Identifying dominant environmental predictors of freshwater wetland methane fluxes across diurnal to seasonal time scales
Identifying dominant environmental predictors of freshwater wetland methane fluxes across diurnal to seasonal time scales
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DOI：
10.1111/gcb.15661
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发表时间：
2021-05-29
影响因子：
11.6
通讯作者：
Jackson, Robert B.
中科院分区：
文献类型：
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作者：
Knox, Sara H.;Bansal, Sheel;Jackson, Robert B.
虽然湿地是大气中甲烷（CH4）的最大天然来源，但由于对CH4动态的复杂生物地球化学控制，湿地在全球CH4收支中具有很大的不确定性。在这里，据我们所知，我们首次对淡水湿地中CH4通量（FCH4）的预测因子在日、多日（天气）和季节时间尺度上的不同湿地类型的变化进行了多地点综合。在基于小波的多分辨率框架中，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）来评估23个涡动相关点的环境预测因子、非线性和滞后对FCH4的重要性。在季节变化较小的样点，土壤和空气温度是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波动的中值分别为17 +/- 11天，滞后于空气和土壤温度的中值分别为8 +/- 16天和5 +/- 15天。在多日尺度上，温度和WTD也是主要的预测因子。大气压力（PA）是另一个重要的多天尺度预测因子，PA的下降与CH4的同步释放一致。在日尺度上，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CH4挥发具有相似的控制作用，并提示加压通风对通气植被的影响。此外，与生态系统光合作用的1- 4小时滞后关系表明，根系分泌物等近期碳基质也可能控制FCH4。通过解决尺度、异步和非线性问题，本研究提高了对湿地FCH4预测因子和时间的理解，为未来的研究和模型提供信息，并有助于限制湿地CH4排放。
While wetlands are the largest natural source of methane (CH4) to the atmosphere, they represent a large source of uncertainty in the global CH4 budget due to the complex biogeochemical controls on CH4 dynamics. Here we present, to our knowledge, the first multi-site synthesis of how predictors of CH4 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 similar to 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 CH4. 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 CH4 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 CH4 emissions.