Effects of wetting and drying cycles on in situ soil particle mobilization

Abstract

International audienceUnderstanding particle mobilization and transport in soils is a major concern for environmental protection and water resource management as they can act as vectors for sorbing pollutants. In natural soils, the existence of a finite size and renewable pool of dispersible particles has been hypothesized. Even though freeze-thaw and wetting-drying cycles have been identified as possible mechanisms of pool replenishment between rainfall events, to date the underlying phenomena ruling the renewal of particle pools are still largely unexplored. We carried out a series of infiltration-drainage experiments to study systematically the effects of periods without rain (pauses) on in situ particle mobilization in undisturbed soil columns. We found that, for a given column, pause duration between two rainfall events has a major influence on subsequent particle mobilization: the mass of leached particles increases with pause duration until it reaches a maximum (mass for a 200-hours pause is 15 time greater than for a 1-hour pause), and then it decreases for even longer pauses. This behaviour was correlated with soil water content, and can be explained by soil matrix weakening due to differential capillary stresses during drying. The consequences of this finding are important because the 15-fold increase in mass of leached particles, when pause duration is changed from 1 hour to 4 days, might overwhelm variations caused by changes in other parameters such as the ionic strength of the incoming solution or the rainfall intensity

Effect of water content on aggregation and contaminant leaching: the study of an urban Technosol

“…Suggested disturbance of the upper layer of the Technosol before the sampling of May could have triggered the observed lower aggregate stability leading to the larger mobilization of particles. Thus, as Majdalani et al (2008) suggested, soil history must also be taken into account in order to understand particle mobilization. Another explanation of the difference of particles mobilization could rely on difference in energy associated with water in samples from May and December.…”

“…Several studies dealing with contaminant transfer have taken soil structure into account (using undisturbed soil columns); however, fewer have focused on variable soil structures. Indeed, colloidal transfer has been shown to be influenced by initial moisture content in real soil by using columns (Kjaergaard et al 2004a, b;Klitzke and Lang 2007;Majdalani et al 2008) and batch experiments (Klitzke and Lang 2007).…”

New molecular evidence for surface and sub-surface soil erosion controls on the composition of stream DOM during storm events

“…4). As the intensity of storm flow conditions and more particularly the flow rate in soils is known to increase colloidal and particulate mobilization (Kaplan et al, 1993;Majdalani et al, 2008;Zhang et al, 2016), to which the organic matter can be bound (Laegdsmand et al, 1999), we hypothesize that hydrological conditions were responsible for this variability between storm events. To test this hypothesis, the distribution of LIGs, which showed more significant molecular changes, was investigated as a function of H for soil solutions sampled during base flow and storm flow conditions (Fig.…”

“…First, DOM could come from the mobilization of colloids and soil particles containing organic matter. Numerous studies have highlighted the mobilization of colloids and soil particles in soil columns (Laegdsmand et al, 1999;Majdalani et al, 2008;Mohanty et al, 2015;Zhuang et al, 2007) and field studies (Jarvis et al, 1999;Zhang et al, 2016) due to an increasing water velocity. The rise of the water table during storm flow conditions induced an increase in the water pressure and velocity in the soil macroporosity, which could be related to a piston-like effect (Zhao et al, 2017).…”

“…This might be due to the increase in H that took place on 7 January, 2 days before event 3. As colloidal and particulate supply located in the soil macroporosity appears to be quantitatively limited and renewable (Jarvis et al, 1999;Majdalani et al, 2008), these pre-event hydrological conditions will impact the supply of colloids available for mobilization. If these pre-event conditions are not favourable to rebuild this supply, as for event 3, colloidal destabilization and therefore changes of molecular composition will not be observed.…”