南水北调东线受水湖区域水循环结构变化及氮迁移转化机理研究

Water delivered by the South-to-North Water Diversion Project (SNWDP) can raise water table of the hyporheic zone in receiving water lake. Increased hydraulic gradients inland from the lake would significantly change the surface water-groundwater interaction and further affect the environmental behaviors of nitrogen in the hyporheic zone. A typical experimental station located in the sub-basin of the Nansihu Lake basin was chosen to evaluate mechanism of water circulation of the basin. Observation wells system in hyporheic zone would also be established to assess the effects of inter-basin water transfer on water circulation and nitrogen cycle. To achieve these objectives, precipitation, soil water, groundwater and river water samples would be regularly collected to analyze their major ions, stable isotopes and different forms of nitrogen etc. Combining the results of field survey, the mechanism of nitrogen cycles in the soil water-surface water –groundwater continuum would be proposed by using CFCs and multiple environmental tracers such as stable isotopes. Proportions of nitrogen loading in lake water inputted by shallow groundwater would be calculated based on mass balance equations. Prediction of this contribution can be carried out by dating the shallow groundwater and identification the groundwater flow system.

南水北调东线大规模调水能够打破受水区南四湖流域原有的水系统平衡，使得局地地表水-地下水交互带水循环结构发生改变，进而影响氮在地下水-土壤水/间隙水-地表水连续体中迁移转化过程。围绕“受水区水循环和氮循环系统对补水过程响应与反馈”这一关键科学问题，本研究在南四湖流域选取典型实验场，构建交互带内地下水分层监测网，通过流域野外采样和长期定点观测相结合的方式，利用多种同位素示踪和地下水测龄技术，在点-面-流域不同尺度上阐明南四湖流域水循环结构特征，揭示交互带内浅层地下水流动系统对补水过程的响应机制；采取对比研究和综合分析相结合的方式，阐明补水过程对氮在交互带内地下水-土壤/间隙水-地表水连续系统中的迁移转化的影响。基于流域氮污染水平、来源解析和地下水滞留时间的研究，在大的格局上把握全流域浅层地下水氮的环境行为与归趋，阐明流域浅层地下水对湖水氮负荷的贡献率及其影响的时间尺度效应。

本研究针对南水北调东线受水湖湖水水质变化特征，阐明补水过程对东线受水湖水质影响程度及机理开展研究。选取南四湖与东平湖开展研究，阐明典型污染物在受水湖泊中含量水平、来源解析和地下水对地表水影响，在大的格局上把握全流域调水对污染物环境行为与归趋。针对受水湖沉积物中重金属污染特征开展研究，构建湖泊沉积历史，反演重金属的污染过程与来源，为区域水污染防治提供科学的支撑。