土粒表面电场对土壤团聚体破碎及溅蚀的影响

团聚体是土壤结构的基本单元,其稳定性是评估土壤抗侵蚀能力的重要指标。土壤团聚体破碎是降雨溅蚀发生的关键一步。土粒表面电场对团聚体稳定性具有重要影响,必然也会深刻影响降雨溅蚀过程。该文以黄土母质发育的黄绵土和塿土为研究对象,采用不同浓度的电解质溶液定量调控土粒表面电场,研究不同电场强度对团聚体破碎及溅蚀的影响。结果发现:1)随电解质浓度的降低,土粒表面电位升高,表面电场增大,黄绵土和塿土团聚体平均重量直径减小,团聚体稳定性降低,降雨溅蚀量增大。2)电解质浓度小于10-2 mol/L,黄绵土和塿土表面电位绝对值分别高于202.0和231.6 mV,此时团聚体稳定性和溅蚀量变化不明显,表明表面电位202.0和231.6 mV分别是影响黄绵土和塿土团聚体稳定性及溅蚀的关键电位。3)随着土粒表面电场的减弱,团聚体破碎后释放的<0.15 mm微团聚体含量减小,>0.25 mm大团聚体含量增加,团聚体倾向于破碎为更大粒级的团聚体。4)电场作用下团聚体的破碎特征对降雨溅蚀具有重要的影响,溅蚀量与团聚体破碎释放的<0.15 mm微团聚体含量呈显著正相关,与>0.25 mm大团聚体含量呈显著负相关。上述结果表明,当降雨进入土壤后,对于干燥的土壤而言,土壤溶液电解质浓度被迅速稀释,土粒表面产生强大的电场,该电场通过影响团聚体破碎程度进而影响降雨溅蚀。该研究有助于加深对降雨溅蚀的科学认识,同时也为土壤团聚体稳定性及降雨溅蚀的人为调控提供了一定的理论依据。

Effects of soil surface electric field on the breakdown and splash erosion of soil aggregate

Soil aggregate stability is the most important indicator for assessing erosion resistance and soil fertility.In contrast,aggregates breakdown is the key step of rainfall splash erosion,where most particles transport and soils loss in water erosion.Surface electric field of soil particles can significantly affect soil aggregate stability,which can inevitably affect the rainfall splash erosion process.The purpose of this study was to clarify the effect of surface electric field on the size distribution of fragments resulting from aggregate breakdown,then to determine the relationship between fragments size distribution and splash erosion,and finally to identify which size fractions of aggregates fragment largely affect splash erosion during rainfall simulation.The Loessal and Lou soils were used from loess parent materials on Loess Plateau.According to the electric double layer theory,the electric field strength can be adjusted by the electrolyte concentration in the soil solution,which can affect the thickness of the diffuse double layer.Therefore,five electrolyte solutions(0.0001,0.001,0.01,0.1 and 1 mol·L?1)were selected to quantitatively adjust the electric field strength of particles.The aggregate stability was evaluated by the wetting sieving method,where the aggregates were immersed in different electrolyte concentrations of NaCl solution,and then sieved in the medium of alcohol with a set of sieves of 1,0.5,0.25 and 0.15 mm.The splash erosion was measured through the rainfall simulation experiment using the NaCl solution with different concentrations as rainfall materials.The results showed that:1)The surface potential and electric field of the Loessal and Lou soils increased with the decrease of electrolyte concentration in bulk solution.Meanwhile,the aggregate stability decreased,whereas the amount of splash erosion increased;2)When the electrolyte concentration was lower than 0.01 mol/L,or the surface potentials of Loessal and Lou soil were higher than 202.0 mV and 231.6 mV,respectively,the aggregate stability and splash erosion amount nearly kept constant,indicating that the surface potentials of 202.0 mV and 231.6 mV were the critical potentials for the aggregate breakdown and splash erosion of Loessal soil and Lou soil,respectively;3)With the decrease of the surface electric field strength of soil particles,the content of particles in the diameter less than 0.15 mm that released from aggregates decreased,whereas the content of the large aggregates(>0.25 mm)increased,suggesting that the aggregates tended to break into the larger fractions as electric field strength decreased;4)The amount of the splash erosion was positively correlated with the content of particles in the diameter less than 0.15mm that released from aggregates,while negatively correlated with the content of the large aggregates(>0.25 mm).This revealed that the fragmentation characteristics of the aggregate breakdown under the electric field have important effects on the rainfall splash erosion.The findings indicated that as the rainfall enters into the soil,the soil bulk solution is diluted;at the same time,the strong electric field immediately generated from the soil particles surface,which will essentially affect the degree of aggregate breakdown,thereby influence the process of splash erosion.This study can enrich our understanding of the rainfall splash erosion,and also provide the theoretical basis for regulating the soil aggregate stability and rainfall erosion.