Shallow groundwater effects on evaporation and soil temperature in two windblown sands (Eutric Cambisol and Chromic Luvisol) in South Africa

The aim of this study was to investigate the effect of shallow groundwater tables on soil surface evaporation and its effect on temperature distribution on two aeolian soils in South Africa, Clovelly (Eutric Cambisol) and Hutton (Chromic Luvisol) soil forms. The study was conducted at a lysimeter under semi-arid climatic conditions. A constant groundwater tables were created at different depths (0 mm, 500 mm, 1000 mm, 1500 mm and a No WT (no water table treatment as a control) and each of the lysimeters were equipped with a 1200 mm long DFM soil moisture probe to measure the profile water content and soil temperature at 6 depths along the profile (every 200 mm depth). The research site was also equipped with a movable shelter to prevent rain water dilution during rainfall events. Finally, evaporation is calculated by the water balance approach. The ANOVA showed that there was a highly significant difference (P < .01) in rate of evaporation from the water table depths and soil types. The minimum and maximum evaporation were recorded in the deepest and shallowest water table depths. The diurnal soil water content shows that the maximum water content in the two soil profiles was recorded in the early morning times (6:00) and the minimum was in the late afternoon times (between 16:00-17:00). The diurnal variation of soil water content also increased with decreasing water table depth. Regarding the soil temperature, the ANOVA showed that the soil temperature was influenced by the interaction between water table and measurement depths. Hence, the top five minimum soil temperatures were recorded in the shallower (≤500 mm) water tables and the top 5 maximums were recorded in the deeper water table depths (1000, 1500 and No WT). Generally, as the groundwater table depth increased from the surface down the profile, the rate of evaporation decreased resulting an increase in the variation of temperature with in the diurnal cycle.