2004

 Physico-chemical monitoring and mathematical modelling (made at IBP SB RAS and ICS SB RAS):

The analysis of the seasonal dynamics of hydrogen sulphide and oxygen concentration, temperature and salinity was made in the water layer of lakes Shira and Shunet. The scientists revealed the seasonal fluctuations of the total content of hydrogen sulphide and hydrosulphuric zone occurrence depth. It was shown that hydrosulphuric zone occurrence depth depends on the density stratification, determined by salinity and temperature profiles. It was revealed that Lake Shunet is characterized by a significantly more defined stratification and stronger vertical gradients of salinity and redox potential as compared to Lake Shira. The hydrosulphuric zone occurrence depth of Lake Shunet didn't show any significant changes during the research period. It was thus proved that the external conditions of sulphur biological cycle in Lake Shunet are more constant than in Lake Shira.

The scientists developed a one-dimensional model of thermal and salt annual regimes of stagnant reservoirs. The model setting was made at lakes Shira and Shunet. In particular, the ice depth in winter period was calculated. The calculated data are consistent with on-site observations.

Microbiological investigations (made at IBP SB RAS, IMB RAS and IBIW RAS):

The seasonal dynamics of phototrophic bacteria was studied in the chemocline of lakes Shira and Shunet. Using original equipment for thin-layer sampling, the researchers discerned thin (about 5 cm) layers of large-scale growth of purple sulphur bacteria (PSB) (the so-called "pink layer"), which has always been located at the same depth as redox zone, i.e. near the upper boundary of hydrogen sulphide diffusion. In summer the quantity of this group of microorganisms in thin layers reached 1.8x10 6 and 1.5x10 8 cells/ml in lakes Shira and Shunet, correspondingly. In winter the chemocline of Lake Shira didn't contain a "pink layer". Apparently, it can be explained by the thickness of the ice cover (1 meter) and insufficient lighting. Lake Shunet , though covered with ice, revealed a well-defined PSB layer, the quantity of bacteria being 5x10 6 cells/ml. Perhaps, such large-scale growth of photosynthetic bacteria during subglacial period is explained by the fact that the chemocline is located not very deeply (about 5 meters), which allows a sufficient amount of light to enter this zone, despite the thickness of ice being 0.9 m. In winter 2003, the chemocline zone of Lake Shira was located significantly deeper - at 15.5 m.

Judging by the morphological character and the typical absorption spectrum, we identified the PSB prevailing in the chemocline of Lake Shira as Lamprocystis purpurea (Chromatiaceae). The chemocline of Lake Shunet, to all appearances, possesses the same type of bacteria. Large-scale growth of sulphur bacteria, both purple and green, can be observed in the chemocline of many stratified lakes. It was Mahoney Lake ( Canada ) that the scientists had believed to contain the largest number of PSB, about 10 8 cells/ml. The results of our investigations allow to conclude that Lake Shunet is the analogue of Mahoney Lake in terms of PSB quantity, which can be explained by the similarity of morphometric and physico-chemical characteristics of both lakes. The integral rate of anoxic photosynthesis in the chemocline of Lake Shunet in summer was 279 mgC/(m 2 day), which is almost the same as in Mahoney Lake (302 mgC/(m 2 day)), if we take into account the method errors.

Protozoological investigations (made at IBP SB RAS):

In the chemocline zone of Lake Shunet, the researchers discovered 6 species of free living infusoria of the following genera: Cyclidium, Euplotes, Holophrya, Strombidium, autotrophic flagellates of Cryptomonas genus and heterotrophic nannoflagellates. The largest possible quantity of protozooplanktons and rotifers was observed in a 15 cm thick layer of water above the layer of purple bacteria, the content of hydrogen sulphide being 0-20 mg/l , in the total absence of oxygen. It was thus shown that in the chemocline of Lake Shunet, and particularly in the thin layer above the place of large-scale growth of sulphur bacteria, a population of protozooplankton, adapted to low oxygen values and presence of hydrogen sulphide, is being developed.

Investigations of phyto- and zooplankton (made at IBP SB RAS and KSU):

The lateral heterogeneity of surface chlorophyll (0-4 m) of Lake Shira was investigated using fluorescence analysis during the period from June to August. Sampling stations were located at transect from the central station, so that from one station to another the depth of the lake changed by 2.0-2.5 m. The variation of chlorophyll concentration in the surface layer was low. The depth of station determined the general character of vertical distribution, the occurrence depth of hydrosulphuric zone and of the chlorophyll upper limits of green algae and cyanobacteria.

The researchers studied the vertical distribution of chlorophyll in the center of Lake Shunet. It was shown that phytoplankton providing oxygen photosynthesis is concentrated in a 20-30 cm thick layer above the hydrosulphuric zone (4.8-5.2 m) and is represented, according to initial estimation, mostly by eukaryotic algae.

The team of scientists studied the interseasonal dynamics (May - August, 2004) of the biomass and chlorophyll of phytoperiphyton at 8 stations, located along the coastline of Lake Shira. The primary investigation of chlorophyll distribution showed that it was the resort area and village household effluent where phytoperiphyton was the most well-developed. The taxonomic structure of phytoperiphyton in spring was represented by green and diatomic algae, and in July and August - by diatomic green and blue-green algae.

The team studied the taxonomic composition of zooplankton at lakes Shira and Shunet depending on the season (samples were taken in November 2003, in May, June, at the end of July and in August of 2004) and on biotope, the collected data was compared to the same of the year 2003. The researchers calculated the indices related to the taxonomic composition allowing to obtain information about the complexity of biocenoses structure. They also collected data about the dimensional structure of the prevailing species in the zooplankton community Arctodiaptomus salinus (Daday) of lakes Shira and Shunet, about its seasonal and interannual variability. The correlation of instars of Arctodiaptomus salinus (Daday) in community was determined depending on biotope, season and year.

The seasonal and interannual dynamics of zooplankton structural characteristics were measured in different biotopes of lakes Shira and Shunet .

Using original migration cylinders, the scientists monitored lakes Shira and Shunet searching for individual vertical migrations of A.salinus. Simultaneous multidirectional individual migrations of zooplankton were registered in Lake Shira. The experiment showed that from 30 to 40% of the biomass of A.salinus population rises from oxygen hypolimnion to epilimnion or goes down, traversing the thermocline and passing from one hydrodynamically-isolated zone to another within 12 hours. In Lake Shunet, within the limits of the oxygen water column (up to 4 meters deep) the intensity of both rising and descending flow of migrating animals was by several times lower as compared to Lake Shira (12-13% of the biomass of A.salinus population).

A series of experiments was carried out with the aim of determination of the feeding range of A.salinus in lakes Shira and Shunet, including the components of phyto- and microzooplankton. The feeding range of B.plicatilis was studied in Lake Shira. Experiments were set up to study the consumption by crayfish of the components of microbial plankton communities - anoxic photosynthetics (purple and green sulphur bacteria) at laboratory cultures and within natural forage. The investigation of the growth rates of crayfish A.salinus and rotifers B.plicatilis was carried out at phytoplankton with prevalence of cyanobacteria and at the culture of green algae for control. The laboratory experiment showed a principal possibility of consumption by crayfish of purple bacteria from Lake Shira, but the survival rate and prolificacy data indicate the low quality of such forage for A.salinus . According to the data of fluorescent analysis in Lake Shunet, cyanobacteria form a 20 cm thick layer immediately above the chemocline. In their natural concentration they turned out to be toxic for A.salinus , but not for Brachionus sp. Apparently, rotifers play an important role in regulation of the quantity of cyanobacteria in Lake Shunet .

Bioluminescent testing of lake water (made at IBP SB RAS):

The scientists studied the effect of the samples taken from lake Shira (along the coastline, at different depth) on the bioluminescence of water-soluble and starch gel immobilized bioluminescent system NADH:FMN -oxidoreductase-luciferase. Changes of bioluminescence kinetic parameters were registered as a result of lake water samples influence. Luciferase indices were calculated. The sensitivity of water-soluble and immobilized bienzymatic system, luminescent bacteria was inestigated in relation to water samples having different salt lake recreational load.

The researchers used model compound solutions to study the mechanisms of effect of several inorganic reductants, containing sulphur with different oxidation degrees, on the bioluminescence of the bienzymatic system NADH:FMN -oxidoreductase-luciferase, with the aim of revealing of the sensitivity of bioluminescent biotests to the influence of redox active compounds. It was established that there is a dependence of bioluminescence kinetic parameters upon the concentration of the exogenous compound. It was shown that the influence of inorganic sulphur-containing compounds is accompanied by both activation and inhibition of bioluminescence. The effect is determined by the concentration of the exogenous compound in the system. The kinetic parameters of bioluminescence were calculated in the presence of reductants. It was established that there is a dependence of the above mentioned kinetic parameters upon the redox potential of the studied reductants. Using model solutions the researchers studied the concentration of water dissolved oxygen in the presence of sulphur-containing compounds.

Reactive oxygen species, too, contribute to the formation of reductive-oxidative characteristics of water environment. Investigation of water samples taken from Lake Shira at different depths allowed to reveal the content of active oxygen radicals which are sulphate reduction reaction intermediates. It was registered that the concentration of active radicals is subject to changes depending on the depth.