Predicting permafrost stability in northern peatlands with climate change and disturbance

Permafrost thaw may cause significant carbon loss from northern organic soils, a large terrestrial carbon pool. To predict permafrost stability in organic soils, we adapted an existing soil temperature model (GIPL 2.0) to peatlands by including a three-layer peat soil column and dynamic soil moisture. GIPL 2.0 numerically solves the 1-dimensional heat transfer equation. We evaluated the model at Daring Lake Fen, a sedge-dominated Arctic Fen in the Northwest Territories, Canada and College Peat, a permafrost muskeg in Fairbanks, AK. We examined the sensitivity of the model to seasonality and total soil moisture, thermal properties and organic layer thickness. We also evaluated active layer depth for future climate scenarios. Finally, we compared the relative magnitude of climate change impacts on soil temperatures to the effects of current and predicted wildfire. We simulated wildfire by removing the surface soil (5 - 15 cm) and increasing air temperatures post-fire due to changes in surface energy balance. We found that air temperature, rather than changes in soil moisture, was the most important predictor of changes in active layer depth and permafrost stability. Also, the seasonality of soil moisture was relatively unimportant, while changes in temperature seasonality were important to active layer depths. In the climate change scenarios (using IPCC scenario A1b), active layer depths and the length of the growing season (determined as soil thawed at 10 cm) increased significantly by 2100. Warmer soil temperatures at depth due to higher air temperatures resulted in an increase of liquid water in the soil and the possibility of increased biological activity. Soil temperatures and active layer depths increased following disturbance, but the increases were relatively short-lived (decades) and were strongly correlated with post-fire temperature changes. The simulated removal of a shallow layer of surface organic soil following disturbance has limited long-term effects on soil temperatures. Therefore, we anticipate that climate change will have much larger effects than disturbance on permafrost stability at cold sites with thick organic soil, unless disturbance causes a long-term shift in vegetation communities and site energy balance