Characterization of water and solute transport in the unsaturated zone of a hypersaline environment

We present a methodology for the analysis of chemical profiles from the unsaturated zone where ions from the sediment are extracted by two methods: centrifugation and water addition. The methodology enables one to (1) assess the ion amounts present in two different phases, pore water and minerals; (2) determine the depth in the unsaturated profile where the degree of saturation of each mineral is reached; (3) establish the principal direction of water flow; and (4) differentiate between upward transport of water either as vapor or as a saline solution. The methodology was applied to the unsaturated zone of the Dead Sea coastal area where the original salinity of interstitial water in these sediments was >300 g/L. Our analysis of the field data suggests that reduction of interstitial water salinity is the result of vertical upward transport of fresh water from a confined aquifer at a depth of 7 m. Flushing, up to the potentiometric surface (depth of 3.5 m), is due to the positive pressure head of the aquifer. Above the potentiometric surface, upward water transport is due to capillary forces, and flow is maintained by evaporation at the soil surface. Evaporation leads to an increase in the salinity of the rising interstitial solution and to the sequential deposition of salts such as NaCl and KM(g)Cl₃·6H₂O.