Assessment of evaporation and water fluxes in a column of dry saline soil subject to different water table levels

Abstract

Abstract:Dry saline soils are common in the arid and hyper-arid basins located in the Chilean Altiplano, where evaporation from shallow groundwater is typically the major component of the water balance. Thus, a good understanding of evaporation processes is necessary for improving water resource planning and management in these regions. In this study, we conducted laboratory experiments with a natural saline soil column to estimate evaporation rates and assess the liquid and water vapor fluxes under different water table levels. Water content, electrical conductivity and temperature at different depths were utilized to assess the liquid and water vapor fluxes in the soil column. We observed movement of water that dissolves salts from the soil and transports them to areas in the column where they accumulate. Isothermal liquid flux was predominant, while thermal and isothermal liquid and thermal water vapor fluxes were negligible, except for deep water table levels where isothermal and thermal water vapor fluxes had similar magnitude but opposite directions. Differences observed in total fluxes for all water table levels were due to different upward and downward fluxes, which depend on changes in water content and temperature within the soil profile. Both the vapor flux magnitude and direction were found to be very sensitive to the choice of empirical parameters used in flux quantification, such as tortuosity and the enhancement factor for local temperature gradients in the air phase within the column.

Modelling evaporation processes in soils from the Huasco salt flat basin, Chile

“…It is interesting to note that the experiments of Hernández‐López et al () assumed that steady state was reached when the experimental variables varied in less than 1%. However, in the previous discussion, the directions of the net water flux in regions 1 and 2 are different, which contradicts the principle of mass conservation under steady state conditions.…”

“…Indeed, our numerical model allowed determining the evaporation front (0.12 and 0.03 m when the water table was at 0.75 and 0.40‐m depth, respectively). Note also that, as described before, the location of the evaporation front obtained from the numerical model agrees fairly well with the observations of Hernández‐López et al ().…”

“…The results of the experiments are discussed in details in Hernández‐López et al (), and here we only present the main findings that are relevant for this modelling study. Because the column was homogeneously packed before the evaporation experiments, the zone of increased electrical conductivity and moisture shown in Figure is likely to be the result of salt movement towards the soil surface as evaporation occurred (Nachshon et al, ), and also because of salt transport as the water level rose.…”

“…The soil water content and electrical conductivity profiles shown in Figure evidenced salt transport and a probable salt accumulation within the soil column (Hernández‐López et al, ). Unfortunately, we did not quantify the deposited salts within the pores using visual techniques such as microscopic imaging.…”

“…Understanding evaporation is also important for the study of sensitive soil systems such as wetlands (de la Fuente and Niño, ; Johnson et al, ). Nonetheless, understanding the evaporation processes in these environments is complex because evaporation occurs under non‐isothermal conditions, where water can be mobilized as liquid water or water vapour (Nassar and Horton, ; Grifoll et al, ; Hernández‐López et al, ). In addition, quantifying evaporation in Altiplano basins is difficult because of the harsh conditions, the spatial variability of the evaporation rates, and also because of the difficulty in accessing this region (Kampf et al, ; Johnson et al, ).…”