Combining eddy-covariance and chamber measurements to determine the methane budget from a small, heterogeneous urban floodplain wetland park
Combining eddy-covariance and chamber measurements to determine the methane budget from a small, heterogeneous urban floodplain wetland park
复制标题
DOI：
10.1016/j.agrformet.2017.01.022
复制
发表时间：
2017-05
影响因子：
6.2
通讯作者：
T. Morin;G. Bohrer;K. C. Stefanik;A. C. Rey-Sanchez;A. Matheny;W. Mitsch
中科院分区：
文献类型：
--
作者：
T. Morin;G. Bohrer;K. C. Stefanik;A. C. Rey-Sanchez;A. Matheny;W. Mitsch
在全球辐射强迫的背景下，温带淡水湿地的甲烷（CH4）排放和碳吸收的作用方向相反。CH4排放率存在很大的不确定性，因此难以确定CH4排放抵消湿地碳固存的程度。城市温带湿地面积小、土地覆盖异质性强，其CH4排放通量的确定面临挑战，本文采用两种不同的CH4排放通量测量方法，克服尺度和异质性问题，确定小型、异质性城市湿地的CH4排放总量。时间间歇点测量从非稳态室提供的信息斑块水平的异质性通量，而连续的，高时间分辨率的通量测量使用涡动协方差（EC）技术提供的信息通量的时间动态。斑块级缩放参数化开发从室数据的规模涡度协方差数据到一个“固定的框架”，它纠正在任何单一的时间点的涡度协方差观测足迹的空间覆盖范围的变化。通过结合两种不同尺度的测量技术，我们解决了这两种技术在异质湿地sites.We确定，由两种方法观测到的通量在统计上是相似的幅度时，带来了相同的时间和空间尺度的缺点。我们还发现，开放水域和大型植物覆盖的湿地面积遵循类似的物候周期，并在一年中的大部分时间排放几乎相等的CH4水平。然而，植被湿地地区经常表现出较强的夏末排放高峰，可能是由于CH4运输通过成熟的植被血管系统。将涡度协方差数据归一化到一个固定的框架，使我们能够确定每个补丁和整个网站的季节CH4预算。总体而言，水生植物区的CH4通量最大，其次是开放水域。CH4通量的空间异质性、塔足迹、待定标数据中的测量值和间隙填充是最终CH4收支的不确定因素。其中，气室的空间位置是CH4估算值不确定性的最大来源。这加强了需要利用站点一级的测量时，估计CH4从湿地通量，而不是只使用放大的点测量。
Methane (CH4) emissions and carbon uptake in temperate freshwater wetlands act in opposing directions in the context of global radiative forcing. Large uncertainties exist for the rates of CH4emissions making it difficult to determine the extent that CH4emissions counteract the carbon sequestration of wetlands. Urban temperate wetlands are typically small and feature highly heterogeneous land cover, posing an additional challenge to determining their CH4budget.The data analysis approach we introduce here combines two different CH4flux measurement techniques to overcome scale and heterogeneity problems and determine the overall CH4budget of a small, heterogeneous, urban wetland landscape. Temporally intermittent point measurements from non-steady-state chambers provided information about patch-level heterogeneity of fluxes, while continuous, high temporal resolution flux measurements using the eddy-covariance (EC) technique provided information about the temporal dynamics of the fluxes. Patch-level scaling parameterization was developed from the chamber data to scale eddy covariance data to a ‘fixed-frame’, which corrects for variability in the spatial coverage of the eddy covariance observation footprint at any single point in time. By combining two measurement techniques at different scales, we addressed shortcomings of both techniques with respect to heterogeneous wetland sites.We determined that fluxes observed by the two methods are statistically similar in magnitude when brought to the same temporal and spatial scale. We also found that open-water and macrophyte-covered areas of the wetland followed similar phenological cycles and emitted nearly equivalent levels of CH4for much of the year. However, vegetated wetland areas regularly exhibited a stronger late-summer emission peak, possibly due to CH4transport through mature vegetation vascular systems. Normalizing the eddy covariance data to a fixed-frame allowed us to determine the seasonal CH4budget of each patch and the overall site. Overall, the macrophyte areas had the largest CH4fluxes followed by the open water areas.Uncertainties in the final CH4budget included spatial heterogeneity of CH4fluxes, the tower footprint, measurement in the data to be scaled, and gap-filling. Of these, the spatial placement of the chambers provided the largest source of uncertainty in CH4estimates. This reinforces the need to utilize site-level measurements when estimating CH4fluxes from wetlands as opposed to using only up-scaled point measurements.