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

A model was developed that predicts the amount of /sup 137/Cs 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 /sup 137/Cs, as well as seasonal differences in /sup 137/Cs deposition and erosion rates. The model was used to estimate minimum resolution of erosion estimates based on detection limits and accuracy of /sup 137/Cs measurement by gamma spectroscopy, as a function of time and erosion rate. The analysis showed that under Saskatchewan conditions, changes in /sup 137/Cs at a given site can be used to estimate erosion rates between 0.5 and 10 kg m/sup -2/ yr/sup -1/ with reasonable precision, provided the sampling interval is at least 15 yr. The relationship of fraction of /sup 137/Cs 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 /sup 137/Cs levels were measured in 1966 and again in 1981. Erosion rates calculated with the model varied from 1 kg m/sup -2/ yr/sup -1/ for a sandy loam soil in continuous forage to 19 kg m/sup -2/ yr/sup -1/ formore » 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 /sup 137/Cs loss, especially when /sup 137/Cs loss was high.« less