Abstract
Biodiversity is a problem not only of visible organisms but also of microorganisms such as unicellular algae and fungi. In the present study I focused on diatoms, which is a kind of unicellular algae, to discuss biodiversity in river habitats. The relationship between species diversity of periphytic diatom assemblages and environmental factors other than water pollution was studied. Thirty-five sampling sites were set along the Iruma-gawa River, Saitama Prefecture, Japan. These sites were located closely and similar in degree of water pollution. Species composition of diatom assemblages in an isolated pond from the main channel of the river was quite different from those in the main channel. Species diversity was negatively correlated with current velocity in the channel. The unique characteristics of isolated ponds along river channels, which seemed to have some relationship with water chemistry (not pollution), should be considered in river environmental management. It appears that the negative correlation between current velocity and diatom species diversity is due to disturbances in algal community succession caused by water flow.
