Vertical textural contract (VTC) increases seawater evaporation from heterogeneous sand

Abstract

The coupled soil texture and salinity effect on evaporation in porous systems is complex. This study investigates how vertical textural contrast (VTC) influences evaporation of artificial seawater (SW) compared to freshwater/deionized (DI) water. We conducted experiments using Hele-Shaw cells packed with a fine sand, a coarse sand, and their mixture, respectively, and monitored changes in evaporation rate and water/salt solution dynamics over 20 days. Using light transmittance to detect 2D distribution of water content and surface salt precipitation, we determined how fine/coarse textural contrast affects water transport and salt accumulation. Our findings demonstrated that VTC prolonged high-level water saturation through lateral water transfer from coarse to fine sand, which increased the evaporation rate in both SW and DI water systems. This lateral transfer was driven by differences in capillary pressure between coarse and fine sands, and SW was found to have limited effects on changing the capillary pressure difference compared to DI water systems. Notably, the increase in evaporation due to VTC was more pronounced in SW systems compared to DI systems, which was attributed to the delayed onset of salt precipitation in the fine fraction of heterogeneous chambers compared to homogeneous systems. Our results clarify the intricate mechanisms underlying saltwater evaporation in porous media and emphasize the critical control of soil textural heterogeneity and salinity in evaporation dynamics.