Submarine groundwater discharge (SGD) serves as an important pathway for the transport of dissolved carbon from land to ocean, significantly affecting the coastal biogeochemical cycles. However, the impact of SGD-derived dissolved carbon on the coastal carbon budget remains poorly understood. This study first quantified SGD and associated dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and total alkalinity (TA) fluxes in Daya Bay using mass balance models based on radium isotopes (Ra, Ra, Ra and Ra). We then constructed carbon mass balance models to evaluate the impact of SGD-derived carbon on the buffering capacity against coastal ocean acidification. The estimated SGD fluxes ranged from 0.80 × 10 to 2.64 × 10 m. The DIC, DOC and TA fluxes from SGD were 17.90–36.44 mmol , 0.93–2.13 mmol , and 21.19–28.47 mmol , respectively. Based on carbon mass balances, the DIC flux from SGD was 19–39 times the riverine input, accounting for 27.16 % ∼ 37.64 % of the total carbon source. These results suggest that SGD is a major contributor to DIC, significantly affecting the coastal carbon budget. Furthermore, the average TA:DIC ratio of groundwater discharging into Daya Bay was approximately 1.13. High TA exports enhance the buffering capacity of the coastal ocean and contribute bicarbonate to the ocean, playing a significant role in the ocean carbon sequestration process. This study demonstrates the importance of SGD-derived dissolved carbon in the assessment of coastal carbon budgets.

中文翻译：

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半封闭海湾海底地下水排放的碳输出：对沿海海洋酸化缓冲能力的影响


海底地下水排放（SGD）是溶解碳从陆地转移到海洋的重要途径，显着影响沿海生物地球化学循环。然而，SGD 衍生的溶解碳对沿海碳预算的影响仍然知之甚少。本研究首先使用基于镭同位素（Ra、Ra、Ra 和 Ra）的质量平衡模型量化了大亚湾的 SGD 以及相关的溶解有机碳（DOC）、溶解无机碳（DIC）和总碱度（TA）通量。然后，我们构建了碳质量平衡模型，以评估 SGD 衍生的碳对沿海海洋酸化缓冲能力的影响。估计的 SGD 通量范围为 0.80 × 10 至 2.64 × 10 m。 SGD 的 DIC、DOC 和 TA 通量分别为 17.90–36.44 mmol、0.93–2.13 mmol 和 21.19–28.47 mmol。根据碳质量平衡，SGD 的 DIC 通量是河流输入的 19~39 倍，占总碳源的 27.16%~37.64%。这些结果表明，SGD 是 DIC 的主要贡献者，显着影响沿海碳预算。此外，排入大亚湾的地下水的平均TA：DIC比率约为1.13。高TA出口增强了沿海海洋的缓冲能力，并向海洋贡献碳酸氢盐，在海洋固碳过程中发挥着重要作用。这项研究证明了 SGD 衍生的溶解碳在评估沿海碳预算中的重要性。