西北地区沙丘凝结水形成机制及对生态环境影响初步探讨

A preliminary study of the formation mechanism of condensation water and its effects on the ecological environment in northwest China

西北地区沙漠及荒漠化地区,包气带的水分来源除来自大气降水外,还来自凝结水,凝结水对包气带中水分的保存、运移及荒漠植被生态起到至关重要的作用。作者在甘肃省河西走廊高台县西的流动沙漠边缘的半固定沙丘上,采用TSCⅡ智能化土壤水分快速测试仪,SN2202数字温度计、CENTER1300相对湿度仪进行了凝结水观测试验。对沙丘表层0～30cm范围内的气温、地表温度、地温和含水量进行连续观测,每2h观测一次,试验历时5d。试验结果表明,在西北沙漠、荒漠化地区有凝结水存在,它的形成不仅对包气带中水分的保存及分布起着重要的作用,并且对维系荒漠化地区的植被生态系统的稳定至关重要。并对凝结水形成机制进行了初步探索;初步确定,日气候变化造成的地表温度与地温温差是凝结水形成的主控因素,包气带中的含水量分布则控制着凝结水的多寡,凝结水主要出现在干沙层与湿润砂层界面上。

Water contents in the unsaturated zone in the deserts and desertified areas in northwest China come from precipitation as well as condensation water. Condensation water plays an important part in the preservation and transport of water in the unsaturated zone and in the development of vegetation in the desertified areas. An experiment of condensation water was conducted in a semifixed sand dune at the edge of a shifting desert of the west of Gaotai in the Hexi Corridor in Gansu Province. A TSCⅡ soil moisture meter, an SN2202 digital thermometer and a CENTER 1300 relative humidometer were employed in the field. Continual measurements of air temperature, ground surface temperature, and moisture content within depths of 0 to 30cm in the dune was carried for 5 days. Experimental data indicate that condensation water does occur in the deserts and deserfied areas in northwest China. It not only plays an important role in the preservation and occurrence of water contents in the unsaturated zone, but also has an significant bearing on maintaining the stability of the vegetation system in the desertified regions. A preliminary approach to the formation mechanism of condensation water is given in this paper. The preliminary study suggests that daily change in climate resulting from defferences in ground surface temperature and geothermal temperature is the predominant factor controlling the formation of condensation water and the distribution of the water content in the unsaturated zone has an important bearing on the quantity of the condensation water. Condensation water mainly occurs along the interface between dry sand and wet sand.