№ 4 (2019)
Статьи
Microbial communities in the estuarine water areas of the rivers in the southeastern part of Lake Baikal
Аннотация
Using the Illumina MiSeq platform, we have studied the diversity of bacteria and archaea in three rivers of the southeastern end of Lake Baikal in the under-ice period of 2018. In analysed 16S rRNA gene libraries of all rivers, we have identified sequences of 12 bacterial phyla: Actinobacteria, Bacteroidetes, Cyanobacteria, Elusimicrobia, Epsilonbacteraeota, Fibrobacteres, Firmicutes, Omnitrophicaeota, Patescibacteria, Planctomycetes, Proteobacteria, and Verrucomicrobia. The contribution of minor taxa to the microbiomes from the estuaries of the rivers Solzan and Bolshaya Osinovka is more significant. Three phyla (Thaumarchaeota, Euryarchaeota and Crenarchaeota) and one superphylum (DPANN) represent archaea. The diversity of bacteria and archaea in the investigated ecotopes has its specifics and is different to that found in the pelagic zone of Southern Baikal. Bacteria show phylogenetic diversity at the level of families and genera, whereas archaea – at the level of phyla. In the microbiomes, we have identified microorganisms involved in various stages of transformation of organic and inorganic substances.
259-265
Lake Gusinoye (the southern part of East Siberia, Russia): sedimentary history inferred from high-resolution reflection seismic data
Аннотация
This paper studies the formation of the sediment cover in Lake Gusinoye. For this purpose, we used high-resolution seismic data. Depression of Lake Gusinoye has a tectonic origin; however, there is no evidence of recent tectonic activity. Sediment thickness in Lake Gusinoye is less than 9 m, and its history is short (<35-45 ka). In addition, seismic stratigraphy records contain three contrasting episodes when the lake level dramatically decreased. It is very likely that there were also other shorter episodes of low-level stands. Thus, seismic structures of lakes Gusinoye and Kotokel have a strong resemblance, and it is most likely that their history began at the same time, ca. 40 ka BP.
266-269
Zooplankton in two small reservoirs of the Tuva Republic
Аннотация
The article provides information on the species composition and quantitative indicators of zooplankton in two small mountain reservoirs of the Tuva Republic: the Eerbek and Turan. They reflect the first and the third years of the ecosystem existence after seasonal drawdown. Regulation shows a typical pattern in the distribution of zooplankton in the reservoirs: an increase in density in the dam section. In general, the reservoir zooplankton has a floodplain type of formation. The existence periods of reservoirs influences the zooplankton structure and its development: regulation in the first year determines the development of crustacean zooplankton (represented mainly by cladocerans), usually with monodominance; over three years, all main groups of zooplankton develop, but drawdowns interrupt the formation on the normal ecosystem in the reservoir.
270-274
Transformation of the chemical composition of waters from the Barguzin River in the Barguzin Bay (Lake Baikal)
Аннотация
We have studied the changes in the chemical composition of the Bargizin River waters that inflow to Lake Baikal under the different water level. We have shown that river and lake waters that involved in the mixing differ in the ion composition and temperature. Despite this, the mixing in the Barguzin Bay under the influence of circulation currents and thermal barrier occurs in a comparatively narrow coastline, which is usually less than four kilometres. Mixed waters distribute north- and northwestward and reach the southern end of the Svyatoy Nos Peninsula. In summer, the distribution scale of river waters in the bay becomes greater but is mainly limited to the surface layer. In the central part of the bay, within one-two kilometres from the river estuary, a lens of lake waters can form. Not only the change in the chemical composition and temperature of the water but also its colour indicate the influx of these waters. The change in the concentrations of individual ions at a distance from the estuary of the Barguzin River occurs linearly, which indicates ordinary dynamic mixing of river and lake water masses.
275-280
Influence of solar radiation on chlorophyll a concentration assessment using fluorescence measured by the submersible sensor in Lake Baikal
Аннотация
Assessment of chlorophyll a concentration based on fluorescence intensity is actively used at present. In natural waters, profile fluorescence is measured using submersible sensors. These sensors are equipped with no special chamber for phytoplankton dark adaptation before measurement. Effect of irradiance in the upper layer leads to a decrease in chlorophyll a fluorescence due to closing some reaction centers of photosystem 2. The conducted research on Lake Baikal has revealed the relationship between the share of open reaction center in photosystem 2 and photosynthetically available radiation in the lake. The relationship between these parameters was described by an exponential function with a high determination coefficient (r2=0.97). Based on the obtained relationship, an algorithm was developed to compensate for the decrease in chlorophyll a fluorescence intensity due to the light influence in situ. The algorithm enables to retrieve the “real” fluorescence profile, which is necessary for the correct retrieval of the vertical distribution of the chlorophyll a content.
281-285