沖縄島米軍中部訓練場内における河川水の化学的研究  [in Japanese] Chemical study of river waters in U.S. military central training area of Okinawa Island  [in Japanese]

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Author(s)

    • 伊敷 牧 ISHIKI Maki
    • 琉球大学大学院理工学研究科 Graduate School of Engineering and Science, University of the Ryukyus

Abstract

沖縄島に置かれた米軍施設,中部訓練場(CTA)内河川水は水質汚濁が少なく,化学組成に関する基礎データの収集に適している。本研究では,CTA内河川水の溶存成分濃度を測定し,沖縄島の他地域と比較することによって,その化学像を明らかにすることを目的とした。<br> その結果,CTA内の河川水は沖縄島北部ケイ酸塩岩石地域(北部訓練場,NTA)の河川水と,沖縄島南部石灰岩地域の地下水との中間的な化学組成を持つことが明らかになった。これは沖縄島の地質を反映した結果だと考えられる。全溶存成分濃度(4.75 meq L<sup>-1</sup>)のうち,海塩起源が平均2.73 meq L<sup>-1</sup>であった。これは日本の河川水におけるその濃度の約7倍であった。ほとんどの河川で海塩起源濃度が全濃度の50%以上を占めていた。岩石の化学的風化反応式に基づいて計算した風化量はCTAとNTAでほぼ同じくらいであったが,そのうちのCaCO<sub>3</sub>溶解量には差があった。CTA内河川流域に存在する石灰岩の影響があることを示している。CTA内河川では,懸濁物流出量>粘土生成量の関係がみられ,森林土壌の損失やそれによる河川・海洋の汚染も問題である。

Many U.S.military bases are located in the central and northern parts of Okinawa Island. A study on the river waters in such military training areas has been difficult to conduct until now. However through the Legacy Project with University of Hawaii, the authors had the opportunity to collect water samples from the central training area (CTA) in the island. The CTA is uniquely situated to gathering data on the chemical composition of unpolluted river waters, since the forest in the CTA has been designated to supplying timber and water. The purpose of the present study is to determine the chemical characteristics of river waters in the CTA.<br> Our results showed that the chemical composition of river water in the CTA was intermediate between those of the groundwaters in limestone areas and the river waters in silicate rock areas of Okinawa Island. This finding reflects the overall geology of the CTA and of Okinawa Island. The total concentration of chemical components supplied from the ocean as sea spray was 2.73 meq L<sup>-1</sup>, which was about 7 times larger than that of average river water throughout Japan, and accounted for over 50% of the total concentration in the rivers. The total amount of rocks chemically weathered in the CTA was almost the same as that in the northern training area (NTA) of the U.S. military. However, the amount of dissolved CaCO<sub>3</sub> differed between the two areas due to the dissolution of limestone in the CTA. The fact that the amount of suspended sediment in the effluent was larger than the formed clay minerals in the CTA may cause serious environmental problems by eroding soil from the forest and polluting the river and ocean by the weathered soil such as red soils.

Journal

  • Japanese Journal of Limnology (Rikusuigaku Zasshi)

    Japanese Journal of Limnology (Rikusuigaku Zasshi) 68(1), 29-40, 2007

    The Japanese Society of Limnology

Codes

  • NII Article ID (NAID)
    130004511415
  • Text Lang
    JPN
  • ISSN
    0021-5104
  • Data Source
    J-STAGE 
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