A. G. Degermendzhi

Microbiological and isotopic-geochemical investigations of meromictic lakes in Khakasia in winter

Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (δ13C) and hydrogen sulfide and sulfate (δ34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.

Ecology of purple sulfur bacteria in the highly stratified meromictic Lake Shunet (Siberia, Khakassia) in 2002–2009

Phototrophic sulfur bacteria form dense accumulations in the chemocline zones of stratified lakes where light reaches the sulfide-containing layers of water. Many works are dedicated to the ecophysiology of these microorganisms in meromictic lakes. However, the role of these microorganisms in the trophic network of these ecosystems, the ways of biomass utilization, and the contribution to the turnover of biogenic elements have so far been insufficiently understood. This work deals with the analysis of many years’ seasonal dynamics of the biomass of purple sulfur bacteria and the physicochemical conditions of their environment in Lake Shunet (Siberia, Khakassia, Russia), unraveling the causes of their anomalous development in the chemocline of this lake, as well as the comparative analysis of such type of ecosystems. Lake Shunet is characterized by markedly pronounced stratification and the high density of purple sulfur bacteria (PSB) in the chemocline, which is comparable to that of Lake Mahoney (Canada) where the number of PSB is the greatest among those known in the world. It was shown that, in the period 2002–2009, the total amount of bacterio-chlorophyll a in the water column of Lake Shunet increased and did not correlate with the seasonal variations in temperature and illumination in the chemocline. It was established that PSB cells in the purple layer experienced the effect of self-shading. The sedimentation rate of purple sulfur bacteria in Lake Shunet was low due to the pronounced density gradient in the chemocline zone. Thus, the high number of PSB in the chemocline was due to the combination of strong illumination, a high sulfide concentration, and a high water density gradient, which was responsible for stable stratification and contributed to the accumulation of the cells in a narrow layer. The data obtained could be useful for the paleoreconstruction of climatically deter-mined changes in the level of the lake and its periods of meromixis by the presence of carotenoids and bacte-riochlorophylls in the bottom sediments.

Carotenoids in bottom sediments of lake Shira as a paleoindicator for reconstruction of Lake States in Khakassiya, Russia

The concentrations of carotenoids buried in the bottom sediments of Lake Shira (Siberia, Khakassiya) have analyzed for the period of the last 2300 years. The bottom sediments were found to contain carotenoids, which are molecular markers of the corresponding groups of Phototrophic organisms. The bottom sediments of Lake Shira were shown to be a promising object for climate reconstructions of the Late Holocene in southern Siberia.

Sedimentation rate in Cheko Lake (Evenkia, Siberia): New evidence on the problem of the 1908 Tunguska Event

We estimated the age and sedimentation rate of bottom sediments in Cheko Lake located in southern Evenkia, in the territory of Tunguska Nature Reserve, near the supposed epicenter of the so-called 1908 Tunguska Event. The vertical distributions of 137Cs and 210Pb activity and visually counted varves in the core of lake bottom sediments indicate that Cheko Lake is significantly older than the 1908 Tunguska Event; therefore, the lake basin cannot be a crater or a trace of the explosion as was supposed earlier by some researchers.

A hypothesis about double surging climate change in the 20th century

46 The cessation of global temperature growth observed in the past 13 years contradicts the prediction based on the IPCC (Intergovernmental Panel on Cli mate Change) models of general atmosphere and ocean circulation [1]. The absence of a direct relation ship between the growing concentration of greenhouse gases in the atmosphere and the global temperature can be interpreted as a manifestation of the eigendy namics of the Earth’s climate system. The idea about the existence of climate regimes (or states), with climate changes occurring by switching between these regimes, was commonly accepted in the 1990s. It was shown that the millennial variations in climatic parameters in the past and those in more recent time could be presented as the result of sharp switches between the states of the Earth’s climate sys tem [2]. It was noted that the biosphere–climate sys tem is essentially nonlinear: inputs and outputs are dis proportional; changes are sudden and sharp rather than slow and continuous; the presence of multiple equilib rium states is normal [3]. The possibility of threshold phenomena implementation and multiple states in the biosphere–climate system was discussed [4, 5]. In our work, a simple and illustrative statistical analysis of near surface temperature time series is implemented. An additional condition corresponding to the scientific approach is selection of the minimal set of initial data allowing us to reconstruct the observed dynamics with sufficient precision. As a result, a new hypothesis has been formulated: climate warming during the 20th century took place in the form of several stepwise switches between regimes instead of continuous changes. We found that adequate description of ocean tem perature dynamics for the period of 1900–2012 in at least two regions—tropical (30° S–30° N) and north ern moderate latitudes (30°–60° N)—requires few parameters: threshold changes of temperature and natural modes of El Niño variability for the tropical zone and the Pacific decadal oscillation (PDO) for the moderate latitudes. Let us consider the sea surface temperatures (SST) in the tropical zone (30° S–30° N) (Fig. 1). Most of the temperature anomalies in this zone are explained by El Niño. At first sight, these natural oscillations should be supplemented by some constant warming trend. However, it can be seen that the temperature dynamics since the mid 1980s until the present is ade quately reconstructed with a linear regression on El Niño and does not require any warming trend (Fig. 1a). On the other hand, regression on El Niño reproduces the period from the year 1950 until the mid 1980s quite well (Fig. 1b, gray line), but inade quately beyond this interval. This suggests that a sharp temperature rise could occur in the mid 1980s. This might be related, for example, to some change in the climate regime in the mid 1980s. Suppose that some additional factor deter mining the climate exists—a climate regime index that is a stepwise function, whose value is zero before change and 1 after change. Considering the value and date of a climatic surge as the parameters of the linear regression model, we can determine that the most suitable time for this hypothetical regime change was in the year 1987. As a result, we can reconstruct tem perature anomalies without constant warming at least since the 1940s. In order to obtain an adequate reconstruction since the 1900s, assume that there was another surge in the first half of the 20th century. Adjustment shows that it could have occurred in the period from December 1925 to January 1926. Hence, the index of the climate regime becomes a two stage function, which is equal to –1 before 1926, 0 in 1926–1987, and 1 after 1987. Note that the values –1, 0, and 1 are indicators of dif ferent climatic regimes under the assumption that the switches of 1925/1926 and 1987 produce equal (0.28°C) changes in the temperature anomalies. Based on this model, an adequate reconstruction is produced from 1900 until the present (Fig. 2). Certainly, there are some differences between the observed and reconstructed graphs. However, the aim of the present work was to distinguish the main factors producing the most adequate reconstructions; there A Hypothesis about Double Surging Climate Change in the 20th Century

Developing the control criterion for a continuous culture of microorganisms

A short survey and a critical analysis of previously proposed criteria for growth control of populations of microorganisms in the chemostat are presented. Based on the analysis of a mathematical model of the steady state of a microbial population in the chemostat, an adequate control criterion is suggested, along with a method to identify the corresponding control factors. The new control criterion is expressed as a product of the factor transformation coefficient and the sensitivity coefficient (SC) of the biomass with respect to the change in the factor at the chemostat inlet (hereinafter, the biomass SC). The control criterion determines the strength of the control exerted by a factor. The method of determining control factors consists in experimental determination of the real SCs for factors and the biomass and calculation on this basis of the corresponding ideal SCs, assuming constant factor transformation coefficients. The ideal SCs are shown to add up to integer values, a constraint that we call quantization relationships. Such relationships are used to test the completeness of the list of control factors. The proposed method was applied to both our own and literature data.

Change in the circulation regime in the stratified saline Lake Shira (Siberia, Republic of Khakassia)

The in-situ data on the vertical structure and stability of the vertical stratification of saline Lake Shira over the past decade (2007–2015) are analyzed. Simplified mathematical models have shown that strong wind in the autumn of 2014 together with rather thick ice in the winter of 2015 caused a change in the circulation regime of this water reservoir from meromictic (incomplete mixing) to holomictic (compete mixing). Based on the results obtained, a circulation regime for deep saline lakes located in the continental climate zone, in particular, in the arid zones of Southern Siberia (Khakassia, Transbaikal, and Altai) can be predicted under various climate scenarios of the future.

Experimental modeling of the influence of the rise in average summer temperatures on carbon circulation in tundra ecosystems

A sealed vegetation chamber was designed and constructed for physical simulation of climate conditions in the Subarctic zone during the spring–summer time. The small laboratory tundra-simulating ecosystem (TSE) was created for comparative evaluation of the rates of soil respiration and of the total balance of carbon fluxes in tundra ecosystems. The test experiment was performed to study the TSE response to a temperature rise in air and soil by 2°C in terms of the intensity of the СО2 flux. It was shown that this increase in temperature would cause a pronounced shift in the balance of СО2 production and utilization in the ecosystem from near-zero values to a stable generation of 24 μmol/h of CO2 per 1 kg of dry biomass.

Comparison of mobility of uranium and technogenic radionuclides in bottom sediments of the Yenisei River

221 The Yenisei River is one of the largest rivers in the world and has been exposed to radiation for more than 50 years due to the activity of producing weapons grade plutonium at the Mining–Chemical Factory (MCF) of ROSATOM in Zheleznogorsk [1–7]. The bottom sediments and flood plain of the Yenisei River are polluted by technogenic radionuclides including trans uranium ones near the factory and at a signifi cant distance downstream along the river. In addition to technogenic radionuclides, uranium isotopes are transported to the Yenisei River from the MCF [8]. It was demonstrated in [8] that the concentration of 238U in water of the Yenisei River and its tributaries in the zone of influence of Rosatom factories reached 4.0 μg/l, which was higher than the concentration of 238U in water upstream from the MCF (0.3–0.6 μg/l) by almost one order of magnitude. Study of the ura nium isotope composition in individual samples of water demonstrates the presence of technogenic ura nium isotope 236U, which provides evidence for the technogenic origin of part of the uranium in the river water in connection with activity of the MCF [8]. Radionuclides coming to water may be accumulated in bottom river sediments and at definite conditions may be released to water, which makes potential dan ger for hydrobionts and man through trophic chains. It was previously mentioned that uranium had high mobility in comparison with other radionuclides, but these investigations were performed mainly for the land ecosystems [9, 10]. Such comparative analysis was not performed for aqueous ecosystems. The Yenisei River basin is a unique object, in which we may investigate the mobility of both uranium isotopes and technogenic radionuclides in all links of the aqueous ecosystem.