Department of Geography, The University of British Columbia, Vancouver, BC, Canada.
Northern Prairie Wildlife Research Center, U.S. Geological Survey, Jamestown, ND, USA.
Glob Chang Biol. 2021 Aug;27(15):3582-3604. doi: 10.1111/gcb.15661. Epub 2021 May 29.
While wetlands are the largest natural source of methane (CH ) to the atmosphere, they represent a large source of uncertainty in the global CH budget due to the complex biogeochemical controls on CH dynamics. Here we present, to our knowledge, the first multi-site synthesis of how predictors of CH fluxes (FCH4) in freshwater wetlands vary across wetland types at diel, multiday (synoptic), and seasonal time scales. We used several statistical approaches (correlation analysis, generalized additive modeling, mutual information, and random forests) in a wavelet-based multi-resolution framework to assess the importance of environmental predictors, nonlinearities and lags on FCH4 across 23 eddy covariance sites. Seasonally, soil and air temperature were dominant predictors of FCH4 at sites with smaller seasonal variation in water table depth (WTD). In contrast, WTD was the dominant predictor for wetlands with smaller variations in temperature (e.g., seasonal tropical/subtropical wetlands). Changes in seasonal FCH4 lagged fluctuations in WTD by ~17 ± 11 days, and lagged air and soil temperature by median values of 8 ± 16 and 5 ± 15 days, respectively. Temperature and WTD were also dominant predictors at the multiday scale. Atmospheric pressure (PA) was another important multiday scale predictor for peat-dominated sites, with drops in PA coinciding with synchronous releases of CH . At the diel scale, synchronous relationships with latent heat flux and vapor pressure deficit suggest that physical processes controlling evaporation and boundary layer mixing exert similar controls on CH volatilization, and suggest the influence of pressurized ventilation in aerenchymatous vegetation. In addition, 1- to 4-h lagged relationships with ecosystem photosynthesis indicate recent carbon substrates, such as root exudates, may also control FCH4. By addressing issues of scale, asynchrony, and nonlinearity, this work improves understanding of the predictors and timing of wetland FCH4 that can inform future studies and models, and help constrain wetland CH emissions.
湿地是大气中甲烷（CH ）的最大自然源，但由于 CH 动态的复杂生物地球化学控制，它们在全球 CH 预算中代表了一个很大的不确定性来源。在这里，我们展示了迄今为止关于淡水湿地中 CH 通量（FCH4）预测因子如何在昼夜、多天（天气）和季节时间尺度上随湿地类型变化的首次多站点综合研究。我们使用了几种统计方法（相关分析、广义加性建模、互信息和随机森林）在基于小波的多分辨率框架中，评估了环境预测因子、非线性和滞后对 23 个涡度相关站点 FCH4 的重要性。季节性地，土壤和空气温度是地下水位深度（WTD）季节性变化较小的站点 FCH4 的主要预测因子。相比之下，WTD 是温度变化较小的湿地（例如季节性热带/亚热带湿地）的主要预测因子。季节 FCH4 的变化滞后于 WTD 的波动约 17 ± 11 天，滞后于空气和土壤温度的中位数分别为 8 ± 16 和 5 ± 15 天。温度和 WTD 也是多日尺度的主要预测因子。大气压力（PA）也是泥炭主导站点的另一个重要多日尺度预测因子，PA 的下降与 CH 的同步释放相吻合。在昼夜尺度上，与潜热通量和水汽压亏缺的同步关系表明，控制蒸发和边界层混合的物理过程对 CH 挥发具有相似的控制作用，并表明通气组织植物中加压通风的影响。此外，与生态系统光合作用有 1-4 小时的滞后关系表明，最近的碳底物，如根分泌物，也可能控制 FCH4。通过解决尺度、非同步性和非线性问题，这项工作提高了对湿地 FCH4 预测因子和时间的理解，这可以为未来的研究和模型提供信息，并有助于限制湿地 CH 排放。
