Peatlands in North America are important to regional carbon (C) inventories. Carbon storage and other C cycling processes in peatlands rely on unique hydroclimatic conditions that may be altered under climate change. In particular, the hydroclimatic conditions that support the storage of ~1.1 Pg C in swamps across southern Ontario, Canada are susceptible to climate change impacts resulting in a shift in the C balance of this ecosystem. These future changes may produce complex biophysical interactions and bidirectional climate feedback. To understand the C dynamics of temperate swamp peatlands under a changing climate, this study assessed the response of swamp biophysical conditions and C flux to mid-century climate conditions in southern Ontario. A calibrated processed-based ecosystem model (CoupModel) was forced with an ensemble of climate projections downscaled from earth system models (under SSP5) by the mid-century (2050s). The projected increase in mean air temperature and precipitation by 2050s triggered 41 ± 11% and 13 ± 3% increase in soil temperature (5cm deep) and evapotranspiration respectively at the swamp, and a reduction (10 ± 1%) in its volumetric soil moisture content. Consequently, drier and warmer conditions raised the swamp’s CO2 efflux through ecosystem respiration (Reco) by 30 ± 2%, while its gross primary production moderately increased by 4 ± 2%. These bidirectional feedbacks contributed to an offset in the swamp’s C balance resulting in 62 ± 8 % reduction in net CO2 uptake. Importantly, our study observed that seasonal timing of warming and precipitation played important role in the swamp’s response.
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