First application of plutonium in soil erosion research on terraces

The spatial distributions of 239+240 Pu and 137 Cs in soils from Longji Rice Terraces were investigated to evaluate soil erosion. The activity concentrations of 239+240 Pu and 137 Cs in the surface soils of the paddy fields were in the range of 0.089–0.734 and 1.80–7.88 mBq/g, respectively. The activities of 239+240 Pu and 137 Cs showed very similar distribution trends, first increasing and then decreasing with increasing elevation. The 240 Pu/ 239 Pu atom ratios in the surface soils ranged from 0.162 to 0.232. The activities of 239+240 Pu and 137 Cs in the soil cores tended to be uniformly distributed within the plowed layer and declined exponentially below this depth. The mean soil erosion rates of Longji Rice Terraces estimated by 239+240 Pu and 137 Cs tracer methods were 5.44 t/(ha·a) and 5.16 t/(ha·a), respectively, which demonstrated that plutonium can replace 137 Cs as an ideal tracer for soil erosion research in the future. Landform features are the main factors affecting the distribution of plutonium and 137 Cs as well as soil erosion in the Longji Rice Terraces.