Mathematical model of 137Cs migration in agricultural landscapes of Ukrainian Polissia in the remote period after the Chornobyl accident

Abstract

The aim of the work was to develop a mathematical model for the radionuclide carryover from Polissia agrolandscapes. The mathematical model was developed to reflect the radioecological situation in a limited area, the center of which is a relatively small settlement (urbanised area, village or hamlet). The conceptual scheme of the mathematical model was presented by four blocks (ecosystems or sub-landscapes), namely the block «Forest ecosystem», «Field ecosystem», «Meadow ecosystem» and «Orchard ecosystem». The model takes into account the following basic processes that affect the redistribution of 137Cs by ecosystems, depending on the ecosystem type: interception, weathering, absorption, tillage, fertilization, irrigation, organic residues decomposition, radionuclide washing out towards lower soil layers, diffusion, radionuclide fixation by soil minerals. The main differences of the created model in comparison with the existing ones are: the use of current indicators of the 137Cs soil-to-plant transition, taking into account anthropogenic effects on agroecosystems, in particular radiation countermeasures, taking into account orchard ecosystems. The mathematical model is formalized as a system of first-order linear differential equation system with fixed factors. The computer implementation of the model was performed in the mathematical package MAPLE (version 10). It was found that the 137Cs content is reducing in all ecosystems. The radionuclide removal depends on the ecosystem type, its exploitation degree, soil conditions and the complex of implemented radiation countermeasures.It was found that providing the implementation of the optimal system of radiation countermeasures and under condition of active ecosystems exploitation, all the modeled ecosystems form the following descending series of radionuclide removal: forest ecosystems — hayfields and pastures (in some cases vegetable areas) — field ecosystems (mainly cereals and legumes) — orchard ecosystems.