Abstract Peatlands have sequestered atmospheric carbon dioxide (CO2) for millennia and can also act as significant sources of atmospheric methane (CH4). Hydrological processes that control water table dynamics, and climatic conditions such as air temperature, play important roles in mediating peatland–atmosphere exchange of these greenhouse gases. These controls are likely to be impacted by climate change, particularly for those peatlands found in cold environments, including mountain regions. In this study, we developed empirical models to simulate hydrological dynamics and ecosystem–atmosphere C exchange in a mountain peatland under three climate scenarios (2012 air temperatures, +2°C and +4°C). Observed water table dynamics and air temperature were used to model ecosystem–atmosphere C exchange during the 2012 growing season. Modelled snowmelt dynamics were used to predict water table position at the beginning of the growing season for warming scenarios, and the subsequent water table dynamics and increased air temperature were used to drive the same C exchange models during the growing seasons. Increased air temperatures led to earlier snowmelt and water table decline, causing water tables to drop by 10 and 19 cm for the +2 and +4°C scenarios, respectively. This led to roughly a two‐fold decrease in growing season net ecosystem production (NEP) in both warming scenarios, as a result of increased ecosystem respiration relative to gross primary production. Methane efflux was positively correlated with NEP and therefore decreased under the warming scenarios, albeit to a lesser degree. These results indicate that reductions in NEP and CH4 efflux are possible in low‐elevation mountain peatlands that are dependent on snowpack‐derived hydrologic inputs. These ecosystems are found at elevations where future winter precipitation will increasingly fall as rain rather than snow and melting of snowpack will occur earlier under warmer conditions.
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