NaCl Crust Architecture and Its Impact on Evaporation: Three‐Dimensional Insights

Abstract

Salt precipitation over porous media due to evaporation is known to affect various important processes, including evaporation itself. Many studies have shown that salt crust precipitation reduces evaporation rate, and it has been suggested that the crust constitutes a barrier to vapor flow. Nevertheless, it remains unclear how a porous medium such as the salt crust does not enable upward liquid water transfer by capillary flow. Herein, we show by various imaging methods that the salt crust grows out of specific nucleation centers, to create an elevated crust approximately 1 mm above the matrix surface, most of which is disconnected from the matrix. This indicates that evaporation from a porous medium that is covered by NaCl efflorescence salt crust may occur below the crust, at the soil surface.

The Effect of Flooding on Evaporation and the Groundwater Table for a Salt-Crusted Soil

“…The salt crust diminishes the evaporation rate significantly, as previously reported by many studies [3,10,23,24] employing different methodologies, including micro-lysimeter measurements [23,24], the Bowen ratio [25], eddy correlation [9,10,26], and a static chamber [27], with studies carried out in both the field and the lab using repacked soil columns [1,3,28]. The main reason for the above effects on transport is that salt crusts also impede water vapor transport into the atmosphere by blocking the gas flow, much like a cover of straw or gravel mulch [12,29]. The salt crust also tends to form a dome [30], which causes a disconnection between the salt crust and the soil matrix, further limiting the evaporation [29].…”

“…The evaporation varied dynamically with salt precipitation [31] and reflected the salt crust formation process [29]. All treatments were performed under the same conditions before the flood (from day 1 to day 40); therefore, we analyzed the evaporation rate using the mean values of all treatments (a total of 15 columns).…”

“…The main reason for the above effects on transport is that salt crusts also impede water vapor transport into the atmosphere by blocking the gas flow, much like a cover of straw or gravel mulch [12,29]. The salt crust also tends to form a dome [30], which causes a disconnection between the salt crust and the soil matrix, further limiting the evaporation [29]. Although there is some dispute regarding certain points, such as whether evaporation occurs from the salt crust surface [31] or below the salt crust [17], many studies, including those mentioned above, do agree that evaporation is inhibited by salt crust formation.…”

Vegetation Controls on Dryland Salinity

“…Lower is tolerance, lower is , indicating that through their resilience to salt, tolerant species may be able to compete with glycophytes. Once transpiration is suppressed, evaporation becomes the dominant process, although during dry outs, salt crust formation can have a major role in lowering evaporation (Nachshon et al, ). However, whether may represent an underestimation of maximum salinity, it still provides an important indication of how salt tolerance can exert an active forcing on salinization dynamics.…”

“…Remarkably, depends on salt tolerance only and represents the concentration for which the ability of plants to uptake water from the soil becomes completely impaired (i.e., is higher for halophytes given their ability to better exploit water in the soil). At , evaporation becomes dominant, although other processes like salt‐crust formation can occur at this stage, leading to a substantial lowering of evaporative rates or even evaporation suppression (Eloukabi et al, ; Fujimaki et al, ; Nachshon et al, ).…”