古尔班通古特沙漠南缘风沙土土壤水分特征与毛管水最大上升高度

Maximum height of capillary rising water and characteristic of soil moisture in the southern edge of Gurbantunggut Desert

为确定古尔班通古特沙漠南缘地下水深埋区毛管上升水的最大上升高度,对划分固沙植物水分来源提供理论依据,于2016年3月〜2018年11月,采用中子仪法对试验地0〜10m土层土壤含水量进行观测,分析沙丘不同坡位土壤含水量的季节变化情况,并利用最大分子持水量与土壤含水量曲线交会法确定试验地毛管水的最大上升高度。结果表明:沙丘不同坡位0〜130cm土层的土壤含水量受外界气象因素影响较大,随季节变化规律明显;130cm土层以下至570〜760cm土层为土壤含水量较为稳定的干沙层;而570〜760cm以下土层的土壤含水量主要受地下水水位波动和毛管上升水的影响,其含水量变化上界可看作是毛管水的最大上升高度。试验地的最大分子持水量为0.0261 cm3·cm-3,且沙丘不同坡位毛管水的最大上升高度分布在250〜290cm之间。

Water is the restraining factor of vegetation restoration and sand management and the key factor of the ecological environment in areas of desertification. Capillary rising water is one of the primary sources of water for plants. If capillary rising water can reach the active layer of a psammophyte root system and put the plants in hydraulic contact with groundwater,it can provide favorable conditions for the psammous plants to utilize the groundwater. The aims of this paper were to determine the maximum height of capillary rising water in the area of a deep groundwater table in the southern edge of the Gurbantunggut Desert,Xinjiang,China and provide a theoretical basis for the division of the water sources of sand-fixing plants. Three soil moisture monitoring points located at the foot of the west slope,the foot of the east slope,and the flat land on the east side of a dune(i.e.,the lowland between two dunes)were arranged along the cross-section of a fixed dune in the area of a deep groundwater table at the southern edge of the Gurbantunggut Desert. A neutron soil moisture probe was used to observe the soil moisture in the 0-10-m soil profile and to analyze the soil moisture changes of the different slopes of variation over the seasons from March 2016 to November 2018. Then,the pressure membrane meter method was used to determine the soil moisture characteristic curve using the soil samples of the soil moisture monitoring points. Additionally,a method of intersection between the largest molecular moisture holding capacity and soil water content curve was used to determine the maximum height of the capillary rising water at the test site. The results showed that the soil water content of the 0-130-cm soil layer at different slopes of the dune was greatly affected by external meteorological factors and that the law of seasonal change was obvious. The soil layer from 130 to 570-760 cm was a dry sand layer with a stable soil moisture content. The soil water content in the soil layer below 570-760 cm was primarily affected by the fluctuation of the groundwater table and capillary rising water,and the upper boundary of its water content change could be regarded as the maximum height of the capillary rising water. Moreover,the maximum molecular moisture holding capacity of the test site was 0.026 1 cm3·cm-3,and the maximum height of the capillary water on different slopes of the dune was distributed from 250 to 290 cm. Finally,according to the root distribution characteristics of the constructive species at the test site,this paper preliminarily assumed that such species,e.g.,Haloxylon ammodendron and Haloxylon persicum,can utilize groundwater through capillary rising water.