| It is very important to study soil erosion process and erosion dynamics on the loess slope, and it may influence the building of soil erosion prediction model. But because of the complexities of problems, the limitations of study methods, it is need more study on the soil erosion process of the Loess Plateau, especially on quantitatively analyzing the changing of different erosion types.In the paper, we mostly studied the change of soil erosion process by a new REE tracer method, based on the theories of hydraulic mechanical subject and radionuclear tracer method, and simulated rainfall was applied to study the sheet erosion changing to rill erosion and the rill erosion process on slope land. The new REE tracer method should be useful to future studying of erosion processes on slope lands.1. Offering and testifying a new REE displacing method to study on the soil erosion of the loess slope.Based on the problems of the change of erosion types on the slope, we used a new REE tracer method, by placing different rare earth elements of different soil depth across a slope in an indoor plot, simulated rainfall and INAA were applied to study sheet erosion changing to rill erosion on slope land. Experimental results showed that the precision of new method was less than ?0% for the tracing elements. The accuracy may be elevated to ?0% when considering the REE contents in the water.2. Studying on the change of sediment rate and erosion rate with the rainfalls time.In the experiment, the change of sediment rate and erosion rate were divided into the gradually increasing stage, rapidly increasing stage and remaining stable stage with the rainfalls time. The change curves fitted Logistic model with a high accuracy. The experimental results indicated that the erosion type was sheet erosion and splash erosion firstly after 10 minutes of rainfalls. Different REE tracers were measured successively in sediment samples. The change of erosion type, and the rill development were understood from the analyzed of REE tracers in the sediment samples.3. Quantitatively studying on the change of accumulated sheet and rill erosion amounts.Sheet erosion rate firstly gradually increased, then rapidly increased and finally remained stable with the rainfalls time, but the rill erosion rate increased more quickly than sheet erosion rate and the value of rill erosion rate was higher than of sheet erosionrate. Besides, when the experimental soil was clay soil of Yangling, the appearance and developing process of rill erosion happened respectively 12-15min and 4-8min earlier than of silt soil of Shaanbei.Accumulated sheet and rill erosion amounts increased with the rainfalls time, and the latter increased quickly than the earlier. The total accumulated rill erosion amounts were 2.5 and 5.5 times more than accumulated sheet erosion amounts. The rill erosion amount contributed 80% to the total erosion amount on the slope.4. Discussing the different stages of soil erosion process on the loess slope.The soil erosion process on the slope was clearly divided into sheet erosion stage, rill erosion developing stage and rill erosion stable stage. Before lOminutes of rainfalls, the percentage of sheet erosion amount to total erosion amount was more than 90%, and it indicated that sheet erosion happened on the slope. This percentage sharply decreased before SOminutes of rainfall time, on the other hand, the percentage of rill erosion amount to total erosion amount increased in curve form with rainfall time. At the end of rainfall, the changes of both of them remained stable. The results were useful to build soil erosion prediction model on the slope.5. Studying the change of slope runoff amount with the rainfalls time.In the experiment, the change of slope runoff amount with rainfall time presented that the slope runoff amount increased rapidly at the beginning of rainfall, and it slowly increased to reach relative stable with the rainfalls time. |
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