Coupling of Hofmeister effect, electrolyte concentration, and mechanical composition in soil loss: Runoff simulation study

Abstract

Electrostatic repulsive forces among soil particles control the intensity of soil loss in runoff and are controlled by the coupling of cation surface reactions (e.g., the Hofmeister effect), electrolyte concentration, and soil particle size composition. In this study, we used different concentrations of Li+, K+, and Cs+ to adjust the cation surface reaction or Hofmeister effect and electrolyte concentration of a neutral purple soil (Entisol). The mechanical composition of the soil was adjusted by adding 0.55–1 mm diameter quartz particles, and the mean surface potential of the soil particles was used to indirectly express the electrostatic repulsive force between particles. The results show that the Hofmeister effect, electrolyte concentration, and mechanical composition are strongly coupled during soil loss, of which the Hofmeister effect plays the most critical role. The physical mechanisms of the coupling effects can be summarized as follows. The electrostatic repulsive force among soil particles depends on the coupling of the Hofmeister effect and electrolyte concentration. Breaking intensity of the soil aggregate, which influences soil loss intensity in runoff, is determined by the electrostatic repulsive force and the production rate of the electrostatic repulsive force-which is controlled by the soil mechanical composition. We conclude that: (1) soil cation surface reactions are a key factor for determining the electrostatic repulsive forces and thus soil loss intensity in runoff; (2) for a given soil, the mechanical composition provides the basic factors that determine the production rate of the electrostatic repulsive force to break soil aggregates; and (3) increasing the soil’s large particle content enhances soil loss intensity but not necessarily soil loss quantity.