亚热带城市湖泊与河流CO_(2)气体通量特征及其影响因素

Characteristics and influencing factors of CO_(2)flux in subtropical urban lakes and river

湖泊、河流等内陆水体是连接陆地生态系统和海洋的“长程碳环路”的重要节点,也是温室气体二氧化碳(CO_(2))排放源,在调节陆地、海洋间的碳迁移转换中发挥着重要作用。相对于自然水体,城市水体因面积小、水深浅且受监测方法限制,水-气界面碳通量经常被忽略。为探讨我国亚热带城市水体温室气体排放特征,本研究以湖南省长沙市典型城市水体,包括洋湖、西湖、松雅湖、月湖4个湖泊和湘江长沙段为研究对象,分别于2022年4和10月采用光化学反馈-腔增强吸收光谱法(OF-CEAS)和扩散模型法对水-气界面CO_(2)通量进行对比测定。结果表明,长沙城市湖泊与河流春季为CO_(2)排放源,秋季为吸收汇,河流水-气界面CO_(2)通量呈显著季节差异。河湖之间CO_(2)通量在春季表现为显著差异,秋季差异不显著。CO_(2)通量与水体溶解氧、水体总氮浓度等呈显著正相关。2种方法的CO_(2)通量对比测定在湖泊上显著相关,但对河流而言相关性不显著。研究揭示的城市湖泊与河流CO_(2)气体的排放特征有利于深入探究城市水体碳的迁移转化,可对全面了解全球气候变化过程和河湖湿地温室气体减排和调控提供科学支撑。

Inland water bodies,such as lakes and rivers,are important nodes of the"long-range carbon loop"connecting terrestrial ecosystems and oceans,as well as sources of greenhouse gas carbon dioxide(CO_(2))emissions.Inland water bodies also play an important role in regulating carbon migration between land and sea.Compared with natural water bodies,carbon fluxes at the water-air interface are often overlooked in urban water due to their small sizes,shallow depths,and limitations in monitoring methods.In order to explore the greenhouse gas emission characteristics of such water bodies in China,this study took four typical urban water bodies in Changsha,Hunan Province,including Lake Yang,Lake West,Lake Songya and Lake Yue,and Changsha section of Xiangjiang River as research objects.The CO_(2)fluxes at the water-gas interface were measured by laser-based gas analyzer that used optical feedback-cavity-enhanced absorption spectroscopy(OF-CEAS)and diffusion model in April and October 2022,respectively.Results showed that lakes and rivers in Changsha city were CO_(2)sources in spring but CO_(2)sinks in fall,and there was a significant seasonal difference in CO_(2)fluxes at the river water-air interface.Moreover,the CO_(2)flux was positively correlated with the content of dissolved oxygen and total nitrogen.The comparative determination of CO_(2)fluxes between the two methods was significantly correlated on lakes,but not on rivers.The study reveals that the CO_(2)emission characteristics of urban lakes and rivers are beneficial to the in-depth investigation of carbon transport and transformation,which can provide scientific support for the comprehensive understanding of global climate change processes and the reduction and regulation of greenhouse gas emissions in inland wetlands.