Preferential Transport of Soil Colloidal Particles: Physicochemical Effects on Particle Mobilization

Abstract

The quantification of particle transport through soil is of great importance for estimating the potential risk of adsorbing contaminants leaching into groundwater. In the present study, we investigated the mobilization of natural soil particles in an undisturbed soil column (diameter = 0.3 m, height = 0.66 m). We tested the effects of physicochemical properties of soil and infiltrating water on the mobilization and transport of soil particles. A square pulse of water was applied at the top of the column. Water was allowed to drain freely at the bottom of the column. We tested two rainfall intensities (11 and 23 mm h−1), three ionic strengths (10−5, 10−3, and 10−1 M), and two initial moisture contents (0.34 and 0.38 m3 m−3). For the whole set of infiltration experiments, the concentration of eluted particles was correlated with the drainage flow intensity, particularly during transient flow. Particle leaching during steady flow varied with the boundary and initial conditions. The highest mobilization of particles was observed for deionized water, the highest infiltration rate and the highest initial soil moisture content. Particle mobilization was limited for high ionic strength associated with the divalent cation Mg2+ During transient flow, mechanical detachment by hydrodynamic shear could lead to particle mobilization. During steady flow, the ionic strength of the incoming solution may alter the energy potential at the soil–water interface, and thus have an effect on the mobilization rate as well.