Chemical Investigation of Natural Waters in Oku-Nikko, Central Honshu

In the Oku-Nikko area, 65 water samples were collected from 29 stations from May 1977 to May 1980 in order to determine the mineral components, and the following results were obtained : (1) The spring waters along the Jigoku-zawa Valley (stns. 1-6) and the ground water at the dormitory of the Utsunomiya University experimental farm (16) were similar in their principal components, suggesting that they might have originated from the same strata of ground water. (2) The two springs (22 and 23) at the Yukawa River side and the Izumikado Pond side seem to flow out from the same source. They have a high mineral content, increasing the chemical constituents of the Yukawa River and causing brook trout (Salvelinus fontinalis) to avoid the stream. (3) In general, the dissolved mineral contents ranged from a state as diluted (stn. 11) as pure rain water to high concentrations (stns. 22, 23). (4) Using the Piper diagram, water types were studied. Among the 29 stations, 13 were found to have calcium-bicarbonate type, that is the normal quality of water. The chemical nature of Lake Chuzenji was found to be in about the center, or an average of the three rivers Yukawa, Jigoku and Yanagi, that feed the lake. (5) The silica content of the Jigoku-zawa (1-6) which originates in the volcanic Mt. Nantai, showed values as high as those of other rivers running through volcanic areas of Japan. However, the silica concentration in Lake Chuzenji was found to be markedly less than that of the rivers that feed it. The same remarkable phenomenon is observed in Lake Biwa.