黄河源沙漠中月牙泉群的特性及形成机理

月牙泉是沙漠里地下水水位抬升在沙丘间形成的小湖泊。近年来黄河源沙漠新增加了数千个月牙泉，这种小湖泊群的形成和增长对于遏制黄河源区的沙漠化和改善源区生态具有重要意义。通过连续4年的野外调研和遥感解译，分析研究了黄河源月牙泉群的形成机理和运动特性。黄河源沙漠围绕黄河故道发育，以卵石和细沙组成的沉积物渗流发育，地下水渗流可传播几十千米补给月牙泉。特别是2002年建成黄河源大坝蓄水，抬高了鄂陵湖水位和临近地区的地下水水位，把鄂陵湖下游沙漠月牙泉的分布从30 km往下游扩展到60 km，沙漠月牙泉个数和面积迅速增加了3倍。新生的月牙泉具有活动性，移动速度3~13 m/a。如果月牙泉得到地下水的持续补给，周边沙丘发育植被逐渐稳定，黄沙发生风化，表层和浅层泥沙级配出现20%的风化黏土细颗粒，最终植被发育，稳定并绿化了沙漠。

Formation mechanisms of crescent spring lakes in Huangheyuan desert

The crescent spring lakes are the small lakes in the desert due to uprising of the ground water table and gushing water from the depressions between sand dunes. There are several thousands of the crescent spring lakes in the Huangheyuan desert, which are important for improving the ecology of the Yellow River source. The authors studied the formation and mechanisms of the crescent spring lakes through field investigations and the remote sensing interpretation from 2011 to 2014. The Huangheyuan desert develops on the old Yellow River bed on the Qinhai-Tibet Plateau. The sediment deposit underneath the ground surface consists of gravel and sand, thus the ground water may flow through the interstices between the particles for several tens of kilometers and provide water to the crescent spring lakes. Climate change and increased precipitation have resulted in uprising of the ground water and formation of many crescent spring lakes in the past decades. The impoundment of the Huangheyuan dam reservoir raised the water level in the Erling Lake to 4 273 m in 2002. Consequently, the ground water table in the Huangheyuan desert was suddenly raised by 20 m and the distribution of the crescent spring lakes extended from 30 km to 50 km from the Erling Lake. The number of the crescent spring lakes increased by 3 times and the total water surface of the crescent spring lakes in the desert was doubled. The new crescent spring lakes are not stable and may move with sand dunes for a distance of 3~13 m a year. If the crescent spring lakes receive water supply for more than a decade, the herbaceous vegetation develops on the sand dunes, the surface sand is weathered and the sediment particles become finer, the desert will be stabilized and become a greenland.