlation coefficient. Each summer season was analyzed separately, since meteorological factors are very different at each beach from year to year.
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The swash sand E. coli concentrations correlated positively with the water E. coli MPN/100 mL twice, at Whitefish Dunes (p = 0.056) and Sunset Park (p = 0.041) in 2006 (Table 1). On two occasions the upshore sand also had positive correlations with the water levels of E. coli, at Fish Creek in 2005 (p = 0.060) and again at Sunset Park in 2006 (p = 0.008). One positive correlation was noted at Sunset Park in 2006 between the submerged sand and the water E. coli MPN/100 mL (p = 0.034). Perhaps the correlations observed between E. coli concentrations in upshore sand and in water may serve as an indication of high levels of contamination. It is probable that contamination events frequently impact the beach sand and the water at the same time (rainfall runoff, avian waste on the beach and in the water, etc.) and could explain this relationship. The presence of indicator organisms in the swash sand substrate could act as a reservoir for the bacteria to potentially contaminate the water (and vice versa), leading to beach monitoring results that misleadingly indicate repeated fecal contamination. The submerged sand correlated positively with the swash sand at Otumba Park Beach (p = 0.035) and Sunset Park (p = 0.102) in 2006 (Table 1). The submerged sand also correlated positively with the upshore sand E. coli averages for 2 consecutive years at Sunset Park Beach (p = 0.060 and p = 0.096, respectively). One positive correlation was noted between the upshore sand and the swash sand at Sunset Park in 2006 (p = 0.005, Table 1). Sunset Park accounted for seven significant correlations between E. coli sampling sites at this location during this study. This location had the highest concentrations of E. coli in submerged sand and suggests that there are distinct and identifiable patterns unique to this beach. Sunset Park and Otumba Park Beaches were the most urban of the studied locations and both had a positive correlation between the swash sand and the submerged sand. These two beaches accounted for the highest and second highest concentrations of E. coli in the swash sand and submerged sand (Figs. 4 and 5). Significant positive relationships between sand E. coli concentrations and water E. coli concentrations indicate that as sand E. coli concentrations rise, concentrations of E. coli in water also increase. The presence of indicator organisms in the sand substrate could act, then, as a reservoir for the bacteria to potentially contaminate the water (and vice versa), leading to beach monitoring results that misleadingly indicate repeated fecal contamination.
This effect would be exacerbated by wind and wave patterns. Correlations between Sand Zone E. coli and Previous or Following Day Water E. coli Concentrations It also was hypothesized that E. coli concentrations in sand would best correlate with E. coli concentrations in the following day’s water. In order to further investigate this relationship between sand and water concentrations, Log10-transformed E. coli concentrations from upshore, swash, and submerged sand areas of the beach were compared with the next day E. coli water concentration and previous day E. coli water concentration. Bailey’s Harbor had a positive correlation between the swash sand average and the next day E. coli water concentration in 2006 (p = 0.080, r2 = 0.491). This was the only beach with a significant relationship between swash sand and water E. coli concentrations. Three beaches revealed at least one significant relationship between a sand E. coli mean concentration and the previous or next day water concentration of E. coli. Otumba Park Beach upshore sand E. coli concentration averages correlated negatively with the previous day E. coli water concentration (p = 0.059, r2 = 0.632), while at Sunset Park Beach, the upshore sand E. coli concentration correlated positively with the previous day E. coli water concentration in both 2005 (p = 0.072, r2 = 0.348) and 2006 (p = 0.076, r2 = 0.433). Interestingly, Otumba and Sunset Park Beaches are both located on the Sturgeon Bay Canal, are less than 1 km apart, and have identical weather and rainfall patterns. Wind direction and wave height could vary between the two beaches, however, and might help explain how differences between regional beaches can occur. At some beaches the swash zone sand E. coli concentration or the submerged sand E. coli concentration correlates with the next day E. coli water concentration, suggesting that sand may act as a reservoir for this indicator organism. Further study is needed to determine if this observation can be generalized to other beaches. CONCLUSIONS E. coli concentrations in sand were highest in the summer months, lower in the fall, and undetectable in winter. During the summer months, five of the six Door County, WI beaches consistently had the
Microbial Concentrations in Sand and their Effect on Beach Water highest concentrations of E. coli in the swash sand, second highest in the upshore sand, and lowest concentrations in the submerged sand. Regardless of the sand sampling location (upshore, swash, or submerged), E. coli concentrations in sand were different from the concentrations of E. coli detected in water. That does not mean that there is no correlation between the E. coli concentration in the sand and the E. coli concentration in the water—merely that no two areas of the beach had consistently similar E. coli averages. Elevated water and sand concentrations of E. coli can be coupled when a time lag (of 24 hours) is implemented between sampling events, which is consistent with the findings of other investigators (Whitman and Nevers 2003). It appears that sand may contaminate water or water may contaminate sand. Factors such as urban vs. rural setting and avian populations should be considered when determining contamination sources of sand for a particular beach, and each beach should be considered individually. ACKNOWLEDGMENTS Funding for this project was provided by the Wisconsin Coastal Management Program with a grant to the Door County Soil and Water Conservation Department (DCSW). The authors would like to thank William Schuster, Amanda Brown, and Vinni Chomeau from the DCSW, Rhonda Kohlberg from the Door County Health Department, and numerous members of the “Beach Group” at UWOshkosh for their input and assistance with this project. REFERENCES Anderson, K.L., Whitlock, J.E., and Harwood, V.J. 2005. Persistence and differential survival of fecal indicator bacteria in subtropical waters and sediments. Appl. Environ. Microbiol. 71(6):3041–3048. APHA (American Public Health Association). 1998. Standard Methods for Examination of Water and Wastewater, 20th ed. Washington, DC. APHA. Beversdorf, L.J., Bornstein-Forst, S.M., and McLellan, S.L. 2007. The potential for beach sand to serve as a reservoir for Escherichia coli and the physical influences on cell die-off. J. Appl. Microbiol.102 (5):1372–1381. Bogosian, G., Sammons, L.E., Morris, P.J.,O’Neil, J.P., Heitkamp, M.A., and Weber, D.B., 1996. Death of the Escherichia coli K-12 strain W3110 in soil and Water. Appl. Environ. Microbiol. 62: 4114–4120. Brettar, I., and Hölfe, M.G. 1992. Influence of ecosystematic factors on survival of Escherichia coli after
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large-scale release into lake water mesocosms. Appl. Environ. Microbiol. 58:2201–2210. Byappanahalli, M.N., Shively, D., Nevers, M., Sadowsky, M., and Whitman, R. 2003. Growth and survival of Escherichia coli and enterococci populations in the macro-alga Cladophora (Chlorophyta). FEMS Microbiology Ecology 46:203–211. Door County Wisconsin Visitor Bureau Website. 2007. Official Vacation Planner Visitor Guide. Door County Chamber of Commerce. Accessed 12 January 2007. http://www.doorcounty.com/. Dufour, A. 1984. Health Effects Criteria for Fresh Recreational Waters. EPA 600/1-84-100. Cincinnati, Ohio, U.S. Environmental Protection Agency. Fogarty, L.R., Haack, S.K., Wolcott, M.J., and Whitman, R. L. 2003. Abundance and characteristics of the recreational water quality indicator bacteria Escherichia coli and enterococci in gull faeces. J. Appl. Microbiol. 94:865–878. Ishii, S., Yan, T., Shively, D.A., Byappanahalli, M.N., Whitman, R.L., and Sadowsky, M.J. 2006. Cladophora (Chlorophyta) spp. harbor human bacterial pathogens in nearshore water of Lake Michigan. Appl. Environ. Microbiol. 72(7):4545–53. ——— , Hansen, D.L., Hicks, R.E., and Sadowsky, M.J. 2007. Beach sand and sediments are temporal sinks and sources of Escherichia coli in Lake Superior. Environ. Sci. Technol. 41:2203–2209. Kinzelman, J.L., Pond, K., Longmaid, K., and Bagley, R. 2004. The effect of two mechanical beach grooming strategies on Escherichia coli density in beach sand at a southwestern Lake Michigan beach. Aquatic Ecosystem Health & Management 7(3):425–432. Kleinheinz, G.T., McDermott, C.M., and Chomeau, V. 2006. Evaluation of avian waste and bird counts as predictors of Escherischia coli contamination at Door County, WI beaches. J. Great Lakes Res. 32: 117–123. Noble, R.T.,Weisberg, S.B., Leecaster, M.K., McGeen, C.D., Dorsey, J.H., Vainik, P., and Orozco-Borbon, V. 2003. Storm effects on regional beach water quality along the southern California shoreline. J. Water & Health 01.1: 23–31. Obiri, D.K., and Jones, K. 1999. Distribution and seasonality of microbial indicators and Thermophilic campylobacters in two freshwater bathing sites on the River Lune in northwest England. Appl. Environ. Microbiol. 87(6):822–32. Olapade, O.A., Depas, M.M., Jensen, E.T., and McLellan, S.L. 2006. Microbial communities and fecal indicator bacteria associated with Cladophora mats on beach sites along Lake Michigan shores. Appl. Environ. Microbiol. 72(3):1932–1938. Sampson, R. W. Swiatnicki, S.A., Osinga, V.L., Supita, J.L., McDermott, C.M., and Kleinheinz, G.T. 2006. Effects of temperature and sand on E. coli survival in
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a northern lake water microcosm. J. Water & Health. 4(3):389–393. Smith, J.J., Howington, J.P., and McFeters, G.A. 1994. Survival, physiological response, and a recovery of enteric bacteria exposed to a polar marine environment. Appl. Environ. Microbiol. 60:2977–2984. U.S. Environmental Protection Agency (USEPA). 2002. Method 1603: Escherichia coli (E. coli) in water by membrane filtration using modified membrane-thermotolerant Escherichia coli agar (Modified mTEC). EPA-821-R-02-023. Wheeler Alm, E., Burke, J., and Spain, A. 2003. Fecal indicator bacteria are abundant in wet sand at freshwater beaches. Water Res. 37(16):3978–82. Whitman, R.L., and Nevers, M.B. 2003. Foreshore sand as a source of Escherichia coli in nearshore water of a Lake Michigan beach. Appl. Environ. Microbiol. 69(9):5555–5562.
——— , Shively, D.A., Pwlik, H., Nevers, M.B., and Byappanahalli, M. 2003. Occurrence of Escherichia coli and enterococci. In Cladophora (Chlorophyta) in nearshore water and beach sand of Lake Michigan. Appl. Environ. Microbiol. 69(8):4714–4719. ——— , Nevers, M.B., Korinek, G.C., and Byappanahalli, M. 2004. Solar and temporal effects on Escherichia coli concentration at a Lake Michigan swimming beach. Appl. Environ. Microbiol. 70(7):4276–7285. Yamahara, K., and Boehm, A. 2006. Beach sands: A diffuse source of indicator bacteria to California coastal waters. [abstract]. In: National Beaches Conference, Oct 11–13; Niagara Falls, N.Y. p. 35. Submitted: 23 October 2007 Accepted: 2 May 2008 Editorial handling: William C. Sonzogni