Process-based modelling of long-term carbon dynamics in a temperate swamp peatland

Temperate swamps hold substantial carbon (C) in their standing biomass and can potentially accumulate peat. In Southern Ontario, Canada, swamp peats are estimated to store ~1.1 Pg C, with this C accumulation supported by distinct hydroclimatic conditions. Previous studies on swamps C fluxes are mostly based on short-term (<5 years) field measurements that limit our understanding of the long-term (>30 years) interactions and feedbacks that exist between temperate swamp C flux and biophysical conditions. In this study, we adopted a process-based model (CoupModel, www.coupmodel.com) to simulate daily plant processes, energy, water, and C fluxes in one of the most well-preserved swamps in Southern Ontario, Beverly Swamp, over a 40-year period (1983-2023). CoupModel reproduced the measured C flux and controlling variables with (coefficient of determination, R²) values of 0.75, 0.94 & 0.6 for soil respiration, surface soil temperature (0-5 cm) and water table depth, respectively. Analysis of the interrelationships (R² values) between the simulated carbon flux and biophysical conditions showed that 88%, 51%, 31%, 68% of soil respiration rates were explained by soil surface temperature, soil volumetric moisture contents (0-30 cm), water table depth and gross primary productivity, respectively.  Our model simulation showed the swamp’s C uptake capacity, as net ecosystem exchange, dwindled over the simulated period but it was a net C sink in most years. This decreasing trend can be attributed to warmer and drier conditions in the region, which may be exacerbated with future climate change predictions. Overall, the study shows that processed-based models (CoupModel) are effective tools for improving our understanding of long-term C dynamics of temperate forested wetlands and the interactions that exist between C flux components and abiotic conditions. This has implications for informed decision-making on the management of temperate swamp ecosystems and the C stored within them.