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NOTES

Colloid Mobilization from a Variably Saturated, Intact Soil Core

^a Dep. of Physics, 7507 Reynolda Station, Wake Forest Univ., Winston-Salem, NC 27109-7507
^b Dep. of Environmental Sciences, 291 McCormick Rd., Univ. of Virginia, Charlottesville, VA 22904-4123
^c School of Environmental Studies, 205 Prospect St., Yale Univ., New Haven, CT 06511-2189
^* Corresponding author (levinjm{at}wfu.edu)

Received 19 August 2005.

Colloids may transport contaminants through unsaturated soils to the groundwater, and colloid mobilization is associated with transient hydrological events and sustained, steady flow. We examined mechanisms of colloid mobilization from an intact, unsaturated soil core during relatively steady flow. We collected the core from a site where soils contain 26% clay and infiltration occurs only at capillary-pressure heads above –20 cm. We measured the colloid-mass flux during consecutive, 1.5-mo periods (P₁, P₂, and P₃) distinguished by capillary-pressure heads (_B) of –18.5, –11.5, and –18.5 cm, respectively. Mean mass flux values were 0.0886, 0.197, and 0.171 mg h^–1 for P₁, P₂, and P₃, respectively. Intervention analysis showed a significant increase in the mass flux of 0.079 mg h^–1 as _B became less negative. Results indicate that the number of soil pores through which water flows has a greater influence on colloid mobilization than do shear forces associated with elevated pore water velocities. Thus, colloid mobilization most likely is affected by a diffusion-limited, colloid-supply mechanism dependent on the number of pores contributing to flow.

Abbreviations: AR, autoregressive • MA, moving average

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