河流CO2与CH4排放研究进展

河流作为连接海-陆两大碳库的主要通道,其水-气界面二氧化碳(CO_2)与甲烷(CH_4)排放构成全球碳循环的重要环节,对全球气候变暖的贡献不容小觑.明确河流水体CO_2与CH_4产排过程、时空特征以及控制因素是认识河流生态学功能以及其对变化环境响应的重要内容.基于当前河流CO_2与CH_4排放研究进展,构建河流碳排放动力学概念框架(内源代谢、陆源输入),并从全球尺度、区域尺度、流域尺度综述了河流碳排放时空变异性特征以及存在的研究不足.在理解碳排放动力学概念框架和时空变异特征的基础上,构建了河流CO_2与CH_4动力学控制因子分层框架(内部因子:有机质、温度、营养盐;外部因子:水文、地貌、人类活动),深入探讨了河流碳排放的关键影响因素.最后,根据当前研究中存在的不足,提出河流碳排放应将纳入区域陆地碳平衡过程,今后研究重点应包括流域尺度上河流CO_2与CH_4内源产生与陆源输入相对贡献的量化研究、不同界面CO_2与CH_4产生与排放过程研究、高时空分辨率的监测数据的补充以及变化环境与人类活动干扰下河流碳排放的响应过程等,为理解河流生态学过程及生态系统功能提供基础,同时为我国进一步深入开展相关研究提供借鉴.

Review of CO2 and CH4 Emissions from Rivers

Streams and rivers play a major biogeochemical role in the global carbon cycle and act as hot spots for carbon dioxide (CO₂) and methane (CH₄) emissions to the atmosphere, excepting their roles of transporting the water and carbon from the terrestrial environment to the ocean. While carbon gases have been of great global concern, systematic reviews are still scarce. Given recent recognition of the pervasiveness of CO₂ and CH₄ in streams and rivers, this study synthesized existing research and discoveries to identify patterns and controls for riverine CO₂ and CH₄, knowledge gaps, and research opportunities. This study presented a conceptual framework for sources and the fates of CO₂/CH₄ from streams and rivers and used this framework to understand the dynamic processes of fluvial carbon evasion and potential anthropogenic disturbances. Multiple environmental influences combined with different contributions of endogenous metabolism and terrigenous input, and the CO₂ and CH₄ in streams and rivers showed significant spatial and temporal variability on a global scale, regional scale, and watershed scale, which indicates a substantial challenge for understanding the larger-scale dynamics. For a clearer recognition of how the changing environment and human activities may modify fluvial CO₂ and CH₄ dynamics, this study constructed a system framework of controls on CO₂ and CH₄ production and persistence in streams and rivers. The framework of controls can be viewed in terms of endogenous environmental controls that influence river metabolism (organic matter, temperature, nutrients, pH, and alternative electron acceptors) and external factors, including geomorphic and hydrologic drivers and human activities (agriculture, damming, and urbanization). We point out that the carbon emissions from rivers should be integrated into the terrestrial carbon budget, and in the future, more attention should be given to research on the sources of CO₂ and CH₄ in rivers, the generation and diffusion of CO₂ and CH₄ at different interfaces, the spatiotemporal variability of riverine carbon emissions, and the response of riverine CO₂ and CH₄ dynamics to the changing environment and human activities.