Monitoring of E. coli and Enterococci in Lake Michigan Beach Sand

Excessive fecal indicator bacteria concentration leads to swimming advisories that are very common to freshwater beaches. To evaluate the concentration and interaction of indicator bacteria in beach sand and water and to examine the factors that affect bacteria concentration, a study was undertaken at Bradford beach, Milwaukee county on the shore of Lake Michigan. In this research, results from monitoring of E. coli and Enterococci in sand and water from Lake Michigan beach were presented. Bacteria counts were obtained using the IDEXX Most Probable Number (MPN) method. An attempt was made to establish a direct ratio of bacteria counts between the two most common eluents used to detach bacteria from sand, i.e., deionized water (DI) and phosphate buffered saline (PBS). The beach sand bacteria count was analyzed using the EPA CANARY event detection software to identify the onset of periods of anomalous water quality. Analysis of beach sand from this study show that for E. coli, it may be possible to establish a relationship between the results generated using two eluents. Results from the model indicates that sand can be a better potential reservoir for indicator bacteria survival than water as a source. The results also show that CANARY may be useful as an early warning system for monitoring beach contamination and may help to identify any abnormal condition very quickly. Also, in this study, the factors that contributed to the high concentration of bacteria resulting in abnormal water quality events are examined which are the impact of Algae in beach water sample and the rainfall effect during the overall month of sampling duration. CANARY software can best indicate the impact of the presence of Algae on bacteria concentration. The analysis of rainfall effect on bacteria concentration was done using statistical software by determining the significance (p-value) between the seasonal mean concentration of E. coli and the mean concentration of E. coli during the sampling duration and from the analyses it is evaluated that rainfall does affect the bacteria concentration. Moreover, the correlation coefficient indicates greater impact of rainfall event on bacteria concentration relative to the presence of Algae level. Regression analysis was also done to estimate the best model that describes the relation between E. coli and water temperature resulting in weak negative linear relationship between the variables.