Metal ion variations from rainfall to stream in a small catchment covered by degraded soil in the Setouchi region [Japan]
2002
Onodera, S. (Hiroshima Univ. (Japan)) | Fujisaki, C. | Naruoka, T. | Birmano, M.D.
In order to clarify the effect of acid rain on the stream water chemistry of mountainous catchments covered by degraded soil in the Setouchi region, we collected water samples of rainfall, soil water, groundwater, spring water and river water as well as making runoff observations in a small experimental catchment located in Takahara city of eastern Hiroshima. The results are summarized as follows: 1) the exchangeable base cation content in soil was extremely low; 2) the strong acid in rainwater was buffered in surface soil by an ion exchange process between base cations and Al**3+. After the infiltration of rainfall, pH of water increased. However, the Al concentration in the surface soil indicates soil acidifications; 3) metal ion in the stream water was composed of base cations except for rainfall periods. On the other hand, Al concentration in the stream water increased, and base cation concentration decreased with the rise in stream discharge during rainfall events; 4) H**+ concentration was higher at the spring point than farther downstream. Al concentration also showed the same trend as H**+, suggesting a greater contribution of groundwater with high pH to the lower stream and acid neutralization by dilution. On the other hand, the increase in Al concentration in stream water during rainfall events indicates acidification by a discharge of acid subsurface water through the surface soil.
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