| Groundwater is often the main or even the only source of domestic and production water in arid areas, while phreatic water evaporation is an important part of the groundwater loss. Salt will migrate into the soil surface with the process of phreatic water evaporation which will cause secondary soil salinization.Large outdoor lysimeter, miniature surface evaporator(d=20 cm) and indoor system of capillary water rising experiment in Groundwater Balance Test Station of Changji,Xinjiang Bureau of Geology and Mineral Resources and Irrigation Experiment Station, Water Conservancy Management Department of Bayinguoleng Autonomous prefecture, Xinjiang were used to carry on water surface evaporation test of different total dissolved solids(TDS), capillary water rise height test of different TDS and lithology, high salinity phreatic water evaporation test of different TDS, different phreatic water depths and different lithology. Rules and mechanism of the impact of TDS upon phreatic water evaporation during non-freezing period were analyzed on this basis of general laws of water surface evaporation and capillary water rising height under the condition of high TDS. HYDRUS-1D numerical simulation software was used to predict process of high-salinity phreatic water evaporation.This study is of great significance on a deeper understanding of high salinity phreatic water evaporation mechanism, guide of salt wasteland development and governance, water and salt regulation of saline-alkali soil, exploitation of underground brine resources and groundwater resources evaluation in arid areas with high salinity phreatic water distribution. The main research results are summarized as follows:(1)There is negative correlation between evaporation from water surface and the level of TDS. Evaporation from water surface decreases as TDS increases. Inhibition of TDS on surface evaporation, however, will decrease after TDS reaches a certain level. Average evaporation from water surface in daytime is larger than that in night under the same external environment when TDS is constant. And both surface evaporation in daytime and night decrease as TDS increases.(2)The impact of high TDS water on capillary water rising of different vadose zone Lithology will not only change the gravitational potential of capillary water but also have an impact on soil structure. Change law of different lithology on capillary water matric potential and gravitational potential is different in different TDS water. When TDS of water is certain, different lithology has different law of soil capillary water rise. Lithology is still the main factor controlling the capillary water rising, while TDS of water play a less important role.( 3) Annual phreatic water evaporation had an opposite trend as atmospheric evaporation capacity EΦ20 with groundwater depth of 0.0m, TDS of 100g/L and lithological characteristics of unsaturated zones of silty clay. The influence of lithological characteristics of unsaturated zones on the evaporation of phreatic water with high salinity was basically the same as freshwater when the groundwater depth was larger than 0.5m. The influence of variation of lithological characteristics of unsaturated zone on phreatic water evaporation was far less than the common influence of TDS and atmosphere evaporation potential on phreatic water evaporation when the groundwater depth was 0.5m and TDS was 30g/L. Phreatic water evaporation decreased gradually with the increase of TDS during non-freezing period with groundwater depth of 0.5 to 1.0m. The inhibition effect of TDS variation on phreatic water evaporation lagged behind with the groundwater depth of 3.0m.(4)Under the condition of high salinity phreatic water evaporation, the shallower phreatic water depth, the higher mean of soil salinity at the same depth of soil profile. When other conditions are certain, salinity of silt clay profile is higher than that of fine sand. Salinity of phreatic water with TDS 30 g/L is higher than that with TDS 100 g/L in upper layer of silt clay column, while in lower layer vice versa. During the experimental period, partial salification depth has a downward trend with the increase of TDS in profile of silt clay.(5)Based on the research of soil solute potential, absolute value of soil solute potential on each profile is increased and evaporation ability of phreatic water in soil column is reduce with the increase of phreatic water TDS. Due to the influence of neutron elegant phenomenon, calibration error of neutron probe equation is larger in depth range of 0 ~ 30 cm in soil surface. Thus, it is not suitable to use neutron probe to measure soil moisture content at this depth range.(6)Simulation calculation of high-salinity phreatic water evaporation at different phreatic water depths was carried out by HYDRUS-1D simulation software. Numerical simulation results proved that the shallower phreatic water depth the higher of phreatic water evaporation in high-salinity phreatic water evaporation. |
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