Permafrost thaw induced drying of wetlands at Scotty Creek, NWT, Canada

Abstract

Northwestern Canada is one of the most rapidly warming regions on Earth. The scale and rapidity of recently observed warming-induced changes throughout this region indicate that it is particularly sensitive to climate warming and capable of rapid responses to perturbations. Unprecedented rates of permafrost thaw in the zone of discontinuous permafrost are transforming forests to wetlands, and changing the distribution and routing of water over the landscape as evidenced by recent increases in basin discharge. However, the impact of increasing basin discharge on basin water storage is not well understood. Water levels on a permafrost plateau, channel fen, and isolated and connected bogs were monitored from 2003–2017 in the Scotty Creek watershed, Northwest Territories. The water level in the channel fen did not significantly change over the period of study, sustained by inputs from the increasingly-connected network of bogs as permafrost barriers thawed. Bogs with varying levels of connection to the drainage network released from storage between 40 and 53 mm of water over the study period. The water level in the monitored isolated bog did not significantly change over this period. Estimates of moisture contributions derived directly from vertical permafrost thaw and from the lateral expansion of contributing areas account for 90% of the observed cumulative increase of 1043 mm in basin runoff between 1998–2012, leaving 109 mm of this increase unaccounted for. Increasing connectivity to the drainage network and transient wetland drainage at the landscape scale resulted from permafrost thaw-induced talik development. The similarity between the magnitude of wetland drainage and that of enhanced runoff suggests that increased connectivity of wetlands to the drainage network may contribute to increasing runoff from the Scotty Creek watershed. Permafrost thaw-induced land cover transition was found to have both short and long-term effects on runoff generation.