Chongqing Key Laboratory of Wetland Science Research of the Upper Reaches of the Yangtze River, Chongqing, 401331, China; Three Gorges Reservoir Area Earth Surface Ecological Processes of Chongqing Observation and Research Station, Chongqing, 405400, China; School of Geography and Tourism, Chongqing Normal University, Chongqing, 400047, China.
Chongqing Key Laboratory of Wetland Science Research of the Upper Reaches of the Yangtze River, Chongqing, 401331, China; Three Gorges Reservoir Area Earth Surface Ecological Processes of Chongqing Observation and Research Station, Chongqing, 405400, China; School of Geography and Tourism, Chongqing Normal University, Chongqing, 400047, China.
Environ Pollut. 2022 Nov 15;313:120098. doi: 10.1016/j.envpol.2022.120098. Epub 2022 Sep 5.
Streams draining urban areas are usually regarded as hotspots of methane (CH) and nitrous oxide (NO) emissions. However, little is known about the coupling effects of watershed pollution and restoration on CH and NO emission dynamics in heavily polluted urban streams. This study investigated the CH and NO concentrations and fluxes in six streams that used to be heavily polluted but have undergone different watershed restorations in Southwest China, to explore the comprehensive influences of pollution and restoration. CH and NO concentrations in the six urban streams ranged from 0.12 to 21.32 μmol L and from 0.03 to 2.27 μmol L, respectively. The calculated diffusive fluxes of CH and NO were averaged of 7.65 ± 9.20 mmol m d and 0.73 ± 0.83 mmol m d, much higher than those in most previous reports. The heavily polluted streams with non-restoration had 7.2 and 7.8 times CH and NO concentrations higher than those in the fully restored streams, respectively. Particularly, CH and NO fluxes in the fully restored streams were 90% less likely than those found in the unrestored ones. This result highlighted that heavily polluted urban streams with high pollution loadings were indeed hotspots of CH and NO emissions throughout the year, while comprehensive restoration can effectively weaken their emission intensity. Sewage interception and nutrient removal, especially N loadings reduction, were effective measures for regulating the dynamics of CH and NO emissions from the heavily polluted streams. Based on global and regional integration, it further elucidated that increasing environment investments could significantly improve water quality and mitigate CH and NO emissions in polluted urban streams. Overall, our study emphasized that although urbanization could inevitably strengthen riverine CH and NO emissions, effective eco-restoration can mitigate the crisis of riverine greenhouse gas emissions.
受污染流域的恢复对重度污染城市溪流中甲烷（CH）和氧化亚氮（NO）排放动态的综合影响
城市流域的排水通常被认为是甲烷（CH）和氧化亚氮（NO）排放的热点。然而，对于曾经受到严重污染但经历了不同流域恢复的重度污染城市溪流中 CH 和 NO 排放动态的耦合效应知之甚少。本研究调查了中国西南部六个曾经受到严重污染但经历了不同流域恢复的溪流中的 CH 和 NO 浓度和通量，以探索污染和恢复的综合影响。这六个城市溪流中的 CH 和 NO 浓度范围分别为 0.12 至 21.32 μmol L 和 0.03 至 2.27 μmol L。计算得出的 CH 和 NO 的扩散通量分别为 7.65±9.20 mmol m d 和 0.73±0.83 mmol m d，远高于以往大多数报告的结果。未恢复的重度污染溪流中的 CH 和 NO 浓度分别比完全恢复的溪流高 7.2 和 7.8 倍。特别是，完全恢复的溪流中的 CH 和 NO 通量比未恢复的溪流低 90%。结果表明，高污染负荷的重度污染城市溪流确实是全年 CH 和 NO 排放的热点，而全面恢复可以有效削弱其排放强度。污水截留和养分去除，特别是减少氮负荷，是调节重度污染溪流 CH 和 NO 排放动态的有效措施。基于全球和区域综合评估，进一步阐明增加环境投资可以显著改善水质，减轻污染城市溪流中的 CH 和 NO 排放。总体而言，本研究强调，尽管城市化不可避免地会加剧河流 CH 和 NO 排放，但有效的生态恢复可以减轻河流温室气体排放的危机。
