Abstract
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 weathering 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.
