Estimation of the Sources of Fecal Coliform Pollution in the Tokoro River Basin Based on a Water System Exposure Analysis Model Using Published Values

The Tokoro River Basin is characterized by relatively small discharge amounts that reflect contaminant infiltration to the contaminant concentration more directly than rivers with large discharge amounts. In this study, the population of fecal coliform, an indicator species of fecal contamination level, was modeled using data of water quality and geographical information analysis of the Tokoro River. The contamination load by source differed according to various factors, including the size of utilized land areas, number of rearing livestock according to each dairy farm, and population density of the relevant areas; specifically, the contamination loads were estimated as 8.1 × 1010–9.8 × 1011 km−2 year−1, 2.1 × 1011 km−2 year−1, 1.3 × 1012–4.4 × 1013 stable−1 year−1, 4.2 × 1010–1.7 × 1013 km−2 year−1, and 5.4 × 1010–3.3 × 1011 km−2 year−1 for the forest and mountain sources, farmland (manure) source, livestock source, urban area source, and human residential areas, respectively. These values were imported to the water exposure analysis model, AIST-Standardized Hydrology-based AssessmeNt tool for chemical Exposure Load (AIST- SHANEL), and the relevant coefficients of determination of the fecal coliform contamination loads were successfully evaluated according to the contamination source.