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.
Abstract. Scotty Creek, Northwest Territories (NWT), Canada, has been the focus of hydrological research for nearly three decades. Over this period, field and modelling studies have generated new insights into the thermal and physical mechanisms governing the flux and storage of water in the wetland-dominated regions of discontinuous permafrost that characterises much of the Canadian and circumpolar subarctic. Research at Scotty Creek has coincided with a period of unprecedented climate warming, permafrost thaw, and resulting land cover transformations including the expansion of wetland areas and loss of forests. This paper (1) synthesises field and modelling studies at Scotty Creek, (2) highlights the key insights of these studies on the major water flux and storage processes operating within and between the major land cover types, and (3) provides insights into the rate and pattern of the permafrost-thaw-induced land cover change and how such changes will affect the hydrology and water resources of the study region.
Climate change is likely to significantly affect the hydrology, ecology, and ecosystem function of peatlands, with potentially important but unclear impacts on mercury mobility within and transport from peatlands. Using a full‐factorial mesocosm approach, we investigated the potential impacts on mercury mobility of water table regime changes (high and low) and vegetation community shifts (sedge‐dominated, Ericaceae‐dominated, or unmanipulated control) in peat monoliths at the PEATcosm mesocosm facility in Houghton, Michigan. Lower and more variable water table regimes and the loss of Ericaceae shrubs act significantly and independently to increase both total Hg and methylmercury concentrations in peat pore water and in spring snowmelt runoff. These differences are related to enhanced peat decomposition and internal regeneration of electron acceptors which are more strongly related to water table regime than to plant community changes. Loss of Ericaceae shrubs and an increase in sedge cover may also affect Hg concentrations and mobility via oxygen shuttling and/or the provision of labile root exudates. Altered hydrological regimes and shifting vegetation communities, as a result of global climate change, are likely to enhance Hg transport from peatlands to downstream aquatic ecosystems.
Northwestern 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 bogs, which have been observed to subsequently develop hummock microtopography. However, the role of microtopographic features in the future trajectory of the transitioning landscape is unclear, including their potential controls on tree re‐establishment. In order to understand the role of hummocks in landscape change, research was conducted at the Scotty Creek Research Station, Northwest Territories, to measure hummock and black spruce tree physical characteristics, and assess tree and hummock spatial coverage in peat plateaus, collapse scar bogs and the advanced transitional feature known as treed bogs. Canopy coverage in all landforms and wetland hummock areal coverage was assessed using a LiDAR (Light Detection and Ranging) canopy gap fraction model and multispectral imagery. Hummocks, which are not underlain by permafrost but contain seasonal ice, support the establishment of black spruce trees due to favourable soil moisture conditions. Hummock flank moisture in treed bogs is intermediate between those of dry peat plateaus and inundated collapse scar bogs. Black spruce trees on peat plateaus and in treed bogs are significantly taller and of greater circumference than those in collapse scar bogs. The spatial distribution of hummocks and canopy coverage of black spruce trees in treed bogs collectively suggest that these features may play an important role in the advanced stages of permafrost thaw‐driven transition of the discontinuous permafrost landscape.
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