An Integrative Model for Soil Biogeochemistry and Methane Processes: I. Model Structure and Sensitivity Analysis

Abstract

Northern peatlands contain a vast pool of soil carbon that may be vulnerable to atmospheric release under changing environmental conditions, potentially causing a positive feedback to the climate system (Frolking et al., 2011;Nichols & Peteet, 2019;Yu, 2012). The magnitude of carbon emissions and their mechanistic responses to changing environments are elusive due to the complexity of hydrologic and biogeochemical processes in peatland systems (Blodau, 2002). Methane (CH 4 ) is one of the key carbon forms leaving peatlands under anaerobic conditions. Given the high radiative warming potential of CH 4 compared to CO 2 (Neubauer & Megonigal, 2015), it is critically important to accurately predict future CH 4 emissions from global peatlands. Peatlands are typically formed over millennial timescales due to organic carbon inputs, long-term water saturation and low temperatures and thus store major amounts of terrestrial carbon (Yu, 2012). It is expected that hydrological and biogeochemical dynamics play important roles affecting CH 4 fluxes from peatlands, but many of these key processes are missing in current Earth system models (Bohn et al., 2015). Therefore, to build a better predictive capacity for CH 4 dynamics in peatlands, it is necessary to fully consider the processes and environmental conditions controlling CH 4 processes, particularly the

An Integrative Model for Soil Biogeochemistry and Methane Processes. II: Warming and Elevated CO2 Effects on Peatland CH4 Emissions

“…The ELM-SPRUCE model was originally developed upon the default CLM4.5 (Oleson et al, 2013) and then modified to better simulate peatland hydrology and vegetation at the SPRUCE site (Shi et al, 2015). The improvements included (a) model representation of microtopography including hummocks and hollows (Shi et al, 2015), (b) an improved hydrology module (Shi et al, 2015), (c) a new moss plant functional type (Shi et al, 2021), and (d) an improved CH 4 module (Ricciuto et al, 2021;Wang et al, 2019;Xu et al, 2015). This new module represents CH 4 production and consumption in association with the existing decomposition subroutines in CLM4.5 (Thornton & Rosenbloom, 2005;Thornton & Zimmermann et al, 2007).…”

“…More recently, Xu et al (2015) developed a microbial functional group-based CH 4 module, and the module has been incorporated into the Community Land Model (CLM) 4.5 and is being incorporated into the Energy Exascale Earth System (E3SM) land model (ELM). The module can provide mechanistic understanding into how warming and eCO 2 affect peatland CH 4 emissions (Ricciuto et al, 2021;Xu et al, 2015).…”

“…In this study, we reported on the simulating effects of warming and eCO 2 on CH 4 cycling in a northern Minnesota peatland under various warming and eCO 2 scenarios by using the ELM-SPRUCE model, a version of ELM designed for this experiment (Ricciuto et al, 2021;Shi et al, 2015Shi et al, , 2021. As the second in a series of two modeling papers, we expanded upon the model description provided by Ricciuto et al (2021) and explored the warming and eCO 2 impacts on CH 4 cycling and further compared the simulated processes against observational data obtained from a global meta-analysis. Uncertainty analyses associated with the simulated CH 4 fluxes under the different treatments are reported as well.…”

Incorporating Microtopography in a Land Surface Model and Quantifying the Effect on the Carbon Cycle

“…Other than their elevation and hydrology, the modeled hummock and hollow soil columns are parameterized identically. The model is able to reasonably reproduce observed changes in water table depth (Shi et al, 2015), responses of CO 2 fluxes to warming (Hanson et al, 2020), vegetation biomass and fluxes for different PFTs (Shi et al, 2021), vegetation phenology (Meng et al, 2021) and seasonal patterns of CH 4 fluxes (Ricciuto et al, 2021). Previous ELM-SPRUCE sensitivity and uncertainty analyses (e.g., Griffiths et al, 2017) focused on soil and vegetation parameters but did not consider microtopographical variations.…”

“…ELM_SPRUCE simulates nitrogen, carbon and water cycling and their interactions at the SPRUCE experiment site. It includes 4 major PFTs including Sphagnum moss (Shi et al, 2021), predicts CH 4 cycling (Ricciuto et al, 2021), and predicts the response of the whole system to variations in metorological drivers and experimental 10.1029/2021MS002721 3 of 15 treatments. Carbon and nitrogen fluxes and stocks are simulated at an hourly time step using 6 plant pools for each PFT, and in 8 litter and soil organic matter pools in each of 10 vertical soil layers in each soil column (Oleson et al, 2013).…”