洞庭湖区农业面源污染严重，严重困扰长江经济带建设。特殊的平原水网特点导致不同土地利用氮磷流失量不确定性大，时空变异规律不清楚，氮磷迁移路径识别困难及沿途消纳过程、消纳能力、影响因素不明确，水质与农田氮磷损失之间的响应关系难以量化等问题。本项目拟通过设置关键监测样带、地理信息系统（GIS）路径识别、膜进样质谱原位反硝化测定、氮氧双同位素溯源、模型模拟与优化等方法，开展如下四个方面研究：1)通过田间定位实验，明确洞庭湖平原区农田氮磷流失通量与主控因素；2)基于新一代GIS路径识别技术和反硝化原位高精度测定等方法，阐明氮磷沿途消纳与迁移转化规律；3)构建“农田排放-沿程消纳-水体负荷”全过程水质响应模型，明确湖泊水质响应机制；4)解析并识别主要源区，提出洞庭湖区氮磷污染阻控策略。以期对我国平原湖区面源氮磷成污过程、农田湿地间水质耦合作用机制提供系统的认识，为水环境高效治理提供理论依据和示范样板。

The agricultural non-point source pollution is serious in the Dongting Lake area, which deeply plagued the development of the Yangtze River Economic Belt. Because of the complex plain-waterway network, there are large uncertainties in the amount of nitrogen and phosphorus (NP) runoff, along with temporal and spatial variability. Moreover, it is difficult to identify the NP transport pathway after runoff, and to understand the removal processes and their influencing factors. As a result, it is hard to establish a quantitative relationship between NP runoff from farmland and water quality. The project intends to carry out the following four works through the representative sampling transects, GIS path identification, denitrification measurement by membrane inlet mass spectrometry (MIMS), nitrogen and oxygen isotopic measurement, model simulation and optimization, etc. Firstly, we will have explicit understanding of NP runoff from farmland and its controlling factors in the lake plain through intensive field experiments. Secondly, based on the new GIS pathway identification tools and MIMS, NP removals and transformation along pathway will be clarified. Thirdly, a whole process model of “farmland discharging-route removing-water loading” is going to be constructed, and the quantitative relationship between NP losses from farmland and water quality will be established. Fourthly, by model simulation, the main source area will be identified, and accordingly pollution control strategies of the Dongting Lake area will be proposed. The completion of this project will provide a scientific understanding of the NP pollution process, water quality between farmland and wetland coupling mechanism in the plain lake area of China, and provide theoretical basis and demonstration model for high-efficiency environmental management.