Accumulation of accelerated erosion products in the bottom of a small dry valley (balka) with cultivated catchment using the radiocesium studies

Accumulation of sediments in the upper sections of a fluvial network is among the main evidences of accelerated erosion on the slopes during the period of agricultural use of the catchment area. The study of the vertical distribution of technogenic 137Cs within the Chernobyl-induced pollution areas makes it possible to estimate the intensity of accumulation over the period after its fallout. The paper presents an attempt of assessing changes in sedimentation rates in the bottom of a small dry valley (balka) with totally plowed catchment area in the southern Tula region. The dynamics of deposition of soil erosion products was identified for the periods 1986-2010 and 1986-2023 by repeated layer-by-layer sampling in the bottom and determining the depth of the Chernobyl-induced peak of 137Cs concentration. Manual drilling was also carried out in the valley floor to determine the thickness of agrogenic sediments that began to accumulate since the end of the 17th century. The results of the study showed that in the post-Chernobyl stage the accumulation was more intensive in comparison with the entire period of agricultural use. The sedimentation process is characterized by significant spatial and temporal heterogeneity. An increase in the rate of accumulation is observed in the upper reaches of the valley and in the bottom narrowings (from 0,4-0,7 to 1,6-3 cm per year). No increase in the depth of the accumulated stratum was recorded in the lower and estuary parts; there is a predominance of overflowing and removal of previously deposited material away from the catchment area. On the average, 39,9-42,3 tons of sediment accumulated in the balka annually after the Chernobyl accident, which is more than twice the average for the entire period of economic development (19,3 tons per year). In the future, while maintaining the observed trend, the slope of the bottom will become steeper, thus activating the existing bottom cuts and producing new ones. The experience gained has shown that repeated radiocesium studies could be an important tool for assessing long-term changes in erosion-accumulative processes and sediment balance within catchments with high anthropogenic load.