LB 7-67 - Simulating soil-atmosphere exchanges and their associated CO₂ fluxes for an ongoing peat extraction site

Background/Question/Methods:

By removing vegetation, installing drainage ditches and harvesting peat, land-use change of pristine peatland into extraction significantly alters the soil-atmosphere interactions, soil hydrological, and thermal regimes, which switches the peatland from a CO₂ sink into a strong source. We adopted the CoupModel (www.coupmodel.com) to simulate the soil-atmosphere exchange and its associated CO₂ fluxes for an ongoing extraction site, located in Rivière-du-Loup, Quebec. COUP was first evaluated against three-year (2018-2021) manual chamber measurements of CO₂ flux, multi-layered soil moisture and temperature profile, and water table depth data. The validated model was then used to assess the sensitivity of model parameters and climate on the simulated CO₂ emissions.

Results/Conclusions:

Over 2018-2021, the average CO₂ emissions measured mainly over summer was 0.73 ± 0.46 g CO₂-C m^-2 d^-1, with 0.76 ± 0.31 g C m^-2 d^-1 for 2018, 0.81 ± 1.1 for 2019 (0.57 ± 0.42 g C m^-2 d^-1 removing the two extreme data), and 0.76 ± 0.31 g C m^-2 d^-1 for 2020. COUP reproduced the measured summer flux data well with an R² of 0.5 and a mean bias of 0.2 g C m^-2 d^-1 and simulated the hydrology and thermal conditions well. Using the simulated data and integrated over a full year, the emission average over 2018 -2021 was reduced to 0.46 g C m^-2 d^-1, or 168 g C m^-2 yr^-1. The hydrothermal conditions of the peat thus respiration are shown to be mainly regulated by the peat-atmosphere surface layer property that regulates the surface energy partitioning. This study provides an excellent and unique opportunity to examine heterotrophic respiration on its own, without the confounding factors of GPP and autotrophic respiration. There are very few settings where whole ecosystem heterotrophic respiration can be measured directly to independently evaluate simulated heterotrophic respiration directly.