人类活动影响下长江三角洲平原河网氮的累积与调控机制

The project focus on the scientific needs of major national strategies for regional ecological security under large-scale human activities in key river basins. Nitrogen pollution control is urgently needed in the river network region of the Yangtze River Delta (YRD) where increasingly nitrogen pollution and frequent occurrence of eutrophication or algal blooms have occurred with rapid economic growth. In this study water samples in representative water bodies of the region are taken and studied through a comprehensive approach of molecular biology, isotope tracing, and numerical simulations. Nitrogen sources and its component characteristics are analyzed. The nitrogen combined forms in water body, the functional microbial community structure, and the spatial distribution of habitat factors are probed. Simulation experiments of interaction of microorganisms and nitrogen are carried out to investigate the impact of the increasing exogenous nitrogen load, the C/N ratio and dynamic changes on the dynamic characteristics of microbial metabolic processes, e.g, ammonification, nitrification, and denitrification and to identify the key factors affecting these processes. Based on the characteristics of nitrogen isotope composition, transformation of nitrogen among the interfaces of air-water, water-microbe, and water-sediment are analyzed and dynamic changes in the capability of sediment and aquatic organisms to retain nitrogen are also studied. Combined with convection and diffusion mechanisms, the transport and transformation of nitrogen in the water cycle are to be established to quantitatively analyze the nitrogen retention ratio and output fluxes. Based on these studies, the mechanism of nitrogen cycle and accumulation in the river network region of YRD is revealed, and the theory of nitrogen biogeochemical cycle is enriched to provide scientific basis for regional nitrogen pollution and eutrophication control, and water ecological security.

本项目围绕"重点流域大规模人类活动的生态影响、适应性和区域生态安全"国家重大战略的科学需求，以社会经济快速增长的长江三角洲为研究对象，针对该区域河网水环境日趋严重的氮污染及其富营养化问题，综合运用分子生物学、同位素示踪及数值模拟等技术手段，通过对代表性水域的系统取样和测试，解析河网水系氮的来源及其组分特征；系统开展微生物-氮相互作用模拟实验，探讨外源性氮负荷增加、C/N及水力要素变化等对氮循环中氨化、硝化、反硝化等微生物代谢过程的动力学特征影响机制，识别影响微生物代谢过程的关键因子；利用氮同位素组成特征，分析氮在水-土、水-生及水-气界面的相间传输及固持规律；结合对流与扩散作用机制，建立河网水循环过程中氮流动和转化的质量平衡，定量解析河网系统氮的持留与输出通量；揭示长江三角洲平原河网氮的循环及累积机制，丰富氮的生物地球化学循环理论，为区域氮污染及富营养化控制、保障水生态安全提供科学依据。

本项目围绕“重点流域大规模人类活动的生态影响、适应性和区域生态安全”国家重大战略的科学需求，针对长江三角洲平原河网日趋严重的氮污染及其富营养化问题，以揭示该区域氮的循环及累积机制为研究目标，选取太湖不同富营养水平湖区（胥湖、五里湖、梅梁湖、贡湖、西太湖）、西部湖区及其入湖南河水系、不同污染水平城市河道为重点研究区域，共计完成75个代表性监测点位2013年~2017年连续5年每年四季18个批次的野外监测，采集与分析沉积物及其柱状样、孔隙水及其上覆水样品4000余个，完成沉积物-水界面柱状流动等室内培养试验300余批次；利用野外实时等水质分析技术、高通量测序及宏基因组测序等分子生物学技术、稳定同位素示踪及其修正的同位素配对技术，系统开展了1）重点研究区域河湖水环境氮的赋存特征及其生境特征研究，2）不同营养水平河湖水环境微生物驱动的氮循环途径及其厌氧氨氧化过程研究，3）不同营养水平河湖水环境氮的转化速率、界面传输及其环境胁迫效应研究，4）重点研究区域河湖水体氮的溯源、通量过程及其控制对策研究。通过上述研究任务的执行，围绕①平原河网不同生境条件下氮的微生物驱动机制及其循环特征、②平原河网不同生境条件下氮的迁移转化途径及其累积机制两个关键科学问题，系统阐述了不同富营养水平湖区、相关河道沉积环境微生物及其功能微生物的群落特征、分子生态网络结构特征，揭示了氮循环功能基因及其厌氧氨氧化基因丰度的时空差异性、氮的循环途径及其转化效率，定量解析了太湖西部河湖系统氮的迁移转化途径、界面交换及其通量过程，研究成果丰富了平原河网地区河湖系统氮的生物地球化学循环理论。相关成果发表论文20篇，其中SCI收录10篇，投稿Water Research、Environmental Microbiology、Chemosphere等杂志论文5篇，并在《南京大学学报》（自然科学版）2016年第52卷第1期发表了“流域水循环系统氮的迁移转化及其污染控制”专栏，申请国家发明专利6项，获授权5项，部分成果已在太湖流域支浜农业面源氮污染治理中得到应用，实现了项目预期目标。