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Abstract: The “biosphere–climate” system is subjected to different influences (influx of anthropogenic CO2 and pollutants, deforestation, harmful land management, biological species depopulation, etc.). Therefore, the vital question arises: “Can these influences lead to irreversible negative changes in the climate–biosphere system or a global ecological catastrophe?” The possibility of irreversible changes may be not very high, but one cannot ignore it. So the main aim of our investigation is to evaluate possible consequences of human impact on the biosphere focusing on irreversible changes of it. Traditional mathematical complicated models describe the biosphere in great detail, but the large number of equations and parameters leads to accumulation of uncertainties in the forecast due to inevitable uncertainties of experimental estimations of model parameters. An approach based on the principle of the worst scenario was proposed. Minimization of mathematical model with respect to this principle is conducted to study limiting (but possible) versions of models in which the contribution of the possible compensatory and smoothing mechanisms is minimal. Namely the most unfavorable scenarios (corresponding to the values of parameters at the boundaries of confidence interval) have to be considered in estimating consequences of anthropogenic impact. One of the fastest CO2 releasing mechanisms, based on the positive feedback effect, was considered in the context of the worst scenario principle. The family of simple mathematical models was created for biosphere dynamics representation on different timescales. The main result of the investigation consists in confirmation of the possibility of negative and irreversible changes in the “biosphere–climate” system, caused by amplification of the positive feedback: “anthropogenic emission of CO2 – temperature increase – additional CO2 emission due to decomposition of soil organics”. Crucial parameters of models, responsible for avalanche-like biosphere changes, are determined. A realizability of hypotheses on anthropogenic causes of Little Ice Age was estimated by corresponding minimal model. Model were used to show the feasibility of the mechanism describing the changing of agricultural field species into indigenous forests in Europe during the Plague, which led to CO2 decrease and temperature fall. [Copyright &y& Elsevier]

The purpose of the study was to compare quantitative analysis methods used in the early stages of closed-loop system prototyping with modern data analysis approaches. As an example, a mathematical model of the stable coexistence of two microalgae in a mixed flow culture, proposed by Bolsunovsky and Degermendzhi in 1982, is considered. The model is built on the basis of a detailed theoretical description of the interaction between species and substrate (in this case, illumination). The ability to control the species ratio allows you to adjust the assimilation quotient (AQ), that is, the ratio of carbon dioxide absorbed to oxygen released. The problem of controlling the assimilation coefficient of a life support system is still relevant; in modern works, microalgae are considered as promising oxygen generators. At the same time, modern works place emphasis on empirical modeling methods, in particular, on the analysis of big data, and the work does not go beyond the task of managing a monoculture of microalgae. In our work, we pay attention to three results that, in our opinion, successfully complement modern methods. Firstly, the model allows the use of results from experiments with monocultures. Secondly, the model predicts the transformation of data into a form convenient for further analysis, including for calculating AQ. Thirdly, the model allows us to guarantee the stability of the resulting approximation and further refine the solution by small corrections using empirical methods., Competing Interests: The authors declare no conflict of interest., (Copyright © AUTHORS.)

A short survey and 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 regulating factors. The new control criterion is expressed as a product of the factor transformation coefficient and the biomass sensitivity coefficient (SC) with respect to the change of the factor at the chemostat inlet (referred to in the sequel as the biomass SC). The control criterion determines the strength of the control exerted by this or that factor. The method of determination of the regulating factors consists in experimental determination of the real SCs for factors and the biomass and in calculating on this basis the corresponding ideal SCs for constant factor transformation coefficients. The ideal SCs are shown to add up to an integer value, a constraint that we call "quantization" relationships. Such relationships are used to test the completeness of the drawn list of control factors. The proposed method was applied to our own and literature data.

A one-dimensional mathematical model of the Yenisei river ecosystem including hydrological, ecosystem and radioecological blocks has been developed. The model was used to evaluate contribution of different processes (transfer by water masses, dilution, radioactive decay, bioaccumulation) into self-purification of the river water from a radiation pollution and calculate pollution density of ecosystem components (bacteria, phyto-, zooplankton, phyto-, zoobenthos, detritus) with 137Cs and 32P.

The aim of the paper is to investigate accumulation of artificial radionuclides by the Yenisei River aquatic plants collected in the area affected by the activity of the Mining-and-Chemical Combine (Zheleznogorsk) from 1997 to 2000. The samples of aquatic plants were of four species: Potamogeton lucens, Fontinalis antipyretica, Elodea canadensis, and Ceratophyllum demersum. The gamma-spectrometric analysis of the samples of aquatic plants for artificial radionuclides revealed a wide spectrum of long-half-life and short-half-life radionuclides. Radionuclides of activation origin were found in the aquatic plants taken both near the Combine and 200 km down of it. The data obtained suggest that the cooling water of the operating reactor is still being released into the Yenisei. The radiochemical analysis of aquatic plants revealed strontium and plutonium isotopes. Among the aquatic plants, the highest concentration factors for the principal radionuclides were recorded in Fontinalis antipyretica (water moss).

The feedback level (FBL) in growth regulation has been determined in the experiments on Escherichia coli O-124 on the basis of the theory developed by Degermendzhy et al (1989). FBL is here determined as a function of variations in growth acceleration caused by discrete decrease in bacterium concentration, the medium chemical composition being preserved. It estimates by integration regular action of all chemical density factors. FBL has been determined on periodic cultivation with glucose. In various phases of growth the native culture was diluted with a filtrate of its own. As the sample had grown up, variations in growth acceleration were calculated against the reference specimens. The value of FBL was definitely anything but zero at the end of the experimental phase and in the phase of growth deceleration, and it was equal to -20 divided by -200 (h.g/l). The feedback component was also calculated from the obtained dependence of the growth rate on the glucose concentration. It amounted to mumax = 0.55 +/- 0.05 h-1, Ks = 2.5 +/- 0.7 mg/l. Regulation relative to glucose was 0.5-40% of FBL. This indicates that there are other regulators of growth. Being sufficiently accurate, the new method may supplement microbiological means of determining the growth regulating cell-density factors.

The models of evolution of Eigen's hypercycles and microbial populations were compared. It has been proved that both above mentioned model descriptions of evolution completely coincide for the case of support constant organization (1). It has been shown that in the case of constant flows (2) for the Eigen's model it is necessary to take into account the dynamics of concentration of energy monomers. The experimental results of microevolution of microbial populations for conditions 1 and 2 are presented.