Abstract
Abstract. Methane (CH4) emissions from wetlands are likely increasing and important in global climate change assessments. However, contemporary terrestrial biogeochemical model predictions of CH4 emissions are very uncertain, at least in part due to prescribed temperature sensitivity of CH4 production and emission. While statistically consistent apparent CH4 emission temperature dependencies have been inferred from meta-analyses across microbial to ecosystem scales, year-round ecosystem-scale observations have contradicted that finding. Here, we show that apparent CH4 emission temperature dependencies inferred from year-round chamber measurements exhibit substantial intra-seasonal variability, suggesting that using static temperature relations to predict CH4 emissions is mechanistically flawed. Our model results indicate that such intra-seasonal variability is driven by substrate-mediated microbial and abiotic interactions: seasonal cycles in substrate availability favors CH4 production later in the season, leading to hysteretic temperature sensitivity of CH4 production and emission. Our findings demonstrate the uncertainty of inferring CH4 emission or production rates from temperature alone and highlight the need to represent microbial and abiotic interactions in wetland biogeochemical models.
Highlights
Methane (CH4) is the second most important climate forcing gas with at least a 28-fold higher global warming potential (GWP) than carbon dioxide (CO2) over a 100-year horizon (Myhre et al, 2013)
The observed CH4 emission hysteresis indicates that models cannot accurately represent CH4 dynamics without representing the large spatial and temporal variability in apparent CH4 emission temperature dependencies
Many contemporary CH4 models parameterize wetland CH4 production as a fixed fraction of net primary productivity or heterotrophic respiration regulated by a single static function of temperature (Melton et al, 2013; Wania et al, 2013)
Summary
Methane (CH4) is the second most important climate forcing gas with at least a 28-fold higher global warming potential (GWP) than carbon dioxide (CO2) over a 100-year horizon (Myhre et al, 2013). Recent assessments have found that CH4 emissions from wetland and other inland waters are the largest and most uncertain sources affecting the global CH4 budget (Kirschke et al, 2013; Poulter et al, 2017; Saunois et al, 2016). A number of knowledge gaps (Xu et al, 2016) need to be addressed to improve CH4 model representations and thereby CH4 climate feedback predictions (Dean et al, 2018) Such efforts are imperative because, among other reasons, permafrost degradation resulting from observed global-scale permafrost warming
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