Abstract
Urbanization near aquatic habitats can result in the introduction of man-made pollutants flowing into basins, each with its sources, residence times, and effects on flora and fauna. One of the most notorious and widespread global pollutants is wastewater, either treated or untreated, into rivers and/or estuaries. A common method for gauging wastewater pollution and determining the relative risk of waterborne illness is quantifying fecal indicator bacteria (FIB) in water samples taken in routine monitoring strategies. Common FIB that are monitored include Escherichia coli and Enterococcus, both with differing survival times and persistence in aquatic environments while also sharing the fact they can both come from non-human sources; this limits their ability to determine if waterbodies have been impacted by wastewater and therefore limits their use in determining health-risks for human. This thesis sought to use additional methods, coupled with FIB quantification, to identify potential sources of FIB into three southwest Florida rivers (two separate studies) that have historically had high FIB counts. Using a combination of nutrient, stable isotope (d15N and d18O), and microbial community analyses paired with robust statistics helped uncover insights that simple FIB enumeration would likely have missed. This research found that the Estero River may have been impacted by many small drainage ditches contributing persistent FIB loading into the waterbody. In addition, both FIB showed different spatial and temporal patterns and sequencing data revealed a large impact of tides on microbial communities, indicating the importance of having multiple methods used in tandem to counter differing FIB sources.
In the other study, FIB were found to not have wastewater as their origin in either Spring Creek or the Imperial River. But Spring Creek, particularly after a large rainfall event, had the presence of Arcobacteraceae, a common bacterial family found in wastewater. This family showed a strong positive relationship with sucralose, total organic phosphorous, and d15N. In general, sucralose and d15N were enriched in Spring Creek and in the range of typical wastewater levels. This evidence pointed towards wastewater systems along that waterway, potentially septic systems, particularly after heavy rainfall. The Imperial River did not appear to have this wastewater impact and seemed to have a distinct microbial community when compared with the higher relative abundances of anaerobic bacteria in Spring Creek. This study also showed multiple lines of evidence pointing towards the substantial impact of flood tides on microbial communities and other water quality constituents, which should be accounted for in future studies of tropical tidally-influenced rivers.
In addition to these findings, the robust and ecological statistical methods used throughout this thesis will lead to more reproducible results from future studies on these rivers as well as provide useful estimates for future meta-analyses. An appendix details their distinctness from standard methodologies and some of their benefits for future researchers to employ.
