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Analytical Methods


Identifying sources of fecal contamination in a watershed is important for implementing appropriate remedial and control strategies and understanding human health risk of the water’s use. It is generally accepted that it is best to take a multi-tiered approach on source tracking (Boehm and others, 2003; Francy and others, 2006), moving from general to specific and from less to more expensive (Field and Samadpour, 2007). Steps to identify sources include (1) sanitary surveys, (2) determining distributions of bacterial indicators in the watershed, (3) understanding how hydrologic and meteorological processes affect these distributions, (4) identifying hot spots of fecal contamination, and (5) identifying the presence of specific pathogens or chemical contaminants and applying microbial source tracking (MST) techniques.

A wide range of techniques are available in the emerging field of MST to help identify sources of fecal contamination. Which methods are chosen for a study depend on the study objectives, the number of potential contamination sources, and the funds available; most often, multiple source tracking tools are needed. At the present time, the OWML routinely analyzes samples for MST markers and for pathogens. The USGS National Water Quality Laboratory analyzes samples for wastewater chemicals that can augment MST sampling efforts. All of these are part of the source tracking toolbox.

Microbial source tracking (MST) is a term used for the process of identifying the source of fecal contamination in the environment. MST techniques are based on the concept that various warm-blooded animal intestinal systems have different selective pressures caused by differences in diet and physiology that select for specific microbial populations. MST attempts to categorize the microbial populations by host animal through identifying some unique genetic (DNA sequence) or phenotypic (observable characteristic or expression, such as antibiotic resistance) trait. Despite some initial success using MST techniques, most of the methods are still experimental (Griffith and others, 2003) and no single MST method is ideal (Field and Samadpour, 2007).


Microbial Source Tracking Markers

Pathogens and Chemicals

References for Source Tracking Tools