EVALUATION OF SHORT TERM RESPONSES OF STREAM BENTHIC INVERTEBRATE COMMUNITY TO SEDIMENT SLUICING OF RETROFITTED CASCADE DAMS

Abstract

 Ecosystem changes associated with dam sedimentation countermeasures such as sediment replenishment and flashing have been reported worldwide. However, little is known about the impacts of sediment sluicing, which have been rarely implemented. In this study, we evaluated the short- and mid- term effects of sediment sluicing on the benthic invertebrates along the Mimi River in Miyazaki Prefecture, Japan. The number of net-spinners consistently decreased in the short term as a result of sluicing. We observed increases in gliders at the site downstream of the lowermost dam in a midterm scale. A non-metric multidimensional scaling method was used to compare the similarity of community structure over time, and a consistent pattern of structural change was observed at the sites affected by sluicing. Therefore, it was suggested that the short-term response to sediment sluicing, rather than to flooding disturbance, could be evaluated in terms of taxa similarity.