黑河下游额济纳地区的环境演变

通过对水系变迁的分析,勾画了黑河下游额济纳地区环境变化的大体框架。黑河下游额济纳地区的环境变迁,演绎了西北干旱地区普遍存在的水系溯源退缩过程。在地质历史时期,这种溯源退缩主要原因是地质运动和气候变化,而近代、现代人类不合理的水土资源开发活动加速了河流水系的溯源退缩,并在一定程度上超过了自然因素的作用。巴丹吉林沙漠曾经是黑河下游的冲积湖积平原。那么如果绿洲消失,额济纳三角洲就有可能再现巴丹吉林沙漠的形成过程,形成新的"额济纳沙漠"。在第四纪早期,额济纳盆地存在两个水流系统,且气候环境较为温暖潮湿;随后两个水流系统逐渐合并,区域气候亦有变干变暖的趋势;至第四纪晚期,气候更加干旱,现代水文网定型。东西居延海不是黑河流域的终端湖,在地质历史上属于黑河流域下游的河道湖。随着黑河水系不断地溯源萎缩,东西居延海及居延泽也存在着一个逐步缩小的过程,并在近现代演变为尾闾湖。显然,东西居延海作为尾闾湖只是一个很短暂的时期。

ENVIRONMENTAL CHANGES OF EJINA REGION IN THE LOWER REACHES OF HEIHE RIVER

According to analysis of the evolution of the river courses, this paper presented the environment changes in the lower reaches of Heihe River approximately. As the common scenes in arid areas in Northwestern China, the environment changes caused by the processes of water system shrinking with tracing to the sources mainly because of the tectonic movement and climate changes in the geologic historical times. The processes were accelerated by the unreasonable development of water and land resources during recent 2,000 years. Badain Jaran Desert were the lower reaches of Heihe River. The Ejina Delta would be Ejina Desert if the Ejina Oasis disappeared as the processes of Badan Jaran Desert formation. In the early Pleistocene, there were two water systems in Ejina Region with the warm and humid climate relatively. Afterwards, the two water systems combined one system with the drought climate. In the late Pleistocene, modern water system was formed as the climate was much more drought. The Juyan Lakes were not the terminal lakes of Heihe River but were river channel lakes in the geological period. They pxperienced processes of reducing and disappearing as the water system shrinking of Heihe River courses, therefore, were terminal lakes in modern times with an ephemeral period obviously.