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Unsaturated Flow Effects on Solute Transport in Soils
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  • Luwen Zhuang,
  • Amir Raoof,
  • Mojtaba G. Mahmoodlu,
  • Sara Biekart,
  • Riemer de Witte,
  • Lubna Badi,
  • Martinus van Genuchten,
  • Kairong Lin
Luwen Zhuang
Sun Yat-sen University

Corresponding Author:luwen.zhuang@outlook.com

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Amir Raoof
Utrecht University
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Mojtaba G. Mahmoodlu
Utrecht University
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Sara Biekart
Utrecht University
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Riemer de Witte
Utrecht University
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Lubna Badi
Utrecht University
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Martinus van Genuchten
Federal University of Rio de Janeiro
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Kairong Lin
Sun Yat-sen University
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Abstract

A major transport process in soils is hydrodynamic dispersion which affects the spreading and arrival of surface-applied pollutants at underlying groundwater reservoirs. When a soil is unsaturated, hydrodynamic dispersion is very much affected by soil water saturation. Centimeter-scale and decimeter-scale column experiments were carried out to explore the effects of fluid saturation and soil type on the unsaturated soil solute dispersivity. Measured in-situ breakthrough curves were analyzed in terms of both classical advection-dispersion and dual-porosity (mobile-immobile) type transport equations. A clear non-monotonic relationship was found between the dispersivity and soil water saturation. The extent of non-monotonicity was more pronounced for relatively coarse-textured soils compared to the finer soils. This finding has been reported rarely before; it explains the inconsistency of saturation-dispersivity relationships in the literature. The relationship between solute dispersivity and water saturation proposed herein may improve the performance of field-scale transport models for the unsaturated zone.