矢作川豊田大橋付近における河道掘削案に対する水生昆虫の生息環境としての評価

Abstract

We assessed the impact of deposit removal from the middle reach of the Yahagi River, central Honshu, Japan, on the physical habitat availability for five species of aquatic insects, viz., three dragonfly (Odonata) species, Macromia daimoji (Corduliidae), Gomphus postocularis (Gomphidae) and Onychogomphus viridicostus (Gomphidae); two stonefly (Plecoptera) species, Oyamia seminigra (Perlidae) and Neoperla (Perlidae), by employing the IFIM / PHABSIM. The weighted usable area (WUA) of the species that live in the cobble substrates with interstitial spaces, Onychogomphus viridicostus, Oyamia seminigra, and Neoperla, were expected to become wider in the estimated riverbed after the deposit removal than in the present riverbed. On the other hand, the WUA of the species that live on the mud and sand substrates in a backwater pool along the channel margin, Macromia daimoji and Gomphus postocularis, were expected to become smaller in the estimated riverbed after the deposit removal than in the present riverbed, if the gravel bar around the backwater pool would be removed. But, it was difficult to accurately assess the physical habitat in the places like the backwater pool after the deposit removal. Therefore, the practice of deposit removal work should follow the process of adaptive management in order to determine the best management strategy.