*3.5.2 210Pbex tracer method*

According to Li *et al.* [34], the 210Pbex tracer method can distinguish the changes in atmospheric particles and human causes of trace elements, the reconstruction of pollution sources, and the history of river deposition and erosion in the past 100 years. However, its limitations include complex sample processing, high accuracy requirements, and difficulty in obtaining the flux of deposition for a particular year. In future, development of this technique is to further improve the quantitative relationship between the amounts of 210Pbex loss and soil erosion. Its combination with other tracers and models is also likely.

#### *3.5.3 7 Beryllium tracer method*

Li *et al.* [34] observed that this method can be applied to evaluate soil erosion under a particular intensity of land use, thereby providing an important basis for the monitoring and control of soil erosion. However, the application of 7 Be tracing still has some problems. For example, the shallowness of 7 Be distribution complicates sampling. It is, however, important to recognize that the use of 7 Be measurements is best suited to situations where significant erosion events are separated by 5 months in order to minimize the effect of previous erosion [39]. Since 7 Be could reflect the effects of soil erosion factors. Therefore, the scope of applications of the 7 Be tracer method can be broadened to explore the comprehensive effect on specific small watersheds based on the hydrological and meteorological conditions of soil erosion [34].
