Concentrations of Radionuclides (226Ra, 232Th, 40K, and 137Cs) in Chernozems of Volgograd Oblast Sampled in Different Years

Data on the concentrations of natural (²²⁶Ra, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides and on the physicochemical properties of chernozems sampled in different years are presented. In 1952, upon the creation of the Penza-Kamensk state shelterbelt, three deep (up to 3 m) soil pits were examined within the former arable field under two-year-old plantations of ash and maple along the transect crossing the territory of the Beloprudskaya Experimental Station of the USSR Academy of Sciences in Volgograd oblast. The samples from these pits were included into the collection of dated soil samples of the Dokuchaev Central Soil Science Museum. Five pits were examined along the same transect in 2009: three pits under shelterbelts (analogues of the pits studied in 1952) and two pits on arable fields between the shelterbelts. In the past 57 years, certain changes took place in the soil structure, bulk density, and the content and composition of humus. The salt profile of soils changed significantly under the forests. The comparison of distribution patterns of natural soil radionuclides in 1952 and 2009 demonstrated their higher contents at the depth of 10–20 cm in 2009 (except for the western shelterbelt). Background concentrations of natural radionuclides in parent materials and relationships between their distributions and the salt profiles of soils have been determined; they are most clearly observed is the soils under shelterbelts. Insignificant contamination with ¹³⁷Cs (up to 34 Bq/kg) has been found in the samples of 2009 from the upper (0–20 cm) horizon. The activity of ¹³⁷Cs regularly decreases from the east to the west; the highest concentrations of this radionuclide are found in the topmost 10 cm. This allows us to suppose that ¹³⁷Cs was brought with aerial dust by eastern winds, and the shelterbelts served as barriers to the wind flow.