E.coli and coliform concentrations in developed and undeveloped nearshore surface water within an inland lake
Abstract
There are a number of sources that impact the microbial water quality of nearshore surface water. These include development, avian species, and rainfall, to name just a few. It is often difficult to elucidate the exact cause of these changes due to numerous variables that cannot be controlled. However, the development of shorelines has often been implicated in eroded nearshore water quality. This study utilized a single lake that has minimal inputs of microorganisms from external sources such as rivers, outfalls, avian species, etc.. The lack can easily be divided into developed and undeveloped regions as the US Forest Service owns a good portion of the lake shoreline. This greatly decreases the variables between sampling locations. The overall objective of this study was to evaluate if residential development along an inland lakeshore would impact E.coli and/or coliforms found in the adjacent nearshore surface water. The developed regions of the lake showed significantly higher (alpha<0.05) concentrations of coliforms and E.coli when compared to undeveloped regions for all three seasons of the study. While the study lasted three sample seasons, each year resulted in very similar overall results to each other. Yearly means of coliforms and E.coli at each sample location group were compared to each other and found that the means between these groups were similar each year and not statistically different. While this project does not suggest what the cause of the increased coliform and E.coli concentrations in the nearshore, it does provide an important contribution to other work that suggests development may adversely impact nearshore water quality. This unique study site could be used for future studies due to unusual ability to control extraneous inputs of coliforms and E.coli.
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Introduction
The use of recreational water sites along lakes, rivers, or oceans, are one of the most popular activities in many parts of the world. However, these waters contain varying levels of health risk as it relates to microbial water quality. Fecal material from swimmers, domestic animals (dogs, cattle, and horses), as well as waterfowl (geese, gulls, and ducks), all lead to increases in microbial loading at beaches [1,3]. Additionally, rainfall and runoff due to rainfall events has been associated with increasing microbial levels in recreational waters along numerous beaches including several coastal areas in Wisconsin [1,2] [Kinzelman, Racine County, WI Health Department, personal communication, 2003]. This runoff can lead to beach closures and potentially unsanitary conditions at recreational water sites [4,5] When one considers the Great Lakes region is home to over 40,000 lakes and over 20% of the worlds freshwater resources, the impact of development on shorelines and water quality is an environmental, economic, and social issue.
The sources of these microbial pollutants are often diverse and are difficult to identify. Heavy rainfall was implicated in increasing bacterial contamination at beaches in several areas of the country [1,6]. On the Santa Monica Bay beaches in southern California, health departments typically issue warnings for the public to avoid recreational water contact for 3 days following a rainfall event [3]. The negative impact of stormwater on beach water quality has led to a myriad of option for controlling stormwater. Some of these include grass buffer partitions [7], stormwater detention basins [8], media filters [9], catch basin inserts, and infiltration units [10] to name just a few.
Conclusion
This is the first study that the author is aware of on the coliforms and E.coli concentrations within a single lake that has minimal inputs of microorganisms from external sources such as rivers, outfalls, avian species, etc.. Additionally, the fact that a good portion of the lake shoreline has never been developed it also presented a unique opportunity to evaluate the differences in coliforms and E.coli in the nearshore environment with minimal differences in location and water conditions. While the concentrations of each parameter found during this study were relatively low, the same trends could be found in locations with markedly higher concentrations of these microorganisms.
The developed regions of the lake showed significantly higher concentrations of coliforms and E.coli when compared to undeveloped regions for all three seasons of the study. While the study lasted three sample seasons, each year resulted in very similar overall results to each other. That is, the trends were the same each year and show a clear relationship between development and an impact on coliform and E.coli concentrations in nearshore water. Additionally, yearly the means of coliforms and E.coli at each sample location group were compared to each other (i.e., undeveloped groups to each other and developed groups to each other) and found that the means between these groups were similar each year and not statistically different. This suggests that even the sample groups within the bigger developed and undeveloped groups behaved similarly.
While this project does not suggest what the cause of the increased coliform and E.coli concentrations in the nearshore water of the developed regions of the lake, there are a number of plausible possibilities that would be supported by other specific studies. Some of these influences could be failing septic systems, infiltration from septic leach fields, runoff from pet waste, increased wild animal activity in cleared areas, cleaned shorelines for swimming, decreased vegetative/filtering on the shoreline, increased overland runoff to the surface water, etc.. Each of these possible sources could be evaluated in future studies to elucidate the relative percent contribution to the nearshore water.