雅鲁藏布江河水中CH_4和N_2O气体浓度及释放特征

Concentrations and emissions of dissolved CH_4 and N_2O in the Yarlung Tsangpo River

河流向大气释放大量温室气体,是陆地生态系统物质循环和能量流动的重要环节。山地河流是温室气体排放的热点区域,但迄今山地河流CH_4和N_2O释放方面的研究较少。为探究高原中大型河流CH_4和N_2O浓度的时空分布特征及其影响因素,对雅鲁藏布江(雅江)干流和主要支流河水中CH_4和N_2O气体进行了季节性采样分析。结果表明,雅江河水中CH_4含量为2.3～864.9 nmol·L-1,N_2O含量为8.2～23.7 nmol·L-1,枯水期CH_4含量和丰水期无显著差异(P=0.112),但枯水期N_2O含量显著高于丰水期(P=0.017),流量和水温可能分别是影响CH_4和N_2O变化的主要因子。雅江河水CH_4和N_2O的释放速率分别为4.3～11.1 mg C·m-2·d-1和0.16～0.37 mg N·m-2·d-1,排放量分别为1.88～4.59Gg C·a-1和0.07～0.16 Gg N·a-1,分别约占全球河流CH_4和N_2O释放量的1.25‰～3.06‰和2.17‰～4.96‰。山地河流CH_4和N_2O的排放需要引起重视,全球河流温室气体释放可能需要进行重新评估。

Rivers release large quantities of greenhouse gases into the atmosphere,which is an important link in the material cycling and energy flow of terrestrial ecosystems. Mountainous rivers are ‘hotspots’ for greenhouse gas emission,but the release of CH4 and N2O from those rivers has been less documented. To explore the spatio-temporal distributions and related controls of CH4 and N2O in middle-large plateau rivers,the seasonal variations of CH4 and N2O in tributary and main stream of the Yarlung Tsangpo River were examined. The results showed that the ranges of CH4 and N2O concentrations in the Yarlung Tsangpo were 2.3-864.9 and 8.2-23.7 nmol·L-1,respectively. There was no significant difference in CH4 concentrations between low-flow and high-flow periods( P = 0. 112),but the N2O contents were higher in low-flow months than in high-flow months( P = 0.017). River water discharge and water temperature were the major factors controlling the dynamics of CH4 and N2O emission,respectively. The release rates of CH4 and N2O in the Yarlung Tsangpo River ranged 4.3-11.1 mg C·m-2·d-1 and 0.16-0.37 mg N·m-2·d-1,respectively. The emission amounts of CH4 and N2O in Yarlung Tsangpo River system were 1.88-4. 59 Gg C · a-1 and 0. 07-0. 16 Gg N · a-1,accounting for 1.25‰-3.06‰ and2.17‰-4.96‰ of global river estimations,respectively. The evasion of CH4 and N2O in mountainous rivers need further detailed studies,which may revise the global estimation of greenhouse gas emission.