Limnological Institute

The fish species Cottus kuznetzovi was described by L.S. Berg in 1903 from the Lena River system. However, two years after its description, Berg synonymized this sculpin with the widely distributed species C. poecilopus Heckel, 1837. It remained a junior synonym until 2009, when this species was redescribed and revalidated. Despite this, some researchers continue to doubt the validity of C. kuznetzovi. The authors obtained new materials from the Arctic region of Eastern Siberia and the upper reaches of the Lena River. This made it possible to apply molecular genetic methods to resolve issues related to the taxonomic status and genetic differentiation of C. kuznetzovi, and also enabled the discovery of this species in new areas. As a result of the analysis of the nucleotide sequences of the mtDNA control region (CR) and the cytochrome b gene (cytb), individuals of the species C. kuznetzovi were identified in the upper reaches of the Lena River, as well as in the Aldan, Indigirka, and Yana river systems. The average p-distance (CR) between different populations was 0.97 ± 0.29%. The presented results indicate a strong genetic isolation of this species from all closely related sculpins. The average p-distances between C. kuznezovi and closely related species of the group “Cottus poecilopus” ranged from 2.50 ± 0.47% to 3.95 ± 0.63% for CR marker, and from 1.50 ± 0.35% to 7.95 ± 0.81% for cytb marker. The validity of this species has been reliably established.

The results of a study of the dynamics of biogenic elements, chlorophyll, biomass, and phytoplankton abundance in the littoral zone of Lake Baikal in June and September 2021–2023 are presented. No consistent differences in the content of mineral forms of nitrogen and phosphorus have been found in different areas of the littoral zone with different anthropogenic loads. It is shown that the coastal areas near human settlements were characterized by high phytoplankton concentrations, as well as by high total nitrogen and total phosphorus with a predominance of organic forms. The influx of water from large tributaries increased the silicon content in littoral areas of the lake that are adjacent to the mouth. The spring subglacial phytoplankton complex began to grow during the maximum annual content of biogenic elements. The summer algal community developed at lower concentrations of mineral nitrogen and phosphorus; its development led to a decrease in the amount of phosphates, up to their complete depletion, as well as to a decrease in the concentration of nitrates and the appearance of nitrites and ammonium in September. Interannual variations in the content of biogenic elements are insignificant during certain periods of measurements. The concentrations of silicon, total nitrogen, and total phosphorus and their mineral forms have not changed compared to previous studies. With respect to the TSI and TLI indices and total algal biomass, the trophic status of the littoral zone of Lake Baikal corresponds to the oligotrophic level with eutrophic elements in June and mesotrophic features in September.

A layer (260–270 cm) of soft carbonate nodules containing numerous valves of ancient diatoms was discovered in bottom sediments of the Bolshaya Zelenovskaya oil-methane seep (Central Baikal). Various methods confirmed the presence of a siderite phase in the carbonate; their enrichment in the heavy isotope δ13C (+14‰ VPDB) and the light isotope δ18O (−8.43‰ VPDB) also has been detected. Carbonate precipitation could have been facilitated by the high organic matter content of ancient diatoms, dissolved inorganic carbon, or CO2, supplied by the flow of mineralized fluids and formed during methanogenesis. High-throughput sequencing of the variable region of the 16S rRNA gene revealed the dominance of archaea of the family Methanoregulaceae (11–35%) and of the class Bathyarchaeia (16–54%) with a significant contribution of representatives of Nitrososphaeria (18%) and Woesearchaeales (10%) in the surface sample, as well as of Hadarchaeota (12%) in the deep carbonate-containing sediment. Bacterial dominants were represented by the phyla Chloroflexota (14–30%) and Acidobacteriota (5.8–11%), as well as representatives of Pseudomonadota (32%) in the surface sample and of Artibacterota (28.5%) in the carbonate-containing sediment. Based on the isotopic composition of δ18O and δ13C, chemical composition of pore waters, and microbial diversity, the manuscript discusses the possible scenario of carbonate precipitation process.

Saccharimonadia were analyzed in Lakes Baikal and Hovsgol using metagenomic sequencing approaches. Twenty-two metagenome-assembled genomes (MAGs) were reconstructed, including 20 from Lake Baikal and 2 from Lake Hovsgol. The two Hovsgol MAGs formed distinct phylogenetic branches: one grouped with a Baikal ubiquitous/surface-associated lineage, while the other clustered with a Baikal MAG lacking depth-stratified data. In contrast, a monophyletic, deep-water clade was identified in Lake Baikal and showed no close genomic relatives outside the lake. Genes involved in DNA repair, defense mechanisms, and host interaction were enriched in deep MAGs, whereas surface-associated MAGs carried higher abundances of genes related to phage interactions, amino acid metabolism, protein synthesis, cell division, and cell wall biosynthesis.

Descriptions of four new species of the genus Opisthocystis Sekera, 1911 are given, including Opisthocystis zaytsevae Krivorotkin et Timoshkin sp. n., Opisthocystis strictostylus Krivorotkin et Timoshkin sp. n., Opisthocystis sekeri Krivorotkin et Timoshkin sp. n., and Opisthocystis tenuistylus Krivorotkin et Timoshkin sp. n., all of them are endemic to Lake Baikal. The first three species were found in the coastal zone of the lake: O. zaytsevae in the shallow waters of Bolshoy Ushkaniy Island; O. strictostylus in the shallow waters of Ayaya Bay (northern basin) and opposite the village of Khuzhir (Olkhon Island, Maloye More Strait); and O. sekeri in the shallow waters of Onokochanskaya Bay (northern basin). O. tenuistylus was discovered on the underwater Akademichesky Ridge at a depth of about 350 m. Illustrated descriptions, differential diagnoses, and brief information on their distribution and ecology are provided for all new species. New extensive information is provided on the morphology and zoogeography of three rare and poorly studied endemic Baikal species of the same genus. These are Opisthocystis multifidus (Nasonov, 1935), Opisthocystis octopropagostylus Lukhnev et Timoshkin, 2014, and Opisthocystis cf. umylinae Timoshkin, 2010. Brief illustrated descriptions and generalized information on their distribution are provided for all species. The taxonomic status of five Baikal species—Opisthocystis bilobatus Nasonov, 1935, Opisthocystis bicurvatus Nasonov, 1935, Opisthocystis campanulatus Nasonov, 1935, Opisthocystis irregularis Nasonov, 1935, and Opisthocystis trifida Nasonov, 1935—is discussed. The diagnoses of these species include only very brief descriptions of the distal stylet ends, with schematic drawings provided for three of them. It was impossible to reliably identify the species listed by N.V. Nasonov. To confirm this, we provide the author’s original drawings and descriptions. As part of the revision of the Opisthocystis fauna in Baikal, we have to assign the status of nomen nudum to these five species. The paper provides their up-to-date list that includes 41 species, with the origin of 40 of them associated with Lake Baikal.

This study is based on data obtained as part of continuous monitoring of small gas impurities (SO2, NO2, NO), mass concentration of aerosol particles PM2.5 and meteorological parameters, which was first implemented at the Tankhoi observation point (southeastern coast of Lake Baikal, Russia) from October 2023 to May 2025. Statistical methods and the non-parametric wind regression receptor model (NWR) were used to analyze temporal variability and identify sources of pollution. It was found that the concentrations of gas impurities have a clearly pronounced winter maximum: the median values for sulfur dioxide and nitrogen in winter reached 9.2 μg/m3 and 13.8 μg/m3, respectively, which is associated with emissions from coal-fired thermal power plants and unfavorable meteorological conditions (inversions, low boundary layer height). In contrast to gases, PM2.5 demonstrated a summer peak up to 43.5 μg/m3 in July–August 2024 due to abnormally hot weather and forest fires. The daily course of sulfur dioxide was characterized by an atypical daily maximum caused by the convective transport of polluted air masses from the upper layers of the boundary layer. During this period, higher concentrations of sulfur dioxide caused by long-range high-altitude transport of emissions from regional thermal power plants can reach the ground surface, leading to an increase in their concentration in the near-surface layer. Using the NWR model, the influence of regional thermal power plants located 100–150 km northwest of the station on the levels of SO2 and NO2 was confirmed. The results also highlight the contribution of local sources, such as vehicles, stoves, and shipping, to the formation of NO and PM2.5.

Silica‑scaled chrysophytes can form siliceous stomatocysts in addition to scales and bristles, but the morphology of these stomatocysts is known for only a few species. Using scanning electron microscopy, we observed numerous plate-scales of the rare species Spiniferomonas minuta on the surface of stomatocyst Stomatocyst 331 Firsova & Likhoshway, whose species identity had been previously unknown. The stomatocyst is primarily spherical to broadly obovate, has an asymmetrically positioned conical pore, and its surface bears conulae, verrucae, and echinate spines. This morphotype was found in the southern part of Lake Baikal in October at a water temperature of 8.8 °C and pH 8.2. A comparative analysis of known stomatocyst morphotypes in Spiniferomonas species revealed considerable morphological diversity.