Solute transport in fine sandy loam soil under different flow rates

Abstract

Due to growing concerns about ground water pollution by agricultural chemicals, the dispersion of solutes in soil has received considerable attention. This study investigates the leaching of a conservative tracer under different water flows. We studied solute dispersion by applying pulses of bromide (Br) tracer at the surface of a fine-Hecla sandy soil loam, during constant, unsaturated water infiltration, at flow rates ( f w) of 0.46, 0.91, 1.54 and 2.14 cm h −1. Ceramic cups were installed at seven depths from 30 to 250 cm, and soil solution was sampled during leaching. Measured solute concentration and the CXTFIT equilibrium model allowed for estimates of average pore-water velocity ( v ) and dispersion ( D). Our data fit the equation D = λ v n , with λ = 1.76 and n = 0.99 ( r 2 = 0.42). Parameter λ increased with increasing depth for f w ≥ 2.14 cm h −1. The dependence of the dispersion coefficient on the water content could be verified only at a higher flux and under a non convective-dispersive process.