长江口海域胶体中有机碳、氮、磷生物地球化学的初步研究

In previous studies on biogeochemistry of dissolved biogenic elements (< 0.45 µm), the colloidal (1 kDa–0.45 µm) and the ‘truly dissolved’ molecules (< 1 kDa) were seldom differentiated mostly due to the technique restriction. The biogeochemical behaviors of colloids in the estuary of large rivers such as the Changjiang Estuary should have been quite complex and active, owing to the dominant influences of water mass circulation and the strong sediment deposition processes there. In this project, two ultrafiltration techniques (stirred ultrafiltration cell and cross-flow ultrafiltration system) are applied, and colloids are extensively extracted and collected from the water samples in the Changjiang freshwater end-member, in the Changjiang Estuary, and in the adjacent East China Sea. Biogenic elements of organic carbon, nitrogen, and phosphorus are to be measured in these colloidal substances to study the chemical compositions, the spatial and temporal variations, as well as their controlling factors. In particular, the biogeochemical responses of carbon, nitrogen, and phosphorus in colloids in the study areas, to the physical processes like the water mass circulation, tides, the fronts of salinity and turbidity, and the flocculation caused by initial mixing of fresh and salty waters, are to be emphasized. Furthermore, the partitioning, transportation, and transformation of carbon, nitrogen, and phosphorus among the three phases of colloids, truly dissolved molecules, and the suspended particulate matter are also to be studied. The outcomes of this project are believed to enrich and deepen our recognition on the biogeochemistry of the important biogenic elements in the Changjiang Estuary and other large river estuaries worldwide.

以往在长江口海域溶解态（< 0.45 µm）生源要素生物地球化学的研究中，受限于技术手段等因素，很少进一步区分胶体态（1 kDa–0.45 µm）和真溶解态（< 1 kDa）。在大河河口如长江口，基于复杂且强势的物理海洋学过程和泥沙动力沉降过程，该处胶体往往具有独特、复杂且活跃的生物地球化学行为，有必要区分开来。在本研究中，将采用两种超过滤技术，在长江淡水端元、长江口以及邻近东海系统采集胶体样品，研究主要生源要素碳、氮、磷在胶体中的化学组成、时空变化规律及受控因素，及其对环流、潮汐、盐度浊度锋面、最大浑浊带、以及盐淡水混合引发的絮凝等重要物理过程的响应。同时对比碳、氮、磷等生源要素在胶体态、真溶解态以及悬浮颗粒态之间分布变化的差异性及其在各态之间的分配转化规律。这项研究成果将进一步丰富和深化对长江口生源要素生物地球化学行为的认识，并为世界大河河口的相关研究提供借鉴。