Rivers play a pivotal role in global carbon (C) and nitrogen (N) biogeochemical cycles. Urbanized rivers are significant hotspots of greenhouse gases (GHGs, N2O, CO2 and CH4) emissions. This study examined the GHGs distributions in the Guanxun River, an effluents-receiving subtropical urbanized river, as well as the key environmental factors and processes affecting the pattern and emission characteristics of GHGs. Dissolved N2O, CO2, and CH4 concentrations reached 228.0 nmol L–1, 0.44 mmol L–1, and 5.2 μmol L–1 during the wet period, and 929.8 nmol L–1, 0.7 mmol L–1, and 4.6 μmol L–1 during the dry period, respectively. Effluents inputs increased C and N loadings, reduced C/N ratios, and promoted further methanogenesis and N2O production dominated by incomplete denitrification after the outfall. Increased urbanization in the far downstream, high hydraulic residence time, low DO and high organic C environment promoted methanogenesis. The strong CH4 oxidation and methanogenic reactions inhibited by the effluents combined to suppress CH4 emissions in downstream near the outfall, and the process also contributed to CO2 production. The carbon fixation downstream from the outfall were inhibited by effluents. Ultimately, it promoted CO2 emissions downstream from the outfall. The continuous C, N, and chlorine inputs maintained the high saturation and production potential of GHGs, and altered microbial community structure and functional genes abundance. Ultimately, the global warming potential downstream increased by 186 % and 84 % during wet and dry periods on the 20-year scale, and increased by 91 % and 49 % during wet and dry periods on the 100-year scale, respectively, compared with upstream from the outfall. In urbanized rivers with sufficient C and N source supply from WWTP effluents, the large effluent equivalently transformed the natural water within the channel into a subsequent "reactor". Furthermore, the IPCC recommended EF5r values appear to underestimate the N2O emission potential of urbanized rivers with high pollution loading that receiving WWTP effluents. The findings of this study might aid the development of effective strategies for mitigating global climate change.

中文翻译：

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污水处理厂污水增加了亚热带城市化河流的全球变暖潜能值


河流在全球碳 （C） 和氮 （N） 生物地球化学循环中起着关键作用。城市化河流是温室气体（GHG、N2O、CO2 和 CH4）排放的重要热点。本研究考察了关浵河（一条接收污水的亚热带城市化河流）的温室气体分布，以及影响温室气体排放格局和排放特征的关键环境因素和过程。湿润期溶解的 N2O、CO2 和 CH4 浓度达到 228.0 nmol L–1、0.44 mmol L–1 和 5.2 μmol L–1， 干燥期分别为 929.8 nmol L-1、0.7 mmol L-1 和 4.6 μmol L-1。污水输入增加了 C 和 N 负荷，降低了 C/N 比，并促进了进一步的甲烷生成和 N2O 产生，其中排污口后不完全反硝化为主。远下游城市化程度增加、水力停留时间长、低 DO 和高有机碳环境促进了甲烷生成。污水抑制的强烈 CH4 氧化和产甲烷反应共同抑制了下游排污口附近 CH4 的排放，该过程也有助于 CO2 的产生。污水抑制了排污口下游的碳固定。最终，它促进了排污口下游的 CO2 排放。连续的 C、N 和氯输入维持了 GHG 的高饱和度和生产潜力，并改变了微生物群落结构和功能基因丰度。最终，与排污口上游相比，下游全球变暖潜能值在 20 年尺度的丰水期和枯水期增加了 186% 和 84%，在 100 年尺度的丰水期和枯水期分别增加了 91% 和 49%。 在污水处理厂污水源供应充足的碳和氮源的城市化河流中，大量污水相当于将渠道内的天然水转化为随后的“反应器”。此外，IPCC 推荐的 EF5r 值似乎低估了接收污水处理厂污水的高污染负荷城市化河流的 N2O 排放潜力。这项研究的结果可能有助于制定缓解全球气候变化的有效策略。