Grid lysimeter study of steady state chloride transport in two Spodosol types using TDR and wick samplers

Solute transport in soils is affected by soil layering and soil-specific mo rphological properties. We studied solute transport in two sandy Spodosols: a dry Spodosol developed under oxidizing conditions of relatively deep gro undwater and a wet Spodosol under periodically reducing conditions above a shallow groundwater table. The wet Spodosol is characterized by a diffuse a nd heterogeneous humus-B-horizon (i.e., Spodic horizon), whereas the dry Sp odosol has a sharp Spodic horizon. Drainage fluxes were moderately variable with a coefficient of variation (CV) of 25% in the wet Spodosol and 17% in the dry Spodosol. Solute transport in 1-m-long and 0.8-m-diameter soil col umns was investigated using spatial averages of solute concentrations measu red by a network of 36 Time Domain Reflectometry (TDR) probes. In the dry S podosol, solute transport evolves from stochastic-convective to convective- dispersive at a depth of 0.25 in, coinciding with the depth of the Spodic h orizon. Chloride breakthrough at the bottom of the soil columns was adequat ely well predicted by a convection-dispersion model. In the wet Spodosol, s olute transport was heterogeneous over the entire depth of the column. Chlo ride breakthrough at 1 m depth was predicted best using a stochastic-convec tive transport model. The TDR sampling volume of 36 probes was too small to capture the heterogeneous flow and concomitant transport in the wet Spodos ol. (C) 2001 Elsevier Science B.V. All rights reserved.