| Ulan Buh desert situated the northwest island has scarce rainfall, large evaporation, butthe lower Jartai lake-basin area in the desert has abundant groundwater resources with shallowgroundwater level, so the groundwater becomes the main way to provide water for shrub-halfshrub vegetation in this area, such as Haloxylon,Nitraria, Ammopiptanthus. Shallowgroundwater upward supply soil water through capillary by the forms of liquid and vapor, thisvertical water cycle sustains the balance of water, salt and heat and the ecological balance ofvegetation.Harsh natural and geographical conditions, combined with the over-exploitation ofgroundwater by Jartai salt industry and Chahal beach oasis agriculture etc, caused thegroundwater level continue to decline, water quality deteriorate, soil salination intensify, largerecession death of desert vegetation appear. The influence on the structure and evolution ofdesert vegetation by transformation between soil water and groundwater and change ofhydro-geological environment become the core and key of the hydro-ecological research inthe region. Around these scientific issues, combining the ways of literature review, datacollection, field investigation and laboratory test, we carry out the research of the coupledwater-vapor-heat migration between groundwater and soil water and vegetation ecologicalsignificance of Ulan Buh desert. We obtained the following main achievements:(1) Soil vertical section is divided into four zones in shallow groundwater area of desert:the root zone, moisture transport zone, capillary saturation zone, phreatic water layer. Soilwater changes frequently with severe range in0~80cm root zone, soil wet layer appear in40~60cm layer, its water mainly comes from shallow groundwater. Shallow groundwater andsoil water interact with each other. The mutual conversion between shallow groundwater andsoil water has a cyclical variation with year and can be divided into three stages: thegroundwater recharge, soil water slow consumption, soil water consumption-recharge.(2) The diurnal variation of the temperature and the water content of near-surface isobvious，and the amplitude of diurnal variation decreases with depth, of which the change isthe most dramatic on surface (0cm), deep soil temperature and soil water content has noobvious diurnal variation, and difference is basically stable between the layers. The amplitudeof annual variation curve of soil temperature decreases with depth, presenting a "rightdeviation" phenomenon.(3) within one day, the vertical distribution of soil temperature curve circulates betweenheat-release and heat-acception, which produces a certain effect on moisture migration. Temperature gradient is the main controlling factor of shallow soil moisture migration. Underthe action of temperature gradient, water vapor transport toward interface with lowtemperature, which caused the change of shallow soil water content. Deep soil water-vapormigration flux is relatively little compared with liquid water flux. HYDRUS-1D software wasused to make a primary comparison between the calculated values and measured values aboutsoil temperature and water content.(4) We select the assessment index system including groundwater depth, height ofcapillary rise of sand soil, soil water content, the annual range of groundwater depth,groundwater salinity, soil salinity, apply the fuzzy comprehensive judgement based on GIS,the Haloxylon-oriented vegetation ecological suitability was divided into suitable area,relatively suitable area, less suitable area and unsuitable area. The suitable area is about1924.71km2, accounting for21.0%of the total area, mainly distributes in the west of Jartaiand the south area from Wobbe to ZhGanwen. The relatively suitable area is about1725.86km2, accounting for18.8%of the total area, mainly distributes in the inter-dune bottomlandand flat dunes near the line of Haolaibao-Heping-Suhai. The less suitable area is about1897.23km2, accounting for20.7%of the total area, mainly distributes in the piedmont ofHelan Mountain, Lang Mont, Byan ula Mountain. The unsuitable area is about3623.01km2,accounting for39.5%, mainly distributes in the middle and rear edge of diluvial fan and bigsand hill from Jartai to Byan Shugui on the central and south of study area. |
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