Process-based modelling of multi-decade carbon dynamics of a cool temperate swamp

Abstract. Swamps are important wetlands globally, but temperate swamps have been understudied even though they store substantial quantity of carbon (C) in their biomass and can accumulate peat. This stored C supports their role as nature-based solutions in climate change mitigation efforts. In particular, Southern Ontario swamps are estimated to store ~1.1 Pg C under distinct hydroclimatic conditions. Previous studies on temperate swamp C fluxes are mostly based on short-term (<5 years) field measurements that limit our understanding of the multi-decadal dynamics that exist between this ecosystem’s C flux and biophysical conditions. To elucidate the long-term interactions and feedbacks that are important to temperate swamp C dynamics, we adopted a process-based model (CoupModel) to simulate daily plant processes, energy, water and C fluxes in one of the most well-preserved swamps in Southern Ontario over a 40-year period (1983–2023). CoupModel reasonably simulated the C flux and controlling variables with coefficient of determination (R²) values of 0.60, 0.95 & 0.61 for soil respiration, surface soil temperature (0–5cm) and water table level respectively when validated with field measurements. Over the simulation period, the swamp’s C uptake capacity as net ecosystem exchange declined but it maintained a net C sink in most years. This declining trend can be attributed to a consistent rise in soil respiration (11 % per decade) that is likely to continue with future climate change predictions. Overall, the study shows that processed-based models are effective tools for improving our understanding of long-term C dynamics of temperate swamps.