Predicting the Temporal Relationship between Soil Cesium‐137 and Erosion Rate

Abstract

A model was developed that predicts the amount of ¹³⁷Cs remaining in soil as a function of time and erosion rate. The model accounts for atmospheric deposition, radioactive decay, tillage dilution, and erosion transport of ¹³⁷Cs, as well as seasonal differences in ¹³⁷Cs deposition and erosion rates. The model was used to estimate minimum resolution of erosion estimates based on detection limits and accuracy of ¹³⁷Cs measurement by gamma spectroscopy, as a function of time and erosion rate. The analysis showed that under Saskatchewan conditions, changes in ¹³⁷Cs at a given site can be used to estimate erosion rates between 0.5 and 10 kg m⁻² yr⁻¹ with reasonable precision, provided the sampling interval is at least 15 yr. The relationship of fraction of ¹³⁷Cs lost vs. erosion as predicted by the model was compared with other methods being used. The model was used to estimate erosion from selected Saskatchewan soils where ¹³⁷Cs levels were measured in 1966 and again in 1981. Erosion rates calculated with the model varied from 1 kg m⁻² yr⁻¹ for a sandy loam soil in continuous forage to 19 kg m⁻² yr⁻¹ for a similar soil in a crop‐fallow rotation. Erosion estimates using the model were higher than those calculated by assuming that soil loss was directly proportional to ¹³⁷Cs loss, especially when ¹³⁷Cs loss was high.