海底地下水排泄（SGD）是海洋溶解无机碳（DIC）的重要来源，显著影响海洋生态环境。准确评估SGD入海碳通量对正确认识SGD在海洋碳循环和平衡中的作用有着重要意义。而厘清咸淡水混合带地下水-海水交互作用过程中DIC和镭同位素的迁移转化及其控制机制对准确量化SGD入海无机碳通量至关重要。本项目拟选取具有砂质海岸的北津湾为研究对象，通过原位地下水动态监测与取样、数值模拟和同位素示踪等技术，耦合潮汐驱动作用下砂质海滩地下水动力过程及DIC和镭同位素的迁移转化过程，揭示地下水-海水交互作用过程中地下水中DIC和镭同位素的分布、运移规律及其控制机制。在此基础上，识别DIC与镭同位素的相关关系，并建立镭同位素质量平衡模型，准确量化SGD向海输入的DIC通量，探讨该过程可能引发的环境效应。本项目的实施将为砂质海岸SGD入海无机碳通量的评估提供新的见解，同时为近岸海洋环境评价和管理提供科学依据。

Submarine Groundwater Discharge (SGD) has been recognized as an important source of dissolved inorganic carbon (DIC) to the ocean that may significantly influence the marine ecological environments. Thus, accurately evaluating the SGD associated DIC fluxes into ocean is of great significance to advance the understanding the role of SGD in global carbon cycling and balance. However, clarifying the transportation-transformation processes of DIC and radium isotopes and control mechanisms in the mixing zone during groundwater-seawater interactions becomes critical for accurately quantifying the SGD associated DIC fluxes. This project intends to select Beijin Bay with the sandy coasts, the northern South China Sea as the study area. In this work, we will use multiple methods including the in-situ groundwater dynamic monitoring and sampling, numerical simulation and isotope technique. The hydrodynamic processes and the transportation-transformation processes of DIC and radium isotopes in groundwater will be combined to reveal how groundwater-seawater interactions affect their distribution characteristics and migration patterns at the sandy beach. Based on above analysis, the possible correlation between DIC and radium isotopes in coastal groundwater will be identified, and then the radium mass balance models will be established to accurately quantify the DIC fluxes from SGD and reveal the potential environmental effects. The results will gain new insights for the estimation of SGD associated carbon fluxes, and provide scientific basis for assessment and management of marine environments.