Abstract
Agricultural reservoirs are now regarded as important habitats for some aquatic organisms, though their value as habitats of algae has clarified little. Diatom is often the most dominant component of freshwater algal communities and its contribution to species diversity can not be negligible. We studied periphytic diatom assemblages in 24 agricultural reservoirs in Awajishima Island, Japan to find major factors controlling diatom species composition. As it has often been reported and discussed, influence of eutrophication to species composition was detected. However, surrounding land cover was estimated to be the most important factor: some dystrophic or soil diatoms characterized diatom assemblages in reservoirs surrounded by woodland. Compositional difference caused by substrate was not detected. It is concluded that water quality management considering eutrophication and land use management where conservation priority is put on woodlands surrounding reservoirs are possible means to conserve diatom assemblages in agricultural reservoirs.
