Macroalgal metabolism and lateral carbon flows can create significant carbon sinks
Macroalgal metabolism and lateral carbon flows can create significant carbon sinks
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DOI：
10.5194/bg-17-2425-2020
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发表时间：
2020-05-05
期刊：
影响因子：
4.9
通讯作者：
Kuwae, Tomohiro
中科院分区：
文献类型：
--
作者：
Watanabe, Kenta;Yoshida, Goro;Kuwae, Tomohiro
大型藻类床作为一种作为大气CO2汇的植被海岸生态系统引起了人们的关注。虽然大型藻类代谢以及无机和有机碳流是大型藻类床吸收CO2的重要途径，但大型藻类代谢与相关碳流之间的关系仍然知之甚少。在本研究中，我们调查了碳流量，包括空气-水CO2交换和预算的溶解无机碳，总碱度，溶解有机碳（DOC），在温带大型藻类床在生产月份的一年。为了评估大型藻类床吸收大气CO2的关键机制，我们估计了大型藻类的代谢和横向碳流（即，大型藻类床和近海区域之间的碳交换）通过使用碳物种的现场测量，现场袋法，降解实验，和质量平衡模型在温带马尾藻床在一个昼夜周期。结果表明，大型藻类代谢和水交换驱动的碳横向流动影响了大型藻类床及其周围沃茨的气水CO2交换。大型藻类代谢导致覆盖沃茨含有低浓度的CO2和高浓度的DOC，有效地出口到近海的大型藻类床。这些结果表明，输出的水可以潜在地降低近海地表水中的CO2浓度，并增加大气中的CO2吸收。此外，海藻床还将6%~ 35%的大型藻类净群落生产量（NCP; 302-1378 mmolCm（-2）d（-1））作为DOC输出到近海。降解实验结果表明，56%~ 78%的大型海藻DOC为难降解DOC（RDOC），其降解时间可达150 d，因此，大型海藻NCP中有5%~ 20%以RDOC形式输出.我们的研究结果表明，与高水交换率相关的栖息地中的大型藻类床可以在其周围产生显著的CO2汇，并向近海地区输出大量的DOC。
Macroalgal beds have drawn attention as one of the vegetated coastal ecosystems that act as atmospheric CO2 sinks. Although macroalgal metabolism as well as inorganic and organic carbon flows are important pathways for CO2 uptake by macroalgal beds, the relationships between macroalgal metabolism and associated carbon flows are still poorly understood. In the present study, we investigated carbon flows, including air-water CO2 exchange and budgets of dissolved inorganic carbon, total alkalinity, and dissolved organic carbon (DOC), in a temperate macroalgal bed during the productive months of the year. To assess the key mechanisms responsible for atmospheric CO2 uptake by the macroalgal bed, we estimated macroalgal metabolism and lateral carbon flows (i.e., carbon exchanges between the macroalgal bed and the offshore area) by using field measurements of carbon species, a field-bag method, a degradation experiment, and mass-balance modeling in a temperate Sargassum bed over a diurnal cycle. Our results showed that macroalgal metabolism and lateral carbon flows driven by water exchange affected air-water CO2 exchange in the macroalgal bed and the surrounding waters. Macroalgal metabolism caused overlying waters to contain low concentrations of CO2 and high concentrations of DOC that were efficiently exported offshore from the macroalgal bed. These results indicate that the exported water can potentially lower CO2 concentrations in the offshore surface water and enhance atmospheric CO2 uptake. Furthermore, the Sargassum bed exported 6 %-35% of the macroalgal net commu-nity production (NCP; 302-1378 mmolCm(-2) d(-1)) as DOC to the offshore area. The results of degradation experiments showed that 56 %-78% of macroalgal DOC was refractory DOC (RDOC) that persisted for 150 d; thus, the Sargassum bed exported 5 %-20% of the macroalgal NCP as RDOC. Our findings suggest that macroalgal beds in habitats associated with high water exchange rates can create significant CO2 sinks around them and export a substantial amount of DOC to offshore areas.