Fallout 137Cs and natural 40K as tracers of topsoil development during slope processes — a case study from the Daugai environs, Southern Lithuania

Investigations of soil erosion by 137Cs method brings uncertainties of different nature. The estimation of the 137Cs local inventory is associated with problems of data comparison and instrumental errors. In order to avoid systematic errors, the rate of soil erosion determined by the 137Cs method is compared with the values obtained for other radioactive elements. Soil parameters must be regarded too. The aim of the work was to test the character of 137Cs and 40K distribution in the topsoil vertical section for determination erosion-accumulation type and ratio in different time spans. The topsoil thickened by different types of erosion-accumulation processes was sampled at a 2–3 cm interval. Soil samples were analysed by means of scintillation gamma spectrometry. The relationship between 137Cs and 40K inventories was weakest in the topsoil formed by mixing of soil material during the installation of artificial drains. Based on climatic characteristics, variations of theoretical soil accumulation rate in the last 50 years were calculated for the topsoil accumulated predominantly by water erosion. 40K and 137Cs correlation in the bottom of vertical section of topsoil or arable horizon are closest and this section may be used as a complementary parameter determining the local inventory value.