南水北调中线水源地河流氮的来源与地球化学循环研究

The South to North Water Transfer Project is a large infrastructure project to solve the serious shortage of water resources in the north of China, and the water source area of the middle route project is the Danjiangkou reservoir. The water quality of Danjiangkou reservoir is directly related to operation of the water transfer project and the sustainable development of social economy in north China. Chinese government have spent large sum of money to control the water pollution in the water source area of the middle route project, however, the content of total nitrogen and nitrate in river and reservoir water is still high. It is largely due to the source of nitrogen and the law and mechanism of nitrogen migration and transformation in the river water is not clear. This project is aim to the water quality security of the middle route of South-North Water Transfer Project. In this project application, the compositions of major and trace elements, different forms of nitrogen, organic carbon and nitrogen, and the corresponding stable isotope (e.g. δ15N, δ18O, δ13C) will be systematically investigated in the representative nitrogen polluted rivers in the water source area and the major rivers pour into the Danjiangkou Reservoir. The main purpose of this project is to explore the temporal and spatial distribution characteristics of nitrogen pollutants. Multiple stable isotopes combined with water chemistry methods will be established to analysis quantitatively various nitrogen sources and their contribution. Furtherly, the processes and mechanisms of transportation and transformation of nitrogen pollutants will be explored in detail, and finally, the contribution of nitrogen pollution will be evaluated for major rivers flow into the Danjiangkou Resevior. Based on this study, we expect to provide scientific basis for river water nitrogen pollution treatment about the water source area of the middle route of the South-North Water Transfer Project.

南水北调工程是解决我国北方地区水资源短缺、实现水资源优化配置的重大基础设施，其中线水源地丹江口水库水质直接关系到中线工程的安全运行和社会经济的可持续发展。国家已投巨资治理水源地污染，但目前河流和水库水体的总氮和硝氮含量依然居高不下，甚至呈继续增长的态势。本项目以南水北调工程中线水源地水质安全为目标，针对水源地河流氮含量超标现状，对水源地典型氮污染河流和主要入库河流进行系统的调查，重点查明河流氮污染物的时空分布特征和规律；利用水化学、元素与氮氧、氢氧、碳等多种稳定同位素地球化学示踪手段，建立科学合理的氮污染物来源及其物质贡献率的定量源解析方法，准确识别代表性河流水中氮的主要来源、量化各类型污染来源对河流水体氮污染负荷的贡献；揭示河流氮污染物迁移转化过程与控制因素，量化主要入库河流对丹江口水库的氮污染负荷的贡献与时空变化规律，为水源地河流治理和氮污染控制，保障水质安全提供基础科学依据。

南水北调工程是我国优化水资源配置，促进京津冀经济社会可持续发展的战略性基础设施，丹江口水库水质安全是工程发挥其社会经济效益的根本保障。目前水源地河流和水库水体的总氮和硝氮含量依然居高不下，查明氮污染物的来源、迁移转化途径及其作用机制，既是重要的基础科学问题也具有明显的社会经济价值。.目前，稳定同位素地球化学研究是建立科学合理的污染物源解析方法，定量获取不同污染源物质贡献、示踪污染物迁移转化途径的有效手段。本项目在系统分析丹江口水库水源地河流流域主要人为活动背景基础上，选取了5条代表性河流，包括：淇河（农业型污染）、金钱河（小城镇型污染）、泗河（城市型污染）、月河（城镇和农业混合污染），以及金水河（自然背景河流）作为研究对象。开展了系统的空间和不同季节的样品采集和数据分析工作，获得了水源地典型氮污染物端元的化学和稳定同位素组成特征，查明了代表性河流氮污染的时空分布特征和规律；利用元素和稳定同位素地球化学研究手段，定量解析了河流水体中硝氮的来源、不同来源的物质贡献量和季节性变化特征；通过氮污染物迁移转化途径的示踪研究和认识，揭示了丹江口水库水源地不同背景河流氮污染来源和归趋的自然和人为过程，探究了典型污染背景河流氮浓度居高不下的原因及氮去除的促进效益和机理。在此基础上，对丹江口库区河流（丹江流域主要入库河流、汉江流域主要入库河流、环库支流以及丹江口水库出库断面）进行了为期2年的周期样品采集，获得了入库河流和出库河流的氮浓度及氮、氧稳定同位素组成的时空变化特征，并利用建立的污染物源解析方法对各个入库河流氮污染主要来源进行了定量解析；结合水文资料获得了各种氮污染来源对丹江口水库的氮输入和输出通量及其时空变化规律，分析并探讨了水源地流域主要的氮污染来源和热点区域。研究结果对探索科学的、具有针对性的治水策略，确保水源地水质安全提供了重要的科学依据。