INFLUENCE OF LONG-TERM SEDIMENT REPLENISHMENT TO ALGAL BIOMASS AND COMMUNITY STRUCTURE DOWNSTREAM OF A DAM

The dynamics of attached algae in terms of their biomass and community structure was analyzed to reveal various relations to disturbances which are defined, these are increased by grain size refining on the river bed in the downstream section of Futase Dam. As a result of a time series analysis, cell densities of algae have been gradually increased in our entire observation sites and exceeded 10,000 cell/mm2 around 2013. Diatoms were the most contributed class to the increase of the cell densities and Homoeothrix janthina and Hydrurus foetidus also led the increase partly. On an analysis of relationship between the algal dynamics and the grain size refining, the algal densities increased and some algal species which are tolerant to the disturbances were identified following decrease of grain size on the river bed.