Colloid Mobilization and Transport in Undisturbed Soil Columns. II. The Role of Colloid Dispersibility and Preferential Flow

Abstract

This study investigated in situ colloid mobilization and leaching from unsaturated, undisturbed soil columns to evaluate the processes controlling colloid mobilization in structured soils. A total of 54 soil columns sampled along a natural clay gradient representing six clay contents (12, 18, 24, 28, 37, and 43% clay) were equilibrated to three different initial matric potentials (IMP) ψ = −2.5 (wet), −100 (moderately wet), and −15500 hPa (dry) followed by 5 d of irrigation at 1 mm h−1 and applying a suction of 5 hPa at the lower boundary. The results revealed that (i) colloid leaching from the initially wet and moderately wet soils decreased with increasing clay content, (ii) colloid leaching from the initially dry soils was low and independent of clay content, and (iii) the leaching of total organic C (TOC) consisted mainly of dissolved organic C (DOC), and drying to −15500 hPa increased the leaching of C. In situ colloid mobilization and leaching was related to measurements of low‐energy water‐dispersible colloids (LE‐WDC). Results indicate that in situ colloid mobilization from the initially wet and moderately wet 12% clay soils subjected to matrix‐dominated flow behavior was controlled mainly by the time‐dependent increase in colloid dispersion, while colloid mobilization from the initially dry soils was limited by the strong and persistent association created during the drying. In the more clayey soils, which were dominated by preferential flow, a lower displacement of high–ionic strength soil water with low–ionic strength rainwater may contribute to the inherently lower dispersibility in controlling colloid mobilization.

Lessivage as a major process of soil formation: A revisitation of existing data

“…This mobilisation increases and reaches a maximum with a drying pause that lasts up to 150-200 h, before decreasing for a longer pause (up to 70 days). No measurement of matric potential is related to these measurements, but this dynamic is in agreement with the experiment conducted by Kjaergaard et al (2004b) that shows a higher particle mobilisation for an initial matric potential near field capacity (−100 hPa) than for an initial condition near the crop welting point (−15500 hPa). These results support the hypothesis that particle mobilisation is related to capillary stresses.…”

“…Experiments conducted by Kjaergaard et al (2004b) and Majdalani et al (2008) showed that the rate of mobilisation is related to the drying intensity i.e. the initial water Table 1 WRB soil types in which lessivage occurs according to Bockheim and Gennadiyev (2000), including the importance of lessivage in these soil types, the surfaces covered and the locations of these soils along with the climates they now experience.…”

“…These experiments simulated eluviation. Only 7 of these studies, which summarise 119 different experiments, could be found in the literature (Jacobsen et al, 1997;Kjaergaard et al, 2004aKjaergaard et al, , 2004bLaegdsmand et al, 2005;Schelde et al, 2002;Shang et al, 2008;Sharma et al, 2008 andZhuang et al, 2007). In these studies, average particle concentrations at the outlet of the soil column ranged from 0.3 mg L -1 to 263.2 mg L -1 , with peak concentrations ranging from 0.9 mg L -1 to 1200 mg L -1 .…”

“…Box plot of particle concentration as a function of soil lutum content. The analysed results are from studies by Sharma et al (2008) and Kjaergaard et al (2004b). The box represents the upper and lower quartiles with the median (in black with the associated value) and the average (in grey).…”

Mobilization and preferential transport of soil particles during infiltration: A core‐scale modeling approach

“…However, far more complex breakthrough curves have been reported. Kjaergaard et al [2004] studied intact macroporous soil columns with different clay content and initial humidity. They showed that for high-humidity/low-clay soils, the leached particle concentration increases during the whole or part of the experiment.…”