Rare Earth Element Tracer Method To Explore The Turnover Path Of Soil Aggregates In The Process Of Splash Erosion

The breakdown and buildup of soil aggregates is a very complicated process,and its stability is closely related to soil erosion process.The breakdown and buildup of soil aggregates is a completely dynamic process.The method of tracer tracing can be used to mark the soil aggregates of different particle sizes.By measuring the migration path of the tracer in the soil,the turnover process of the soil aggregates can be explored.The study found that by measuring the concentration changes of rare earth elements in various size aggregates,the migration path between different size aggregates can be well quantified,so as to study the dynamic change process of aggregate turnover,but the turnover of aggregates in the erosion process In research,this method has not been applied yet.Therefore,this paper selects Quaternary red clay,uses rare earth elements to mark soil aggregates,and then combines them into recombined aggregates of different sizes marked by different elements.The process is carried out under the conditions of different rain intensity,different rainfall time and different initial water content.Rain splash erosion test,to study the influence of different factors on the splash erosion process,and by measuring the concentration of rare earth elements in each size aggregate before and after the test,substituting it into the transfer matrix model of the aggregate,quantifying the difference in the different size aggregates The migration path in the splash erosion process,discuss the turnover path of soil aggregates in the splash erosion process.The main conclusions are as follows:(1)In the rare earth element tracing method,the wet sieving recovery rate of labeled aggregates by wet mixing method reached 91.8-105.8%,indicating that there was almost no loss of rare earth elements during the wet sieving process,and the wet sieving effectively improved the relationship between the rare earth elements and the aggregates.The binding ability between the aggregates of different sizes and the binding ability of rare earth elements is different,and the binding ability of the microaggregates of 0.053-0.25 mm with the rare earth elements is the strongest.By comparing the ratio of the predicted value to the measured value of each particle size aggregate,and the linear relationship between the measured value of MWD and the predicted value,the linear relationship is about 1:1.It can be seen that the rare earth element has a relationship between 2-5 mm and 0.25-2 mm in the experiment.The tracing effect of the four particle-size aggregates,0.053-0.25 mm,and <0.053 mm are relatively good.It quantifies the dynamic change process of turnover between different particle-size aggregates.(2)In the splash erosion test,the splash erosion rate changes with time and presents a dynamic potential of up and down waves,which has the characteristics of steep rise and fall.The main source of splashed particles is small macroaggregates of 0.25-2 mm,accounting for 86.02-98.86%.Its enrichment rate ER value greater than 1 is easy to be migrated,and the stability of large macroaggregates of 2-5 mm is not strong,and its enrichment rate varies greatly.Compared with the natural aggregates,the natural aggregates structure of the labeled aggregates is not tight,and the erosion resistance is weak.Increasing the initial water content of the labeled aggregates can make the loose particles of the labeled aggregates quickly agglomerate after being wetted,and the erosion resistance is enhanced.In the whole experiment,the measured value of MWD is mainly concentrated in the range of 0.9-0.95 mm,which is lower than the initial value of 1.02 mm of labeled aggregates,indicating that the main mechanism is the process of breaking large aggregates into smaller aggregates of different particle sizes.(3)In the study of the turnover path of aggregates,there is no path to agglomerate into 2-5 mm large macroaggregates in all experiments.During the splash erosion process,there are agglomerations to form 0.25-2 mm small macroaggregates and 0.053-0.25 mm microaggregates.In the path,12.75-30.99% of the microaggregates and 36.72-46.38% of the silt and clay sized aggregates agglomerated into small macroaggregates,and 20.08-24.94% of the silt and clay sized aggregates were agglomerated into microaggregates.In the rain test,68.81-88.24% of large macroaggregates were broken into small macroaggregates,only 4.35-6.56% and 4.89-9.15% of small macroaggregates were broken into microaggregates,and 16.2-25.16% of microaggregates broken into the silt and clay sized aggregates,increasing the rain intensity will cause the large macroaggregates to break into more and smaller aggregates,but it does not affect the agglomeration ability inside the aggregates.Under high rain intensity,there is only a broken path for the migration of aggregates in the overall flow direction.As the rainfall time increases,the large-sized aggregates will also be broken,and the overall flow direction of the migration of the aggregates will gradually become a single broken path,and the rainfall time will not affect the agglomeration ability inside the aggregates.Increasing the initial water content will have a protective effect on the aggregates,and change the overall flow direction between different particle size aggregates,effectively reduce the fragmentation of the aggregates,improve the agglomeration ability of the aggregates,and effectively reduce the 2-5 mm large macroaggregates And the fragmentation of 0.053-0.25 mm microaggregates,promote the agglomeration of 0.053-0.25 mm microaggregates and<0.053 mm silt and clay sized aggregates,and improve the agglomeration ability of the aggregates.