基于数据同化模式的珠江口陆源污染物通量及其对底层水体缺氧的影响研究

The study of terrestrial pollutant fluxes and its impacts on bottom water hypoxia in the Pearl River Estuary (PRE) is of great importance in practice for environmental protection and sustainable development in this region, and also helps to enhance our understanding of the formation mechanisms of and the contribution of terrestrial inputs to eutrophication and bottom water hypoxia in this region. This study aims to integrate the Pearl River network, the PRE and its adjacent coastal sea as an entity and to develop a data-assimilative model of marine ecosystems by using the Ensemble Kalman Filter assimilation method to optimally merge observations into the mathematical model, thereby updating the simulations of flow fields along with the water quality constituents. The data-assimilative model will be applied to study the fluxes of main pollutants (e.g., nitrogen, phosphorus) in different seasons, the spatio-temporal patterns of phytoplankton production and dissolved oxygen, and their responses to the variations in terrestrial pollutant inputs in the PRE. Moreover, the occurrence, extend and duration of bottom water hypoxia in the PRE will be reproduced using the model and the associated dominant kinetics will be illustrated. The combined effects of the terrestrial organic matters and marine organic matters (algal detritus) as well as their respective contributions to bottom water hypoxia in the PRE will be further demonstrated based on a series of scenario simulations.

开展珠江口陆源污染物通量及其对底层水体缺氧的影响研究，不仅对该海域的生态环境保护和可持续发展具有重要的现实意义，而且有助于深化对该海域富营养化和底层水体缺氧现象的形成机制及陆源贡献等科学问题的认识。本项目拟将珠江河网区和珠江口及其近岸海域作为研究整体，运用集合卡尔曼滤波同化方法，将实测资料与数学模型相结合，构建珠江口水环境数据同化模式，实现流场和水质要素模拟结果的共同优化更新；在此基础上，研究珠江口海域氮、磷等主要污染物在不同季节的通量输送规律，以及浮游植物初级生产过程和溶解氧的时空分布特征及其对陆源污染物输入变化的响应程度和机制，模拟再现珠江口底层水体缺氧现象的存在位置、影响范围和持续时间，并探讨其主导动力学机制；结合情景案例模拟分析，进一步揭示陆源有机物和海源有机物（藻类碎屑）对珠江口底层水体缺氧的协同效应与各自贡献。

开展珠江口陆源污染物通量及其对底层水体缺氧的影响研究，不仅对该海域的生态环境保护和可持续发展具有重要的现实意义，而且有助于深化对该海域富营养化和底层水体缺氧现象的形成机制及陆源贡献等科学问题的认识。本项目建立了珠江三角洲一维与三维耦合模型，细致描述研究区域的水动力和水质过程，经实测资料验证表明，模型成功再现了水体和底泥中的营养盐及溶解氧浓度的时空分布，以及水体-底泥界面的营养盐通量与底泥耗氧动态过程。在此基础上，构建了不同典型水文条件下珠江河网区与河口区主要污染物的通量收支模式，量化生物过程、化学过程、沉积过程等对污染物收支的贡献，阐明了各污染物的主控动力学机制；基于模拟结果构建溶解氧收支模式，阐明了底泥耗氧与大气复氧在底层水体缺氧的形成与维持过程中所起的主导性作用；提出了“动力再分配”概念，将溶解氧相关的物理过程与生物化学过程分离，更为直观地揭示了动力过程对生物化学过程的调节作用及其对缺氧的影响；模拟预测了上游河流溶解氧水平、颗粒性有机碳以及氮磷营养盐等输入变化对底层水体缺氧的影响，揭示了珠江口海域缺氧对陆源输入变化的响应程度及相关调控机制。另外，运用局地化集合卡尔曼滤波同化方法，构建了珠江口水环境数据同化模式，并进行了同化性能评估，以及进行了优化布点策略探讨。