The rurrent status of Kushiro Mire and an overview of restoration projects

DOI Web Site 6 Citations 33 References
  • NAKAMURA Futoshi
    Department of Forest Science, Graduate School of Agriculture, Hokkaido University
  • NAKAMURA Takatoshi
    Forest Research Station, Field Science Center for Northern Biosphere, Hokkaido University
  • WATANABE Osamu
    Sapporo Nature Research Interpretation Office
  • YAMADA Hiroyuki
    Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University
  • NAKAGAWA Yasunori
    Northern Forestry Research and Development Office, Forest Research Station, Field Science Center for Northern Biosphere, Hokkaido University
  • KANEKO Masami
    Department of Regional Environmental Studies, Faculty of Environmental Systems, Rakuno Gakuen University
  • YOSHIMURA Nobuhiko
    Department of Forest Science, Graduate School of Agriculture, Hokkaido University
  • WATANABE Tsunao
    Eastern Hokkaido Regional Office for Nature Conservation, Nature Conservation Bureau, Ministry of the Environment

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Other Title
  • 釧路湿原の現状と自然再生事業の概要
  • クシロ シツゲン ノ ゲンジョウ ト シゼン サイセイ ジギョウ ノ ガイヨウ

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Abstract

Kushiro Mire, a marsh located near the mouth of the Kushiro River, is suffering from the cumulative effects of pollution caused by land-use development in the watershed. A high wash load is of particular concern and accounts for approximately 95% of the total suspended sediment load that flows into the marsh. Research has found that turbid water floods the margins of the marsh; this is due to riverbed aggregation in a channelized stream reach that provides agricultural drainage. An analysis of Cs-137 concentrations determined that the rate of fine sediment deposition was approximately three to eight times higher in the channelized reach than in a reach of the natural river. This rapid sediment deposition has lowered groundwater levels and enriched the nutrient content of the marsh soil. Consequently, woody species are rapidly invading the margins of the marsh, causing concern about a vegetation shift from reed-dominated marsh to woodland To address the physical and biological changes that are taking place in Kushiro Mire, various restoration projects have been planned and are being implemented under the Kushiro Mire Conservation Plan. Two examples of projects in the Kushiro Mire Conservation Plan are a forest restoration near Takkobu Lake and a wetland restoration of a crane habitat. Fine sediments and nutrients have been accumulating in Takkobu Lake because of agricultural development and soil erosion in the uplands. The number of aquatic species in the lake has also been decreasing. An environmental assessment was undertaken in collaboration with "Trust Sarun", a non-profit organization, and sites were selected for conservation and restoration work. A larch forest was purchased to prevent it from being clear-cut and thus increasing sediment loading in the lake. The forest will be restored to its natural state. In addition, the Ministry of Environment in the Hirosato District acquired a wetland restoration site that was originally designated as an "ordinary area," i.e., the least regulated area of a national park. The restoration site is an abandoned agricultural field with an old drainage system developed in the 1960 s; it is an important breeding habitat for red-crowned cranes (Grus japonesis) Based on a preliminary investigation, and under careful supervision to avoid disturbing the cranes, soil excavation and seeding experiments have been undertaken.

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