Methane and nitrous oxide concentrations and fluxes from heavily polluted urban streams: Comprehensive influence of pollution and restoration. (15th November 2022) - Wang, Xiaofeng
Abstract: Streams draining urban areas are usually regarded as hotspots of methane (CH4 ) and nitrous oxide (N2 O) emissions. However, little is known about the coupling effects of watershed pollution and restoration on CH4 and N2 O emission dynamics in heavily polluted urban streams. This study investigated the CH4 and N2 O 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. CH4 and N2 O concentrations in the six urban streams ranged from 0.12 to 21.32 μmol L −1 and from 0.03 to 2.27 μmol L −1, respectively. The calculated diffusive fluxes of CH4 and N2 O were averaged of 7.65 ± 9.20 mmol m −2 d −1 and 0.73 ± 0.83 mmol m −2 d −1, much higher than those in most previous reports. The heavily polluted streams with non-restoration had 7.2 and 7.8 times CH4 and N2 O concentrations higher than those in the fully restored streams, respectively. Particularly, CH4 and N2 O 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 CH4 and N2 O 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 CH4 and N2 O 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 CH4 and N2 O emissions in polluted urban streams. Overall, our study emphasized that although urbanization could inevitably strengthen riverine CH4 and N2 O emissions, effective eco-restoration can mitigate the crisis of riverine greenhouse gas emissions. Graphical abstract: Image 1 Highlights: Heavily polluted urban streams are powerful emitters of CH4 and N2 O. Comprehensive restoration can effectively mitigate riverine CH4 and N2 O emission. Sewage interception and nutrient removal can reduce urban stream CH4 &N2 O fluxes. Temperature and precipitation drive the seasonal variations of CH4 &N2 O fluxes.