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

- The mean activity concentration of 137Cs in soils of the southern European Russia is 20.5 Bq/kg.
- The higher the content of humus in the soil and the lower its pH value, the higher the proportion of adsorbed 137Cs.
- The maximum 137Cs activity concentration is recorded in the upper 0- to 3-cm soil layer.
- The total 137Cs activity in the steppe soils decreases with time by 1.5-2.0 times.

Data are presented on the concentration and vertical distribution of the artificial isotope 137Cs 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 137Cs 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 137Cs is concentrated in the upper 0 to 15 cm soil layer) and (2) with the maximum concentration of 137Cs 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 137Cs 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.