Epilithic diatom flora of Ai River, Osaka, west-central Japan, and its relationship to the river environments

Abstract

We studied epilithic diatom assemblages and their association with the environments of the Ai River, a subsidiary stream of the Yodo River, in west central Japan. Diatom samples were collected in August and December, 2009. Melosira varians that tends to be grazed by aquatic animals was usually dominant, especially in the lower parts of the river. In the upper parts of the river, sessile diatoms such as Achnanthidium minutissimum and Planothidium lanceolatum were abundant in summer, while Diatoma vulgaris and Nitzschia dissipata were abundant in winter. Rhoicosphenia abbreviata which firmly adheres to the substrata by a short stalk was dominant at the site with the highest stream gradient. Luticola ventriconfusa was dominant in the lowest part of the river, suggesting tidal influences. DAIpo （Diatom Assemblage Index to water pollution） was higher in the upstream to midstream parts than in the headwater. This pattern significantly corresponded to the river gradient.