珠江河口硝态氮铵化-厌氧氨氧化-反硝化耦合过程驱动的氮素归趋机制研究

Nitrogen is one of the key elements affecting estuary eutrophication occurrence and evolution. There are both utilizable biological active nitrogen and the microbes involved in nitrogen cycling in the surface sediment and soil and water conservation system in estuary. And moreover, there is also a close connection between the nitrogen transformation ways, i.e., dissimilatory nitrate reduction to ammonium , anareobic ammonium oxidation ,and definitrification. The changes of the unique environmental factors in estuary could lead to the different responses of microorganisms to the above two competitive ways on the nitrogen transformation, in which the nitrogen nutrient balance could be destroyed if the nitrogen element retention in the water is significant. The aim of this project is: To study the effect of the activity of the functional microbial and the key environmental factors in estuary on the reaction rates of dissimilatory nitrate reduction to ammonium and anareobic ammonium oxidation coupling process; To examine the different nitrogen transformation in the multiphase system due to the different exogenous inorganic nitrogen pollutants and their concentrations, from which the parameters for the different reaction rate, coupling threshold, and decision mechanism can be obtained and clarified; According to the hydrodynamic characteristics of the back of saline in the pearl river estuary, we can establish the nitrogen fate model for the dissimilatory nitrate reduction to ammonium - anareobic ammonium oxidation - definitrification coupled process in estuary. The research will provide the important guidance to the calculation the acceptable environment capacity of nitrogen pollution, the prediction of nitrogen pollution in the estuary of southern China, as well as the solutions for solving the water pollution caused by nitrogen element. ...

氮是影响河口区富营养化发生和演变的关键要素。河口区表层沉积物及其水土体系不仅存在参与氮循环的微生物和活性氮素，具在空间具备密切联系的氮转化途径，即：硝态氮铵化、厌氧氨氧化、反硝化。河口区特有环境因子的变化使微生物对上述具竞争性的氮素转化途径产生不同响应，若氮素在水体中的滞留显著则会破坏氮素平衡。本项目考察具生物活性的氮素在多相水土体系里通过上述三种生物转化途径，获得不同反应速率参数耦合度阈限并阐明判定机制；同时研究功能微生物活性及河口关键环境因子对三者耦合度的影响；结合珠江河口咸潮上溯的水动力特征，建立硝态氮铵化-厌氧氨氧化-反硝化耦合的氮素归趋模型。最终从微观上确定硝态氮铵化生成氨氮优先被厌氧氨氧化利用，或直接造成氨氮积累，形成内源污染的来源之一，从宏观上明确此部分氮素的归宿。该研究将对南方河口区的环境纳氮容量及预测、寻找水体氮素污染有效解决途径，提供科学依据。

近海的赤潮与河口区输入过量的活性氮有密切关系，河口区特有环境因子的变化使微生物对硝态氮铵化(DNRA)/厌氧氨氧化/反硝化氮素转化途径产生不同响应，特别是DNRA造成了水体中的活性氮滞留显著则会导致河口区富营养化。以珠江河口的黄茅海为研究区域，通过实测河口海域环境条件，采样进行实验室模拟连续流培养，开发了高效低成本的同位素氮检测技术，获得沉积物水土体系中DNRA /厌氧氨氧化/反硝化速率的定量表达；采用编码功能酶基Nrfa为基础的分子生物学实验手段，研究河口水动力环境下沉积物中的功能细菌（包括硝化、反硝化、厌氧氨氧化和DNRA细菌）群落结构演化行为；结合珠江河口咸潮上溯的水动力特征，建立对河口区经由DNRA -厌氧氨氧化-反硝化耦合的氮素归趋模型。从水动力与污染物特点可见，距崖门水道距离近，受到入海污染物影响产生的因素与相关功能微生物生存环境有关，从宏观上表现DNRA与水体中的氮磷、盐度等有关系。实验使用常见气相色谱质谱联用仪，使用市售易得相应色谱柱和试剂进行条件探索、优化，得到能同时测定自然水体中氨氮及同位素的方法，在10~10000ug/L具有良好线性，线性回归达0.999以上，这一研究的发现，将在对活性氮的污染现状和转换研究不依赖于价格昂贵的同位素检测仪器。DNRA功能微生物在水-土界层的丰度与活性研究采用实时聚合酶链式反应用于目标基因的扩增，进行了微生物群落构成及多样性分析，构建了具有DNRA功能的微生物系统发育树。可见珠江河口存在的DNRA功能微生物群落大部分是世界热带或亚热带河口区的普遍物种。最终得到DNRA -厌氧氨氧化-反硝化潜在速率，耦合进入已验证三维波流泥沙数学模型，预测黄茅海的硝态氮主要以向外海扩散为主，DNRA造成的活性氮内循环仅占水土界面氮通量的3%-5%。