Identification Of Putative Geographic Sources Of Bacterial Pollution In Lake Erie By Moleular Fingerprinting

In 2005, roughly 20,000 days of closing or advisories impacted Great Lakes beaches, of which 75% were attributed to unknown source of fecal pollution. However, most municipalities have failed to identify and control sources of fecal pollution affecting beaches. Since fecal contamination is mainly responsible for swimming advisories at Lake Erie Beach (Oregon, OH), this study aimed to identify the putative ditches as geographic sources of bacterial pollution at Lake Erie Beach. Previous research implicated Berger Ditch as a contributor of fecal pollution to the beach. However, we hypothesized that other nearby ditches might also play a role in the pollution of Lake Erie Beach. Throughout one year, monthly and partial biweekly water samples collected from the beach and nearby tributaries, including Berger Ditch- (east end of beach), and Tobias- and McHenry Ditches (west end), were analyzed for (i) E. coli density, and (ii) the genetic structure of whole E. coli communities assessed by PCR-denaturing gradient gel electrophoresis (DGGE) of the beta-glucuronidase gene (uidA). Since this study represented the initial use of DGGE fingerprinting for bacterial source tracking, BOX-PCR, an established library-dependent method, was used to validate the results of DGGE analysis. The results showed that E. coli density and community structure in Lake Erie Beach and the three ditches were dynamic and seasonally variable during the year-long sampling period. The weak correlation between E. coli density in the ditches and the beach water demonstrated that monitoring bacterial densities is limited in its utility for bacterial source tracking and is best combined with complimentary methods. Community structure analysis as assessed by DGGE effectively described the relationship of E. coli communities in the ditches and the beach. While the results suggested that all three ditches sampled were involved in the bacterial pollution at some time, the contribution was likely seasonally-based. Tobias Ditch, in particular, was highly rainfall dependent, while Berger Ditch was the most consistent contributor of the three ditches. BOX-PCR of E. coli libraries validated the results of DGGE analysis, indicating that DGGE was a reliable method for rapidly screening the putative geographic sources of bacterial pollution in Lake Erie Beach.