Contrasting Biophysical Controls on Carbon Dioxide and Methane Outgassing From Streams
Contrasting Biophysical Controls on Carbon Dioxide and Methane Outgassing From Streams
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DOI：
10.1029/2021jg006328
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
L. Rovelli;L. Olde;C. Heppell;A. Binley;G. Yvon‐Durocher;R. Glud;M. Trimmer
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文献类型：
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作者：
L. Rovelli;L. Olde;C. Heppell;A. Binley;G. Yvon‐Durocher;R. Glud;M. Trimmer
人们认为，小源头水流会向大气中大量排放与气候相关的二氧化碳 (CO2) 和甲烷 (CH4)。尽管这些源头的二氧化碳和甲烷明显过饱和，但这两种碳气体的起源和命运的控制仍然很少受到限制，特别是对于温室气体更强的甲烷而言。在这里，通过测量基于流的二氧化碳和甲烷的产生，同时测量它们向大气中的排气速率，我们确定了每种气体的独特生物物理控制机制。我们发现，虽然二氧化碳主要从流域输入（与排放量成比例），但二氧化碳的放气可以通过河流内代谢来调节，以在春季和夏季抵消高达 30% 的放气。相比之下，CH4 对流量季节变化表现出非线性响应，并且主要在与沉积物类型相关的河床中产生。此外，一旦从河床中释放出来，CH4在地表的脱气和水流驱动的稀释发生得比生物甲烷氧化要快得多，并且CH4使水基本上没有受到生物的改变。将源头流的强烈碳循环纳入全球碳循环将需要对地球系统模型中的每种碳气体进行不同的参数化。
Small headwater streams are recognized for intense outgassing to the atmosphere of climate‐relevant carbon dioxide (CO2) and methane (CH4). Though these headwaters are markedly oversaturated for both CO2 and CH4, the origins and controls over the fate of these two carbon‐gases are still poorly constrained, especially for the stronger greenhouse gas CH4. Here, by measuring stream‐based production of CO2 and CH4, concurrently with their rates of outgassing to the atmosphere, we identify distinct biophysical control mechanisms for each gas. We show that while CO2 is largely imported from the catchment in proportion to discharge, CO2 outgassing can be modulated by in‐stream metabolism to offset outgassing by up to 30% in spring and summer. In contrast, CH4 shows a non‐linear response to seasonal changes in discharge and is predominantly produced in the streambed in relation to sediment type. Further, once released from the streambed, outgassing of CH4 at the surface and flow‐driven dilution occur far more rapidly than biological methane oxidation and CH4 leaves the water largely unaltered by biology. Incorporating the intense carbon cycling of headwater streams into the global carbon cycle will require distinct parameterizations for each carbon gas in Earth system models.