土砂還元実施後の二瀬ダム下流における水生昆虫群集の経年的な動態変化と低水路空間における河床材料の移動性について

抄録

For clarifying the effects of sand supply on the down stream riffle of Futase-Dam, field survey data on bed material and invertebrate composition from autumn to early spring were analyzed. Particle size distribution was shifted to small size after the sand supply. During winter season, from autumn to early spring, changes in invertebrate community showed different temporal pattern before and after the sand supply. These tendencies occurred after sand supply are no increase in the abundance of net-spinning caddis-worms (Torichoptera), increase in autumn EPT% and increase in M_N (movability number) during winter. This study has proposed to use diversity-movability loop based on Tsuda hypothesis. Before sand supply, community succession to climax under armored bed which is extremely stable habitat can be estimated in the loop. Moreover, the effects of sand supply on invertebrate community can be recognized as retrogressive succession in the loop caused by unstable stream bed.