Variation in Species Composition of Diatom Assemblages in an Unpolluted River.

Abstract

Spatial variation of attached diatom assemblages was surveyed in an unpolluted river, the River Saguri in Niigata Prefecture, Japan, and the causes of the observed variation were analyzed. The result of cluster analysis indicated that the spatial variation of diatom assemblages was correlated to stream order and current velocity. Relative abundance of Fragilaria vaucheriae (Kutz.) Peters, Gomphonema angustum Ag. and Rhoicosphenia abbreviata (Ag.) Lange-B. in the assemblages collected from the first-order streams was less than that in the assemblages collected from the higher-order streams. In the first-order streams, a group of diatoms such as Gomphonema gracile Ehr., G. hebridense Greg., and Navicula angusta Grun. occurred when the current velocity was quite slow. There was little variation in the species composition between different substrata.