2025 Volume 48 Pages 1-10
In this study, we examined the confirmation and characteristics of fecal contamination by measuring the coliform and Escherichia coli (E. coli) counts in the Kinki region’s water bodies. In Lake Biwa, categorized as type AA, many points exceeded environmental standards under the old standard using coliform groups, but the counts were below the standard values under the new standard using E. coli. In rivers, a positive correlation was observed between the old and new standards for each type, but the E. coli counts in type A rivers were widely distributed compared with those in type B and C rivers. Furthermore, a detailed investigation at the location of Miyamaebashi Bridge in the Katsura River suggested that E. coli from sewage treatment plant effluent impacted water quality. E. coli survival rates significantly decreased after 2-3 days at water temperatures of 20 ℃ and 30 ℃, but 73-85% survival was observed at 5 ℃ even on the third day, confirming that upstream E. coli loads can affect downstream E. coli concentrations at low water temperatures. Predictions of E. coli concentrations from pollution sources to downstream locations closely matched observed values. Thus, it was revealed that under normal river flow and weather conditions, areas far from pollution sources could still be affected.
