Long‐term trends in wetland event response with permafrost thaw‐induced landscape transition and hummock development

Abstract

AbstractNorthwestern Canada's discontinuous permafrost landscape is transitioning rapidly due to permafrost thaw, with the conversion of elevated, forested peat plateaus to low‐lying, treeless wetlands. Increasing hydrological connectivity leads to partial drainage of previously isolated wetlands, which subsequently develop hummock–hollow microtopography. Ultimately, the ecohydrological feedbacks associated with climate‐driven permafrost thaw have led to the expansion of treed wetlands in plateau–wetland complexes. Field research and aerial imagery analyses were conducted at the Scotty Creek Research Station, Northwest Territories, to examine the development of hummock terrain over time and the resultant impacts on the hydrological response of wetlands connected to the basin drainage network. The area of peat plateaus underlain by permafrost declined between 2010 and 2018. The total area of hummock terrain increased in the basin in the same time period, with an overall decrease in the hummock perimeter‐to‐area ratio as small individual hummocks increased in size and aggregated into larger hummock complexes occupied by re‐establishing trees. With the development and expansion of hummock terrain, the tortuosity of flowpaths draining wetlands increased. The average wetland water level recession constants following precipitation events became shorter over the 15 year period of record (2003–2017). The average time of water level rise in response to precipitation events decreased over time, as precipitation was directed quickly to runoff. As permafrost thaw reduces the cover of peat plateaus in exchange for increased wetland area, the presence of treed wetlands appears to be transitioning plateau–wetland complexes into permafrost‐free forest, facilitated by the growth of hummock terrain. Permafrost thaw‐induced wetland transition triggers ecohydrological feedbacks with the potential to alter the availability and sustainability of freshwater resources.