Effect of Variable Horizon Thickness on Solute Transport

Abstract Significant variability of solute mass recovery, solute velocity, and dispersion occur in layered field soils. The effect of horizontally variable soil horzion thickness on vertical solute movement has not been examined in detail. The objective of this study was to determine the effect of varying B horizon thickness on solute transport. Steady‐state transport experiments were conducted on a Fox sand (a fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) in Ontario, Canada. A uniform pulse of KCl was applied at the soil surface on a 65‐m 2 area and subsequently leached through the soil profile using a drip irrigation system and a constant surface flux density of water. After 13.1 cm of water had been applied, resident Cl − concentration distributions were measured by excavating a 10‐m‐long trench and sampling vertically every 0.1 m to a depth of 1.5 m and horizontally every 0.2 m. A total of eight parallel trenches, 0.15 m apart, were sampled. Moment analysis was used to calculate solute recovery, mean solute travel depth, and solute travel depth variance for each of the individual vertical samplings. Results indicate significant lateral movement of tracer resulting in greater recovery of tracer in deep B horizon tongue areas. The recovery and movement of solutes in this soil was largely controlled by the spatial pattern of B horizon depth, and the spatial variance structure of B horizon thickness was closely related to the scale dependence of in situ solute transport. The results suggest that the horizontal variability of horizon thickness should be taken into account for monitoring and modeling purposes in this soil.