Institute for Advanced Study, Shenzhen University, Shenzhen, 518060, China; College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China; Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China.
Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China; University of Chinese Academy of Sciences, Beijing 100049, China.
J Environ Sci (China). 2020 Jul;93:98-108. doi: 10.1016/j.jes.2020.03.007. Epub 2020 Apr 9.
Nitrogen pollution is a serious environmental issue in the Danjiangkou Reservoir region (DRR), the water source of the South-to-North Water Diversion Project of China. In this research, seasonal surveys and a bi-weekly time series survey were conducted in the Qihe River Basin, one of the most densely populated agricultural basins in the DRR. Hydrochemical compositions (NO and Cl), dual isotopes (δD-HO, δO-HO, δN-NO, and δO-NO), and a Markov Chain Monte Carlo isotope mixing model were jointly applied to unravel the sources, migrations, and transformations of the nitrate (NO) in the basin. It was revealed that the mixing between different sources was the main process controlling the isotopic compositions of the riverine NO in the upper-middle reaches. In contrast, denitrification occurred in the lower reaches. For the first time, the sources of NO were quantified at a basin scale in the DRR. Overall, the river transported 484.2 tons/year of NO-N to the reservoir, of which 32.6%, 36.4%, 28.0%, and 3.0% was from soil organic nitrogen, chemical fertilizer, residential sewage and atmospheric precipitation, respectively. The NO-N fluxes of the different sources were regulated by the monsoon climate and anthropogenic activities. For example, high precipitation and intense fertilization resulted in severe nonpoint source pollution. Denitrification thrived in soils and reservoirs in wet seasons. Temperature could regulate the migration, nitrification and denitrification processes. Based on the results, we suggest that the management strategies dealing with nitrogen pollution issue in the DRR should follow the specific spatiotemporal characteristics of NO sources, migration and transformation mechanisms.
丹江口水库地区（DRR）是中国南水北调工程的水源地，存在严重的氮污染问题。本研究以丹江口水库地区人口最密集的农业流域之一——淇河流域为对象，开展了季节性调查和两周一次的时间序列调查。利用水化学组成（NO 和 Cl）、双同位素（δD-HO、δO-HO、δN-NO 和 δO-NO）和 Markov 链蒙特卡罗同位素混合模型，揭示了流域硝酸盐（NO）的来源、迁移和转化。结果表明，不同来源的混合是控制中上游河流 NO 同位素组成的主要过程。相比之下，下游发生了反硝化作用。本研究首次在丹江口水库流域尺度上量化了 NO 的来源。总的来说，河流每年向水库输送 484.2 吨/年的硝态氮，其中 32.6%、36.4%、28.0%和 3.0%分别来自土壤有机氮、化肥、生活污水和大气降水。不同来源的硝态氮通量受季风气候和人为活动的调节。例如，高降水和高强度施肥导致了严重的非点源污染。在雨季，土壤和水库中反硝化作用旺盛。温度可以调节氮的迁移、硝化和反硝化过程。基于这些结果，我们建议针对丹江口水库地区氮污染问题的管理策略应遵循 NO 来源、迁移和转化机制的特定时空特征。
