2020年01月，我研究组博士研究生赵秧秧等在地学顶级期刊Limnology and Oceanography发表题为“Dynamics of inorganic carbon and pH in a large subtropical continental shelf system: Interaction between eutrophication, hypoxia and ocean acidification”的研究论文，首次量化了底层耗氧有机物占表层富营养化产生有机物的比例，并评估了富营养化、缺氧以及河-海水混合对近岸水体酸化的影响。
本研究于2017年夏季在珠江口-南海北部陆架近岸水域采集并测定了表、中、底层海水样品的溶解无机碳（DIC）及其碳稳定同位素（δ13CDIC）、pH、总碱度（TA）和溶解氧（DO）等参数，以期通过DIC和pH的空间分布及其变化解析表层富营养化与底层缺氧的耦合关系以及两者与海洋酸化之间的相互作用过程。
珠江口及其邻近陆架水域在垂向上呈明显的双层结构：表层河流冲淡水集中在珠江口西侧，表现为低DIC、高pH特征；而底层在珠江口口门外存在严重缺氧，表现为高DIC、低pH特征。采用多端元混合模型，我们发现相对于保守混合量，表层冲淡水区DIC亏损主要由初级生产和向大气释放CO2等过程造成，而底层DIC添加主要是由陆源和海源有机物共同降解矿化产生。从拉格朗日观测角度，向大气释放CO2是水团在内河口释放CO2和在河口外吸收CO2的净结果。基于δ13CDIC质量守恒，表层富营养化产生的海源有机物对底层氧气消耗的贡献为67±18%，此结果与Su et al. (2017)相一致。进一步采用双层箱式模型估算，这部分支持底层耗氧以及缺氧形成的海源有机物占表层富营养化产生的有机物总量约为45±13%。引入酸碱缓冲因子（βDIC），我们定量解释了富营养化和缺氧对海水酸化的减缓或增强的放大效应；但是与河流淡水输入相比，这两者对海水酸碱缓冲能力的影响较弱。
▲ 珠江口及其邻近陆架水域（a）ΔDIC vs. ΔDO、（b）ΔpHT,25vs. ΔDIC、（c）ΔpHT,25vs. ΔDO、（d）保守混合βDIC（βDICcons）vs. ΔDIC、（e）ΔβDICvs. ΔDO和（f）βDICconsvs. ΔDO的关系。三角形和圆形标记分别代表陆架水域表层和底层样品，而灰色方形标记代表珠江口内伶仃洋样品。（a）图中蓝色、黑色和红色实现分别指示陆架水域表层、底层以及伶仃洋样品的ΔDIC相对于ΔDO的变化速率。（b）图中黑色和红色实线分别指示陆架水域底层和伶仃洋样品的ΔpHT,25相对于ΔDIC的变化速率；而蓝色虚线表示陆架水域表层样品的ΔpHT,25相对于ΔDIC的变化速率范围。图中均采用II型线性回归（来源：ASLO）
该研究成果由赵秧秧、刘婧、Kanittha Uthaipan博士研究生、宋雪硕士、许懿工程师、何碧烟教授（集美大学）、刘红斌教授（香港科技大学）、甘剑平教授（香港科技大学）以及戴民汉教授共同完成，戴民汉教授为通讯作者。该成果对预测和缓解富营养化引起的近岸缺氧与海洋酸化具有重要意义。
We examined the dynamics of dissolved inorganic carbon (DIC) and pH in the Pearl River Estuary (PRE) and the adjacent northern South China Sea (NSCS) shelf in summer, aiming for a better understanding of the inter- action between eutrophication, hypoxia, and ocean acidification. Using a semi-analytical diagnostic approach based on validated multiple end-member water mass mixing models, we showed a −191±54 μmol kg−1deficit in DIC concentrations in an extensive surface plume bulge, corresponding to a significant pH increase of ~ 0.57±0.19 units relative to conservative mixing. In contrast, DIC additions in the bottom hypoxic zone reached ~ 139±21 μmol kg−1, accompanied by a decrease in pH of −0.30±0.04 units. In combination with stable carbon isotopic compositions, we found biological production and CO2outgassing to be responsible for DIC deficits in surface waters, while degradation of organic matter (OM) accounted for DIC additions in bottom waters. The PRE-NSCS plume system as a whole served as a net source of atmospheric CO2from the perspective of Lagrangian observations, because strong CO2outgassing in the inner estuary overwhelmed the CO2 uptake in the plume despite strong phytoplankton blooms. Using a two-layer box model, we further estimated that at least ~ 45±13% of eutrophication-driven OM production in the surface plume accounted for 67±18% of the DIC addition and oxygen consumption in bottom waters. Eutrophication also buffered ocean acidification in surface waters while hypoxia enhanced it in bottom waters, but their effects on acid-base buffering capacity were secondary to the amplification of coastal ocean acidification caused by freshwater inputs.
Citation: Zhao, Y., Liu, J., Uthaipan, K., Song, X., Xu, Y., He, B., Liu, H., Gan, J. and Dai, M., 2020. Dynamics of inorganic carbon and pH in a large subtropical continental shelf system: Interaction between eutrophication, hypoxia, and ocean acidification. Limnology and Oceanography, doi:10.1002/lno.11393
全文链接：https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lno.11393
