Landscape-level terrestrial methane flux observed from a very tall tower
Landscape-level terrestrial methane flux observed from a very tall tower
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DOI：
10.1016/j.agrformet.2014.10.017
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发表时间：
2015-02
影响因子：
6.2
通讯作者：
A. Desai;Ke Xu;H. Tian;Peter A. Weishampel;J. Thom;D. Baumann;A. Andrews;B. Cook;J. King;R. Kolka
中科院分区：
文献类型：
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作者：
A. Desai;Ke Xu;H. Tian;Peter A. Weishampel;J. Thom;D. Baumann;A. Andrews;B. Cook;J. King;R. Kolka
模拟陆地甲烷源和汇的规模和可变性对生态系统模型提出了挑战，因为导致陆地和淡水生态系统甲烷排放的生物物理和生物地球化学过程，就其性质而言，是偶发的和空间上不连续的。因此，基于短涡度协方差塔或静态室的实地活动的区域甲烷排放量的模型预测具有很大的不确定性，因为与这些排放量的幅度、空间尺度或频率方面的区域估计相比，侧重于特定已知甲烷排放源的测量将有偏差。鉴于预测未来陆地甲烷通量对限制未来大气甲烷增长率的相对重要性，显然需要减少时空不确定性。2010年，美国威斯康星州帕克福尔斯附近的Ameriflux塔（US-PFa）在地面以上122 m处的代表五大湖地区的混合湿地-高地景观中进行了闭路甲烷通量测量。两年的通量观测显示，甲烷（CH 4）的年平均排放量为785 ± 75 mg C单键CH 4 m − 2 yr −1，而CO2的年平均排放量为−80 g C单键CO2 m − 2 yr −1，两者之间的比例为1%。甲烷通量的年际变化为平均通量的30%，这是由2012年夏末干燥条件下甲烷排放的抑制所驱动的。虽然相对较小，但来自非常高的塔测量的甲烷源的大小大部分在先前使用附近湿地的静态室测量的范围内，但大于将这些通量简单缩放到塔足迹。在甲烷通量的季节模式模拟的动态土地生态系统模型（DLEM）相似，但幅度取决于模型参数化和输入数据，特别是关于湿地的范围。该模型无法模拟短期（次每周）的变化。温度被认为是一个更强的驱动程序，区域CH 4通量比水分供应或净生态系统生产在每日至每月的规模。总之，这些结果强调了区域甲烷通量的驱动因素的多时间尺度依赖性，以及长时间连续时间序列对其表征的重要性。
Simulating the magnitude and variability of terrestrial methane sources and sinks poses a challenge to ecosystem models because the biophysical and biogeochemical processes that lead to methane emissions from terrestrial and freshwater ecosystems are, by their nature, episodic and spatially disjunct. As a consequence, model predictions of regional methane emissions based on field campaigns from short eddy covariance towers or static chambers have large uncertainties, because measurements focused on a particular known source of methane emission will be biased compared to regional estimates with regards to magnitude, spatial scale, or frequency of these emissions. Given the relatively large importance of predicting future terrestrial methane fluxes for constraining future atmospheric methane growth rates, a clear need exists to reduce spatiotemporal uncertainties. In 2010, an Ameriflux tower (US-PFa) near Park Falls, WI, USA, was instrumented with closed-path methane flux measurements at 122 m above ground in a mixed wetland–upland landscape representative of the Great Lakes region. Two years of flux observations revealed an average annual methane (CH4) efflux of 785 ± 75 mg Csingle bondCH4m−2yr−1, compared to a mean CO2sink of −80 g Csingle bondCO2m−2yr−1, a ratio of 1% in magnitude on a mole basis. Interannual variability in methane flux was 30% of the mean flux and driven by suppression of methane emissions during dry conditions in late summer 2012. Though relatively small, the magnitude of the methane source from the very tall tower measurements was mostly within the range previously measured using static chambers at nearby wetlands, but larger than a simple scaling of those fluxes to the tower footprint. Seasonal patterns in methane fluxes were similar to those simulated in the Dynamic Land Ecosystem Model (DLEM), but magnitude depends on model parameterization and input data, especially regarding wetland extent. The model was unable to simulate short-term (sub-weekly) variability. Temperature was found to be a stronger driver of regional CH4flux than moisture availability or net ecosystem production at the daily to monthly scale. Taken together, these results emphasize the multi-timescale dependence of drivers of regional methane flux and the importance of long, continuous time series for their characterization.