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Diffusion-Limited Mobilization and Transport of Natural Colloids in Macroporous Soil

^a L. Wollesen de Jonge, Department of Crop Physiology and Soil Science, Danish Institute of Agricultural Sciences, P.O. Box 50, DK-8830 Tjele, Denmark
^b Department of Environmental Engineering, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^c Department of Social and Environmental Engineering, Faculty of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739, Japan

View larger version (36K): [in a new window]   Fig. 1. Results from the flow interruption experiment (Exp. 2). Colloid concentration in the column effluent as a function of accumulated outflow. Left panels: before flow interruption; right panels: after flow interruption (0.5 h, 1 d, or 7 d).

View larger version (109K): [in a new window]   Fig. 2. Schematic of a single equivalent macropore with particle exchange between three phases: mobile water, immobile water, and crust. Horizontal arrows indicate particle diffusion between phases, and vertical arrows indicate convective particle transport.

View larger version (17K): [in a new window]   Fig. 3. Sensitivity analysis of the three model parameters subject to calibration. The concentration of particles in the mobile water phase at the soil column outlet when varying the initial particle concentration in the immobile phase and crust (Cstart), the diffusion coefficient in the immobile phase (Dim), and the diffusion coefficient in the crust (Dcr).

View larger version (21K): [in a new window]   Fig. 4. Modeling result for Exp. 1. Observed (symbols) and simulated colloid concentration in the column effluent. Upper panel: Column 5 (high infiltration rate); lower panel: Column 7 (low infiltration rate).

View larger version (19K): [in a new window]   Fig. 5. Modeling result for Exp. 2. Observed (symbols) and simulated colloid concentration in the column effluent before and after the flow interruption. Columns 11 (30-min flow interruption), 14 and 17 (1-d flow interruption), 18 and 19 (7-d flow interruption). Note the different concentration axis for Column 19.

View larger version (23K): [in a new window]   Fig. 6. Simulated colloid concentration in the immobile phase (Cim) at the center of the soil column. Columns 11, 17, and 18 representing 30-min flow interruption, 1-d flow interruption, and 7-d flow interruption, respectively. Note the different time axes.

View larger version (14K): [in a new window]   Fig. 7. Sensitivity analysis with respect to the thickness of the immobile phase, xim. Observed (symbols) and simulated (four overlapping curves) colloid concentration in the effluent of Column 13. The immobile phase thickness was set to 10, 30, 60, and 100 µm, and the calibrated diffusion coefficients and Cstart of the four respective simulations are given in Table 3.