白駒池堆積物から推定される古環境  [in Japanese] Paleoenvironment inferred from a sediment core of Lake Shirakoma  [in Japanese]

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Abstract

白駒池は,山岳域(標高2115m)の貧栄養―腐植栄養湖である。本研究では,白駒池の水深8m地点で採取した94cmの柱状堆積物試料を有機地球化学的に解析し,白駒池の古環境変遷を復元した。<SUP>14</SUP>C年代測定の結果,平均堆積速度は0.21mmy<SUP>-1</SUP>であった。堆積物の層相から有機質泥層(コア深度0-47cm)は湖での堆積物,泥炭質層(47-70cm)は水深の浅い移行期での堆積物,植物遺骸を多く含む泥炭層(70cm以深)は湿原での堆積物と考えられた。したがって,湿原から移行期を経て,約2200年前に白駒池が形成されたと推定した。C/N原子比と4α,23, 24-trimethyl-5α-cholest-22-en-3β-o1の変動から湖形成初期には,水深が浅く,内部生産が大きかったと推定した。有機質泥層には,過去2200年間の古気候変動を反映していると考えられる脂質成分が残されていた。また,堆積物中には,dehydroabietaneと18-norabieta-8, 11, 13-trieneが含まれていた。これらのアビエチン骨格をもつ化合物は,流入河川の懸濁物で検出され,針葉樹を主体とする流域の古植生を復元するのに役立つ分子指標となるかもしれない。

This study attempts to reconstruct the paleoenvironment of Lake Shirakoma, an oligotrophic-dystrophic lake located at high altitude (2115 m) in central Japan, based on the chemical analyses of a sediment core. A 94 cm core was taken in the center of L. Shirakoma at a water depth of 8m. The radiocarbon dating indicates that the average sedimentation rate is 0.21 mm y<SUP>-1</SUP>. According to the observation of sediment facies, 0-47 cm depth is regarded as organic-rich mud, 47-70 cm as peat mud and below 70 cm as peat. The bottom peat layers containing much plant debris indicates that the former stage of this lake should be wetland, which was far shallower than the present state. The fact means that L. Shirakoma was formed 2200 years ago from a wetland. In the transition stage from a wetland to a lake, the water depth might be shallow and the in-lake productivity in water might be high, because of lower C/N atomic ratio and higher 4α, 23, 24-trimethyl-5α-cholest-22-en-3β-ol concentration at the layers. On the other hand, there are a few molecules indicative of land-plant inputs during the past 2200 years. Dehydroabietane and 18-norabieta-8, 11, 13-triene are detected both in an extant inflow stream and in the sediment from L. Shirakoma. Those abietane compounds may provide a tool to estimate the paleovegetation in the catchments.

Journal

  • Japanese Journal of Limnology (Rikusuigaku Zasshi)

    Japanese Journal of Limnology (Rikusuigaku Zasshi) 66(2), 81-92, 2005

    The Japanese Society of Limnology

Codes

  • NII Article ID (NAID)
    130003645178
  • Text Lang
    JPN
  • ISSN
    0021-5104
  • Data Source
    J-STAGE 
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