2020年3月，我研究组博士研究生苏剑钟在地学权威期刊《Limnology and Oceanography》发表题为“Source partitioning of oxygen-consuming organic matter in the hypoxic zone of the Chesapeake Bay”的研究论文，首次准确量化了切萨皮克湾缺氧区耗氧有机物基本来自海源浮游植物的初级生产。
作者使用两端元混合模型计算出非保守的碳酸盐变化量，并使用化学示踪物、化学计量关系和质量守恒进一步解析出总溶解无机碳的改变主要受控于水柱中的呼吸作用（43%），沉积物中的硫酸盐还原（39%），大气二氧化碳的吸收（13%）和碳酸钙溶解（5%）多个生物地球化学过程。因为有氧呼吸和硫酸盐还原的有机物降解过程中碳稳定同位素分馏量很小，所以降解产物（二氧化碳）和被降解的有机物的碳稳定同位素值基本相等。作者通过总溶解无机碳浓度和同位素的质量守恒计算出耗氧有机物的特征值为（-19.4±0.3‰），接近于海源浮游植物的特征值（-19.9±1.7‰）。因此作者认为切萨皮克湾内耗氧有机物基本来自于海源，而陆源有机物几乎没有贡献。此前，作者的另一研究表明在珠江口缺氧区耗氧有机物65%来自海源，其余35%来自陆源。作者进一步比较讨论了切萨皮克湾和珠江口缺氧区耗氧有机物来源存在差异的主要原因是两个大型河口系统拥有不同的水文、物理条件，有机物输入和生物活性。考虑到在两个系统中耗氧有机物都主要来自营养盐驱动的初级生产，作者指出营养盐管理和减排将有利于控制和缓解缺氧区、无氧区的形成。
该研究成果由苏剑钟博士（我实验室2020届博士毕业生，现为特拉华大学地球海洋和环境学院博士后)、蔡卫君教授、Jeremy M. Testa教授，Deb P. Jaisi教授，Jeffrey Cornwell教授以及戴民汉教授共同完成。该成果对大型河口的物质收支分析以及对引发缺氧形成的生物地球化学过程的理解具有重要意义。
英文摘要：We surveyed the carbonate system along the main channel of the Chesapeake Bay in June 2016 to elucidate carbonate dynamics and the associated sources of oxygen-consuming organic matter. Using a two endmember mixing calculation, chemical proxies, and stoichiometry, we demonstrated that in early summer, dissolved inor-ganic carbon (DIC) dynamics were controlled by aerobic respiration in the water column (43%), sulfate reduc-tion in the sediment (39%), atmospheric CO2 invasion (13%), and CaCO3 dissolution (5%). A mass balance of the DIC concentration and its stable isotope suggested that the apparent δ13C of oxygen-consuming organic matter was −19.4 ±0.3‰. The bulk composition of particulate organic matter also reflected a dominance of algal material (C/N = ~ 6, δ13C> −25‰). Therefore, we concluded that the decomposition of autochthonous organic matter (i.e., eutrophication-stimulated primary production) was the dominant process consuming oxy-gen, while allochthonous organic matter (terrestrially derived) made minor contributions to oxygen consump-tion in the hypoxic zone in June 2016. These findings in the Chesapeake Bay contrast with another hypoxic estuarine ecosystem, the Pearl River Estuary in China where allochthonous organic matter contributed signifi-cantly to oxygen consumption. The differences between these two systems in terms of hydrology, quantity and quality of organic matter, and physical characteristics are discussed to yield new insights on the formation and maintenance of hypoxia. In both systems, autochthonous organic matter dominates oxygen depletion, indicat-ing that nutrient management and reduction are useful actions to control and mitigate the occurrence of hyp-oxia for the restoration of ecosystem.
Citation: Su, J.Z., W.-J. Cai, J. Brodeur, N. Hussain, B.S. Chen, J.M. Testa, K.M. Scaboo, D.P. Jaisi, Q. Li, M.H. Dai, and J. Cornwell, 2020. Source partitioning of oxygen-consuming organic matter in the hypoxic zone of the Chesapeake Bay. Limnology and Oceanography, doi: 10.1002/lno.11419.
