Diatom Assemblages in the Sediment Traps in Lake Onega

Abstract

The paper presents the first study of the composition and structure of the diatom assemblages from sediment traps installed in different parts of Lake Onega. 171 species and intraspecific diatom taxa were observed belonging to 59 genera. The predominance of planktonic diatoms is favored by large depths of the lake and a small area of the littoral zone. Aulacoseira islandica and A. subarctica, the most abundant species in spring phytoplankton in Lake Onega dominate in the sediment-traps diatom assemblages. In the sites subject to anthropogenic eutrophication, Aulacoseira ambigua is numerous as well. In a number of sites Lindavia radiosa and Pantocsekiella tripartita are among the subdominating species, while P. schumannii, Stephanodiscus neoastraea and Stephanodiscus sp. are less common. Higher proportions of periphytic Tabellaria fenestrata were recorded in the sites with the largest areas colonized by macrophytes. In all sampling sites, neutrophilous oligo-mesotrophic and oligo-hypereutrophic taxa prevail in the diatom assemblages. The predominance of two or three species in the diatom assemblage results in low values of the floristic diversity index. More diverse diatom assemblages were found in rathers isolated bays. Concentrations of diatom valves and chrysophyte cysts in sediment traps material were also calculated.