Observation of water and solute movement in a saline, bare soil, groundwater seepage area, Western Australia. Part 1: Movement of water in near-surface soils in summer

In order to elucidate the relationship between evaporation, salinisation, and annual water and salt balances in semi-arid and arid regions, hydrological and meteorological observations were undertaken over 3 years in a small, salinised, bare-soil, groundwater seepage area in Western Australia. This paper focuses on water behaviour near a bare saline soil surface during the dry summer. Analysis of observed data on soil vapour density using a vapour diffusion transfer model can account for the daily upward vapour flux from the soil surface that occurs in midsummer. The dry soil undergoes cycles of drying during the day, accompanied by salt crust formation and wetting during the night. In late summer, the same zones show a wetting trend owing to a marked atmospheric vapour invasion and condensation at night regardless of evaporation during daytime. The daily average vapour flux at the ground surface in mid-and late-summer, respectively, estimated through the vapour transfer model in the dry soil layer was similar to 0.35 and 0.03 mm/day. Comparison of vapour fluxes at the ground surface measured with a portable surface evaporimeter with modelled estimates of vapour transport in soil showed agreement of the proposed model to field results at low wind speed, but not at the higher wind speeds. This identifies the active role of turbulent surface wind speed on vapour transfer in the dry soil layer below the ground surface.