巴丹吉林沙漠高大沙山湿沙层水分特征

Wet Sand Layer Moisture of Mega-dunes in the Badain Jaran Sand Sea

湿沙层水分及其运移过程是沙漠地区水循环的重要环节。巴丹吉林沙漠高大沙山湿沙层规模巨大,本文对巴丹吉林沙漠高大沙山湿沙层水分特征进行了初步分析。结果表明:湿沙层水分具有区域相似性特征,含水量多小于3%;吸附水和沙粒空隙间的水汽是湿沙层水分两种主要的类型,沙粒粒级级配影响吸附水水量变化,两种水分在沙山垂直剖面上的运移过程及相互转化可能维持了湿沙层水分的相对平衡状态;沙丘表层形成的"逆温层"以及由此引起的沿沙丘表层向沙丘内部的热量传递,形成与湿沙层水分蒸发相反的空气运动方向,使得湿沙层水分在夏季晴朗的白天受到保护;夏季受温度梯度影响,湿沙层中的水汽和膜状水向沙山底部缓慢运移;冬季受温度梯度和水势的双重影响,沙山底部潜水面附近的水汽和膜状水向上缓慢运移,补给湿沙层;湿沙层水分来源包括大气降水、大气水汽、凝结水及地下水等。

Wet sand layer moisture and its movement process is the important link for water cycle in desert areas. The mega-dunes in the Badain Jaran Sand Sea contain very huge wet sand layer. The result showed that there was a regional similarity characteristics for wet sand layer moisture with water content less than 3 %. Adsorbed water and water vapor existed in the pore among sand grains were the two primary water types for wet sand layer, and their movement process and reciprocal transformation along the vertical sec- tion of mega-dunes might maintain the relatively poised state of wet sand layer moisture, and grain size dis- tribution had important influence on adsorbed water and its water content. The formation of ＂thermal inver- sion layer＂ in the dune surface layer caused the movement of heat and air to the dune interior, which had an opposite air flow direction with the moisture evaporation of wet sand layer. This was why wet sand layer moisture could maintain in sunny days of summer. Affected by temperature gradient in summer, the water vapor and film water contained in wet sand layer moved slowly toward the bottom of the mega-dunes. Under the dual influence of temperature gradient and water potential gradient in winter, the water vapor and film water near phreatic surface in the bottom of mega-dune moved upward to the top of the mega-dunes and re- charged the wet sand layer. The wet sand layer could get recharged water from atmospheric precipitation, water vapor, condensate water and underground water.