旱区沙地大埋深包气带水循环动力机制及其地表植被群落响应

The larger depth vadose zone is the crucial part of the Critical Zone, in which the internal water circulation is the key process to drive the evolution of ecology and biogeochemical evolution. On the basis of our preliminary works, with the larger depth vadose zone of Mu Us sandy land as the research object, the objective of this project is to study the hydrodynamic driving mechanism of the groundwater. Through the indoors interaction experiment of parameters, it clarifies the mutual coupling relation of water, vapor and heat in the parameters expression. Through the systematic monitoring of the water, vapor and heat factor in the different layers of the profile, it expounds their migration and distribution rules under the action of freeze-thaw process and interface effects. By establishing the isotope mass transfer model of water -vapor- vegetation uptake and jointing water - vapor – heat and vegetation uptake coupling model simultaneously, it tracks the driving mode of water cycle and the response to driving forces under different special and temporal scale (surface and deeper) so as to explore different water cycle, source, migration direction and flux and their influence on vegetation community structure in the surface, which reveals the unified hydrological cycle mechanism and their feedback to ecological process from the surface to deep groundwater. Based on the project research, we can re-examine the inner drive mechanism of vadose water circulation, from the new perspectives of the Critical Zone’s multi-scale, multiple interfaces, multi-process and elements. It provides the basis for the research of ecological and biogeochemical evolution and efficient service to the ecological civilization construction work in arid regions as well.

大埋深包气带是地球关键带的核心地带，其中的水循环是驱动内部生态与生物地球化学演化的关键过程。项目拟在前期研究基础上，以毛乌素沙地地下水大埋深区为研究对象，围绕水循环动力驱动机制开展研究。通过室内水分和温度参数交互实验，明确影响水汽热运移参数的互耦关系；通过剖面各层位水、汽、热因子系统监测，阐明冻融过程和界面作用下液态水、汽态水和热的运移及分布规律；通过建立水-汽-植同位素质量迁移模型，同时联合水-汽-热与植被吸水耦合模型，追踪不同时空尺度(地表和深部)下水汽循环轨迹，探究水循环过程对驱动因素的响应、水汽来源、运移方向和通量及其对植被群落结构的影响，揭示地表与深部统一水文循环机制及其生态过程的反馈。通过项目研究，在基于地球关键带多尺度、多界面，多过程、多要素的新视角，重新审视包气带水循环内在驱动机制，为关键带生态、生物地球化学演化研究提供基础，并有效服务于旱区水资源利用和生态文明建设工作。

包气带水循环是驱动内部生态与生物地球化学演化的关键过程，探究大埋深包气带系统生态-水文耦合物理过程及其背后机理，对深化干旱半干旱地区地表能量转换和内部质量迁移、水资源利用与地表水文生态效应过程等意义重大。本项目以毛乌素南缘地下水大埋深区为研究对象，通过室内水分和温度参数交互实验，明确了影响水汽热运移参数的互耦关系；通过野外调查、建立裸地与不同植被地原位监测系统（包括气象因素、土壤水热、植被耗水等），围绕地表与包气带深部统一水文循环机制及其生态过程反馈目标，开展了包气带冰-水-汽-热耦合过程程序研发与模型构建、裸地包气带水循环机制、典型植被耗水特性、植被影响下土壤水循环过程、基于同位素的生态-水文作用过程等研究，取得如下主要成果：（1）研发了冻融过程包气带水汽热耦合运移数值计算程序，并可用于不同质地和环境条件下的土壤水汽热耦合运移过程研究。（2）明确了土壤孔隙中水汽压与水汽密度时空分布特征，量化了不同土壤深度水汽通量及其迁移驱动因素，为后续在生态水文、水灾害等方向研究中综合考虑气态水影响奠定基础。（3）厘清了干旱、湿润和冻融关键过程驱动作用下土壤水分通量变化规律，揭示了季节性冻土区包气带土壤水分迁移机制，证实了开展水汽热耦合运移研究的必要性，深化了季节性冻土区土壤水循环理论。（4）阐明了不同时间尺度植被蒸腾速率的生物物理驱动因素，明晰了典型植被在休眠期（冻结期）与生长季的耗水规律，拓展了现有生态水文交叉学科的研究领域。（5）探究了灌丛覆盖下土壤液态水和水汽通量日变化规律及其对干旱与湿润水文过程的响应，阐明了生长季植被对土壤水、汽传输过程的影响，为生态脆弱区植被恢复提供科学支撑。（6）基于降水-土壤水-植被耗水氢氧同位素特征，精细刻画了沙柳土壤干旱和降水入渗水文过程及植被耗水策略，为沙地植被系统生态水文耦合过程研究提供坚实基础。