Application of the Bacteria Decision-Support Tool in the Hillsborough River Watershed
The methodologies consist of three main parts, that when combined, comprise the Decision-Support Tool. The tool was developed to facilitate the identification of bacterial sources and the implementation of bacterial total maximum daily loads (TMDLs). The over arching strategy is based on the “Annapolis protocol” recommended by the World Health Organization (WHO) (2003) and the “phased monitoring approach” recommended by the National Research Council (NRC) (2004) to address elevated bacterial levels in recreational waters. The WHO (2003) and NRC (2004) strategies recognize that the use of water quality indicator organisms (IOs), such as fecal coliforms E. coli, and enterococci to assess water quality and predict human health risk, is confounded by many variables. A weight-of-evidence approach is therefore recommended to compensate for the uncertainty associated with the various tests and observations currently used by regulatory agencies. The overall approach described here uses a combination of information: (a) bacterial IO data to target specific locations with likely fecal contamination; (b) site-specific field surveys to identify the sources of contamination and assess them based on their potential risk of infection to humans; and (c) microbial source tracking (MST) to detect source-specific microbes to assist in the prioritization and implementation of management actions to address bacteriological water quality impairments.
1. Microbial Water Quality Assessment. The first step of the Decision-Support Tool prioritizes water bodies with known bacterial impairments at the basin (watershed) or sampling station level. This is accomplished by categorizing water quality conditions at each location based on IO concentrations (e.g., fecal coliforms) from existing monitoring data. This step focuses the investigation by prioritizing monitoring locations based on their respective microbial water quality assessment (MWQA) rating, resulting in a significant saving of time and money.
2. Contaminant Source Surveys. Once the MWQA has been used to prioritize impaired water bodies or specific sites within the basins, a weight-of-evidence approach is used to compile a comprehensive contaminant source survey (CSS) of the major potential bacteria sources within an impaired watershed. Relevant information may be collected through historical data analysis, field surveys, intensive one-on-one interviews with local stakeholders, public workshops, field reconnaissance, and, if necessary, microbial source tracking. The intensity of the CSS is based on the results from step 1 (MWQA classification). Since local stakeholders participate in all aspects of the survey, the results represent a strong consensus as to the most probable sources. Once potential sources are identified, management actions for removing the sources can be developed and initiated, or the parties involved can move to the next step of the Decision-Support Tool.
3. Water quality sampling, including advanced Microbial Source Tracking techniques. Due to the relatively large expense associated with Microbial Source Tracking (MST), the final component of the Decision-Support Tool is reserved for those watersheds with the highest MWQA and CSS results. Step 3 uses a decision tree-based approach to water quality sampling that is designed to build on the results of the CSS. To minimize cost and time, this approach uses lower-cost, more basic analytic methods first (e.g., the combined use of multiple indicator bacteria in surface waters and sediments), followed by higher-cost, more sophisticated methods (e.g., source-specific laboratory assays). Use of multiple MST methods increases the confidence in source identification and allows for more potential source-types to be investigated.
Upon completion of the contaminant source surveys and microbial source tracking (the second and third parts of the methodology), the tool is used to classify the level of impairment and to track the success of management actions in improving water quality over time.
In a recent study, library-independent MST methods based on PCR were used to detect specific sources of fecal contamination. Bacteroidales, an anaerobic bacterial group of fecal origin, is one of the target groups used to test for human-, ruminant-, and horse-specific contamination. Another PCR-based method used for detection of human contamination was the esp gene of Enterococcus faecium (Scott et al. 2004). Human polyomaviruses, which are nonpathogenic viruses shed in urine and feces, have high carrier rates in human populations and are ubiquitous in sewage. This PCR-based method has also been implemented as part of the “toolbox” of MST methods. As MST methods are continually being developed and validated, PBS&J works with local laboratories, including USF, to utilize the most current and cost-effective methods available. Quantitative PCR assays for human-specific sources have been implemented in more recent studies, and will provide the basis for more refined interpretation of MST results.
Keywords: Bacteroides; Enterococcus faecium; Escherichia coli; Hillsborough River; Indicator organism; basin management action plan; enterococci; fecal coliforms; human polyomavirus; microbial source tracking; total maximum daily load; water quality
Document Type: Research Article
Publication date: 2009-01-01
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