Features of 137Cs distribution and dynamics in the main soils of the steppe zone in the southern European Russia

Data are presented on the concentration and vertical distribution of the artificial isotope Cs-137 in soils (chestnut soils, chernozems, solonetzs, solonchaks, meadow soils and alluvial soils) of the steppe zone in the southern Russia. The work has been focused on the study of radiocesium distribution in undisturbed virgin lands. It has been shown that the mean concentration of the radionuclide in the upper (0 to 15 cm) soil layer is 20.5 Bq/kg. The proportions of adsorbed Cs-137 in the soils increase with increasing humus content and decreasing pH level. Two types of the profile distribution of radiocesium were distinguished: (1) with the maximum concentration in the upper soil layer and a relatively abrupt decrease with depth (the majority of Cs-137 is concentrated in the upper 0 to 15 cm soil layer) and (2) with the maximum concentration of Cs-137 shifted into the soil profile down to a depth of 45-55 cm. This difference is related to the soil type, humus content, pH value, and regional climatic conditions. Long-term (2000-2013) studies of the vertical distribution of Cs-137 in soil profiles have revealed a decrease in its total activity by 1.5 to 2.0 times. It has been shown that the migration of radiocesium in soil profiles depends on the soil type and the diffusion of the radionuclide itself, as well as on convective transfer, transpiration, infiltration, and colmatage. (C) 2015 Elsevier B.V. All rights reserved.