Water Table Depth and Soil Salinization: From Pore‐Scale Processes to Field‐Scale Responses

Abstract

The accumulation of salts in soils adversely influences plant growth and biological activity resulting in loss of yields and soil ecosystem services. Water table depth plays an important role on solute distribution through the unsaturated zone. We focus on the relationship between saline water evaporation from soil surfaces and water table depths. When the water table was hydraulically connected to the surface, we found more evaporatively driven sodium chloride precipitation at the surface with deeper water tables relative to shallow ones. We attribute this result to lower surface water contents that reach solubility limit sooner and support an expanding salt crust. Thermal imaging confirmed that when surface is hydraulically connected to the water table, capillary flows through the porous precipitated salt maintain the evaporative flux. Macroscopic continuum‐scale numerical simulations demonstrate higher solute concentration closer to the surface in the case of deeper water tables supporting the microscopic picture attributed to fewer evaporation and solute deposition sites at the surface with deeper water tables. Insights from the laboratory‐scale experiments and numerical studies were used to describe soil salinity at much larger scales. We employed two global‐scale databases for topsoil salinity, soil texture, and water table depths to link our laboratory‐scale findings with long‐term and field‐scale observations. The results illustrate the importance of pore‐scale physics and processes on constraining the field‐scale responses.

Predicting long-term dynamics of soil salinity and sodicity on a global scale

“…We selected the predictors based on the relevance to soil salinization processes as follows: surface evaporation, plant transpiration, fertilizers, poor drainage, and a rising water-table depth ( 15 , 66 , 67 ). In addition, the interactions of five main factors influencing soil formation processes, comprising climate, topography, living organisms, parent material, and hydrologic dynamics, were considered ( 59 , 63 ).…”

Effects of evolving salt precipitation on the evaporation and temperature of sandy soil with a fixed groundwater table

“…However, other studies described contrasting results, whereby evaporation did not decrease when salt precipitation occurred, at least when the hydraulic connection between the salt crust and water table was maintained or the salt crust remained wet (Eloukabi et al, 2011(Eloukabi et al, , 2013Sghaier & Prat, 2009;Shokri-Kuehni, Norouzi Rad, et al, 2017;Veran-Tissoires et al, 2012). Recently, Shokri-Kuehni et al (2020) reported a relationship between the saline water evaporation rate in soil and water table depth. A laboratory experiment combined with infrared thermography further confirmed that water transport through the salt crust was possible if the water table was hydraulically connected to the surface and that this phenomenon prevented reduction in the evaporation rate despite the presence of the salt crust.…”

“…Vadose Zone Journal Shokri-Kuehni, Vetter, et al, 2017), and CO 2 sequestration (Ott et al, 2014); it also accelerates rock weathering processes (Rodriguez-Navarro & Doehne, 1999). However, the dynamics of salt precipitation and evaporation processes are poorly understood because salt precipitation rates, fractions of soil surface covered by salt precipitation (hereafter cover fraction), and evaporation processes are controlled by complex interactions between the texture of soils, ambient conditions, water table depth, and types of saline solution (Eloukabi et al, 2013;Nachshon, Shahraeeni, et al, 2011;Norouzi Rad & Shokri, 2012;Shokri-Kuehni, Norouzi Rad, et al, 2017;Shokri-Kuehni et al, 2020). Saline water evaporation causes salt accumulation and precipitation on the soil surface, which in turn leads to evolution of the soil pore structure (Jambhekar et al, 2015).…”

“…ularly in regard to the upward growth of salt precipitation is not well understood. However, the upward growth of salt precipitation garnered less attention in research than its lateral growth (Fujimaki et al, 2006;Jambhekar et al, 2015;Rose et al, 2005;Sghaier & Prat, 2009;Shokri-Kuehni, Vetter, et al, 2017;Shokri-Kuehni et al, 2020;Zhang et al, 2014). Interestingly, several studies found that the salt crust can be elevated by the upward growth of salt precipitation, causing most of the salt crust to disconnect from the soil surface during the evolution of the precipitated crust; it was found that this can prevent the local transport of soil water through the salt layer and potentially reduce the evaporation rate (Dai et al, 2016;Li & Shi, 2019;Licsandru et al, 2019;Nachshon et al, 2018).…”

Obstacles, Interfacial Forms, and Turbulence: A Numerical Analysis of Soil–Water Evaporation Across Different Interfaces

“…For flow around obstacles and interfacial forms, the effects of shading and direct radiation would affect the evaporation rate around these forms, as well as contribute to the flow dynamics via thermal buoyancy and altered flow parameters. In addition to this, enhancements to the porous media model would also allow for the simulation of related environmental problems such as subsurface gas migration or evaporation driven salt precipitation, as an expansion to the work described in Shokri-Kuehni et al (2020). Modifications to this model including multi-component gas transport or mineralization could be performed to allow for this.…”