| China is one of the countries with more serious soil erosion.Serious soil erosion not only destroy cultivated land,resulting in soil quality and fertility decline,but also lead to river sediment deposition and eutrophication of water bodies,and further causing adverse effects on agriculture and ecological environment and economic development.The Loess Plateau is the main soil erosion area in China.Water erosion is the main form of erosion in this area,which accounts for about 33%of the total area of the Loess Plateau.Splash erosion is the key step of rainfall erosion,which is mainly divided into aggregate breakdown and fine particles migration.After the soil aggregates are broken into fine particles,on the one hand,the released fine particles are splashed and moved away by the water;on the other hand,the released fine particles can clog soil pores and result in surface sealing,decrease soil infiltration and increase runoff.At present,the studies about splash erosion in the Loess Plateau are mostly focused on external forces（such as raindrop impact forces,shear strength of flowing water）.However,it has been shown that the external forces were much less than the internal forces（ie.,electrostatic repulsive pressure,hydration repulsive pressure and van der Waals attraction）;thus,the external forces probably were not the main driving force for aggregate breaking.As a result,in this study,six typical loess soils in the Loess Plateau were selected as the objects.We systematacially investigated the coupling effects of soil internal and external forces on particle size distribution and migration characteristics of the typical loess aggregates in the process of rainfall by artificial rainfall simulation device.The results obtained in this study were as follows:（1）The coupling effects of soil internal and external forces on aggregates breaking and migration during rainfall was clarified.Through changing the electrolyte concentration of soil bulk solution,the soil particle surface potential and electric field intensity and soil internal forces were quantitatively obtained.The lower the electrolyte concentration of soil bulk solution,the greater the soil internal forces,resulting in lower soil aggregates stability.The electrolyte concentration of 10-2mol·L-1was a key concentration affecting aggregates stability.Soil aggregates were broken down by the soil internal forces and were migrated by external forces.In this study,the Cinnamon soil,Loessal soil,Lou soil,Heilu soil and Sand loess were all dominated by microaggregates of<0.053 mm after soil aggregate breaking.The mass percentage of soil aggregates tended to decrease gradually with increasing particle size at the same electrolyte concentration.With the increase of electrolyte concentration,the aggregate content of<0.053 mm decreased gradually,while the aggregate content of>0.053 mm increased gradually.At different splash erosion distances,the Cinnamon soil,Loessal soil,Lou soil and Heilu soil were still dominated by microaggregates of<0.053 mm,and the longer the splash erosion distance,the greater the percentage of microaggregates of<0.053 mm.While the percentage of particle size of the Sand loess and the Aeolian sandy soil were related to their own soil properties.（2）The coupling effects of soil internal and external forces on soil splash erosion amounts and its distribution during rainfall process were revealed.The results showed that the increase of internal forces during rainfall resulted in the increase of fine soil particles,which affected the total splash erosion amounts.With the increase of soil internal forces,the total splash erosion amounts of Cinnamon soil,Loessal soil,Lou soil,Heilu soil and Sand loess increased sharply at first and then tended to be stable,and the relationship between soil internal forces and splash erosion amounts showed good exponential relationship（P<0.05）.The total splash erosion amounts of Aeolian sandy soil nearly showed no change with the decreasing electrolyte concentrations.The total splash erosion amounts were also affected by soil external force.With the increase of the external force,the splash erosion amounts increased;and the stronger the soil internal forces,the greater the increase in the total amount of erosion.The results showed that both internal and external forces affected the amount of soil splash erosion.With the increase of the splash erosion distance,the splash erosion amounts of the six soils decreased gradually,and mainly distributed at0～20cm.Finally,we established the statistical prediction equations about soil splash erosion amount,soil internal forces,splash erosion distance and rainfall height;that is M=a·S-b·N c·H d.In which,M is the soil splash erosion amount,S is the splash erosion distance,N is the soil internal force,H is the rainfall height,and a,b,c and d were the empirical coefficients.（3）The effects of different internal forces on slope erosion of soil were investigated.With the increase of rainfall duration,the cumulative loss of different soils showed different trends.The cumulative loss of Loessal soil and Sand loess sharply increased at first and then tended to be constant,while the change trend of Aeolian sandy soil was relatively gentle,and the change trend of cumulative loss of Cinnamon soil,Lou soil and Heilu soil under different internal forces were also different,which was mainly attributed to the different soil properties.With the decrease of electrolyte concentration,the cumulative loss of Cinnamon soil,Loessal soil,Lou soil,Heilu soil and Sand loess increased gradually;This showed that rainfall erosion increased with the increase of soil internal forces.The cumulative loss of Aeolian sandy soil did not change under each electrolyte concentration,which was consistent with the results of splash erosion.There were good linear relationships between the aggregate stability and the cumulative loss of Cinnamon soil,Loessal soil,Lou soil,Heilu soil and Sand loess,respectively.The larger the aggregate stability was,the smaller the soil cumulative loss was. |
PDF Full Text Request