The direct discharge of untreated human fecal pollution from diffuse sources can pose a serious health risk in recreational, drinking reservoir, irrigation, and aquaculture waters. Diffuse human fecal pollution can originate from a variety of sources such as leaky or damaged sewer lines, faulty septic systems, illicit waste disposal, and sanitary/combined sewer overflows. Evidence-based water safety management planning for diffuse fecal pollution typically relies on measurements of general fecal indicator bacteria (FIB), namely E. coli and enterococci providing an estimate of the concentration from all animal sources present in the area of interest. Because many impaired waters are polluted by more than one animal source and FIB do cannot discriminate between pollution types, safety planning can be limited when relying solely on FIB measurements. Microbial source tracking (MST) can help discriminate between pollution sources to identify diffuse human fecal pollution. In this case study, human-associated MST methods are combined with low-order headwatershed sampling, precipitation information, and high-resolution geographic information land use data to identify diffuse sources of human fecal pollution.
This study was conducted in nine headwatersheds of the East Fork Watershed (EFW) situated in southeast Ohio, USA. Fecal pollution in the EFW headwatersheds is a chronic problem year round with FIB densities significantly increasing after wet weather events. Headwatersheds vary in size and land use intensity from densely forested to suburban with residential human waste management practices including septic systems and sanitary sewer lines.
Due to limitations of FIB, it remains unclear whether fecal pollution in EFW headwaters originates from human waste management practices (sewer lines and/or septic systems) or other sources such as local wildlife. To characterize the presence of diffuse human fecal pollution, nine headwatersheds were sampled representing a gradient of human waste management practices (septic density of 0 to 89.4 counts/km2) using local hydrology and high-resolution geographic information land use mapping. MST measurements of human-associated genetic markers were then grouped by wet and dry weather conditions followed by correlation analysis to identify trends in diffuse human fecal pollution.
The interdisciplinary strategy used in this study successfully identified septic system density during wet weather events as the likely source of diffuse human fecal pollution. In contrast, paired measurements of FIB did not correlate with septic density suggesting that chronic fecal pollution in EFW is not from human sources. Together these findings provide valuable pollution-source targeted information for water safety management planning to help improve water quality in the EFW.
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