Key Laboratory of Ministry of Education for Coastal and Wetland Ecosystems, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China.
Fujian Xiamen Environmental Monitoring Central Station, Xiamen 361022, China.
Water Res. 2024 Nov 15;266:122349. doi: 10.1016/j.watres.2024.122349. Epub 2024 Aug 29.
Rivers play a pivotal role in global carbon (C) and nitrogen (N) biogeochemical cycles. Urbanized rivers are significant hotspots of greenhouse gases (GHGs, NO, CO and CH) 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 NO, CO, and CH concentrations reached 228.0 nmol L, 0.44 mmol L, and 5.2 μmol L during the wet period, and 929.8 nmol L, 0.7 mmol L, and 4.6 μmol L during the dry period, respectively. Effluents inputs increased C and N loadings, reduced C/N ratios, and promoted further methanogenesis and NO 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 CH oxidation and methanogenic reactions inhibited by the effluents combined to suppress CH emissions in downstream near the outfall, and the process also contributed to CO production. The carbon fixation downstream from the outfall were inhibited by effluents. Ultimately, it promoted CO 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 EF values appear to underestimate the NO 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.
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（GHGs，NO、CO 和 CH）排放的重要热点。本研究考察了 Guanxun 河（一条受污水影响的亚热带城市化河流）中的 GHGs 分布，以及影响 GHGs 分布和排放特征的关键环境因素和过程。在雨季，溶解的 NO、CO 和 CH 浓度分别达到 228.0 nmol/L、0.44 mmol/L 和 5.2 μmol/L，而在旱季则分别达到 929.8 nmol/L、0.7 mmol/L 和 4.6 μmol/L。污水输入增加了 C 和 N 负荷，降低了 C/N 比，并促进了出海口后的不完全反硝化作用主导的进一步甲烷生成和 NO 生成。下游更远的城市化程度较高、水力停留时间较长、低 DO 和高有机 C 环境促进了甲烷生成。污水的强烈 CH 氧化和产甲烷反应抑制了出海口下游的 CH 排放，这一过程也促进了 CO 的生成。出海口下游的碳固定受到污水的抑制。最终，促进了出海口下游的 CO 排放。污水的连续 C、N 和氯输入维持了 GHGs 的高饱和度和产生潜力，并改变了微生物群落结构和功能基因丰度。最终，在 20 年的时间尺度上，与出海口上游相比，湿季和旱季下游的全球增温潜势分别增加了 186%和 84%，在 100 年的时间尺度上，湿季和旱季分别增加了 91%和 49%。在城市化河流中，污水处理厂（WWTP）污水提供了充足的 C 和 N 源供应，大量污水等效地将河道内的天然水转化为后续的“反应器”。此外，政府间气候变化专门委员会（IPCC）推荐的 EF 值似乎低估了接收 WWTP 污水的高污染负荷城市化河流的 NO 排放潜力。本研究的结果可能有助于制定减轻全球气候变化的有效策略。
