A Quantitative Model for Estimating Mean Annual Soil Loss in Cultivated Land Using ^<137>Cs Measurements

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The radioisotope ^<137>Cs has been widely used to determine rates of cultivated soil loss, Many calibration relationships (including both empirical relationships and theoretical models) have been employed to estimate erosion rates from the amount of ^<137>Cs lost from the cultivated soil profile. However, there are important limitations which restrict the reliability of these models, which consider only the uniform distribution of ^<137>Cs in the plough layer and the depth. As a result, erosion rates they may be overestimated or underestimated. This article presents a quantitative model for the relation the amount of ^<137>Cs lost from the cultivated soil profile and the rate of soil erosion. According to a mass balance model, during the construction of this model we considered the following parameters: the remaining fraction of the surface enrichment layer (F_R), the thickness of the surface enrichment layer (H_s), the depth of the plough layer (H_p), input fraction of the total ^<137>Cs fallout deposition during a given year t(F_t), radioactive decay of ^<137>Cs (k), and sampling year (t). The simulation results showed that the amounts of erosion rates estimated using this model were very sensitive to changes in the values of the parameters F_R, H_s, and H_p. We also observed that the relationship between the rate of soil loss and ^<137>Cs depletion is neither linear nor logarithmic, and is very complex. Although the model is an improvement over existing approaches to derive calibration relationships for cultivated soil, it requires empirical information on local soil properties and the behavior of ^<137>Cs in the soil profile. There is clearly still a need for more precise information on the latter aspect and, in particular, on the retention of ^<137>Cs fallout in the top few millimeters of the soil profile and on the enrichment and depletion effects associated with soil redistribution (i.e. for determining accurate values of F_R and H_s).
社団法人日本土壌肥料学会の論文

A Quantitative Model for Estimating Mean Annual Soil Loss in Cultivated Land Using ^<137>Cs Measurements

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