Dynamics of water vapor flux and water separation processes during evaporation from a salty dry soil

SummaryEvaporation from a salty soil generates salt accumulation near the surface with the subsequent deterioration of the soil quality. Salinization mechanisms are poorly understood despite their global impact. Vapor flux and solute transport were studied under evaporation conditions. Laboratory experiments consisted of open sand and silt columns initially saturated with epsomite (MgSO4·7H2O) or halite (NaCl) solutions. Salt precipitation occurred only above the evaporation front, which occupied a very narrow region. Vapor flowed both upwards and downwards from this front. The downward vapor flow condensed further down the column, diluting the solution. This gave rise to two areas: a high salinity area above the evaporation front, and a diluted solution area below it. The effects of thermal, suction and osmotic gradients on water fluxes were studied in order to better understand the underlying mechanisms of this phenomenon.

Research highlights
► Evaporation experiment of open soil columns initially saturated with a salt solution.
► Vapor flows downwards from a very narrow evaporation front due to a temperature gradient.
► Downward vapor flow condensates diluting the solution always below the evaporation front.
► Water separation process: high salinities above the front and dilution below it.