Summer methane fluxes from a boreal bog in northern Quebec, Canada, using eddy covariance measurements
Summer methane fluxes from a boreal bog in northern Quebec, Canada, using eddy covariance measurements
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DOI：
10.1016/j.atmosenv.2013.09.044
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发表时间：
2013-12
影响因子：
5
通讯作者：
D. Nadeau;A. Rousseau;C. Coursolle;H. Margolis;M. Parlange
中科院分区：
文献类型：
--
作者：
D. Nadeau;A. Rousseau;C. Coursolle;H. Margolis;M. Parlange
位于加拿大詹姆斯湾低地的一个北方沼泽被用开放路径气体分析仪测量，以监测整个2012年夏天甲烷的湍流通量。大部分连续的涡旋协方差测量使得能够研究每小时、每天和季节尺度上的甲烷动力学。为了剔除由于稳定层结下大气输送效率低下而低估了生物甲烷通量的数据段，我们采用了一种新的方法，该方法基于大气稳定参数ζ=z/land the Friction velocityu∗，其中z是测量高度，L是Obukhov长度。现场测量显示，至少存在一次持续的沸腾事件，由低气压、地下水位下降和机械湍流增加引发--这表明甲烷气泡的大规模释放可能是甲烷在北方沼泽中的重要传输机制。对对流条件下大气甲烷相似标度的有效性也进行了评估，甲烷浓度的归一化标准差与ζ没有很好的标度，突显了沼泽地区天然甲烷生产和释放的不均一性。总体而言，甲烷的每小时排放量在−2.0到32.1 mg/−2 h−1之间，夏季平均值为2.4 mg/CH4m−2 h−1。在日尺度上，对甲烷排放的两个主要控制因素是地下水位和地表以下0.3m的泥炭温度。与其他研究相反，季节性甲烷排放在地下水位与地表的最大距离时达到峰值，大约在8月中旬。甲烷排放没有明显的昼夜规律，这表明甲烷是在泥炭深处产生的。季节排放量估计为4.4g CH4m−2，并与使用不同测量技术在类似地形上进行的其他观测结果进行了很好的比较。鉴于甲烷的释放和传输很大程度上受到气候和植被覆盖等当地特征的影响，本研究强调有必要在持续测量北部泥炭地甲烷通量的情况下进一步监测甲烷的释放和输送。
A boreal bog located in the James Bay lowlands, Canada, was instrumented with an open-path gas analyzer to monitor the turbulent fluxes of methane throughout the summer of 2012. The mostly continuous eddy covariance measurements permitted the study of methane dynamics at the hourly, daily and seasonal scales. To exclude data segments for which the biological methane fluxes were underestimated due to inefficient atmospheric transport under stable stratification, we applied a novel approach based on both the atmospheric stability parameterζ=z/Land the friction velocityu∗, wherezis the measurement height andLthe Obukhov length. The field measurements revealed the existence of at least one sustained ebullition event, triggered by low barometric pressures, a declining water table and increasing mechanical turbulence – suggesting that large-scale release of methane bubbles can be an important transport mechanism of methane in boreal bogs. The validity of similarity scaling for atmospheric methane under convective conditions was also assessed and the normalized standard deviations of methane concentrations did not scale well withζ, highlighting the heterogeneity in natural methane production and release across the bog. Overall the hourly emissions ranged between −2.0 and 32.1 mg CH4m−2h−1, with a summertime mean of 2.4 mg CH4m−2h−1. At the daily scale, the two main controls on methane emissions were found to be the water table position and the peat temperature at 0.3 m under the surface. Contrary to other studies, seasonal methane emissions peaked when the water table was at its maximum distance from the surface, around mid-August. No clear diurnal pattern could be found in methane emissions, indicating that methane was produced quite deep within the peat. The seasonal emissions were estimated at 4.4 g CH4m−2, and compared well with other observations over similar landscapes using different measurement techniques. Given that methane releases and transport are greatly affected by local characteristics such as climate and vegetative cover, this study emphasizes the need for furtherin situcontinuous measurements of methane fluxes across northern peatlands.