湖底地下水补给对渗漏型湖泊CO2汇的影响机制

湖泊是调控内陆碳循环的重要环节，其水文过程显著影响着温室气体的平衡动态。地下水不仅是湖泊水量的重要源汇项，而且对湖泊碳收支的贡献不可忽视。在地下水超采区，湖泊渗漏（即：湖底地下水补给，LGR）普遍存在，准确评估LGR通量是正确认识渗漏型湖泊碳汇过程中地下水作用的重要前提。本项目拟选取典型渗漏型湖泊——白洋淀为研究场地，通过湖水-地下水分层监测采样、氡同位素（222Rn）示踪技术和涡度协方差理论方法，探究LGR作用下碳循环的季节变化特征和人工补水响应规律，识别地下水-湖水-大气两个关键界面CO2交换通量的相关关系，验证关键科学假设，即LGR抑制沉积物-湖水界面CO2扩散和促使CO2迁移埋藏的过程效应，从水文地质学角度揭示LGR对渗漏型湖泊CO2汇的影响机制。通过本项目的实施将为全面认识渗漏型湖泊CO2汇的过程因素提供新的见解，并为此类湿地补水修复和环境评价提供科学依据。

Lakes are vital links in regulating the inland carbon cycle, whose hydrological processes significantly affect the greenhouse gas balance dynamics. Groundwater is not only a major source or sink of lake water, but also contributes significantly to the lake carbon budget. In groundwater overexploitation areas, lake leakage (i.e., lacustrine groundwater recharge, LGR) is commonly ongoing. Accurate assessment of LGR fluxes is a key prerequisite for correctly understanding the role of groundwater in the carbon sink processes at leaky lakes. This project plans to research at one typical leaky lake, namely, Baiyangdian Lake. With stratified monitoring and sampling lake water and groundwater, radon isotope (222Rn) tracing technology and eddy covariance method, the seasonal variation characteristics and response pattern to artificial water replenishment of carbon cycle under LGR processes can be explored. The correlation between CO2 exchange fluxes at the two key interfaces of groundwater-lake-atmosphere will be identified, so as to validate the principle scientific hypothesis, i.e., the effect of LGR processes on both inhibiting the diffusion and promoting the migration-burial of CO2 at the sediment-lake interface. These will reveal the influence mechanism of LGR on CO2 sink for the leaky lake, from the perspective of hydrogeology. The implementation of this project will provide an innovative insight for comprehensively understanding the procedural factors of CO2 sinks in leaky lakes, and provide a scientific basis for such wetland replenishment restoration and environmental assessment.