Spatial and vertical distribution of Cs-137 in soils in the erosive area of southeastern Serbia (Pinja and South Morava River Basins)

Abstract

The area of southeastern Serbia, the Pinja and South Morava River Basins, is under the influence of very strong erosion, and the aim of this study was to investigate the vertical and spatial distribution of the Cs-137 in the eroded soils of this area. Vertical soil profiles were collected with 5-cm increments from the uppermost layer down to 20, 25, 30, 40, and 50 cm of depth, depending on the thickness of the soil layers, i.e., down to the underlying parent rocks. Measurements of Cs-137 activity concentration were performed by using the HPGe gamma-ray spectrometer ORTEC-AMETEK (34 % relative efficiency and high resolution 1.65 keV at 1.33 MeV for Co-60), from its gamma-ray line at 661.2 keV. The mean Cs-137 activity concentration across all 18 soil profiles (for all soil layers) was found to be 20 Bq kg(-1). In the greatest number of soil profiles, the Cs-137 activity concentration was generally highest in the first soil layer (0-5 cm) and decreased with soil depth, while in a few soil profiles, the peak of either the Cs-137 activity concentration occurred in the second soil layer (5-10 cm) or the Cs-137 activity concentration was almost equal throughout the entire soil profile. The mean Cs-137 activity concentration in the first soil layer (0-5 cm) was found to be 61 Bq kg(-1), and the high coefficient of variation of 92 % pointed out high spatial variability and large range of the Cs-137 activity concentrations in the study area. The obtained results indicate that in the greatest number of soil profiles, Cs-137 is present in the upper layers, with concentration decreasing with depth, as is typical in uncultivated soil. Its spatial distribution was very uneven among the surface soil layers of the investigated sites. One of the main reasons for such pattern of Cs-137 in the study area may be soil erosion. Additional investigations which would support this hypothesis are required.