干旱区干涸湖床地下水—土壤—植被连续体对粉尘释放的控制机理研究

In many arid and semiarid lands, saline lakes, playas, and similar landforms are disturbed as a result of human activity. Diversion and/or consumptive use of surface or groundwaters has created the effect of a climate change in numerous drainage basins, resulting in the desiccation of lakes and reactivation of eolian processes at many locations. Playas are natural sites for extensive eolian activity because of the deposition of clastic and chemical sediments in basins by surface water (via fluvial transport) and groundwater (via efflorescence). Generation of fine particulate dust (PM10)from such landforms play a creates a severe air pollution hazard. Using the playa of Chagannuoer Lake, a large mineral aerosol source in Inner Mongolia, as the study site, field studies were designed to examine various sediment types with respect to their vulnerability to wind erosion and to their general hydrologic setting.Three transects were selected for repeat characterization of physical and mineralogic properties over a 2 year period. Sediment and groundwater samples at all transects were typically taken at different depths to examine the interactions between playa hydrology and playa-surface sediments. One proposed mitigation strategy for PM10 involves establishment of native vegetation to stabilize and trap fugitive sand. This study also investigate soil and groundwater chemistry and the distribution of native plant species in relation to salts and toxic ions in the soil and groundwater along the three transects from vegetated dunes or shorelines to nonvegetated playa surfaces. The interaction mechanism of groundwater-soil-vegetation and its effect on the generation of fine particulate dust will also be investigated. The purpose of the research is to find the suitable groundwaterand soil conditions for local plant survival. Through the restoration of local plant fixed saltation so as to control the emission of aeolian dust. This study will provide scientific support for saline dust storm disaster prevention and ecological restoration for the central and western regions of Inner Mongolia.

针对干涸湖床风蚀输出盐碱粉尘加重大气颗粒物污染的问题，以内蒙古浑善达克沙地边缘的查干诺尔湖干涸湖床及湖滨带为研究区，以风蚀动力学、景观地球化学和地下水依赖型生态系统的基本理论为指导，运用实地观测、采样分析、统计分析和GIS空间分析相结合的方法，研究地下水对干涸湖床沉积物地球化学过程的影响；分析不同地下水条件下干涸湖床表层盐分积累的动态特征及其对盐碱粉尘释放的影响；探究干涸湖床地下水和土壤化学对本地植物生长和分布的控制作用；获取不同地下水—土壤—植被状况下干涸湖床的易蚀性程度及其对风蚀颗粒物的释放、阻滞与固定能力；揭示地下水—土壤—植被连续体的综合效应对干涸湖床粉尘释放的控制机理；在适合本地植物生存的地下水—土壤环境条件下进行本地物种的生态恢复控制和减缓粉尘释放。旨在为内蒙古中西部地区盐碱尘暴灾害防治和生态恢复提供科学支撑，为内陆湖区生态安全调控与管理提供科学依据。

气候变化和人类活动影响下，干旱区湖泊持续萎缩或完全干涸。裸露的干涸湖床成为积盐中心，在大风天气驱动下输出盐碱粉尘，驱动着盐的地球化学循环。本项目以内蒙古浑善达克沙地边缘的查干诺尔湖、巴拉卡斯湖等干涸湖床及湖滨带为研究区，运用实地观测、统计分析、GIS空间分析和模型模拟相结合的方法，研究地下水对干涸湖床沉积物地球化学过程的影响；分析不同地下水条件下干涸湖床表层盐分积累的动态特征，探究干涸湖床地下水和土壤化学对本地植物生长和分布的控制作用；获取不同地下水—土壤—植被状况下干涸湖床粉尘释放规律；揭示地下水—土壤—植被连续体的综合效应对干涸湖床粉尘释放的控制机理。主要研究结果如下：干涸湖床盐分受气候、降水、植被、地下水等综合因素影响，盐分的季节性变化明显，对降雨事件敏感。查干淖尔湖干涸湖床盐分含量和结壳厚度呈现从湖中心到湖滨递减的分布格局，而结壳硬度无明显特征。结壳厚度与沉积物盐分含量显著相关，与含水量不相关。湖心表层沉积物的电导率约为3-4ms/cm,湖滨约为0.08-0.16ms/cm，盐分含量主要受浅层地下水埋深和地下水化学控制。在地下水和盐分含量影响下，干涸湖床植被群落由湖心到湖滨呈现同心环状分布格局，建群种依次是芦苇、盐爪爪、芨芨草、红砂和小针茅，再向外有斑块状分布的合头藜群落，群落空间分布异质性明显，梯度变化显著。地下水埋深由湖心向外围逐渐增加，地下水TDS逐渐减小，地下水埋深为4m左右且TDS较低时，植被群落呈现最大的植被覆盖度、地上生物量和植株高度。地下水、盐分含量和土壤有效磷含量是控制干涸湖床植被分布的核心因素。干涸湖床的表面条件（土壤湿度，植被覆盖、盐分含量和结壳）强烈影响着粉尘释放。基于随机理论发展了沙粒跃移轰击理论并开发了对流湍流模型。将临界摩擦风速（u*t）和跃移系数(c0)视为服从概率分布的参数，确定了它们的最优估计以及概率密度函数。本研究为人工干预下干涸湖床的植被恢复提供指导并推动了风蚀模型的发展。

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