粤港澳大湾区典型城镇化地区河流氮素的时空分布特征及源解析

选取粤港澳大湾区典型城镇化地区广州市的流溪河—西航道—前航道为研究对象，分别于2020年7月和2021年1月开展野外调研采样活动，收集40个地表水水样样品，通过室内分析，利用水化学和同位素（δ¹⁵N-\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}、δ¹⁸O-\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}和δ¹⁵N-\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}）等指标，探讨研究区河流氮素的时空分布特征及其来源，研究城市化对河流氮素的影响。结果表明：从上游到下游，人类活动对Cl^-、\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N、\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}-N、DIN（溶解态无机氮）的质量浓度影响逐渐突显；丰水期\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N、DIN较枯水期高，主要归因于外源输入的影响强于降雨量与上游来水稀释的综合作用；在溶解态总氮的组成分布上，\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N与\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}-N分别是丰水期、枯水期的主要存在形态，说明丰水期人类活动影响十分显著。丰水期\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N与Cl^-的质量浓度具有较强的正相关关系，说明丰水期\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N与Cl^-可能具有相近或相同的来源。离子比值及稳定同位素的溯源结果具有较高的一致性，均显示上游农田化肥、土壤有机氮、养殖污水为上游河道的主要氮来源，而土壤有机氮、城市污水则为下游河道氮的主要来源。

Spatiotemporal Characteristics and Sources of River Nitrogen in Typical Urbanized Areas in the Guangdong-Hong Kong-Macao Greater Bay Area

A typical urbanized area in the Guangdong-Hong Kong-Macao Greater Bay Area, Liuxi River-West Channel-North Channel in Guangzhou City, was used to reveal the impacts of rapid urbanization on riverine nutrients. Two field campaigns were implemented in both wet and dry season, e.g. July 2020 and January 2021. Forty surface water samples were collected to analyze indicators such as major ions and stable isotopes (δ¹⁵N-\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}, δ¹⁸O-\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-} and δ¹⁵N-\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}) The spatiotemporal characteristics and sources of river nitrogen in the study area were explored by using hydrochemistry and isotopes (δ¹⁵N-\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}, δ¹⁸O-\mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-} and δ¹⁵N-\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}) methods. The results show that from upstream to downstream, the influences of human activties on the mass concentrations of Cl^-, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N, \mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}-N, DIN (Dissolved Inorganic Nitrogen) are gradually prominent. The concentrations of \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N and DIN in the wet season are higher than those in the dry season, mainly due to the the more intensive influence of exogenous input than the combined effect of rainfall and upstream water dilution. In the composition distribution of dissolved total nitrogen, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N and \mathrm{N}{\mathrm{O}}_{\mathrm{3}}^{-}-N are the main forms in the wet and dry season respectively, indicating significant impact of human activities in the wet season. There is a strong positive correlation between \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N and Cl^- concentration in the wet season, indicating that \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}-N and Cl^- may have similar or the same sources in the wet season. Results of ion ratio of Na/Cl and stable isotope tracing are highly consistent. This indicates that upstream farmland chemical fertilizer, soil organic nitrogen and aquaculture sewage are the main sources of nitrogen in the upstream, while the soil organic nitrogen and urban sewage are the main sources of nitrogen in the downstream. The research results can provide data support and theoretical basis for river water environment protection and water resources management in the study area.