Centric diatom algae of the Selenga River and its delta branches

Different stages of the study of taxonomical composition of centric diatoms in the Selenga River are considered. A revision of the species composition and a general systematic list are made. New for the Selenga River diatom species are discovered. The role of small-sized centric diatoms in different years and vegetation periods is assessed. A comparison of the composition and the level of development of centric diatoms in 1958–1959 and 2002–2005 is made.     

Plankton composition and water chemistry in the mixing zone of the Selenga River with Lake Baikal

Chemical and biological components of the Selenga River waters, the largest tributary of Lake Baikal, differ significantly from the lake waters. Active transformation processes of river waters into the lake ones occur in the vast barrier-like zone in the river-sea boundary areas. This study presents results on the spatial distribution and dynamics of water chemistry as well as the quantity and diversity of phyto- and bacterioplankton at a distance of 14 km off the Selenga River mouth. The most representative tracers of river and lake waters are total amount of ions and sulphates. Principal changes of chemical and biological parameters were fixed at 1–3 km off the Selenga River mouth that was determined as a mixing zone. Intense development of phytoplankton and eukaryotic picoplankton causing the decrease of nitrate and phosphate concentrations and organic matter rise were registered in this area. Gradual replacement of river phytoplankton by the lake one, abundance reduction of microorganisms and organotrophic bacteria and percentage increase of oligotrophic and psychrotolerant bacteria occurred in the mixing zone. Replacement of PC-rich picocyanobacteria by PE-rich ones was also recorded here. At a distance of 5–7 km off the shore, nutrient concentration and plankton composition were similar to those of Lake Baikal.     

Materials on the flora of diatoms (Centrophyceae) from lakes of the Baikal Region and Transbaikalia

The species composition of Centrophyceae (Bacillariophyta) in the phytoplankton of nine lakes in the Baikal Region and Transbaikalia was studied using electron microscopy (SEM) methods. Nineteen species and varieties of Centrophyceae were recorded; Aulacoseira distans var. septentrionalis and Cyclotella arctica were registered in this region for the first time. Aulacoseira baicalensis, Cyclotella minuta, and Stephanodiscus inconspicuus were also found in the studied lakes and attributed to being endemic to Lake Baikal.     

Sterols of marine microalgae Pyramimonas cf. cordata (Prasinophyta), Attheya ussurensis sp. nov. (Bacillariophyta) and a spring diatom bloom from Lake Baikal

The free sterol compositions of two marine microalgal species Pyramimonas cf. cordata (Prasinophyta), Attheya ussurensis sp. nov. (Bacillariophyta), and diatom bloom samples from Lake Baikal were determined by gas chromatography, gas chromatography-mass spectrometry and (for some sterol constituents) using nuclear magnetic resonance spectra. A variety of sterol profiles were found. The principal sterol in the prasinophyte P. cf. cordata, collected in the Sea of Japan near Vladivostok, was 24(R)-ethylcholesta-5,22E-dien-3beta-ol (poriferasterol), but not 24-ethyl-5,24(28)Z-dien-3beta-ol, as reported earlier in the related species Pyramimonas cordata. The principal sterol in the marine diatom A. ussurensis sp. nov. was identified as 24-ethylcholest-5-en-3beta-ol. The sample of diatom bloom caused by Stephanodiscus meyerii with admixtures of several other diatom species, contained cholesterol and 24-methylcholesta-5,24(28)-dien-3beta-ol as main sterol constituents.     

Bacillariophyta in mountainous water bodies of the Barguzin Ridge

The species composition of Bacillariophyta in mountain glacial lakes of the Barguzin Ridge (the Cis-Baikal Region) is studied for the first time. More than 200 taxa, including new ones for the flora of Russia (60), are found. The predominance of representatives of the class Pennatophyceae (92%) in the species composition is recorded. The problem of discovering Baikal endemics in high-mountain water bodies is considered.