Quantification of the sediment budget of a river basin, based on reconstruction of the post-fallout redistribution of Chernobyl particle-bound $^{137}$Cs

Abstract : Quantitative assessment of the sediment budget of a fluvial system is a key approach to understanding its geomorphic behaviour and an essential tool for investigating the redistribution of particle-bound contaminants along the sediment cascade. Here, we present a study involving the application of several independent approaches for quantifying the post-fallout (1986-2009) redistribution of Chernobyl particle-bound $^{137}$Cs and the basin-scale sediment budget for the River Plava basin situated in the northern part of the Srednerusskaya Upland (Central European Russia). The techniques employed include $^{137}$Cs-based sediment tracing, two soil erosion models and the analysis of soil profile morphology. The results show that most of the sediment originating from human-accelerated soil erosion on cultivated slopes is redeposited on the uncultivated lower parts of the slopes or in the bottoms of infilled gullies, hollows and 1-3rd order valleys. The River Plava valley itself represents a system dominated by efficient transport, with very limited floodplain sediment storage. The $^{137}$Cs-contaminated sediment export from the River Plava basin outlet exerts a significant impact on the River Upa. Its floodplain sediment contamination by $^{137}$Cs downstream of the River Plava mouth increases by almost an order of magnitude.