Retention and Solute Transport Properties in Disturbed and Undisturbed Soil Samples

Lívia Previatello Da Silva,Luciano Alves De Oliveira,Quirijn De Jong Van Lier,Jarbas Honorio De Miranda,Marcus Metri Correa

doi:10.1590/18069657rbcs20151045

Lívia Previatello Da Silva, Luciano Alves De Oliveira + Show 3 more

Open Access

https://doi.org/10.1590/18069657rbcs20151045

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Abstract

Solute transport parameters can be determined in miscible displacement experiments, usually performed in columns with disturbed (sieved) soil samples. Experiments with undisturbed samples are uncommon, due to the difficulty of taking undisturbed samples at the size required for these experiments. Structural alteration of the disturbed material implies modifications in the pore geometry that determines hydraulic properties, including hydraulic conductivity and retention and properties related to miscible displacement. An existing model for prediction of breakthrough curves based on retention properties was tested using material from a medium-textured Ferralsol, and alterations caused by sample disturbance were investigated. Soil water retention curves and miscible displacement parameters were determined in breakthrough experiments with nitrate salts in columns filled with undisturbed and disturbed soil samples. Data obtained from the undisturbed samples showed a higher dispersion, suggesting homogenization of pore geometry and a reduction in the representative elementary volume by the disaggregation and sieving of the soil material. The transport parameters for nitrate determined in disturbed and undisturbed samples were significantly different and the model was able to simulate the observed breakthrough curves after fitting the pore connectivity parameter.

Highlights

Quantifying the components of the solute transport process is important for understanding management practices to control ion movement in soil (Bresler, 1981)
The miscible displacement process affecting solutes in porous media can be physically described by the solute transport equation, relating displacement to the movement of the interface between transported and transporting fluids
Saturated hydraulic conductivity in the disturbed soil columns was 0.535 m d-1, on average, and 0.134 m d-1 in the column with undisturbed structure. The difference between both values is in agreement with the retention curves, which show an increase in macroporosity for the disturbed soil

Summary

Introduction

Quantifying the components of the solute transport process is important for understanding management practices to control ion movement in soil (Bresler, 1981). The miscible displacement process affecting solutes in porous media can be physically described by the solute transport equation, relating displacement to the movement of the interface between transported and transporting fluids The solution of this equation includes three components describing solute transport: the dispersion-diffusion coefficient (D), the retardation factor (R), and the Péclet number (P) (Ruiz et al, 2010). These transport parameters can be determined in the laboratory by performing a breakthrough experiment, to be analyzed by analytical or numerical physical-mathematical models (Anami et al, 2008; Fonseca et al, 2009; Rose et al, 2009; Doltra and Muñoz, 2010; Silva et al, 2012). In contrast with analytical solutions, the numerical models do not require boundary conditions that usually are not satisfied during experiments

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