Effect of Hydrogeochemical Properties of Watersheds on Inland Water Acidification -Comparison of Acid-neutralization Due to Chemical Weathering between Acidified and Non-acidified Watersheds-

摘要

In future, freshwaters in Japan are likely to become acidified by increasing acid deposition in eastern Asia. In order to predict the long-term acidification of freshwaters, it is necessary to evaluate acid neutralization mechanism in Japanese watersheds. In this paper, an estimation method for acid-neutralization by chemical weathering is proposed, and applied to acidified and non-acidified watersheds in order to compare acid -neutralization mechanism. The principal results are : (1) Japanese non-acidified watersheds receive approximately the same amount of acidic deposition as an acidified watershed in U.S.A.. (2) In Japanese non-acidified watersheds, acid deposition is neutralized by chemical weather- ing of primary minerals. On the other hand, in the acidified watershed, chemical weathering ~ rates of primary minerals are much smaller than those in Japanese non--acidified watersheds. Therefore, acid deposition is not neutralized in this watershed. (3) Typical properties of watersheds vulnerable to acidification are: 1 ) Dominant primary minerals in soil and bedrock are stable against acid deposition. 2 ) Soil thickness (weathering zone) is relatively small. 3 ) The ratio of chemical weathering ratio to acidic deposition is relatively small.