Study of river water chemistry and effect of acid deposition at two mountainous Two catchments of the Toyama-sawa and Goshiki-sawa Rivers in Oku-nikko

DOI Web Site 26 References
  • IIZUMI Yoshiko
    Environmental Science, Science of Resources and Environment, United Graduate Shool of Agricultural Science, Tokyo University of Agriculture and Technology
  • YOKOYAMA Hideya
    Department of International Environmental and Agricultural Science, Graduate School of Agriculture, Tokyo University of Agriculture and Technology
  • OGURA Norio
    Department of International Environmental and Agricultural Science, Graduate School of Agriculture, Tokyo University of Agriculture and Technology Professor Emeritus of Tokyo University of Agriculture and Technology

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Other Title
  • 奥日光山岳河川（外山沢・五色沢）における水質特性と酸性沈着の影響評価
  • オクニッコウ サンガク カセン トヤマ サワ ゴ シキサワ ニ オケル スイシツ トクセイ ト サンセイ チンチャク ノ エイキョウ ヒョウカ

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The present studies were carried out in order to explore the current status of river and ground waters quality and to evaluate effect of acid deposition at two watersheds of the Toyama-sawa and Gosiki-sawa Rivers in Oku-nikko from August 2000 to October 2001.<BR>The results showed that increase in the ionic concentrations of Na+, Mg2+ and Ca2+ of river water and groundwater tend to occur during the winter season (from December to February) in the Toyama-sawa River catchment. It was considered that the concentrations of ionic components derived from soil and rock increased because the infiltration amounts of meteoric water decreased as a result of snow cover. The decreases in Na+, Mg2+ and Ca2+ in river water and groundwater of the Toyama-sawa and Goshiki-sawa were related to melted snow and/or heavy rain.<BR>It is considered that almost all Cl- in river water and groundwater was deposited from the atmosphere. With this premise in mind, we compared the water quality of the two rivers and groundwater with precipitation using an equivalent the ratio of SO42-/Cl- and NO3-/Cl-. Our results showed that the ratio of SO42-/Cl- in the Toyama-sawa was similar to that in the precipitation data, whereas that ratio in the Goshiki-sawa was much higher. It is assumed that the high concentration of SO42- in the Goshiki-sawa was caused by volcanic activity. In contrast, the ratio of NO3-/Cl- in the Goshiki-sawa showed values similar to those in the precipitation data. However, this ratio in the Toyama-sawa was higher than that in the deposition data. In particular, the values of groundwater and soil extraction were higher than those of precipitation. These results suggest the possibility that the Toyama-sawa watershed is in the second stage of nitrogen saturation as defined by Aber et al. (1989).

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