Controls for multi-scale temporal variation in ecosystem methane exchange during the growing season of a permanently inundated fen
Controls for multi-scale temporal variation in ecosystem methane exchange during the growing season of a permanently inundated fen
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DOI：
10.1016/j.agrformet.2015.02.002
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发表时间：
2014-05
影响因子：
6.2
通讯作者：
F. Koebsch;G. Jurasinski;M. Koch;Joachim Hofmann;S. Glatzel
中科院分区：
文献类型：
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作者：
F. Koebsch;G. Jurasinski;M. Koch;Joachim Hofmann;S. Glatzel
湿地是大气甲烷(CH4)的最大自然来源。在永久浅淹湿地，CH4交换的季节变化主要受温度和物候的控制。此外，生态系统的CH4交换在较小的时间尺度上变化很大，例如几天或几周。在当地土壤-植物-大气连续体上控制CH4排放的几个单一过程已经得到了很好的研究，但它们在生态系统水平上的相互作用还不是很清楚。将小波分析应用于准连续涡动协方差CH4通量时间序列，描述了永久淹水温带沼气生长季内生态系统CH4交换的时间变化。此外，我们讨论了特定时间尺度的控制，并调查了它们在生长季过程中的影响变化。在两周到三个月的大时间尺度上，温度解释了生态系统CH4交换的大部分变化。总体而言，浅水层温度作为解释变量的影响最大，而气温和土壤温度作为解释变量在6月份水位略有下降时变得越来越重要。生态系统CH4交换的日变化在生长季过程中发生变化：在4月底的一段短时间内，植物活动(以冠层光合作用表示)引起了生态系统CH4交换的日变化，高峰期在中午左右。在接下来的几周里，水柱内对流混合的每日循环(以水温梯度表示)逐渐变得重要，并导致夜间甲烷排放较高，从而使昼夜甲烷排放模式趋于平稳。此外，切变引起的湍流导致了生态系统CH4交换在时间尺度上的短期波动，长达两小时。我们的研究强调了考虑潜在过程的非平稳性的多尺度方法的必要性，以充分描述生态系统CH4交换的复杂性。此外，我们表明，CH4的释放过程，如水柱的对流混合，主要被考虑用于水生生态系统(见Godwin等人，2013；Poindexter和Variano，2013)中最近的例外情况，在浅水淹没的陆地生态系统中也可能是重要的。
Wetlands are the largest natural sources for atmospheric methane (CH4). In wetlands with permanent shallow inundation, the seasonal variation of CH4exchange is mainly controlled by temperature and phenology. In addition, ecosystem CH4exchange varies considerably on smaller temporal scales such as days or weeks. Several single processes that control CH4emissions on the local soil–plant–atmosphere continuum are well investigated, but their interaction on ecosystem level is not well understood yet. We applied wavelet analysis to a quasi-continuous eddy covariance CH4flux time series to describe the temporal variation of ecosystem CH4exchange within the growing season of a permanently inundated temperate fen. Moreover, we addressed time scale-specific controls and investigated whether their impact changes during the course of the growing season.On large time scales of two weeks to three months, temperature explained most of the variation in ecosystem CH4exchange. In general, the temperature in the shallow water column had the largest impact as explanatory variable, however, air temperature and soil temperature became increasingly important as explanatory variables when water level dropped slightly up to June. The diurnal variation of ecosystem CH4exchange shifted during the course of the growing season: During a short time period at the end of April, plant activity (expressed by canopy photosynthesis) caused a diurnal variation of ecosystem CH4exchange with peak time around noon. In the following weeks, the daily cycle of convective mixing within the water column (expressed by the water temperature gradient) gradually gained importance and caused high night-time CH4emissions, thereby levelling off the diurnal CH4emission pattern. Moreover, shear-induced turbulence caused short-term fluctuations of ecosystem CH4exchange on time scales up to two hours.Our study highlights the need for multi-scale approaches that consider the non-stationarity of the underlying processes to adequately describe the complexity of ecosystem CH4exchange. Moreover, we show that CH4release processes such as convective mixing of the water column which have been mainly considered for aquatic ecosystems (see recent exceptions in Godwin et al., 2013; Poindexter and Variano, 2013) might also be of importance in shallowly flooded terrestrial ecosystems.