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Published March 24, 2020 | Published
Journal Article Open

Interplay between Fingering Instabilities and Initial Soil Moisture in Solute Transport through the Vadose Zone


Modeling water flow and solute transport in the vadose zone is essential to understanding the fate of soil pollutants and their travel times towards groundwater bodies. It also helps design better irrigation strategies to control solute concentrations and fluxes in semiarid and arid regions. Heterogeneity, soil texture and wetting front instabilities determine the flow patterns and solute transport mechanisms in dry soils. When water is already present in the soil, the flow of an infiltration pulse depends on the spatial distribution of soil water and on its mobility. We present numerical simulations of passive solute transport during unstable infiltration of water into sandy soils that are prone to wetting front instability. We study the impact of the initial soil state, in terms of spatial distribution of water content, on the infiltration of a solute-rich water pulse. We generate random fields of initial moisture content with spatial structure, through multigaussian fields with prescribed correlation lengths. We characterize the patterns of water flow and solute transport, as well as the mass fluxes through the soil column. Our results indicate a strong interplay between preferential flow and channeling due to fingering and the spatial distribution of soil water at the beginning of infiltration. Fingering and initial water saturation fields have a strong effect on solute diffusion and dilution into the ambient water during infiltration, suggesting an effective separation between mobile and inmobile transport domains that are controlled by the preferential flow paths due to fingering.

Additional Information

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received: 11 February 2020; Accepted: 18 March 2020; Published: 24 March 2020. Author Contributions: Investigation L.C.-F., M.J.S.-N., X.F. and R.J. All authors have read and agreed to the published version of the manuscript. Funding for this research was provided by Spanish Ministry of Economy and Competitiveness under grant CTM2014-54312-P (to L.C.-F.), by the Abdul Latif Jameel World Water and Food Security Lab (J-WAFS) at MIT (to R.J.), by the MIT International Science and Technology Initiatives (MISTI), through a Seed Fund grant (to R.J. and L.C.-F.), and by the Miller Fellowship for Basic Research in Science (to X.F.). The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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