清澄な河川,宇川(京都府)の珪藻植生

抄録

The diatom community in a less polluted river, the U-kawa River in Kyoto Prefecture, was investigated to find the community characteristics and the relationship between the community and river zonation system based on the geographical features by KAKI (1944). The diatom community was made up of 15-42 forms at each station and characterized by some groups, according to ecological valency in terms of organic pollution, suggesting that the diatom ecological valency by LANGE-BERTALOT (1978, 1979) may be applicable. The dominant species in the community changed from upstream to downstream as follows Gomphonema minutum→Achnanthes convergens→Nitzschia frustulum→Fragilaria vaucheriae var. perminuta, and α-mesosaprobic indicator species in traditional concept were found in this less polluted river. No distinct relationship was also found between the community and river zonation. Species diversity(Shannon-Wiener, DI (bit)) of the communities varied from 1.597 to 4.256 and the communities having lower species diversity were predominated by a blue-green alga, Homoeothrix janthina. The present results indicate that the very high similarity of the diatom communities in different river zones might be due to the dominance of H. janthina which grows over different river zones and forms the uniform microenvironments for diatoms, thus leading to the formation of fairly similar communities.