We demonstrate noninvasive quantitative imaging of colloid and solute transport at millimeter to decimeter (meso-) scale. Ultraviolet (UV) excited fluorescent solute and colloid tracers were independently measured simultaneously during co-advection through saturated quartz sand. Pulse-input experiments were conducted at constant flow rates and ionic strengths 10-3, 10-2 and 10-1 M NaCl. Tracers were 1.9 m carboxylate latex microspheres and disodium fluorescein. Spatial moments analysis was used to quantify relative changes in mass distribution of the colloid and solute tracers over time. The solute advected through the sand at a constant velocity proportional to flow rate and was described well by a conservative transport model (CXTFIT). In unfavorable deposition conditions increasing ionic strength produced significant reduction in colloid center of mass transport velocity over time. Velocity trends correlated with the increasing fraction of colloid mass retained along the flowpath. Attachment efficiencies (defined by colloid filtration theory) calculated from nondestructive retained mass data were 0.013 ± 0.03, 0.09 ± 0.02, and 0.22 ± 0.05 at 10-3, 10-2, and 10-1 M ionic strength, respectively, which compared well with previously published data from breakthrough curves and destructive sampling. Mesoscale imaging of colloid mass dynamics can quantify key deposition and transport parameters based on noninvasive, nondestructive, spatially high-resolution data.
Paper reports on novel non-invasive and non-destructive approach for examining spatial variation in colloid mass transport. Previous methods relied on tracers which conceal spatial information or destructive techniques that introduce sampling errors. Bridge is Heathwaite's PhD student (based at Sheffield) jointly supervised by Banwart. RAE_import_type : Journal article RAE_uoa_type : Earth Systems and Environmental Sciences