毛乌素沙地沙丘干沙层水分特征初步研究

Preliminary Study on Soil Moisture Content in Dried Layer of Sand Dunes in the Mu Us Sandland

干沙层对抑制蒸发保护沙漠地区的生态水具有重要作用.在毛乌素沙地进行水分实验观测表明,当地干沙层的厚度在12～20 cm,干沙层内部的平均含水量在0.42%～0.54%,且水分由地表向下边界呈指数增加,R2在0.88～0.99之间.干沙层的厚度变化与所处沙丘的位置、沙面活动程度以及有无植被覆盖等有关.降雨对近地表干沙层的消失和产生有重要影响,近地表干沙层的发育是水分下渗、蒸发和水汽凝结共同作用的结果.

The study area （37°38＇42＂-37°42＇42＂N, 108°50＇54＂- 108°58＇00＂E） is located in the southern marginal zone of the Mu Us Sandland in the northern part of Jingbian County, Shaanxi Province. In the area it belongs to the semiarid climate, the annual precipitation is 395.4 mm, the rainfall occurs mainly during the period from July to September and its proportion occupies 80 % of the annual precipitation, and the annual evaporation is as high as 2 361.6 mm; the annual temperature is 7.8 ℃, and the diurnal-nocturnal temperature difference is high; the annual sunshine duration is 2 768.8 hours, strong winds occur frequently, especially in winter and spring, the annual days of occurring strong winds are 19.2 days, the annual average and maximum wind speeds are 3.2 m/s 24.0 m/s respectively, and the direction of prevailing wind is NW. In the study area soil is dominated by aeolian sandy soil, the soil fertility is poor, the natural vegetation is sparse, and the areas of mobile-dune regions and semi-fixed sandlands occupy 31.6% and 36.5% respectively. Dried sand layer plays an important role in restricting evaporation and conserving ecological water in deserts. The experiment in the Mu Us Sandland reveals that the thickness of dried sand layer varies in a range of 12-20 cm, the soil moisture content in the dries sand layer varies in a range of 0.42 % -0.54 % and is increased downward in an exponential way, and R2 varies in a range of 0.88-0.99. The thickness of dried sand layer is related to the dune location, mobile degree of sand surface, vegetation types and coverage, etc. Rainfall affects significantly the soil moisture content, the dried sand layer disappears and the peak values of soil moisture content occur in succession and reduce downward after rainfall. Evaporation brings about a reoccurrence of the dried sand layer.