Microbial Source Tracking for Bathing Water Quality Assessment: E. coli and Bacterial Communities in Coastal Environment

Microbial contamination in coastal environments and groundwater is explored within this thesis, focusing onfecal contamination from anthropogenic sources and microbial community dynamics. The spread andpersistence of microbial contaminants in complex aquatic environments with multiple intermittent and pointsources of contamination, was studied in order to lay a groundwork for developing more robust monitoringframework of water quality.A combination of molecular methods, chemical analyses, and classical microbiological techniques wasutilized to study several different sites. In the first study, remediation strategies performed in a sitecontaminated with chlorinated solvents were evaluated. Chemical monitoring, compound-specific isotopeanalysis, and 16S rRNA gene sequencing were performed to assess remediation effectiveness and microbialcommunity shifts during biotic and abiotic degradation of contaminants. Subsequent studies were performedin an urban coastal environment, where sediment and water microbial communities were investigated witha particular focus on fecal indicator bacteria (Escherichia coli and intestinal enterococci) and other sewageassociatedtaxa. Results indicate that sediments can act as reservoirs for E. coli, and that fecal indicatorbacteria monitoring could benefit from introduction of additional bacterial groups as sewage indicatorbacteria. Phenotypic and genotypic characterization of sediment-associated E. coli further revealedadaptations that may facilitate survival in marine sediments, including virulence factors, biofilm formation,and halotolerance. In a longitudinal study of sediment microbial communities, it was found that treatedeffluent from a wastewater treatment plant was a significant source of both E. coli and sewage-associatedtaxa, while combined sewer overflows caused a more localized and transient effect on the microbialcommunity. Additionally, the presence of sewage-associated taxa in sediments distant from knowndischarge points suggested contribution from intermittent sources, such as stormwater. Analysis of microbialcommunities in urban bathing water revealed that the microbial communities are influenced by environmentalparameters such as temperature and rainfall, and that sewage- and gut-associated bacterial groups havecomplex spatial and temporal distribution. While the fecal and sewage indicator bacteria could be connectedto environmental parameters and anthropogenic influences to some degree, spatial sensitivity was very high.E. coli was found to be an incomplete indicator of anthropogenic impact on coastal waters.Overall, this thesis highlights the importance of combining microbial community analysis, source tracking,and environmental data to achieve a more nuanced understanding of microbial contamination in aquaticenvironments. The results contribute to the development of more effective monitoring and managementstrategies for protecting water quality and public health in urban coastal areas.