额济纳绿洲浅层地下水动态监测研究及其进展

SHALLOW GROUNDWATER REGIME AND ITS DRIVING FORCES IN THE EJINA OASIS

浅层地下水动态是影响与制约我国西北干旱区黑河流域下游额济纳绿洲生态系统维持与修复的根本要素之一.本文通过梳理近年来额济纳绿洲浅层地下水动态变化的研究成果,结合典型观测站点的地下水水位与盐分自动监测（2010～2013年）,回顾了该地区地下水监测站网的发展阶段,归纳了地下水年际动态变化特征及其空间变化类型,综述了其驱动因素.地下水动态长期观测的综合分析结果表明,该地区浅层地下水水位自20世纪50年代起开始下降,一直持续到20世纪90年代末期,2000年生态输水之后,地下水位整体得到回升.根据地下水时空动态变化特征及其驱动因素,可以将研究区划分为4个典型区域：以河道渗漏补给与植被蒸腾作用为主的河岸带;以区域地下水侧向补给与潜水蒸发作用为主的荒漠戈壁带;以地下水依赖型生态系统蒸散发与区域地下水侧向补给作用为主的天然绿洲区;以地下水开采与人工回灌作用为主的人工绿洲区.研究认为,间歇性河流的渗漏补给以及荒漠-绿洲生态系统的蒸散发是该地区浅层地下水系统动态变化的主要驱动因素.此外,人为配置地表水资源与局部开采地下水资源加剧了地表水与地下水之间的相互转化,改变了浅层地下水系统的天然动态.为了定量识别生态输水配置下的地表水-地下水相互转化及其与生态环境之间的关系,下一阶段的研究应以地表水/地下水系统动态联合监测为基础,深入开展关键水文过程野外试验研究,同时强化人类调控下的水文过程多尺度综合模拟.

Shallow groundwater dynamics is crucial for the maintenance and restoration of ecosystems in the Ejina Oasis,an island shaped natural oasis that is located within the Gobi Desert of the lower Heihe River basin in Northwestern China.Based on the comprehensive analysis of recent research on the shallow groundwater regime in the Ejina Oasis,combined with our monitoring results of groundwater level and salinity at the typical field sites during the period of 2010 ～ 2013,the basic stages of groundwater monitoring were concluded,and also the characteristics of spatial and temporal variations in shallow groundwater system and their driving forces were summed up.Overview of the long-term groundwater dynamics indicates that the shallow groundwater level started to decline after 1950,reaching its minimum extent in the end of the twentieth century; however,a noticeable increase in groundwater table has been observed since 2000 due to the environmental flow controls.The Ejina Oasis can be categorized into four typical patterns that reflect the dominant hydrological processes：（1） The riparian zone,controlled by riverbank filtration and plant evapotranspiration; （2） The Gobi Desert area,dominated by lateral flow recharge and groundwater evaporation; （3） The natural oasis area,controlled by lateral flow recharge and plant evapotranspiration; and （4） The man-made oasis area,dominated by surface-groundwater interactions caused by human activities.Groundwater recharge from ephemeral river systems and evapotranspiration of desert-oasis ecosystems are considered to be the main driving forces in the shallow groundwater dynamics of this region.Additionally,over-allocating the limited surface water resources as well as local groundwater exploitation has intensified the surface water and groundwater exchange,which changed the natural regime of shallow groundwater system.For quantifying water flux exchange between surface water and groundwater and estimating the impact of water exchange on the ecosystems,the next step in the research should be based on the comprehensive monitoring of the surface-groundwater systems,and also the field study on the key hydrological processes.In addition,the multi-scale integrated hydrological modeling by considering the human activities affect should be strengthened.