Biogeochemical and hydrological impacts of a low-severity wildfire in the wetland-dominated zone of discontinuous permafrost

• Main Author: Ackley, Caren J.
• Format: Text
• Language: English
• Published: Scholars Commons @ Laurier 2019
• Subjects: peat; peatland; wildfire; Scotty Creek; runoff water chemistry; permafrost; Hydrology; Canada; Northwest Territories; Peat
• Online Access: https://scholars.wlu.ca/etd/2141; https://scholars.wlu.ca/context/etd/article/3260/viewcontent/CarenAckley_MSc_thesis.pdf

Northern regions are experiencing rapid climate warming. As these regions warm, the occurrences of naturally ignited wildfires are increasing in frequency, severity and area burned, calling for a more thorough understanding of post-fire eco-hydrological impacts. Changes in runoff chemistry, and soil moisture and thermal regimes, have been attributed to the significant loss of organic matter (OM) and exposure of deeper soils, leading to enhanced permafrost degradation, ground surface subsidence and the conversion of peat landscapes from long-term C sinks to sources. However, low-severity wildfires often result in minor OM loss. Due to the significant and immediate threats posed to the health of ecosystems and local communities, the impacts of large, high-severity burns have been a primary research focus while the implications of low-severity wildfires remain understudied. Boreal peatlands in the zone of discontinuous permafrost are ecologically-sensitive areas, where even minor land surface disturbances, such as wildfire, cause changes in surface vegetation and soil properties that alter the water and surface energy balances. In 2014, a low-severity wildfire burned approximately half of a 5 hectare treed permafrost plateau in the wetland-dominated landscape of the Scotty Creek drainage basin, Northwest Territories, Canada, located in the zone of discontinuous permafrost. This provided a unique opportunity to examine post-fire changes in runoff chemistry, plateau energy dynamics, water inputs, and ground thaw regimes within a single, partially burned landform unit. Beginning in March 2016, approximately 1.5 years following the wildfire event, runoff water samples were collected from the saturated layer as thaw progressed. Intensive repeated measurements of ground thaw dynamics, coupled with laboratory analyses of changes in near-surface (0-20 cm depth) peat physical and hydraulic properties, were used to explain changes in runoff water chemistry. Seasonal peat porewater showed elevated nutrient and ion ...