土壤内外力共同作用下溅蚀团聚体粒径分布及迁移特征

Combined effects of soil internal and external forces on the size distributions and movement characteristics of splashed soil fragments

为探究土壤内外力共同作用对降雨溅蚀过程的影响,通过调控不同降雨高度,采用不同浓度电解质溶液作为降雨材料进行人工模拟降雨试验,研究土壤内外力共同作用下溅蚀团聚体的粒径分布及迁移特征。结果表明:1)随电解质浓度降低,土壤内力先急剧增大后保持稳定;团聚体稳定性先急剧降低后保持稳定;土壤总溅蚀量先急剧增大后保持稳定。表明土壤内力作用深刻影响团聚体稳定性和降雨溅蚀。2)在土壤内力作用下大团聚体破碎后形成的≤0.053 mm微团聚体含量最高;且随土壤内力的增大,≤0.053 mm微团聚体含量增加。3)随降雨高度增加,外力作用增强,土壤总溅蚀量增加,溅蚀团聚体中>0.053 mm团聚体含量增加。土壤总溅蚀量与颗粒间静电斥力表现出良好的指数关系(R^(2)>0.94)。4)当内力作用不变时,不同溅蚀距离处的溅蚀量随溅蚀距离的增大而减小,且溅蚀物主要集中分布在0~10 cm的范围内;不同溅蚀距离内均以≤0.15 mm的土壤团聚体为主。同一距离处,随土壤内力作用的增大,团聚体破碎后释放的微团聚体数量越多,溅蚀量也越大。可见,降雨溅蚀过程中土壤团聚体粒径分布及空间迁移受土壤内外力作用的共同影响。

[Background]The Loess Plateau is one of the most severe regions that suffer from soil and water erosion in China.Soil erosion has been occurred in about 33%coverage of the Loess Plateau.Rainfall splash erosion is the key step of soil water erosion,leading to the breakdown of soil aggregates and movement of soil fragments,which can subsequently aggravate soil erosion.[Methods]In the present study,cinnamon soil was chosen and different electrolyte concentrations of NaCl solutions were used as the rainfall materials under two rainfall heights for carrying out rainfall simulation experiments.When the raining was over,total amounts of splash erosion,amounts of splash erosion at different splash distances and contents of aggregates in different sizes were calculated to investigate the size distributions and movement characteristics of splashed soil fragments.The relationships between soil internal/external forces and aggregate stability were explored.[Results]1)With decreasing electrolyte concentration of simulated rainfall,soil internal forces increased sharply first and then remained stable;the aggregate stability decreased sharply first then remained stable;whereas the amounts of splash erosion increased sharply first and then remained stable.Therefore,soil internal force was an important factor affecting aggregate stability and rainfall splash erosion.2)In the process of rainfall splash,soil aggregates broke down into macroaggregates by soil internal forces,and then microaggregates in different sizes released.After the breakdown,the contents of microaggregates in≤0.053 mm were the highest.Furthermore,with the increase of soil internal forces,the amounts of microaggregates in≤0.053 mm increased,while the amounts of aggregates in>0.053 mm decreased.3)With increasing rainfall height,soil external force increased;the total splash erosion amount increased;and the content of aggregates in>0.053 mm increased.Moreover,with the increase in rainfall height,the splash erosion amount increased with the increase of soil internal force.There was a good exponential relationship between splash erosion amount and electrostatic repulsive force(R2>0.94).4)The movement characteristics of splashed fragments were affected by the combined effects of soil internal and external forces.Under the same internal force,the amounts of splash erosion decreased with increasing distance.The splashed fragments were distributed mainly within 10 cm.Soil aggregates in≤0.15 mm were dominant at different splash erosion distances.At the same distance,with the increase of soil internal forces,the amounts of microaggregates released after the macroaggregates breakdown increased,thus splash erosion amounts increased.[Conclusions]During the rainfall splash erosion,the particle size distribution and spatial movement characteristics of soil aggregates are affected by the combined effects of soil internal and external forces.The present study provides theoretical references for the establishment of accurate erosion predication model and the development of water erosion control technology.