A geochemical investigation of the Shira-kawa River

Abstract

The Shira-kawa River is one of the most important tributaries in the upper reaches of the Mogami River. This drainage system starts from Mt. Iide and is jointed by the Matsu-kawa River at Toyoda, Nagai City. In this paper, the geochemical features of the river are reported. The results are summarized as follows :
1. As for the water quality of the whole drainage system, samples taken from various stations show neutral reaction and, on the whole, they are poor in dissolved substances.
2. So far as the water quality of the trunk river is concerned, the chemical oxygen demand and the contents of chloride, sulfate and silicate ions increase with the increase of distance from its origin.
3. After joined by the Koshira-kawa River and the Hagiu-gawa River, the water quality of the main stream undergoes an abrupt change.
4. The examination of the analysed data at the Toyoda station revealed a linear relationship between calcium ion and each of chloride ion and bicarbonate ion. Regarding dissolved iron and silicate ion, the concentration peak occurs in April coincident with rapid thaws at the same observing station. Such is not the case with other mineral contents.