Gas Transfer Velocities Evaluated Using Carbon Dioxide as a Tracer Show High Streamflow to Be a Major Driver of Total CO2 Evasion Flux for a Headwater Stream
Gas Transfer Velocities Evaluated Using Carbon Dioxide as a Tracer Show High Streamflow to Be a Major Driver of Total CO2 Evasion Flux for a Headwater Stream
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DOI：
10.1029/2018jg004388
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发表时间：
2018-07
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影响因子：
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通讯作者：
Mollie J. McDowell;Mark S. Johnson
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文献类型：
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作者：
Mollie J. McDowell;Mark S. Johnson
二氧化碳（CO2）从源头流逃逸是控制内陆沃茨陆源碳命运的主要过程。然而，采样技术的局限性抑制了准确表征流中CO2逃逸的努力，特别是具有陡峭坡度、复杂形态和具有挑战性地形的源头流。CO2源动力学与湍流条件相结合控制CO2的气体传输速度（kCO 2），因此驱动CO2逃逸。我们目前的估计kCO 2和CO2逃避陡峭，湍流的源头流在西南部不列颠哥伦比亚省，加拿大，收集使用自动原位CO2示踪技术。气体传输速度与排放成正比，平均kCO 2为36.8米/天，范围为13.5至169米/天。在高流量事件期间，气体传输速度最高，所有CO2排放量的84%发生在排放量高于Q50（中位数排放量）时（92.6 L/s）。广泛使用的模型高估了气体传输速度的平均相对误差为24%，但低估了k600值高于165米/天。我们对一系列径流的气体传输速度的测定表明，CO2逃逸可能高于先前从直接测量或模型中估计的值，特别是在高流量事件期间。这些研究结果表明，需要直接，频繁，原位测定KCO 2，以准确地表征CO2逃逸动态陡峭的源头流。
Evasion of carbon dioxide (CO2) from headwater streams is a dominant process controlling the fate of terrestrially derived carbon in inland waters. However, limitations of sampling techniques inhibit efforts to accurately characterize CO2 evasion from streams, and particularly headwater streams with steep gradients, complex morphologies, and challenging terrain. CO2 source dynamics coupled with turbulence conditions control gas transfer velocities of CO2 ( kCO2 ) and therefore drive CO2 evasion. We present estimates of kCO2 and CO2 evasion from a steep, turbulent headwater stream in southwestern British Columbia, Canada, collected using an automated in situ CO2 tracer technique. Gas transfer velocities scaled positively with discharge, with a median kCO2 of 36.8 m/day and a range of 13.5 to 169 m/day. Gas transfer velocities were highest during high‐flow events, with 84% of all CO2 emissions occurring when discharge was higher than Q50, the median discharge (92.6 L/s). Widely used models overestimated gas transfer velocities with a mean relative error of 24% but underestimated k600 values above 165 m/day. Our determinations of gas transfer velocities for a range of streamflow suggest that CO2 evasion may be higher than previously estimated from direct measurements or models, particularly during high‐flow events. These findings illustrate the need for direct, frequent, in situ determinations of kCO2 to accurately characterize CO2 evasion dynamics in steep headwater streams.