中文摘要：

浮游植物光合作用产生的溶解有机质（dissolved organic matter,DOM）是海洋中溶解有机质的重要来源,浮游植物死亡后释放的新鲜溶解有机质活性高、数量大、生物可利用性高,其降解过程中对溶解氧（dissolved oxygen,DO）的消耗显著。但到目前为止,对此类溶解有机质的降解过程以及其耗氧情况还鲜有研究。本文基于2013年8月东海航次,对浮游植物（硅藻为主）死亡后释放的新鲜有机质进行人工受控培养,研究其降解过程及对DO的消耗,并评估该降解过程对低氧现象形成的贡献。研究发现：培养体系中溶解有机碳（dissolved organic carbon,DOC）和DO浓度皆随时间呈指数下降,总溶解态碳水化合物（total carbohydrate,TCHO）也出现明显降解;体系的初始DOC浓度越高,降解速率常数k（DOC）、k（DO）越大,k（DOC）受DOC浓度、活性以及DO浓度的影响;培养过程中细菌丰度明显增加,添加Hg Cl2的对比实验表明细菌在降解过程中起到重要作用。本文的研究结果表明,浮游植物死亡后释放的溶解有机质的快速降解及其对溶解氧的消耗,对长江口低氧环境的促成具有重要意义。

英文摘要：

Dissolved organic matter（DOM） derived from marine phytoplankton is one of the main sources of DOM in the ocean. The biodegradation of fresh DOM released from dead phytoplankton can reduce significantly dissolved oxygen（DO） due to its high bioactivity and huge amount. At present, such a degradation process and the corresponding oxygen consumption are poorly studied. In this study, we sampled seawater in three stations by net collection in Changjiang River estuary, filtrated with 200 μm mesh and frozen at –20°C for at least 24 h. Samples were incubated to investigate the mechanism of degradation process and the consumption of dissolved oxygen, and possible link to hypoxia off the estuary. The results show that both dissolved organic carbon（DOC） and DO showed an exponential decay, during which total dissolved carbohydrate degraded significantly. Moreover, the degradation rate constant of DOC was influenced by the concentration and activity of DOC, so did the DO content. Bacteria density increased more apparently in our experiment without Hg Cl2 addition than with the adding, indicating the bacteria plays an important role in the degradation of DOM. Therefore, rapid degradation of DOM and the resulting consumption of oxygen would have an important impact on hypoxia off the Changjiang River estuary.