Carbon cycles in coastal waters are highly sensitive to human activities and play important roles in global carbon budgets. CO₂ sink–source behavior is regulated by spatiotemporal variations in net biological productivity, but the contribution of macrophyte habitats including macroalgae aquaculture to atmospheric CO₂ removal has not been well quantified. We investigated the variations in the carbonate system and dissolved organic carbon (DOC) in human-impacted macrophyte habitats and analyzed the biogeochemical drivers for the variations of these processes. Cultivated macroalgal metabolism (photosynthesis, respiration, calcification, and DOC release) was quantified by in situ field-bag experiments. Cultivated macroalgae took up dissolved inorganic carbon (DIC) (16.2–439 mmol-C m⁻² day⁻¹) and released DOC (1.2–146 mmol-C m⁻² day⁻¹). We estimated that seagrass beds and macroalgae farming contributed 0.8 and 0.4 mmol-C m⁻² day⁻¹ of the in situ total CO₂ removal (5.7 and 6.7 mmol-C m⁻² day⁻¹, respectively) during their growing period in a semi-enclosed embayment but efficient water exchange (i.e., short residence time) in an open coastal area precluded detection of the contribution of macrophyte habitats to the CO₂ removal. Although hydrological processes, biological metabolism, and organic carbon storage processes would contribute to the net CO₂ sink–source behavior, our analyses distinguished the contribution of macrophytes from other factors. Our findings imply that macroalgae farming, in addition to restoring and creating macrophyte habitats, has potential for atmospheric CO₂ removal.

沿海水域的碳循环对人类活动高度敏感，在全球碳预算中发挥着重要作用。 CO ₂汇-源行为受净生物生产力的时空变化调节，但包括大型藻类水产养殖在内的大型植物生境对大气CO ₂去除的贡献尚未得到很好的量化。我们研究了受人类影响的大型植物栖息地中碳酸盐系统和溶解有机碳（DOC）的变化，并分析了这些过程变化的生物地球化学驱动因素。通过原位野外袋实验对培养的大型藻类代谢（光合作用、呼吸、钙化和 DOC 释放）进行量化。培养的大型藻类吸收溶解的无机碳（DIC）（16.2–439 mmol-C m ^-2  day ^-1）并释放DOC（1.2–146 mmol-C m ^-2  day ^-1）。我们估计，海草床和大型藻类养殖在其生长期贡献了原位总 CO ₂去除量的0.8 和 0.4 mmol-C m ^-2  day ^-1（分别为 5.7 和 6.7 mmol-C m ^-2  day ^{-1 ）。半封闭的海湾但在开放的沿海地区进行有效的水交换（即短的停留时间）排除了检测大型植物栖息地对CO} ₂去除的贡献。尽管水文过程、生物代谢和有机碳储存过程都会对CO ₂净汇-源行为做出贡献，但我们的分析将大型植物的贡献与其他因素区分开来。我们的研究结果表明，大型藻类养殖除了恢复和创造大型植物栖息地外，还具有去除大气中CO ₂的潜力。