Thermokarst and export of sediment and organic carbon in the Sheldrake River watershed, Nunavik, Canada

Abstract

[1] A spatiotemporal computation of permafrost decay covering the period from 1957 to 2009 and validated by field investigations was made over a 76 km 2 river catchment straddling the tree line, in the discontinuous permafrost zone, east of Hudson Bay, in order to estimate the amounts of sediments and organic carbon released by thermokarst. Lithalsas and palsas are the dominant permafrost landforms, whereas thermokarst ponds, landslides, active layer failures, and gullies are the main features of permafrost degradation. Results show that 21% of the existing permafrost in 1957 had disappeared in 2009, resulting in a 96% growth of the thermokarst pond cover and a 46 to 217% increase of the number of active erosion landforms. An increase of stream connectivity related with the degradation of permafrost potentially allowed for an increase of sediments and carbon delivery to the main stream by a factor of 1.6. Volume of active landslides and gullies also increased by 12 to 38%, enhancing sediment and organic matter yields. Significant differences in permafrost degradation and in sediment and carbon inputs were observed along an east-west transect, from sites located at the head of the watershed near the tree line to sites located downstream close to the Hudson Bay coast. Thermokarst ponds in the forest tundra area released 2.3 times more sediments and dissolved organic carbon per unit of area in the fluvial system than in the shrub tundra area. Despite these yields by thermokarst, the Sheldrake River catchment currently does not seem to be yielding proportionally more sediments and carbon than a permafrost-free river catchment.Citation: Jolivel, M., and M. Allard (2013), Thermokarst and export of sediment and organic carbon in the Sheldrake

Paleolimnology of thermokarst lakes: a window into permafrost landscape evolution

“…Palsas and lithalsas, formed by ground ice aggradation and related surface heaving, are widespread in the region and typical of the discontinuous permafrost landforms in subarctic Québec (Allard and Seguin 1987). Recent increases in air/ground temperatures and snow cover along the eastern shore of Hudson Bay have contributed to widespread reduction of permafrost extent, resulting in increasing surface areas occupied by subarctic thermokarst ponds (Payette et al 2004;Vallée and Payette 2007;Jolivel and Allard 2013). However, the exact timing of their inception as well as the processes controlling their sedimentological and limnological evolution in response to past paleoenvironmental changes in their vicinity were poorly known until recently.…”

Periphytic diatom community structure in thermokarst ecosystems of Nunavik (Québec, Canada)

“…1b) (Allard and Séguin 1987). Each studied area thus contains many thermokarst lakes and cryogenic mounds that are currently in a variable state of degradation (Bouchard et al 2013;Jolivel and Allard 2013). A total of 11 thermokarst lakes were sampled in four valleys or survey areas.…”

“…The BGR valley (forest tundra, discontinuous permafrost) contained numerous lithalsas with ice-rich cores as well as some degrading palsas (Calmels et al 2008;Jolivel and Allard 2013). The apparent color of these lakes ranged from brown-beige to blue, and most of them were surrounded by clay-rich peripheral ridges with inorganic soils on which vegetation was low-lying and scattered.…”

Impact of permafrost thaw on the turbidity regime of a subarctic river: the Sheldrake River, Nunavik, Quebec

“…Base flow may cease in winter, since subpermafrost groundwater may be nonexistent or too deep to discharge in the catchment and because taliks can be only poorly connected with springs on the river beds. Soil warming, thinning and decay of permafrost, earlier breakups, decline of snow cover duration, and increase in shrub, forest, and peatland covers are factors affecting the hydrology of high-latitude rivers under ongoing climate change (Magnuson et al 2000;Sturm et al 2001;Payette et al 2004;Brown and Romanovsky 2008;Jolivel and Allard 2013;Lesack et al 2014). For example, it is broadly expected that the sediment load of high-latitude rivers would increase by 30% for every 2°C of warming of the averaged catchment temperature (Syvitski 2002).…”

“…Thawing of permafrost is known to release large volumes of sediments through thermokarst processes such as thaw slumping and thermal erosion (Jolivel and Allard 2013;Kokelj et al 2013). The released sediments are mobilized by soil erosion, in overland flow and in water courses; they feed sedimentation (Guo et al 2004;Goni et al 2005;Jolivel et al 2015) and get involved in biogeochemical processes (Emmerton et al 2008;Galand et al 2008;Vonk et al 2015) in lakes, deltas, and coastal seas.…”