The use of a numerical mass-balance model to estimate rates of soil redistribution on uncultivated land from 137Cs measurements

A numerical mass-balance model is developed which can be used to estimate rates of soil redistribution on uncultivated land from measurements of bomb-derived Cs-137 inventories. The model uses a budgeting approach, which takes account of temporal variations in atmospheric fallout of Cs-137, radioactive decay, and net gains or losses of Cs-137 due to erosion and deposition processes, combined with parameters which describe internal Cs-137 redistribution processes, to estimate the Cs-137 content of topsoil and the Cs-137 inventory at specific points, from the start of Cs-137 fallout in the 1950s to the present clay. The model is also able to account for. potential differences in particle size composition and organic matter content between mobilised soil particles and the original soil, and the effect that these may have on Cs-137 concentrations and inventor ies. By running the model for a range of soil erosion and deposition rates, a calibration relationship can be constructed which relates the Cs-137 inventory at a sampling point to the average net soil loss or gain at that location. In addition to the magnitude and temporal distribution of the Cs-137 atmospheric fallout flux, the soil redistribution rates estimated by the model are sensitive to parameters which describe the relative texture and organic matter content of the eroded or deposited material, and the ability of the soil to retain Cs-137 in the upper part of the soil profile. (C) 1998 Elsevier Science Ltd. All rights reserved.