This study deals with mechanism of water quality formation in rivers and lake waters in the drainage basin of Lake Chuzenji. Water samples were collected at 15 stations in 9 lakes, 14 in 7 rivers and 16 in springs or wells from April 1983 to November 1984 (Figs. 1 and 2).
Chemical analyses of the main inorganic constituents dissolved in the water samples collected revealed that surface and underground waters in this region are generally low in dissolved chemical constituents, except for the hot springs on the northern shore of Yunoko (U-3), two springs along Yukawa (U-12, U-13) and Jigokugawa (U-11) (Fig. 4). Most waters belong to Ca·HCO3 type. The water quality of Yunoko is controlled by the qualities of the spring and hot spring waters on the shore of the lake. Jigokugawa (Hell River) has higher concentrations not only in main constituents but also in minor PO4-P and NO3-N than other waters in this region except for the hot spring water. The high concentrations of the main constituents seem to originate from dissolution of volcanic rocks.
Table 6 shows that the water quality calculated theoretically from chemical loads which are brought into Lake Chuzenji through rivers and precipitation shows a good agreement with the measured water quality of the lake water except soluble silica. Soluble silica becomes insoluble due to the biological activity of diatom.
