事例研究 CASE　STUDY

水田小排水路における水路構造が水生生物に及ぼす影響

松井　明^*・ 佐藤　政良

筑波大学大学院生命環境科学研究科　〒305-8572　つくば市天王台１-１-１

Akira MATSUI^* and Masayoshi SATOH: Influence of canal structure on aquatic animals in the farm drain of a paddy field.. Ecol. Civil. Eng. 9(2), 191-201, 2006.

Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1, Ten-no dai, Tsukuba City, Ibaraki 305-8572, Japan

Abstract:Conventional paddy farmland consolidation in Japan has been said to have negative impacts on biodiversity in rural areas. Especially, transforming earthen irrigation and drainage canals into concrete canals has caused catastrophic damage to aquatic animals.The canal structure and flowing water for the non-irrigation season in the farm drain of a paddy field is very significant for aquatic animals utilizing a paddy field as a spawning ground. The purpose of this study was to clarify the influence of canal structure, that is, the canal bed and side materials, on aquatic animals based on a field survey of the distribution of fishes and aquatic insects at two sites in the same farm drain of a paddy field in Shimodate City, Ibaraki Prefecture, Japan. The sampling interval was one month during the period from April 2002 to March 2003. The results indicated the followings: (1) Overall, the biomass of aquatic animals at an earth canal in the farm drain was larger than that at a concrete canal. (2) Misgurnus anguillicaudatus (Dojou) was the most frequently captured fishes. Orthetrum albistyrum speciosum (Shiokaratombo) was the most continually captured aquatic insects. (3) Misgurnus anguillicaudatus appeared to be affected by the canal bed material composed of mud but relatively unaffected by the side material. (4) Orthetrum albistyrum speciosum appeared to be affected by the particle size composition of the canal bed material and preferred argilliferous soil to sandy soil. (5) To enrich the biodiversity in the farm drain of a paddy field for the future, our results suggested that maintaining an earth canal is highly priority.alinity increase affects many aspects of the ecosystem, and its consequences may differ depending on the location of lake (i. e. distance from sea).

Key words: Aquatic insect, Canal structure, Farm drain, Fish, Paddy field

摘要

本研究は，茨城県下館市の水田地区のなかで，１年中流水がある小排水路を取り上げ，土水路およびコンクリート水路の２地点（同一水路内）において，2002年４月から2003年３月の間，毎月１回定期的に水生生物の採捕調査を実施した結果，以下のことを明らかにした．
１．水田小排水路に生息する水生生物の採捕量（個体数および種類数）は，全般に土水路がコンクリート水路と比較して大きい傾向を示した．
２．魚類に関しては，２地点ともドジョウが最も多く採捕された．水生昆虫に関しては，２地点ともシオカラトンボ（幼虫）が最も多く採捕された．
３．ドジョウの生息にとって，河床材料が泥であることが重要であり，側壁材料の影響は比較的小さいと推定された．
４．シオカラトンボの生息にとって，河床材料の粒径組成が関与している可能性が考えられた．
５．今後の生物保全に配慮した水田小排水路の整備は，できる限り土水路を維持することが重要である．

2005年1月20日受付，2006年7月11日受理
* e-mail: matsuiakira1972@yahoo.co.jp