COMPARISON OF BENTHIC INVERTEBRATE ASSEMBLAGES BETWEEN PRE AND AFTER IMPOUNDMENT AT UP- AND DOWNSTREAM OF DAM

This topic presents the effect of water temperature on benthic invertebrate growth and assemblages at downstream site of the Dam in winter, in Japan. The surface layer water of dam was released, and the temperature was always 3-5 degrees higher than the upstream. This was because of tentative manipulation of dam. Life cycles of dominated species were faster and their body size were all larger in the downstream than the upstream. Kamimuria tibialis (Perlidae) as a predator grew faster. Also, its body weight was much heavier than in the upstream, even its body length is the same in the upstream. Periphyton biomass was also much higher, especially, filamentous species were dominated at slow current site in the downstream. Regardless of abundance of periphyton, Heptageniidae as a grazer were not increased compared with the upstream. Besides discharge control, water temperature changes invertebrate assemblages quickly. This result implies that restrict of the movement of species is need to consideration.