Paleolimnological investigation of recent acidity changes in Sawanoike Pond, Kyoto, Japan |
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| Authors: | Shunnichi Yoshikawa Shigeo Yamaguchi Akio Hata |
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| Institution: | (1) Kyoto City Institute of Public Health and Environmental Sciences, 1-2 Mibu higashitakada-cho Nakagyo-ku, Kyoto, 604-8845, Japan;(2) Kyoto City Institute of Public Health and Environmental Sciences, 1-2 Mibu higashitakada-cho Nakagyo-ku, Kyoto, 604-8845, Japan;(3) Faculty of Business, Osaka City University, 3-138 Sugimoto 3-chome, Sumiyoshi-ku, Osaka, 558, Japan |
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| Abstract: | Sawanoike Pond, an artificial reservoir constructed ca. 150 yrs. ago, lies in an area geologically sensitive to acidification and contains water that is presently weakly acidic (pH 5.5; alkalinity 15  eq 1-1). Sediments from a core obtained from the northern part and a core from the central part of the pond were analyzed for organic matter, total organic carbon, total nitrogen, natural and artificial radionuclides, pollen, diatoms, metals and spheroidal carbonaceous particles. A peaty silt layer at the bottom of the central core was replaced by a silt layer initially rich in humic substances, but became more mineral-rich near the surface. Although most of the dominant diatoms throughout the cores were acidophilous taxa, some acidobiontic species increased moderately in abundance after the middle 1960's. Diatom-inferred pH values for the northern core are relatively low before about 1930, then increase, reaching a maximum level between the 1930's and the late 1940's. They then decrease to the surface and reach minimum level during the middle 1980's. Diatom-inferred pH declined by 0.4-0.5 units in the northern core and 0.2-0.3 units in the central core since ca. 1910, when vegetation around the shore changed to a community similar to that of recent years. An increase in labile Pb, Zn, Cd and spheroidal carbonaceous particles, indicative of atmospheric deposition of fossil fuel combustion by-products, preceded the decline in inferred pH. The inferred pH decline of the pond could be an acidification due to acidic precipitation caused by fossil fuel combustion. |
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| Keywords: | paleolimnology acidification sediment chemistry diatoms metals spheroidal carbonaceous particles pollen radionuclides Japan |
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