Seasonal Change of the Diatom Assemlage and DAIpo in an Unpolluted River (the Takami River) and a Polluted River (the Saho River)

Abstract

Seasonal changes of the attached diatom assemblages and DAIpo (diatom assemblage index to organic water pollution) values were researched based on the comparison of the data in an unpolluted river (the Takami River) with those in a polluted one (the Saho River) in Nara Prefecture. Results were obtained as follows :
1. In the unpolluted site of the Takami River, DAIpo values were constant throughout all seasons. However, when the algal community exfoliated in cold season, we obtained the diatom assemblage with lower DAIpo value than natural unexfoliated community, even if the standing crop of it is large.
2. In the polluted site of the Saho River, DAIpo values were very lower in summer than in winter.