上海城市河流温室气体排放特征及其影响因素

为研究城区和郊区河流3种温室气体(N₂O、CH₄和CO₂)排放通量的差异,分别于春季(2013年4月)、夏季(2013年7月)、秋季(2013年10月)和冬季(2014年1月),利用浮箱法和扩散模型法对上海市城区河流(苏州河)和郊区河流(淀浦河)的温室气体排放通量进行了观测；并探讨了人类活动干扰下环境因子对温室气体排放的影响. 结果表明:研究区内2条河流是温室气体的排放源,城区河流N₂O和CH₄的扩散排放通量和浮箱排放通量年均值均比郊区河流大1~2个量级, CO₂两种排放通量在城郊区2条河流的年均值相当. 苏州河N₂O、CO₂和CH₄扩散排放通量年均值分别为15.88、6 748.27和84.98 μmol/(m2·h)；淀浦河分别为0.61、2 978.98和9.61 μmol/(m2·h). 苏州河N₂O、CO₂和CH₄浮箱排放通量年均值为15.77、4 041.61和6 721.08 μmol/(m2·h)；淀浦河为0.60、1 214.77和59.58 μmol/(m2·h). 城市河流呈现出高氮负荷及缺氧的特征,是影响中心城区河流N₂O、CO₂和CH₄扩散排放通量偏高的重要因素. CH₄浮箱排放通量和扩散排放通量的差异显示,城市河流中的富碳氮缺氧环境条件有利于随机气泡排放的发生,增强了温室气体的排放. 

Greenhouse Gas Emission Characteristics from Urban Rivers in Shanghai

The floating chamber and diffusive models were used to investigate the differences of greenhouse gas (N₂O, CH₄ and CO₂) fluxes between an urban river (Suzhou River) and a suburban river (Dianpu River) in Shanghai during April, July and October in 2013 and January in 2014. The influence of environmental variables on greenhouse gas emissions under the disturbance of anthropogenic activities was also discussed. The results demonstrated that the two rivers were main sources of N₂O, CH₄ and CO₂. N₂O and CH₄ fluxes from the urban river were one to two magnitudes higher than those from the suburban river. CO₂ fluxes from the two rivers were at the same magnitude. Estimated annual N₂O, CO₂ and CH₄ fluxes by the diffusive model were 15.88,6748.27 and 84.98 μmol/(m2·h) in Suzhou River, and 0.61,8.98 and 9.61 μmol/(m2·h) in Dianpu River. Estimated annual N₂O, CO₂ and CH₄ fluxes by the floating chamber method were 15.77,1.61 and 6721.08 μmol/(m2·h) in Suzhou River, and 0.60,4.77 and 59.58 μmol/(m2·h) in Dianpu River. Significant correlations between dissolved oxygen, nitrate, ammonium and N₂O fluxes indicated that the enrichment of dissolved inorganic nitrogen and depletion of oxygen might enhance microbial denitrification, resulting in high N₂O fluxes from the urban river. At the same time, high emissions of CH₄ occurred in hypoxia conditions in the urban river. Water temperature greatly controlled CO₂ fluxes, probably through stimulating the microbial activities of CO₂ production. The difference between floating chamber and diffusive model fluxes of CH₄ indicated that the nitrogen-rich and oxygen-deficit conditions in urban river were favorable for bubble events, which could enhance CH₄ emission.