Using 137Cs tracer technique to evaluate erosion and deposition of black soil in Northeast China

Soil and water losses through erosion have been serious in the black soil region of Northeast China. Therefore, a sloping cultivated land in Songnen Plain was selected as a case study to: 1) determine the Cs-137 reference inventory in the study area; 2) calculate erosion and deposition rates of black soil on different slope locations; 3) conduct a sensitivity analysis of some model parameters; and 4) compare overall outputs using four different models. Three transects were set in the field with five slope locations for each transect, including summit, shoulder-slope, back-slope, foot-slope, and toe-slope. Field measurements and model simulation were used to estimate a bomb-derived Cs-137 reference inventory in the study area. Soil erosion and deposition rates were estimated using four Cs-137 models and percentage of Cs-137 loss/gain. The Cs-137 reference value in the study area was 2232.8 Bq m(-2) with Cs-137 showing a clear topographic pattern, decreasing from the summit to shoulder-slope, then increasing again at the foot-slope and reaching a maximum at the toe-slope. Predicted soil redistribution rates for different slope locations varied. Among models, the Yang Model (YANG-M) overestimated erosion loss but underestimated deposition. However, the standard mass balance model (MBM1) gave predictions similar to a mass balance model incorporating soil movement by tillage (MBM2). Sensitivity analysis of the proportion factor gamma and distribution pattern of Cs-137 in the surface layer demonstrated the impact of Cs-137 enrichment on calculation of the soil erosion rate. Factors influencing the redistribution of fallout Cs-137 in landscape should be fully considered as calculating soil redistribution rate using Cs-137 technique.