Water quality in the upper reaches of the Akaya River, a tributary of the Tone River

Abstract

The Tone River is a first-class river originating in the Mikuni Mountains on the border between Niigata and Gunma prefectures and flowing into the Pacific Ocean and Tokyo Bay. With a basin area of 16,840 km², it is the largest river in Japan and plays a major role in flood control, the environment, and water utilization in the Tokyo metropolitan area. The Akaya River has its headwaters near Mt. Hirabesan (elevation 1984 m), one of the Mikuni Mountains, and joins the Tone River near Shimotsu, Minakami-cho, Tone-gun, Gunma Prefecture. The headwaters of the Akaya River are known to retain a rich natural environment and possess a valuable ecosystem, with national institutions and local communities working together to conserve and restore biodiversity1). In this study, a water quality survey was conducted in the upper reaches of the Akaya River, a tributary of the Tone River, where a valuable ecosystem remains in the headwaters, in an attempt to understand the basic water environment of the river water.