SOLUTE TRANSPORT AT THE PEDON AND POLYPEDON SCALES

Soil solute transport parameters are usually measured at the pedon sca le, but predictions of transport at the polypedon scale are often requ ired. Our objectives were to compare pedon- and polypedon-scale convec tion dispersion equation (CDE) transport parameters measured in a fiel d leaching experiment and to compare deterministic and stochastic pred ictions of polypedon-scale transport. The study was conducted near Wat kinsville, Ga. on a 12.5 by 30.5 m plot. Time domain reflectometry (TD R) waveguides (30 and 60 cm in length) were installed vertically at 80 locations to measure water content and impedance. The plot was irriga ted and a Cl pulse was used as a tracer. We found very good agreement between the average CDE parameters measured at the pedon scale and tho se estimated at the polypedon scale in the 0-30 and 0-60 cm depth inte rvals. Although the variability in average pore velocities between ped ons was large, the variability in velocities within a pedon caused by hydrodynamic dispersion was greater. As a result, a deterministic appr oach based on the CDE more accurately predicted the estimated polypedo n scale breakthrough curve (ETC) at 30 and 60 cm depths than a stochas tic approach based on the convective lognormal transfer function (CLT) . This indicates that the pedon serves as a representative elementary volume (REV) for solute transport in this soil.