| Soil erosion and its causing soil quality degradation are one of the critical environmental problems in the world, especially on Loess Plateau in China. The study of soil erosion law has an important significance for ecology system construction and reconvertion. However, there are some difficulties to study soil erosion processes in details by the traditional monitoring techniques because of itself limitation. The nuclear tracer technology applied in studies on soil erosion has been taken attention to studying some laws of soil erosion because of its particular advantage. The methods of sampling, experiment in field, analysis in laboratory was discussed in this paper. The research includes study of some characteristics of Cs-. 210Pbe,cand 7Be in soil, and the way of using them to trace some erosion laws. Many results are very important. 1. It is the first to study the distribution of ?7Cs.% 210Pbex in soil particles and the compositive changes of soil grain when they were delivered on the different slopes and main gully. The results show that the amounts of Cs and 210Pbex are highest in soil clay and adsorbed by clay mainly. In addition, the soil grains were delivered on the different slopes, the different soil particles can not be selective to deliver out of the plot at least in SUm long slope. But it is obvious selective when flood carry sediment in main gully, so the data need to revise if the Cs amounts in flood sediment will be used to calculate erosion amounts in studied watershed. 2. The spatial distribution patterns of soil erosion and deposition in a small watershed on Loess Plateau was studied systematically by using Cs tracer, which can offer scientific evidence for small watershed management. The contents of Cs in 198 soil profiles are analyzed. The sampling sites are located in a small watershed with a total area about 0.17km2. The results show that the contents among the profiles vary with different landforms sampled. These offer scientific evidences for soil erosion and deposition. In addition, the Cs content distribution in the small watershed was mapped by using the surface analysis. And the soil erosion modulus at each sampling sites is calculated according to a series models, and then the erosion intensity in the watershed are graded and mapped, which successfully demonstrates the potential for using 憮Cs as a tracer to study spatial distribution of soil erosion and deposition. In addition, the sediment in the studied small watershed came from the gully slope mainly, occupying 72.4% of the total amount sediment in the watershed. 3. It is the first to study soil erosion processes quantitatively on cultivated slope in the world by using and Cs as tracers and the data from the experiment are used to discuss the interrill erodibility in WEPP. Based on the different distribution of e and Cs in soil profiles, simulation rainfall was employed to study erosion processes in this research. The results show that e concentrations in sediment are obviously to reflect the sheet erosion on the slope, and the amounts of sheet erosion and nIl erosion can be calculated with time by using the distribution characteristic of e and Cs. The total sheet erosion amounts are increasing, however, ru erosion became dominant erosion style with time and trended to activate. In addition, based on the traditional method, the ru volume w...
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