Relationship between the Water Quality of River Waters Flowing into Lake Biwa and the Geological Environment of the Riverheads.

Concentrations of eight major inorganic components (Ca2+, Mg2+, Na+, K+, Cl-, SO42-, SiO2 and HCO3-) were measured in water samples from 22 rivers flowing into Lake Biwa. The water quality of these river waters is discussed in relation to the geological environment around their riverhead. The riverhead environment around Lake Biwa was geologically divided into four areas such as granite-, Ko-biwako-, slate- and limestone area.The amounts of the inorganic components in the river water samples from the four areas decreased in the following order: limestone-> Ko-biwako-> granite-> slate area. The proportion of each component seemed to reflect the geological features of the riverheads: Ca2+ and HCO3- were dominant in the limestone group; SO42- in the Ko- biwako group; Na+ and SiO2 in the granite group, and Mg2+ and Cl- in the slate group.