Net ecosystem exchange over heterogeneous Arctic tundra: Scaling between chamber and eddy covariance measurements
Net ecosystem exchange over heterogeneous Arctic tundra: Scaling between chamber and eddy covariance measurements
复制标题
DOI：
10.1029/2007gb003027
复制
发表时间：
2008-06-20
影响因子：
5.2
通讯作者：
Baxter, Robert
中科院分区：
文献类型：
--
作者：
Fox, Andrew M.;Huntley, Brian;Baxter, Robert
净生态系统交换（NEE）的阿比斯科附近的苔原地区使用涡度协方差（EC）数据和腔室测量估计。这片苔原是异质的，有六个主要元素形成了一个景观镶嵌图。室测量补丁的个别马赛克元素被用来模拟NEE作为辐照度和温度的函数。绘制了EC桅杆周围的区域，并使用足迹模型来模拟归因于每个镶嵌元素的不同源分数。各种升级的方法被用来估计NEE的比较从欧共体的观测计算的NEE。结果表明，EC测量这样一个异质网站是强大的镶嵌元素之间的NEE的变化，也有很大的不同，在其源馏分。然而，他们也发现了一个大的（类似于60%）的偏差，在一个40天的研究期内的累积负NEE的绝对幅度模拟各种升级的方法相比，从EC观察计算的值。这种偏差的程度，如果适用于整个苔原地区的估计，是相当大的相对于全球碳预算的其他组成部分。各种假设来解释这种偏见进行了讨论，并在可能的情况下，评估。需要确定更系统的采样策略时，进行腔室测量，以评估在何种程度上的主观性腔室位置可能占大部分的观察到的偏差。如果这是偏差的来源，那么使用腔室测量的放大方法通常可能高估CO2吸收。
Net ecosystem exchange (NEE) was estimated for an area of tundra near Abisko using both eddy covariance (EC) data and chamber measurements. This area of tundra is heterogeneous with six principal elements forming a landscape mosaic. Chamber measurements in patches of the individual mosaic elements were used to model NEE as a function of irradiance and temperature. The area around the EC mast was mapped, and a footprint model was used to simulate the varying source fraction attributable to each mosaic element. Various upscaling approaches were used to estimate NEE for comparison with NEE calculated from the EC observations. The results showed that EC measurements made for such a heterogeneous site are robust to the variations in NEE between mosaic elements that also vary substantially in their source fractions. However, they also revealed a large (similar to 60%) bias in the absolute magnitude of the cumulative negative NEE for a 40-day study period simulated by various upscaling approaches when compared to the value calculated from the EC observations. The magnitude of this bias, if applied to estimates for the entire tundra region, is substantial in relation to other components of the global carbon budget. Various hypotheses to account for this bias are discussed and, where possible, evaluated. A need is identified for more systematic sampling strategies when performing chamber measurements in order to assess the extent to which subjectivity of chamber location may account for much of the observed bias. If this is the origin of the bias, then upscaling approaches using chamber measurements may generally overestimate CO2 uptake.