Saltmarshes are a blue carbon ecosystem accumulating large quantities of organic carbon in sediments. Some of this carbon can be transformed into dissolved inorganic carbon (DIC) and methane (CH₄) that may eventually be exported to the ocean or atmosphere. Although extensive studies have quantified specific components of the carbon budget such as carbon burial, limited attention has been given to pore-water-derived carbon and total alkalinity (TA) exports to the ocean. Here, we quantified lateral exports to the ocean (outwelling) of 202 ± 160 and 78 ± 75 mmol m⁻² d⁻¹ of DIC and TA, respectively. The TA : DIC concentration ratio in the creek waters was ~ 1, implying TA production from anaerobic mineralization in sediments. The lateral TA exports were comparable to the local (94 ± 48 mmol m⁻² d⁻¹) and national (~ 50 mmol m⁻² d⁻¹) organic carbon burial. High TA exports could locally increase the ocean buffering capacity and contribute bicarbonate to the coastal ocean, acting as a long-term carbon storage. Pore water traced by radon contributed 28–37% and 58–69% of DIC and TA exports. Separating the two major DIC components (i.e., CO₂ emissions and alkalinity exports) is essential to resolve the carbon sequestration potential from saltmarshes. Here, dissolved CO₂ emissions to the atmosphere accounted for 3–5% of total DIC outwelling. CH₄ emissions played a minor role offsetting around 0.3 to 6% of the carbon sequestration. Overall, we demonstrate that alkalinity export into the ocean can be an overlooked carbon sequestration pathway in saltmarshes at rates comparable to carbon burial.

中文翻译：

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向海洋输出碱度是大潮盐沼的主要碳封存机制

盐沼是一个蓝色碳生态系统，沉积物中积累了大量的有机碳。其中一些碳可以转化为溶解的无机碳 (DIC) 和甲烷 (CH ₄ )，最终可能会排放到海洋或大气中。尽管广泛的研究已经量化了碳收支的特定组成部分，例如碳埋藏，但对孔隙水衍生的碳和向海洋的总碱度 (TA) 输出的关注有限。^{在这里，我们量化了 202 ± 160 和 78 ± 75 mmol m -2} d ^-1向海洋的横向出口（外流）分别为 DIC 和 TA。小溪水中的 TA : DIC 浓度比约为 1，这意味着沉积物中厌氧矿化产生了 TA。横向 TA 输出与当地 (94 ± 48 mmol m ^-2 d ^-1 ) 和国家 (~ 50 mmol m ^-2 d ^-1 ) 有机碳埋葬相当。高 TA 出口可以在当地增加海洋缓冲能力，并为沿海海洋贡献碳酸氢盐，作为长期碳储存。氡追踪的孔隙水占 DIC 和 TA 出口的 28-37% 和 58-69%。分离两个主要的 DIC 成分（即 CO ₂排放和碱度输出）对于解决盐沼的碳封存潜力至关重要。在这里，溶解的 CO₂排放到大气中的排放量占 DIC 外流总量的 3-5%。CH ₄排放在抵消大约 0.3% 至 6% 的碳封存中发挥了次要作用。总体而言，我们证明向海洋输出碱度可能是盐沼中一个被忽视的碳封存途径，其速率与碳埋藏相当。