Abstract
We measured alkalinity and dissolved inorganic components in mountainous river waters located in western Aomori Prefecture to evaluate rock weathering during the ground water processes and run off. Surveyed rivers, Asai River and Biwata River, are small tributaries of the class A River Hirakawa and volcanic deposit and tuffaceous rock are the major geological feature of the drainage. We started the observation from January 2019, and 1 or 2 times of samplings per month have been continued so far. Increasing concentration gradients toward downstream were observed for major inorganic constituents throughout the year, suggesting the supplies from the river basin. Owing to the weathering of volcanic deposit, concentrations of dissolved silica in Asai and Biwata rivers are much higher than these in Hirakawa river main stream and rivers having drainage basin in adjacent mountainous area, Shirakami Mountains, which consists of old sedimentary rock. Sodium concentration ratio to sea salt calculated, under assumption that all chloride is originated from sea salt, was decreased in the snow melt season, because the sodium concentration ratio in the wet depositions is very close to the sea water. In the summer season, sodium concentration ratio increased. The increasing groundwater ratio to the total river flow and the promotion of silicate mineral weathering due to the increasing temperature are suggested.
