ダム直下におけるヒゲナガカワトビケラの生産量と試験湛水の影響

抄録

This topic presents the effect of trial impoundment of dam on secondary productivity of Stenopsyche marmorata (Trichoptera) at immediately downstream of Takizawa dam, in Japan. S marmorata has very high productivity among all invertebrate species and bivoltine life cycle. Production statistics for S.marmorata in Nakatsu-gawa river calculated by the increment-summation method and the instantaneous growth method, respectively. Values for non-wintering generation, wintering generation and annual production during individual years for the entire study period are given separately. Annual productions were 26.09/23.75 g/m² for 2006-2007, and 46.18/58.11 g/m² for 2007-2008 by increment method / instantaneous method. Because of the minimum outflow were maintained during the long period of trial impoundment, the survival rate of the fourth and fifth instars of larvae were significantly higher than the other study. Also, its individual body weight was heavier than the others. The biomass and productivity strongly depend on river gravel bed size distribution and flowing phytoplankton from the dam.