Understanding spatial variability of methane fluxes in Arctic wetlands through footprint modelling
Understanding spatial variability of methane fluxes in Arctic wetlands through footprint modelling
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DOI：
10.1088/1748-9326/ab4d32
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发表时间：
2019-10
影响因子：
6.7
通讯作者：
K. Reuss-Schmidt;P. Levy;W. Oechel;C. Tweedie;C. Wilson;D. Zona
中科院分区：
文献类型：
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作者：
K. Reuss-Schmidt;P. Levy;W. Oechel;C. Tweedie;C. Wilson;D. Zona
北极变暖的速度是全球平均速度的两倍。这种变暖可能会进一步刺激北方湿地的甲烷（CH4）排放，并增强该地区的温室效应。北极湿地在地球化学、植被、微地形和水文学方面具有极强的异质性，因此甲烷通量在米尺度内可能有很大差异。涡度相关法是估算偏远地区CH4通量的最有效方法之一。然而，当这些EC塔采样的地区（即塔足迹）根据定义是非常异质的，由于包括各种环境条件和植被类型，建模环境控制的甲烷排放变得更具挑战性，混淆努力，以减少这些景观的基线甲烷排放量的不确定性。在这项研究中，我们评估了足迹变化对甲烷通量的影响，从两个EC塔位于阿拉斯加北坡的湿地。这些网站的每个本地域包含发达的多边形苔原以及排水热岩溶湖盆。我们发现，时空变化的足迹，有一个显着的影响所观察到的甲烷通量，贡献3%和33%之间的方差，这取决于网站，时间段和建模方法。多个指标被用来定义空间异质性，其解释力取决于网站和季节。总体而言，归一化差异水指数的CH4通量的最一致的解释能力，虽然一般只有在音乐会上使用时，至少有一个其他空间指数。空间偏差（此处定义为塔周围0.36平方公里区域的平均值与足迹加权平均值之间的差异）在10.51%至10.18%之间，具体取决于指数。这项研究强调了足迹建模的必要性，以推断在这些高度异质的苔原生态系统的EC塔测量的碳通量的代表性，并需要评估空间变异性时，将EC网站级数据升级到一个更大的域。
The Arctic is warming at twice the rate of the global mean. This warming could further stimulate methane (CH4) emissions from northern wetlands and enhance the greenhouse impact of this region. Arctic wetlands are extremely heterogeneous in terms of geochemistry, vegetation, microtopography, and hydrology, and therefore CH4 fluxes can differ dramatically within the metre scale. Eddy covariance (EC) is one of the most useful methods for estimating CH4 fluxes in remote areas over long periods of time. However, when the areas sampled by these EC towers (i.e. tower footprints) are by definition very heterogeneous, due to encompassing a variety of environmental conditions and vegetation types, modelling environmental controls of CH4 emissions becomes even more challenging, confounding efforts to reduce uncertainty in baseline CH4 emissions from these landscapes. In this study, we evaluated the effect of footprint variability on CH4 fluxes from two EC towers located in wetlands on the North Slope of Alaska. The local domain of each of these sites contains well developed polygonal tundra as well as a drained thermokarst lake basin. We found that the spatiotemporal variability of the footprint, has a significant influence on the observed CH4 fluxes, contributing between 3% and 33% of the variance, depending on site, time period, and modelling method. Multiple indices were used to define spatial heterogeneity, and their explanatory power varied depending on site and season. Overall, the normalised difference water index had the most consistent explanatory power on CH4 fluxes, though generally only when used in concert with at least one other spatial index. The spatial bias (defined here as the difference between the mean for the 0.36 km2 domain around the tower and the footprint-weighted mean) was between ∣51∣% and ∣18∣% depending on the index. This study highlights the need for footprint modelling to infer the representativeness of the carbon fluxes measured by EC towers in these highly heterogeneous tundra ecosystems, and the need to evaluate spatial variability when upscaling EC site-level data to a larger domain.