POLLUTION-BIOLOGICAL STUDIES OF THE RIVER TOKORO-GAWA, HOKKAIDO

Abstract

To assess the degree of water pollution in the Tokoro River, Kitami, Hokkaido, the benthic micro-organisms were studied and discussed according to the saprobic system. The river rises from Mt. Ishikari-dake and flows down through the Kitami Plain to the Okhotsk Sea. Samples were taken at seven stations in the lower half of the river in August, 1960 (see Fig. 1). Examining the predominant species found in each station and their status in the saprobic system, it is indicated that the river is rather clear and may belong to β-mesosaprobic waters (Table 1). The water is, however, contaminated considerably at Wakamatsu-bashi, Kitami City, where the waste water of palp mill flows in. The β-polysaprobic species become predominant in this station. The water quality recovers gradually to the α-or β-mesosaprobic level at the station Chushi-bashi, about 15km below Kitami City. Downstream, the stream maintains its β-mesosaprobic status until it flows into the sea. A map showing the degree of water pollution in various parts of the river was drawn from the data obtained in this study (Fig. 2).