Spatial and Seasonal Variation of Diatom Assemblages Composition in a Partly Polluted River

Environmental factors affecting the species composition of periphytic diatom assemblages were analyzed in the partly polluted Asa River, in Tokyo, Japan, using principal component analysis, individual differences scaling and direct gradient analy sis. The effects of water pollution, seasonal change of temperature, and substrate were detected, among which pollution was the most influential in this river. Substrate had only a little effect. The existence of both direct and indirect effects (through water quality and temperature) was suggested.