富营养化湖泊有机氮氨化作用及其生态效应

As one of the most important part of lake ecosystem, the organic nitrogen plays key roles in the nutrient biogeochemical processes and cycling as well as in the biological processes of aquatic organisms. The ammonification of dissolved organic nitrogen (DON) would be the major approach for supporting the growth of phytoplankton and sustaining blooms. By the application of ultraviolet-visible absorption spectra (UV-Vis), three-dimensional fluorescence spectrum and fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the spatial and temporal distribution as well as the compositions and potential sources of DON in Taihu Lake can be identified. The stable nitrogen isotope dilution method coupled with the ammonium oxidation/membrane interface mass spectrometer (OX/MIMS) are used in both the field and laboratory experiments to elucidate the ammonification of DON, and the potential environmental factors can also be demonstrated. The ratios of regeneration rate of ammonium and uptake rate of ammonium by phytoplankton are calculated to imply the ecological effects of ammonium regeneration on the growth of phytoplankton and primary production in Taihu Lake. Finally, the contribution of ammonium regeneration to total nitrogen budget in Taihu Lake can be evaluated by combining the calculations of the nitrogen amount from different ways of inputs and outputs such as nitrogen-fixation and denitrification from previous studies. Therefore, the key roles of DON in manipulation of both eutrophication and nitrogen cycling in freshwater lakes will be comprehensively understood, which can provide scientific basis for the management and restoration of nutrient pollution in lakes.

有机氮是湖泊生态系统的重要组分，是营养物质生物地球化学循环和生命过程的重要环节。溶解态有机氮氨化作用将是富营养化湖泊浮游植物生长和水华维持的重要补偿途径。采用紫外-可见吸收光谱、三维荧光光谱和傅里叶变换-离子回旋共振质谱分析方法，明确太湖不同湖区水体DON时空分布规律及其来源组成特性；结合稳定氮同位素稀释和氨氮氧化/膜接口质谱仪技术，开展野外原位培养实验和室内控制实验，阐明不同湖区DON氨化作用及其影响因素；考察水体氨氮再生速率与吸收速率相关关系，揭示氨氮再生对浮游植物生长和初级生产力的影响效应；结合太湖湖区固氮量、反硝化脱氮量等氮输入和输出量分析，评估水体氨氮再生量对氮负荷的贡献，丰富湖泊富营养化发生机制和氮循环理论，为开展湖泊污染治理与修复提供科学依据。

氮的来源、转化和归趋是影响湖泊生态系统结构和功能的重要因素。有机氮是水域生态系统的重要氮库，直接参与氮的固定、再生及氨基化等过程。有机氮氨化过程是维持浮游植物生长最重要的氮补偿途径之一，但受到极大的忽视。本研究在湖泊水体氮的供给-利用的闭环过程中补充了关键的供给环节，揭示了藻类自我维持和氮吸收-供应的关系。项目以太湖为对象，通过野外面上调查和逐月观测，同位素稀释培养、三维荧光和傅里叶变换-离子回旋共振质谱等有机氮分析等手段研究太湖有机氮组成及变化、分析了有机氮氨化潜势的时空规律及贡献，揭示了有机氮氨化再生过程对水华暴发的维持机制。.研究发现了太湖水体氨氮再生和消耗速率存在由西北向东南地区降低的趋势，河道及河口区是全湖氨氮的再生热点，夏季显著高于其他季节且表现出明显的氨氮需求。光暗再生过程之间的显著差异揭示出有机氮的光降解和生物降解差异，且以夏季为显著；光暗消耗过程对比表明浮游植物吸收在氨氮消耗过程中占据主导地位。太湖水体氨氮年再生量为28.53万t，是河流输入、大气沉降、沉积物释放等其他来源总和的10倍。.进一步揭示其机制，发现有机氮氨化过程与浮游植物总生物量、蓝藻生物量及其比例、颗粒氮和溶解有机碳浓度以及活性氮组分(蛋白质和脂类)的相对丰度显著相关。随机森林回归分析和偏最小二乘路径分析模型均表明氨化过程的主控因素为水温和叶绿素a、浮游植物总生物量和蓝藻生物量等与藻类相关的参数的控制。相比于其他藻类种群，蓝藻以更高的蛋白类组分（色氨酸）C3和微生物源腐殖酸类物质C4有利于氨化过程，并通过对氨氮的有利竞争确保在浮游植物群落中形成优势及维持。在此基础上，建立了蓝藻水华与有机氮氨化之间的内部循环模式，并提出了蓝藻自我维持的关键机制。.项目共发表论文21篇，包括water research， Science of the Total Environment，Environmental Pollution等SCI收录论文13篇，培养研究生6名。