Some features of the radiocaesium method applied to study of soil losses due to erosion on the periglacial area of the Upper Oka basin

In our study, we consider features the application of caesium-137 to the assess soil losses on an arable slope located in the periglacial zone of the Russian Plain. The study is conducted on the example of an experimental area (an agricultural field in the basin of the Sukhaya Orlitsa River, upper Oka basin within the Oryol region). We discuss the expediency of the polygonal-block structures (located at the paleocryogenic origin watershed surface) accounting when establishing a background value of caesium-137. The specific activity of caesium-137 acts as an indicator of washout degree of soils. We assessed the values of the coefficients of variation for caesium-137 radioactivity using set of soil samples collected along two transects (#114 and #91224) on the watershed surface (86 samples). The coefficients of variation are small (up to 0.12). We prove that the statistical evaluation of the caesium-137 variability have not be a basis when establishing background value of caesium-137 radioactivity. Our study shows that it is necessary to estimate the background value at block elevations where the soil profile has a plow sole at the depth of the arable horizon (caesium-137 radioactivity sharp decrease is observed directly below arable horizon). We compare also the results of caesium-137 specific activity estimations (made at three locations at block elevations of watershed surface, where layer-by-layer soil sampling was conducted) and the average radioactivity estimated at 86 locations (on transects #114 and #91224). We show that the average caesium-137 radioactivity (estimated at 86 locations) being taken as a background radioactivity value leads to underestimation of the soil loss intensity is by ~7.3 tons per 1 hectare per year. We conclude that the specific activity in the experimental area should be estimated basing on layerby-layer soil samples collected at block elevations (despite the low variability caesium-137 radioactivity values in a set of 86 sample). 

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