Comparison of acid neutralization by chemical weathering between acidified and non-acidified watersheds

In eastern Asia, emission of acid materials and acid deposition will increase with industrialization in future, and freshwaters in Japan are likely to become acidified. In this article, an evaluation method for acid-neutralization by chemical weathering was applied to one acidified watershed in U.S.A. and three non-acidified watersheds in Japan, and effect of hydrogeochemical properties on chemical weathering and stream water chemistry was discussed. In three non-acidified watersheds in Japan, areal chemical weathering rates of primary minerals are much larger than those observed in U.S.A. Watersheds in both countries show no difference in mineralogy, while the soil thickness (weathered profile) in watersheds is contrastive between acidified and non-acidified watersheds. Therefore, it is concluded that acidity is neutralized by chemical weathering of primary minerals in thick weathered profiles in Japanese watershed. In non-acidified Japanese watersheds which has the smallest acid-neutralization capacity in three observed watersheds, stream water will not acidify even if the acid deposition increases as much as two or three times the observed level. From the viewpoint of Japan's nationwide streamwater chemistry, more than 90% of the watersheds have far greater acid-neutralization capacities than this watershed, and will not be acidified even in cases where the acid deposition increase as much as two or three fold.