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We analysed the relationship between the chemical complex (concentration of dissolved ions, nutrients, pH) and biological parameters (primary production, biomass of phytoplankton, abundance and activity of bacterial communities) at estuaries of rivers and coastal waters of Southern Baikal during the under-ice period. Correlation network analysis revealed CO2 to be the main limiting factor for the development of algae and microbial communities in the coastal zone of Lake Baikal. This study indicates that primarily reverse synthesis of bicarbonate and carbonate ions associated with the development of phytoplankton and accumulation of dissolved CO2 during photosynthesis regulates pH in the Baikal water. We did not detect the anthropogenic factors that influence the change in pH and acidification. Near the Listvyanka settlement (Lake Baikal, Listvennichnaya Bay), there was a great number of organotrophs and thermotolerant bacteria with low bacterioplankton activity and high concentration of organic carbon. This evidences eutrophication due to the influx of organic matter having an anthropogenic source. Nutrients produced during the bacterial destruction of this matter may explain the changes in bottom phytocenoses of Listvennichnaya Bay. [ABSTRACT FROM AUTHOR]

This paper provides a novel report of methane hydrates rising from bottom sediments to the surface of Lake Baikal, validated by photo and video records. The ascent of hydrates in the water column was confirmed by hydroacoustic data showing rising objects with velocities significantly exceeding the typical speeds (18–25 cm s−1) of gas bubbles. Mathematical modelling along with velocity and depth estimates of the presumed methane hydrates coincided with values observed from echograms. Modelling results also showed that a methane hydrate fragment with initial radius of 2.5 cm or greater could reach the surface of Lake Baikal given summer water column temperature conditions. Results further show that while methane bubbles released from the deep sedimentary reservoir would dissolve in the Lake Baikal water column, transport in hydrate form is not only viable but may represent a previously overlooked source of surface methane with subsequent emissions to the atmosphere. Methane hydrates captured within the ice cover may also cause the formation of unique ice structures and morphologies observed around Lake Baikal. Sampling of these ice structures detected methane content that exceeded concentrations measured in surrounding ice and from the atmosphere demonstrating a link with the methane transport processes described here. [ABSTRACT FROM AUTHOR]

Methane production by microbial communities from Lake Baikal bottom sediments with different chemical composition of pore water was studied. Methane production was more active in the media supplemented with H2: CO2 and H2 + CH3COONa, rather than on media with acetate as the sole source of carbon and energy. Addition of methanol stimulated methane production only in the case of microbial communities from upper silts. Ability of the communities to produce methane correlated reliably with the concentrations of the NO3-, SO42−, Cl-, and CH3COO- ions in the pore water of the relevant sediments. Cultivation of communities from the mud volcano sediments resulted in development of methanogenic archaea of the family Methanocellaсеае in the media supplemented with H2: CO2 and H2 + CH3COONa, while methanogenic archaea in the communities cultivated without additional substrates belonged to the genera Methanoregula, Methanobacterium, and Methanosaeta. [ABSTRACT FROM AUTHOR]

The patterns of renewal of bottom waters in Lake Baikal under the influence of deep convection and intrusion of cold waters have been considered based on the data of temperature surveys of Lake Baikal conducted in 1993-2009. The volumes of the cold bottom layer with the maximums of 200-470 km in individual years and the values of its total cooling (−20-60 × 10 MJ) have been determined for South, Middle, and North Baikal. The renewal process is asynchronous and proceeds with different activity in these parts of the lake, which indicates that the mechanisms that cause deep convection in the context of the great latitudinal length and differences in the climate and hydrological processes manifest themselves regionally. The volume of intrusions has been determined. Its average value for the period was higher in South Baikal (20 km) than in Middle Baikal (9.8 km) and North Baikal (8.6 km). The volume of the intrusions in these parts of the lake was 30-70 km in some years. [ABSTRACT FROM AUTHOR]

The microbial communities of the estuarine zone and the mixing zone of river and lake waters in the Selenga River estuary were studied using the fluorescence in situ hybridization (FISH) method. The microorganisms belonging to the phylogenetic group Gammaproteobacteria were found to predominate in the river estuary, constituting up to 17% of the total bacterial community. Among cultivable microorganisms, organotrophic bacteria were predominant (2040 CFU/ml) in this zone, which results in high rates of microbial production (6.0 μg C/(l day). The microbial community structure changed with distance from the river estuary; representatives of the Alpha-, Beta-, and Gammaproteobacteria were present in equal proportions; psychrotolerant and oligotrophic bacteria were numerous. The rate of heterotrophic carbon dioxide assimilation decreased to 3.8 μg C/(l day). At 5–7 km from the river estuary, where the hydrologic, physical, and chemical conditions are similar to those of lake waters, members of the Betaproteobacteria, which are typical of the open waters of Lake Baikal, are the major representatives of planktonic microorganisms. [ABSTRACT FROM AUTHOR]

In Lake Baikal, frontal zones are a factor forming the pelagic structure, including area limits of pelagic communities. The spacial distribution of Baikal micro-organisms and diatom algae is known to be influenced by the vertical circulation of Lake Baikal deep waters during the spring thermal bar. In June 2001, we studied the distribution of plankton invertebrates and ways in which it depends on physico-chemical and biological parameters of water in the vicinity of spring thermal bars. Samples were taken through June 11–13th along three transects, across the middle basin of Lake Baikal and the Selenga shallow waters, namely at the Boldakovo River, Cape Sukhinskiy and the Kukuy branches of the Selenga River. As a consequence of the lake possibly being warmed later than usual, and compare with a previous study in 1993, the upper layers with temperatures close to 4 °C, were located near the shore where water depth was 14–100 m, from north to south. The littoral waters, warmed above 4 °C and reaching 12.7 °C near Cape Sukhinskiy, are known to differ from the open lake in hydrochemical indexes, raised number of bacterioplankton and the structure of algae coenoses (in particular, the presence of algae which indicate the spread of the Selenga River waters). An unusual vertical distribution of autotrophic picoplankton in terms of raised concentrations at the bottom, 60 m deep, occurred at the Cape Sukhinskiy transect within a thermal bar zone. This indicated the descent of upper waters rich in picoplankton. The zooplankton structure in the littoral also differed from that in more open waters where temperatures were below 4 °C, mainly by its richer diversity increased by littoral inhabitants. The pelagic amphipod Macrohectopus branickii preferred cold waters less than 4 °C. Crustaceans and rotifers were separated into different groups according to spacial distribution. [ABSTRACT FROM AUTHOR]