沙层水分小尺度地域分异特征——以沙坡头沙区为例

The features of small-scale regional differentiation of sand layer moisture——a case study of the Shapotou area

水分是沙漠地区生态环境的限制因子,研究沙漠沙层水分分布规律对在沙区种植人工植物进行固沙有显著指导意义。通过对沙坡头沙区两个典型流动沙丘不同坡向、不同部位以及两个洼地进行采样,研究该区水分平衡与小尺度水分分异特征与规律,结果表明:(1)流动大沙丘顶部沙层水分含量一般在1.00%以下,中部水分含量一般在1.00%—2.00%,底部水分含量一般在2.00%—3.00%,均以薄膜水形式存在。洼地沙层2.0—3.0m左右深度有饱和重力水甚至地下水出现。(2)流动大沙丘的迎风坡沙层水分高于背风坡,沙丘水分含量均是底部最高,中部次之,顶部最低。(3)沙坡头区沙层水分属于快速入渗型水分正平衡,洼地或平坦地段是大气降水向下入渗的主要渠道。

Background,aim,and scope Water is the limiting factor of the ecological environment in desert areas.Studying the moisture content,forms and distribution characteristics of sand layers has guiding significance for planting artificial plants to fix sand in desert area.Materials and methods In this paper,two typical mega-dunes and two depressions were sampled to study the moisture content,forms and distribution characteristics of sand layers in Shapotou area.Results The variation of moisture content in sand layers of mega-dunes can be divided into four levels.The first level is characterized by moisture varied actively,which occurs from the surface to a depth of approximately 0.4 m.The second level occurs from a depth of approximately 0.5 m to 1.0 m.The third level occurs from a depth of approximately 1.0 m to 2.0 m.The fourth level occurs at a depth below 2.0 m.On the other hand,the variation of moisture content in the sand layers of depressions can be divided into three levels.The moisture content in the first level is below 5.00%,between 5.00%and 25.00%in the second level,and above 25.00%in the third level.Discussion In general,any moisture content less than 5.00%should be called film water,higher than 5.00%should be called gravitational water.The moisture content in both of the megadunes were less than 5.00%,indicating that the moisture present is film water.The peak of moisture content in most boreholes appears in the middle or upper middle sections,but also some reached to a depth(below 0.5 m)that not affected by evaporation.This finding indicates that atmospheric precipitation is one of the sources supplying groundwater in Shapotou area.Gravitational water appears in the bottom of the depressions,and connects with the capillary water and groundwater.Conclusions The results show that:(1)the moisture content at the top of the mega-dunes is below 1.00%,in the middle of it between 1.00%and 2.00%,at the bottom of it between 2.00%and 3.00%,which indicates they are all film water.(2)The moisture content on the windward slopes of the mega-dunes are higher than the leeward slopes.The highest moisture content exists at the bottom of mega-dunes,followed by the middle,and lowest at the top.Saturated gravitational water or groundwater often occurs at a depth of approximately 2.0 m to 3.0 m in the sand layers.(3)There exists positive moisture balance in the sand layers due to the rapid infiltration in Shapotou area,and the depressions or flat sections are the main channels for atmospheric precipitation infiltrate downward.Recommendations and perspectives It is possible to adopt trees and grass,or utilize greenhouses to control desertification in depressions or flat lots where more groundwater exists,according to the regional differentiation law of moisture content.On the other hand,engineering measures such as clay or gravel barriers and“grass grids”should be adopted to control desertification in mega-dunes comprehensively.