Caesium-137 fallout depth distribution in different soil profiles and significance for estimating soil erosion rate

Abstract

Caesium-137 (137Cs) has been widely used for the determination of soil erosion and sediment transport rate. However, depth distribution patterns of 137Cs in the soil profile have not been considered. As a result, the erosion rates may be over-estimated or underestimated. This paper presents the depth distribution of 137Cs fallout in different soil profiles using published data. Three types of depth distribution functions of 137Cs are given by using statistical regression methods, the exponential type, the peak type and the decreasing type (including uniform distribution). Relationships between 137Cs loss and soil erosion rate are given by introducing the regression functions. The influence of depth distribution of 137Cs on the estimation of the soil erosion rate was simulated. Simulation results showed that very different soil erosion rates could be deduced for different depth distributions when 137Cs loss is the same, which indicates that the depth distribution pattern should be considered when soil erosion is estimated by using 137Cs. Simulation results also suggested that it is most important to determine the depth distribution of 137Cs near the soil surface and the annual relative loss of 137Cs by using the depth distribution of 137Cs as a criterion to estimate the soil erosion rate.