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Stable and radioactive isotopes are extensively used as tracers of numerous processes in the planetary and terrestrial environment. The relative abundances of isotopic species measured by their ratios provide indications of the origin of various materials and differences in the abundance ratios that develop in different processes make it possible to identify the mechanisms behind a variety of phenomena in extraterrestrial space, within the solid Earth, on its surface, and in the biosphere. The improvements in the sensitivity and precision of mass spectrometers used for the determination of isotope abundances are continually expanding the number of isotopes that can be identified in natural materials aswell as the understanding of the mechanisms that drivemany parts of the Earth’s system. The involvement of carbon dioxide in many geochemical inorganic as well as biogeochemical processes focused long ago attention on the behavior of the different isotopic species of CO and made possible many new interpretations of processes in the atmosphere, on land, in the oceanic and continental waters, and within the biosphere. The goal of this Chapter is to review the essentials of the isotope geochemistry of carbon dioxide and the mechanisms of its isotopic fractionation, and to discuss the broader aspects of the global carbon cycle that are based on the carbonisotope geochemistry.

On the basis of theoretical and experimental studies a method of assessment and prognosis of the radionuclides migration soils has been created.

Experimental methods for the determination of transfer characteristics and their assessment, and also the methods for prediction of radionuclide migration in frozen grounds should provide a clear distinction between driving forces and fluxes of the convection and diffusion transfer.

The proposed mathematical models are phenomenological and the transfer coefficients involved in these models are recommended to be determined experimentally.

The methods were developed for investigation of diffusion and convection transfer characteristics of radionuclides in thawing and frozen grounds with the allowance for the sorption by solid phase of the soils. On the basis of the experimental data obtained the information constraints for the mathematical models of the radionuclides migration in soils have been set. On the basis of researches in the field, lab test and mathematical modelling the impact of physical-chemical factors and the soil component composition changes upon the radionuclides Cs1, Sr migration and sorption in natural dispersed systems (peat, sand, bentonite, kaolin, sapropel has been investigated.

The impact of electrolytes, including compounds of Cs and Sr stable isotopes upon the radionuclides behaviour in peat soils has been made known, allowing controlling their mobility.

The forecast assessments of radionuclides migration in the peat soil (the peat deposit Pogonyanskoye, the Polessye radiation-ecology reserve) under the natural and anthropogenic factors impact had been carried out.

The landscape based GIS is an effective tool for the structuration and classification of the ecosystems, for the field experimental data collection, analysis and extrapolation, as well as the ecotoxicological parameterisation of the ecosystems and solution the regional and local ecotoxicological problems.

Safety assessment models for potential sites selected for underground repositories of high level and long-lived radioactive waste requires the prediction of phytoavailability of such radionuclides at the regional scale. In this context, the areas in which the radionuclides may be highly mobile or accumulate have to be well known, as they will contribute to a maximal dose for Man. The parameters controlling the phytoavailability of the radionuclides are mostly defined by experiments based on sieved-soil sample and a methodology is needed to extrapolate these parameters to the regional scale by taking into account the variability of the soil properties within the landscape. A mapping of three radionuclides phytoavailability (Ni, Tc and U) was conducted here using the MapInfo mapping software. The distribution frequency of the phytoavailability parameters was represented over the 186 km area of the French laboratory for the study of deep underground nuclear waste disposal, in Bure. Isotopically exchangeable pool of Ni, E and pH of the soil were the two phytoavailability parameters chosen respectively for and for U and were both measured on sieved samples coming from the soil units defined at 1 : 50 000. The redox potential, E was the parameter used for Tc and was measured in the field. For each radionuclide, class of soils were built according to their properties in term of radionuclides phytoavailability and maps of phytoavailability were drawn at 1: 25 000.

Results allowed a prediction of the phytoavailability of the Ni, Tc and U at a regional scale, based on the superimposition of the laboratory measurement of the parameters significantly controlling the mobility and the phytoavailability of the three radionuclides and knowledge of soils over the area. Critical areas were also determined where either accumulation in soils may be highest or accumulation in plants may be highest. They also allowed defining the most likely transfer parameters for the three radionuclides in the area of Bure.

The landscape based GIS is an effective tool for the structuration and classification of the ecosystems, for the field experimental data collection, analysis and extrapolation, as well as the ecotoxicological parameterisation of the ecosystems and solution the regional and local ecotoxicological problems.

On the basis of theoretical and experimental studies a method of assessment and prognosis of the radionuclides migration soils has been created.

Experimental methods for the determination of transfer characteristics and their assessment, and also the methods for prediction of radionuclide migration in frozen grounds should provide a clear distinction between driving forces and fluxes of the convection and diffusion transfer.

The proposed mathematical models are phenomenological and the transfer coefficients involved in these models are recommended to be determined experimentally.

The methods were developed for investigation of diffusion and convection transfer characteristics of radionuclides in thawing and frozen grounds with the allowance for the sorption by solid phase of the soils. On the basis of the experimental data obtained the information constraints for the mathematical models of the radionuclides migration in soils have been set. On the basis of researches in the field, lab test and mathematical modelling the impact of physical-chemical factors and the soil component composition changes upon the radionuclides Cs1, Sr migration and sorption in natural dispersed systems (peat, sand, bentonite, kaolin, sapropel has been investigated.

The impact of electrolytes, including compounds of Cs and Sr stable isotopes upon the radionuclides behaviour in peat soils has been made known, allowing controlling their mobility.

The forecast assessments of radionuclides migration in the peat soil (the peat deposit Pogonyanskoye, the Polessye radiation-ecology reserve) under the natural and anthropogenic factors impact had been carried out.

The processes of land waterlogging, bank erosion and soil salination and alkalisation take place on the coastal landscapes of Kyiv, Kaniv and Kremenchuk reservoirs. We identified some regions on these reservoirs coast according to the intensity and peculiarities of such processes.

An important environmental characteristic of landscapes on Kyiv and Kaniv reservoirs coast is their pollution by nuclear wastes. The radionuclides (Cs) have penetrated into the soil profile to the depth 15–25 cm, but their predominant part is concentrated in sods, forest litter and the upper 7-10-cm layer of soil. On elevated banks the nuclear wastes are subject to surface erosion while on low banks is a slight accumulation of radionuclides in the capillary fringe of soils waterlogged by seepage waters.

Thus, our studies allowed us to estimate correctly the changes induced by radioactive contamination caused by Chernobyl nuclear accident at the level of soil invertebrate communities and to reveal the pattern of their disturbance under constant radiological pressure. All evidence shows that soil mezofauna complexes in different biogeocenoses exposed to irradiation for a long time react clearly by a noticeable suppression. It is concluded from the results that the haematological characteristics can serve as convenient bioindicators of the radioactive contamination in the biogeocenoses. Percentages of all cell types observed and their structural changes may be recommended as criteria for comparison.

The way of multidimensional ecological scaling is developed. Within the framework of this procedure the ecological monitoring multidimensional data are converted into Ecosystem Index (EI). (This may be considered as a model of “ecological thermometer”).

This method is based on the following procedures: reduction of the dimensionality of monitoring data, discrimination, clusterisation, classification and multiple regression.

The scaling factors for ecological scale are introduced in terms of Multidimensional Reference Ecological Images, which are assigned by experts.

The state of the ecosystem is reflected on the scale by value EI which may be interpreted as Ecological Risk.

The evolution of the ecosystem position along scale may be used for decisionmaking. The method is demonstrated in two examples: contamination of several ecological chains by single radionuclide and contamination of single chain (soil) by several radionuclides.