倒流木の除去が河川地形および魚類生息場所におよぼす影響 Effects of experimental removal of woody debris on channel morphology and fish habitats

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著者

    • 阿部 俊夫 ABE Toshio
    • 北海道大学大学院農学研究科森林管理保全学講座 Department of Forest Science, Graduate School of Agriculture, Hokkaido University
    • 中村 太士 NAKAMURA Futoshi
    • 北海道大学大学院農学研究科森林管理保全学講座 Department of Forest Science, Graduate School of Agriculture, Hokkaido University

抄録

倒流木を実験的に除去し,河川地形と魚類生息への倒流木の影響を検証した.北海道北部の緩勾配山地河川に,除去区と対照区を設け,1993年秋に地形や生息場所特性,魚類生息密度を調査した後,除去区の倒流木を除去し,翌春と翌秋に再調査を行った.<BR>倒流木の除去後,土砂の堆積量は一時的に増加した.地形変化は,対照区では倒流木に,除去区では流路平面形状に規制される傾向にあった.淵の体積は減少せず,個数のみが減少した.カバー量は減少した.魚類生息密度は,サクラマス幼魚では明瞭に低下したが,底生性のフクドジョウでは変化は小さかった.<BR>緩勾配河川での倒流木除去は,砂礫堆発達と側方洗掘による淵再生をもたらし,淵体積の減少は生じにくいと考えられた.倒流木は,カバーと淵個数を増加させることで,サクラマス生息へ好影響を与えていると結論できた.今後の河川管理では,倒流木の河川生態学的価値も考慮する必要がある.

Experimental removal of coarse woody debris (CWD) was conducted in a low-gradient, second-order stream covered by deciduous riparian forest in northern Hokkaido, Japan. We examined channel morphology, habitat variables and fish densities in 2 study reaches (cleaned and control, 100 m length) during autumn (Sept.-Oct.) of 1993, spring (May - Jun.) and autumn (Sept. - Oct.) of 1994. Immediately after the first survey, CWD and other small organic materials within the cleaned reach were removed by hand or hand-winch. Aggraded areas in the cross-sections of the cleaned reach were larger than those of the control reach during the autumn of 1993 - spring 1994. Cross-sectional changes tended to correlate with channel variables, such as curvature and width, in the cleaned reach, and with CWD amounts in the control reach. After CWD removal, small pools associated with CWD disappeared and pool number decreased, but pool volume did not vary. Cover area decreased, but depth, velocity, and substrate did not change in the cleaned reach. Density of juvenile masu salmon (Oncorhynchus masou) declined rapidly, but that of stone loach (Noemacheilus barbatulus toni), a benthic fish, did not show any significant changes.<BR>Deposition of sediment after CWD removal was associated with development of gravel bars at channel bends or wider sections. Pools were recreated by lateral scouring at the opposite sides of banks where gravel bars developed. We concluded that CWD pieces play an important role in forming pools and controlling pool number, although they are not effective in increasing pool volume in low-gradient meandering streams. Thus, a decline in masu salmon population could be attributed to a decrease in cover and pool number in this stream.

収録刊行物

  • 応用生態工学 = Ecology and civil engineering  

    応用生態工学 = Ecology and civil engineering 2(2), 179-190, 1999-11-19 

    Ecology and Civil Engineering Society

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各種コード

  • NII論文ID(NAID)
    10021976042
  • NII書誌ID(NCID)
    AA11528360
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • 雑誌種別
    大学紀要
  • ISSN
    13443755
  • NDL 記事登録ID
    4955280
  • NDL 雑誌分類
    ZN1(科学技術--建設工学・建設業) // ZR1(科学技術--生物学)
  • NDL 請求記号
    Z74-B482
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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