EFFECT OF VARIABLE HORIZON THICKNESS ON SOLUTE TRANSPORT

Significant variability of solute mass recovery, solute velocity, and dispersion occur in layered field soils. The effect of horizontally va riable soil horizon 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-stat e transport experiments were conducted on a Fox sand (a fine-loamy ove r sandy or sandy-skeletal, mixed, mesic Typic Hapludalf) in Ontario, C anada. A uniform pulse of KCI was applied at the soil surface on a 65- m(2) area and subsequently leached through the soil profile using a dr ip irrigation system and a constant surface flux density of water. Aft er 13.1 cm of water had been applied, resident Cl- concentration distr ibutions were measured by excavating a 10-m-long trench and sampling v ertically 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. Mome nt analysis was used to calculate solute recovery, mean solute travel depth, and solute travel depth variance for each of the individual ver tical samplings. Results indicate significant lateral movement of trac er resulting in greater recovery of tracer in deep B horizon tongue ar eas. The recovery and movement of solutes in this soil was largely con trolled by the spatial pattern of B horizon depth, and the spatial var iance structure of B horizon thickness was closely related to the scal e dependence of in situ solute transport. The results suggest that the horizontal variability of horizon thickness should be taken into acco unt for monitoring and modeling purposes in this soil.