Key Lab of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education/College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, PR China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, PR China.
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, PR China.
Sci Total Environ. 2022 Dec 10;851(Pt 1):158136. doi: 10.1016/j.scitotenv.2022.158136. Epub 2022 Aug 18.
Nitrogen (N) transport from terrene to river water is a major source of N in estuarine water, contributing to eutrophication, harmful algal blooms and hypoxia. However, there is a lack of holistic and systematic research on N sources and transformation in the freshwater river-estuarine water continuum. In this study, multiple stable isotope signatures of nitrate (δN-NO, δO-NO), ammonium (δN-NH), and suspended particulate nitrogen (δN-PN) were employed to differentiate the sources and transformations of N and calculate the proportional contribution of NO sources by Bayesian model in Qiantang River (QTR)-Hangzhou Bay (HZB) during the dry season. The results showed that: (1) Evidences from isotopic signatures suggested the occurrence of N transformation instead of conservation mixing. (2) Negative correlations between the δN-NO and δN-NH, the relationships between δN-NO and NO-N concentrations, and smaller δO-NO values were found in almost all surface water, indicating that nitrification was the dominant N transformation. (3) In addition to the nitrification evidence, significant correlations between δN-PN and δN-NH revealed that assimilation and nitrification jointly affected the N transformation in the QTR's upstream, midstream and lower tributaries, which are unaffected or less affected by tides. (4) The lack of a relationship between δN-NO and δO-NO or ln(NO) indicated that denitrification was weakened in all surface waters. (5) Qualitative identification of N pollution sources and quantitative calculation of NO-N potential sources revealed that sewage was the dominant source of N in the QTR and the HZB, while the internal nitrification was also important factor in determining N levels. This study provided evidence to further understand the sources, transport, and transformation of N in the river-estuary continuum, which deepens the understanding of the land-ocean integrated management of N contaminant.
氮（N）从陆地向河水的输送是河口水中 N 的主要来源，导致富营养化、有害藻类水华和缺氧。然而，对于淡水河-河口水连续体中 N 的来源和转化，缺乏整体和系统的研究。在这项研究中，利用硝酸盐（δN-NO、δO-NO）、铵（δN-NH）和悬浮颗粒氮（δN-PN）的多种稳定同位素特征来区分 N 的来源和转化，并通过贝叶斯模型计算钱塘江（QTR）-杭州湾（HZB）枯水期 NO 源的比例贡献。结果表明：（1）同位素特征的证据表明存在 N 转化而不是保守混合。（2）在几乎所有地表水都发现 δN-NO 和 δN-NH 之间存在负相关，δN-NO 和 NO-N 浓度之间的关系以及较小的 δO-NO 值，表明硝化作用是主要的 N 转化。（3）除了硝化作用的证据外，δN-PN 和 δN-NH 之间的显著相关性表明，同化和硝化共同影响了受潮汐影响较小或不受潮汐影响的 QTR 上游、中游和下游支流的 N 转化。（4）δN-NO 和 δO-NO 或 ln(NO) 之间缺乏关系表明所有地表水的反硝化作用都减弱了。（5）N 污染源的定性识别和 NO-N 潜在源的定量计算表明，污水是 QTR 和 HZB 中 N 的主要来源，而内部硝化作用也是决定 N 水平的重要因素。本研究为进一步了解河-河口连续体中 N 的来源、输运和转化提供了证据，加深了对陆海综合管理 N 污染物的理解。
