Taxonomic composition of the epilithic diatom flora from rivers Vit and Osum, Bulgaria

Abstract. This paper presents the epilithic diatom flora from rivers Vit and Osum. Twenty-eight sampling sites were chosen along the river catchments, from the springs to the inflows (the Danube River). A total of 114 diatom taxa (103 species and 11 varieties) from 36 genera were identified in the epilithon of the studied rivers. The epilithic diatom floras from rivers Vit and Osum had high floristic similarity, Cs = 0.737 (with 66 common spesies). To characterize the diatom distributional patterns, nonmetric multidimensional scaling was used Two types of diatom assemblages were found throughout the studied rivers. The diatom assemblages from the upper reaches of the studied rivers were dominated by Achnanthidium pyrenaicum, A. minutissimum, Encyonema minutum, E. silesiacum, Gomphonema olivaceum, G. pumilum, Reimeria sinuata, Amphora pediculus, and Cocconeis pediculus. The diatom assemblages found in the lower reaches of the studied river