节水改造对大型干旱灌区水盐运移过程的影响机理及生态环境效应

To improve the utilization efficiency of water resources, water-saving rehabilitation improvements have been carried out for large-scale irrigation districts. However, these measures have caused a series of problems about ecological environment, which include changing the process of water cycle, reducing the groundwater quantity, impacting on the vegetation cover and species diversity. In this project, Hetao Irrigation District, located in Inner Mongolia, China, is selected as a research area, and a series of field experiments will be carried out. On the basis of the experimental data, the impact of water-saving rehabilitation on the process of water and salt transport will be analyzed with a distributed water and salt balance model developed in this project. Based on RS and GIS, the dynamic changes of land use and vegetation covers will be studies. With the investigate results of main factors of ecological environment, the relationship between the land use and vegetation covers dynamic changes and temporal and spatial distribute of main factors of ecological environment will be analyzed. Taking into account the distribution of canals and ditches, a three-dimensional transport model of water and salt in the unsaturated-saturated zones will be improved with data assimilation methods. Using this model, the impact of water-saving rehabilitation on ecological environment will be assessed quantitatively. According to the assessment results, the threshold value of ecological safety will be determined, and the management measures for sustainable use of water and land resources will be made. This study can provide a theory basis and technical support for sustainable development of large-scale irrigation district.

节水改造工程在给我国大型灌区带来正效应的同时，也带来一系列生态环境问题，包括改变灌区水文循环过程、减少地下水入渗补给、影响植被种类和生物多样性等。本项目选择内蒙河套灌区为研究区，通过微区控制试验、田间定位监测和灌区样带调查等手段，借助RS/GIS、数据同化、统计分析和数值模拟等关键技术和方法，建立土壤含水量和含盐量对潜水蒸发变化的响应关系，构建灌区尺度的分布式水盐运移平衡模型，定量分析节水改造对灌区水盐运移过程的影响，确定灌区主要生态环境要素时空分布格局与土地利用/覆被变化之间的互馈关系，完善考虑渠系分布的三维饱和-非饱和带水盐运移模型，评估与预测节水改造对灌区生态环境效应的影响，提出维持植被与作物正常生长的生态安全阈值和水土资源可持续利用的适应性管理对策，为灌区经济社会可持续发展和生态型灌区建设提供理论依据和技术支撑。

节水改造工程在给我国大型灌区带来正效应的同时，也带来一系列生态环境问题，包括改变灌区水文循环过程、减少地下水入渗补给、影响植被种类和生物多样性等。本项目选择内蒙河套灌区为研究区，通过微区控制试验、田间定位监测和灌区样带调查等手段，借助RS/GIS、数据同化、统计分析和数值模拟等关键技术和方法，分析了不同时间尺度地下水位变化的主控因素，指出影响季节尺度和日尺度变化的主控因素分别为温度和辐射；建立了地下水埋深对潜水蒸发变化的响应关系，结果显示指数函数关系拟合较好；构建了灌区尺度的分布式水盐运移平衡模型，定量了分析节水改造对灌区水盐运移过程的影响，评估与预测了节水改造对灌区生态环境效应的影响，指出水资源联合利用的节水方案可有效提升水资源利用率（减少引黄水量52%），并降低地下水位近70cm；采用RS、GIS和数理统计分析相结合的方法分析了生态环境要素时空分布特征及其影响因素；量化分析了灌溉对区域尺度地下水水化学的影响，结果显示蒸发浓缩和溶滤作用对灌区地下水水化学特征的影响占主导地位，且秋浇之后地下水TDS平均增加了约33%；提出了维持植被与作物正常生长的生态安全阈值（地下水埋深应维持在1.5-2.5m范围），为灌区经济社会可持续发展和生态型灌区建设提供理论依据和技术支撑。