Abstract
In the river engineering field, it has been more important to evaluate a river environment from the ecological viewpoint, recently. This research examined what kind of water quality influences the benthic community, and that the traditional ecological-indices can be adapted to the assessment of the present river environment. In this research, the benthic community data of National Censuses on River Environments was used. The results showed that the difference in the Biotic Index of the usual Beck-Tsuda method could not be observed among the examined points in clean rivers because of its excessive sensitivity to a number of species, and that the index did not correspond to the water quality situation. However, the pollution-non-tolerant species of the Beck-Tsuda method were influenced by the water quality situation of NO3- and DOC in the present clean rivers. To examine that how fluctuation of the water quality influences the biodiversity of benthic community, the relationship between the Pielou index and the coefficient of variation of water quality was examined. The result showed that the fluctuation of the water quality reduced the biodiversity.
