Abstract
Peatland carbon cycling is critical for the land–atmosphere exchange of greenhouse gases, particularly under changing environments. Warming and elevated atmospheric carbon dioxide (eCO2) concentrations directly enhance peatland methane (CH4) emission, and indirectly affect CH4 processes by altering hydrological conditions. An ecosystem model ELM-SPRUCE, the land model of the E3SM model, was used to understand the hydrological feedback mechanisms on CH4 emission in a temperate peatland under a warming gradient and eCO2 treatments. We found that the water table level was a critical regulator of hydrological feedbacks that affect peatland CH4 dynamics; the simulated water table levels dropped as warming intensified but slightly increased under eCO2. Evaporation and vegetation transpiration determined the water table level in peatland ecosystems. Although warming significantly stimulated CH4 emission, the hydrological feedbacks leading to a reduced water table mitigated the stimulating effects of warming on CH4 emission. The hydrological feedback for eCO2 effects was weak. The comparison between modeled results with data from a field experiment and a global synthesis of observations supports the model simulation of hydrological feedbacks in projecting CH4 flux under warming and eCO2. The ELM-SPRUCE model showed relatively small parameter-induced uncertainties on hydrological variables and their impacts on CH4 fluxes. A sensitivity analysis confirmed a strong hydrological feedback in the first three years and the feedback diminished after four years of warming. Hydrology-moderated warming impacts on CH4 cycling suggest that the indirect effect of warming on hydrological feedbacks is fundamental for accurately projecting peatland CH4 flux under climate warming.
Highlights
Peatlands store 16–33% of the global terrestrial soil carbon (Bridg ham et al, 2006; Gorham, 1991), and play an important role in regu lating climate change
This study focuses on the hydrological feedbacks on CH4 emissions under a warming gradient and an ambient and an elevated CO2 (800 ppm) atmosphere in a Minnesota peatland using the ELM-Spruce and Peatland Responses Under Changing Environments (SPRUCE) model (Ricciuto et al, 2021; Yuan et al, 2021), which is a new version of the Energy Exascale Earth System (E3SM) land model (ELM)
As modeled using ELM-SPRUCE, warming and elevated CO2 (eCO2) largely influ enced canopy hydrological processes: the cumulative effects of eCO2 over the 5-year simulation were positive on whole-ecosystem canopy interception and transpiration, whereas warming effects were negative for canopy evaporation and transpiration (Fig. 1D-F)
Summary
Peatlands store 16–33% of the global terrestrial soil carbon (Bridg ham et al, 2006; Gorham, 1991), and play an important role in regu lating climate change. Water table level (WT) is a vital parameter controlling peatland CH4 emission (Dise et al, 1993, 2011; Laine et al, 1996; Moore and Roulet, 1993; White et al, 2008). Any level of climate warming might alter hydrological processes and soil microbial physiology (Nykanen et al, 1998), thereby modifying CO2 and CH4 emission and changing C storage in peatlands (Bridgham et al, 1995; Keller et al, 2004). A WT drop might promote the oxidation of CH4 and reduce CH4 emission (Zhang et al, 2007)
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