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Colloid Mobilization and Transport in Undisturbed Soil Columns. I. Pore Structure Characterization and Tritium Transport

^a Environmental Engineering Section, Dep. of Life Sciences, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^b Dep. of Agroecology, Danish Institute of Agricultural Sciences, P.O. Box 50, DK-8830 Tjele, Denmark
^c Currently Danish Institute of Agricultural Sciences, Department of Agroecology, P.O. Box 50, DK-8830 Tjele, Denmark

View larger version (26K): [in a new window]   Fig. 1. Illustration of pretreatment procedures and tracer experiment.

View larger version (43K): [in a new window]   Fig. 2. Experimental setup consisting of soil column (10 cm in diameter, 8 cm long), irrigation device connected to a precision pump, column base with a nylon monofilament screening fabric (31 µm), resting on a 2-mm stainless-steel grid, collection vacuum chamber with outlet connected to a Mariotte device controlling the suction, rubber tube with two-piece pressure-controlled open and close device, and fraction collector.

View larger version (27K): [in a new window]   Fig. 3. Response of matric potential on (a) water retention characteristics, and (b) air permeability. Equivalent pore diameter of (a) water occupied, and (b) air-filled pores corresponding to the applied pressure potential is illustrated at the second x axis. Error bars: ±SE.

View larger version (28K): [in a new window]   Fig. 4. Pore structure characteristics determined at –100 hPa as a function of clay content and initial matric potential (IMP) before (initial, filled symbols) and after (final, open symbols) the tracer experiment: (a–c) measured air-filled porosity, a,100; (d–f) measured air permeability, ka,100; (g–i) estimated equivalent pore diameter, d100; and (j–l) estimated number of pores 30 µm, n100. Error bars: ±SE correspond to measurements on three replicate columns for each clay soil.

View larger version (35K): [in a new window]   Fig. 5. Tritium (3H2O) breakthrough curves plotted as relative concentration (C/C0) against number of eluted pore volumes (V/V0) as a function of clay content and initial matric potential (IMP) of –2.5, –100, and –15500 hPa. Dotted line marks one pore volume. Replicates corresponding to measurements on three replicate columns are represented by different symbols.

View larger version (37K): [in a new window]   Fig. 6. Selected tritium (3H2O) breakthrough curves plotted as relative concentration (C/C0) against number of eluted pore volumes (V/V0) with calculated best fit using either (a) the mobile–immobile model (MIM), or (b–f) the two mobile–one immobile model (2MIM) and the mobile–immobile model (MIM). Note that two different x and y axes are used.