砂质海滩地下淡水排泄与孔隙水交换对营养盐输入贡献

海底地下水排泄（SGD）是海洋中营养物质的重要来源，显著影响海洋生态环境。地下淡水排泄和孔隙水交换是SGD中两种不同的动力机制，准确评估SGD输入的营养盐通量依赖于SGD动力机制的研究。本项目拟选取阳江市典型砂质海滩为研究对象，通过原位地下水动态监测与取样、达西定律和镭钍同位素（224Ra/228Th）不平衡体系等方法，探究潮汐驱动下砂质海滩地下水动力特征，以及沉积物中224Ra的亏损状态，从沉积物的角度揭示沉积物-水界面处孔隙水交换空间变化规律。基于地下水中营养盐的变化特征，定量评估地下淡水排泄和孔隙水交换输入的营养盐通量，厘清两种动力机制对营养盐的输入贡献。本项目的实施有助于提高海岸带地下水-海水相互作用对营养盐输入的认识，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 nutrients to the ocean and it may significantly influence the marine ecological environments. Submarine fresh groundwater discharge and porewater exchange are two different dynamic mechanisms in SGD. The accurately evaluating nutrient fluxes from SGD depend on the study of the dynamic mechanism of SGD. This project intends to select a typical sandy beach in Yangjiang City as the research area. In this work, multiple methods including the in-situ groundwater dynamic monitoring and sampling, Darcy’s law and 224Ra/228Th disequilibria, will be used to analyze the hydrodynamic processes in the aquifer. The 224Ra deficit with respect to 228Th will be used to reveal the spatial variation of porewater exchange across the sediment-water interface of the sandy beach. The nutrient fluxes from fresh submarine groundwater discharge and porewater exchange will be quantitatively evaluated based on the spatial variation of nutrients in groundwater. Further, the contribution of two dynamic mechanisms to nutrient inputs will be clarified. This project will help improve the understanding the interactions between groundwater and seawater affecting nutrient inputs in the coastal zone, and provide scientific basis for assessment and management of marine environments.