沖縄島の湧水と河川水の化学的特徴と同位体組成  [in Japanese] Chemical characteristics and isotopic compositions of spring and river waters in Okinawa Island  [in Japanese]

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Author(s)

    • 佐竹 洋 SATAKE Hiroshi
    • 富山大学理学部生物圏環境科学科 Department of Environmental Chemistry and Biology, Toyama University
    • 渡久山 章 TOKUYAMA Akira
    • 琉球大学理学部海洋自然科学科 Department of Chemistry, Biology, and Marine Science, College of Science, University of the Ryukyus

Abstract

Spring waters from limestone terrains of the southern area of Okinawa Island have been analysed for chemical and isotopic compositions. The isotopic compositions of river waters from the central and northern areas of the island have also been measured. Spring and river water samples were collected during the following periods: spring waters from April 26th to June 28th, river waters June 1 st and 2nd, and July 20, 21 and 22, 1996, respectively. P<sub>CO2</sub> of spring waters is 10<sup>-2.3</sup> to 10<sup>1.1</sup> atm. These high P<sub>CO2</sub> are probably caused by a large supply and fast decomposition of litter, owing to the climatic characteristics of the island. High concentrations of Ca<sup>2+</sup> and HCO<sub>3</sub><sup>-</sup> in spring waters may be caused by the reaction of limestone with CO<sub>2</sub>. High concentrations of SO<sub>4</sub><sup>2-</sup>, HCO<sub>3</sub><sup>-</sup> and excess Na<sup>+</sup> (Na<sup>+</sup> of non sea water origin) are found in spring waters from the southern area. These Ca-SO<sub>4</sub>・HCO<sub>3</sub> type spring waters are possibly formed by oxidation of pyrite occurring in the bedrock (Shimajiri Group). Equilibrium relationships among the spring water, feldspar, and clay mineral suggest that spring waters may be equilibrated with kaolinite. The NO<sub>3</sub><sup>-</sup>-N content of spring waters has been increased by contamination with chemical fertilizers and waste waters from domestic areas. The increment is striking in the central areas, comparing with data of 1987. Values of δD and δ<sup>18</sup>O for spring and river waters are -36 to -18‰ and -5.6 to -3.3‰, respectively. These values are almost the same with those of groundwaters in Hateruma and Yonaguni Islands, located about 2° south of Okinawa Island. This is probably due to that the water vapor in these areas are mainly recharged from the sea around the islands. The d-parameter (d=δD-8δ<sup>18</sup>O) of spring and river waters ranges from 2.8 to 13.4 with an average of 8.6. This indicates that these waters are mainly recharged with precipitations from the Pacific Ocean airmass in summer.

Journal

  • Chikyukagaku

    Chikyukagaku 35(1), 27-41, 2001

    The Geochemical Society of Japan

References:  49

Cited by:  6

Codes

  • NII Article ID (NAID)
    110008680015
  • NII NACSIS-CAT ID (NCID)
    AN00141280
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    0386-4073
  • NDL Article ID
    5711955
  • NDL Source Classification
    ZM41(科学技術--地球科学)
  • NDL Call No.
    Z15-645
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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