Improved Models for Estimating Soil Erosion Rates from Cesium‐137 Measurements

Fallout cesium‐137 ( 137 Cs) measurements have been used in investigations of water‐induced soil erosion in a wide range of environments and in many different areas of the world over the past 20 yr. However, the existing calibration procedures commonly used for deriving quantitative estimates of soil redistribution rates from 137 Cs measurements involve several limitations and uncertainties. Existing approaches to calibration and their associated limitations and uncertainties are briefly reviewed and improved models for converting 137 Cs measurements to estimates of rates of water‐ and tillage‐induced soil redistribution, applicable to both cultivated and undisturbed soils, are proposed. Results obtained from existing field investigations and laboratory experiments indicate that redistribution of fallout 137 Cs within the soil profile and across the land surface is influenced by several factors. These include time‐dependent fallout input, initial distribution within the surface layer, post‐depositional redistribution resulting from mechanical, physical, chemical, and biological processes operating in the soil system and the grain size selectivity associated with soil erosion and sediment transport processes. It is important to consider these factors when deriving estimates of soil redistribution rates using the 137 Cs technique, and they have been incorporated into the improved models. The use of these models is demonstrated using data from a case study undertaken in a small catchment in Devon, UK, involving both cultivated and undisturbed soils.