楠溪江硝态氮来源定量识别及其不确定性分析

选择温州市楠溪江流域为研究区，通过水化学分析和硝态氮中氮氧稳定同位素示踪技术，对水体硝态氮时空分布特征、迁移转化过程和污染来源进行识别，结合稳定同位素源解析模型（SIAR），定量识别不同污染源的贡献率，并在此基础上应用概率统计方法对模拟结果的不确定性进行分析.结果表明：研究区水体氮素赋存形态以硝态氮为主；硝态氮含量呈现明显的时空变化，时间上，丰水期硝态氮浓度高于枯水期，空间上，支流硝态氮浓度高于主河道；硝化作用主导了流域内硝态氮的转化过程，化肥、土壤有机氮和粪便污水是楠溪江水体硝态氮的主要来源；SIAR模型计算显示大气沉降、化肥、土壤有机氮、粪便污水对枯水期水体硝态氮的贡献率分别为3.0%~12.9%，25.5%~32.7%，28.7%~36.2%和24.7%~37.5%，对丰水期水体硝态氮贡献率为2.5%~14.3%，28.5%~40.0%，28.8%~39.7%和18.9%~29.90%.模拟结果的不确定性分析表明SIAR模拟结果存在一定程度的不确定性，不同污染源贡献率的不确定性从大到小排序为：土壤有机氮>化肥>粪便污水>大气沉降.

Quantitative identification of riverine nitrate sources and uncertainty analysis in the Nanxi River

Accurate identification of nitrate sources is the key step for effectively mitigate riverine nitrate pollution. In this study, the Nanxi River watershed located in Wenzhou city was selected as the research area. Hydrochemical analysis and nitrogen and oxygen stable isotopes in nitrate were used to identify spatio-temporal variation, migration and transformation, and pollution sources of nitrate. Then, combining the stable isotope analysis in R (SIAR) model to quantitatively identify the contributions for different pollution sources. On this basis, the probabilistic method was employed to analyze the uncertainty of modelling results. Nitrate was the main form of nitrogen in this study area; there existed significant spatio-temporal variation of riverine nitrate content, temporally, the nitrate concentration in wet season was higher than that in dry season, spatially, the nitrate concentration in tributary was higher than that in main stream. Microbial nitrification was the primary nitrogen transformation process within the Nanxi River watershed, chemical nitrogen, soil organic nitrogen and manure and sewage were the main contributors of nitrate to the river; SIAR modeling revealed that the contributions of atmospheric deposition, chemical nitrogen, soil organic nitrogen, and manure and sewage were 3.0%~12.9%, 25.5%~32.7%, 28.7%~36.2%, and 24.7%~37.5%, respectively, in the dry season, and 2.5%~14.3%, 28.5%~40.0%, 28.8%~39.7%, and 18.9%~29.9%, respectively, in the wet season. The uncertainty analysis demonstrated that uncertainties existed in some extent during nitrate source identification, the uncertainty for different sources followed:soil organic nitrogen > chemical nitrogen > manure and sewage > atmospheric deposition.