ИСТИНА

On the territory of Central Russia, the most detailed studies on sediment budget and redistribution of particulate Cs-137 were carried out in the basin of the Upa River. Recently the major part of sediments eroded from arable lands re-deposited either within cultivated slopes or in the upper reaches of the fluvial network (slope hollows and bottoms of dry valleys) due to serious decreasing of erosion during snow-melting in European part of Russia. Decades a re-sampling technique applied with bomb-derived Cs-137 fallout is widely used method to assess soil redistribution rates within cultivated fields. But it requires long-time periods to be successfully implemented. The given approach hasn't been used in areas with high level of Chernobyl-derived Cs initial fallout. The results of the first experience of re-sampling study within the small agricultural catchment within the Upa river basin in Tula region are presented. Statistically reliable changes in the Cs-137 deposits for time window 1997 - 2023 were identified for the studied cultivated catchment. The mean decrease in Cs-137 deposits is about 11% for 26 years. Assessed changes in Cs-137 deposits was used in soil erosion radiocesium conversion model. The result is consistent with USLE and WaTEM/SEDEM models. The concentration of Cs-137 in sediments re-deposited in dry valley bottoms during the post-Chernobyl period experienced a sharp decrease in the first years after Chernobyl-derived Cs-137 initial fallout and then remains relatively stable with a smooth downward trend. As it was learned earlier from examination of bottom sediments in artificial reservoir rapid decrease of particulate Cs-137 concentration in sediment yield. The leading factors of such decrease was effective remediation measures and changes in sediment budget components. The study was conducted within the framework of project of RSF № 23-77-10045.