著者

東田 盛善 佐竹 洋 渡久山 章

出版者

日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.35, no.1, pp.27-41, 2001

被引用文献数

6

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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_CO2 of spring waters is 10^-2.3 to 10^1.1 atm. These high P_CO2 are probably caused by a large supply and fast decomposition of litter, owing to the climatic characteristics of the island. High concentrations of Ca²⁺ and HCO₃^- in spring waters may be caused by the reaction of limestone with CO₂. High concentrations of SO₄^2-, HCO₃^- and excess Na⁺ (Na⁺ of non sea water origin) are found in spring waters from the southern area. These Ca-SO₄・HCO₃ 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 NO₃^--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 δ¹⁸O 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-8δ¹⁸O) 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.

著者

東田 盛善 隈田 昌良 佐竹 洋

出版者

一般社団法人日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.40, no.3, pp.111-123, 2006-08-25 (Released:2017-01-26)

参考文献数

30

被引用文献数

2

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One hundred and eight samples of daily precipitation on Ishigaki Island were collected from Dec. 4, 1997 to Dec. 5, 1998 and were analysed for chemical and isotopic compositions. δD and δ18O values of daily precipitation ranged from -82 to 11‰ and -12.1 to -0.5‰, respectively. These values were higher in winter than in summer. The d value (d=δD-8δ18O) ranged from 7 to 35 and showed seasonal variation in which it was high in winter and low in summer. This indicated that precipitation of the winter season on Ishigaki Island is derived from the continental cold airmass. Amount effects of precipitation on isotopic composition were observed throughout the year. Furthermore two trends of amount effects were observed in summer. High concentrations of chemical components were found in precipitation with high wind velocity caused by typhoons and the seasonal winds in winter on Ishigaki Island. In particular, the typhoons significantly increased the concentration of chemical components. Annual average of Cl- concentration was nearly equal to the Cl- concentration in winter precipitation along the Sea of Japan side on Honshu Island, and the annual deposition rate of NaCl was about 7 times larger than the national average. The calcium ion of non sea salt origin in precipitation is probably supplied through the dust containing CaCO3 from the limestone-rich soil of Ishigaki Island and NH4+ by chemical fertilizers used in the island. The annual average value of the NO3-/nss SO42- ratio, 0.64, was twice as larger as the ratio of Tokyo (0.35). It may be caused by photochemical reaction forming nitric acid in Ishigaki Island under the strong insolation of the subtropical climate. High concentrations and large deposition rates of nss SO42- were observed in fall to winter, when d values of precipitation were high. The ratio of NO3-/nss SO42- was observed to be low in winter on Ishigaki Island. This indicated that the sulfuric acid was transported from the Asian Continent to Ishigaki Island by the continental cold airmass. The pH ranges from 4.1 to 6.9 and its annual mean was 5.4. This mean value of pH was higher than those of Honshu Island (e.g., Tokyo 4.7). Nss Ca2+/NH4+ ratio, 1.7, was much higher than those of Honshu Island (e.g., Tokyo 0.33). This suggests that nss Ca2+ is main acid neutralizer rather than NH4+. This result reflects the environmental characteristics of Ishigaki Island which is covered with limestone-rich soil.

著者

東田 盛善 佐竹 洋 張 勁

出版者

Japan Radioisotope Association

雑誌

RADIOISOTOPES (ISSN:00338303)

巻号頁・発行日

vol.60, no.5, pp.203-213, 2011

被引用文献数

2

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南西諸島の13島(種子島,屋久島,中之島,奄美大島,徳之島,沖永良部島,与論島,沖縄島,久米島,宮古島,石垣島,波照間島および与那国島;24°N~30°N)の地下水試料(134)と一月毎に採水した石垣島於茂登トンネル湧水の同位体組成を測定した。それらの島々の地下水のδDおよびδ<SUP>18</SUP>O値の平均値は-31~-20‰および-5.8~-4.5‰の範囲にあり,その値は緯度が高くなるにつれて減少した。δ<SUP>18</SUP>Oについての緯度効果は-0.14‰/N(deg.)と推定された。南西諸島地下水のδ<SUP>18</SUP>Oについての緯度効果は,本州よりも小さかったが,それは南西諸島に降水をもたらす気団に亜熱帯海域に起源を持つ水蒸気が持続的に補給されているためである。δ<SUP>18</SUP>Oについての温度効果は0.20‰/℃と推定された。また,採水高度によって求めたδ<SUP>18</SUP>Oについての高度効果は,九州最高峰の宮之浦岳(1935m)を擁する屋久島において0.10‰/100mであった。一月毎に採水された石垣島於茂登トンネル湧水のδDおよびδ<SUP>18</SUP>O値は,観測期間にはほとんど一定であったが,降水が地下水面に浸透する間によく混合されているためだと思われる。南西諸島の夏季降水のd値はほとんど同じ(約10)であるが,冬季には北部に位置する種子島,屋久島および中之島のその値(>25)は,それら以南の島々の値(<22)に比べて高くなることが推定された。