Assessment of Accumulation of Accelerated Erosion Products on the Bottom of a Dry Valley with a Cultivated Catchment Using Repeated Radiocesium Studies

The accumulation of sediments in the upper links of the fluvial network is one of the main pieces of evidence for the development 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 in the Chernobyl pollution areas makes it possible to estimate the intensity of accumulation over the period after its precipitation. The paper presents the experience of assessing changes in sedimentation rates in the bottom of a small dry valley with a fully plowed catchment area in the south of Tula oblast. The dynamics of deposition of soil erosion products for the periods 1986–2010 and 1986–2023. It was detected by depth incremental sampling in the bottom and determining the depth of the Chernobyl 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 there was a more intensive accumulation 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 areas of narrowing of the bottom: from 0.4–0.7 to 1.6–3 cm per year. In the lower and estuarine parts, there was no increase in the capacity of the accumulated stratum, there is a predominance of overflowing and removal of previously deposited material outside the catchment area. On average, after the Chernobyl accident, 39.9–42.3 t of sediment accumulated in the gulch annually, which is more than twice the average for the entire period of economic development of 19.3 t per year. In the future, while the observed trend will be maintained, there will be an increase in the slope of the bottom, which may lead to the activation of existing and the appearance of new bottom cuts. The experience gained has shown that repeated radiocesium studies can be an important tool for assessing long-term changes in erosion-accumulative processes and sediment balance within catchments with high anthropogenic load.