Field scale transport of bromide in an unsaturated soil: 2. Dispersion modeling

Abstract

The solute concentrations measured in the field experiment of G. L. Butters et al. (this issue) are used to compare two models of vadose zone solute transport: the deterministic one-dimensional convection-dispersion model, which represents solute transport far from the source of solute entry, and the stochastic-convective lognormal transfer function model, which represents solute transport near the source. The stochastic-convective model provided an excellent representation of the spreading of the solute pulse to a depth of 3 m after calibration at 0.3 m. Conversely, the deterministic model dramatically underpredicted solute spreading beyond 0.3 m after calibration. An analysis of the area-averaged solute concentration revealed a nearly linear scale effect in the dispersivity to a depth of at least 14.8 m. A change in the growth pattern of dispersion observed in the breakthrough curve at 4.5 m was attributed to a soil texture change near 3 m, which caused the apparent dispersivity of the pulse to decrease between 3.0 and 4.5 m, after which it increased significantly between 4.5 m and the final profile sampling between 0 and 25 m.

Relação da velocidade de escoamento da solução e do comprimento da coluna de solo com os parâmetros de transporte de potássio em um latossolo e um neossolo

“…Para a condição de campo ou em escalas de aquífero, está bem estabelecido que a dispersividade (λ) aumenta com o aumento do percurso (Butters & Jury, 1989;Gelhar et al, 1992;Basha & El-Habel, 1993). No entanto, resultados de estudos com colunas em laboratório em que foi avaliado o efeito do comprimento da coluna sobre a dispersividade são inconsistentes.…”

A three‐dimensional field study of solute transport through unsaturated, layered, porous media: 1. Methodology, mass recovery, and mean transport

“…These cores were carefully driven horizontally into the shaved sidewall of the pits to obtain approximately undisturbed soil samples. Butters [1987] measured the particle size distribution in the field from samples obtained by soil coring. To supplement his results, particle size analyses were performed using the pipette method [Day, 1965] for all applications were 57.6, 39.3, and 2.7 mol m -3 for Ca(NO3)2, KC1, and H3BO 3, respectively.…”

Longitudinal and lateral dispersion in an unsaturated field soil

“…Without understanding the mechanisms and extent of lateral dispersion it is not possible to predict even roughly the downward displacement of solutes injected at the surface [Ellsworth et al, 1991;Flahler et al, 1996]. It has been experimentally demonstrated that stratifications in soil affect solute dispersion considerably, often causing an abrupt decrease of the longitudinal dispersion and an increase of lateral mixing [Butters and Jury, 1989; Roth et al,…”