全球河流水气界面二氧化碳排放通量研究进展

Research progress on carbon dioxide emission fluxes at the water-air-interface of global rivers

  • 摘要: 河流仅占地球非冰川陆地表面积的0.58%,但其在全球碳循环中起着至关重要的作用。过去对全球河流水气界面二氧化碳(CO2)排放的研究存在较多盲点,导致全球河流CO2排放通量的估算结果存在很大的不确定性。近年来,随着测量手段的改进及全球数据累积量的增多,国内外许多研究对此进行了修订与更新。本文分别从时间与空间角度对全球河流二氧化碳分压(pCO2)和CO2排放通量的差异性以及相关影响因素进行总结,明确目前全球河流CO2排放通量及气候变化与人为扰动对该通量的影响。结果显示:河流与溪流表层水体pCO2具有极强的时空异质性,全球河流与溪流pCO2整体呈现从低纬度向高纬度递减的趋势,热带河流和溪流pCO2普遍高于温带、北方和北极地区;河流与溪流pCO2存在明显的季节差异,夏季普遍高于冬季。目前全球溪流和河流的年CO2排放通量最新估算结果为(2.0±0.2)Pg/a,河流及溪流水体CO2排放通量随河流分支等级的升高而逐渐下降,细小河流在河流生态系统碳排放中的作用需引起关注;不同地理环境下的河流与溪流在CO2的产生与排放机制上表现出独特性,气候变化和人为扰动(筑坝、城市化、农业灌溉等)会增加河流CO2排放通量估计的不确定性。此外,全球河流与溪流水气界面的CO2排放通量计算仍存在一定的时空偏差,为了提高CO2排放通量评估的准确性,需在精细化的河网尺度上对其进行量化。

     

    Abstract: Rivers cover only 0.58% of the earth's non-glacial land surface, but they play a vital role in the global carbon cycle. In the past, there were many blind spots in the study of carbon dioxide (CO2) emissions at the water-air interface of global rivers, resulting in great uncertainty in the estimation of global river CO2 emission fluxes. In recent years, with the improvement of measurement methods and the accumulation of global data, many studies worldwide have revised and updated the fluxes. This paper summarizes the spatial and temporal variability of global river partial pressure of CO2 (pCO2) and CO2 emission fluxes as well as the related influencing factors from the temporal and spatial perspectives, respectively. It further assesses the impacts of climate change and anthropogenic perturbations on river carbon fluxes. The results demonstrate that the pCO2 in the surface waters of rivers and streams exhibits significant spatial and temporal heterogeneity, and it decreases from low latitudes to high latitudes, while pCO2 in tropical rivers and streams is generally higher than that of temperate, northern and Arctic regions. There are obvious seasonal differences of pCO2 values in the surface waters of rivers and streams with a generally higher value in summer than in winter. At present, the latest estimate of the annual CO2 emissions from global streams and rivers is (2.0 ± 0.2) Pg/a, and CO2 flux from streams and rivers gradually decreases with the increase of river branch grade. The role of small rivers in carbon emissions within river ecosystems requires attention. The rivers and streams situated within distinct geographic contexts possess unique mechanisms of CO2 production and emission. Climate change and human disturbances (such as dam construction, urbanization, agricultural irrigation, etc.) can increase the uncertainty of CO2 flux estimation from rivers. Furthermore, the estimation of CO2 emission fluxes at the water-gas interface of rivers and streams across the globe continues to be subject to spatial and temporal biases. These biases necessitate further quantification and refinement at a more granular river network scale to enhance the accuracy of CO2 flux assessments.

     

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