New paper in Biogeosciences: Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation

March 14, 2016 in Article, post by Perreault.N

Field surveys were conducted over two years in the Qarlikturvik valley of Bylot Island, NU to assess the impacts of thermo-erosion gullies on the vegetation of surrounding low-centered wet polygons. Based on 197 sites located around three gullies, plant species richness, plant species abundance and graminoid above-ground biomass of breached polygons were compared to those of two baseline habitats – intact wet polygons and intact mesic environments.

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The inception of ice wedge degradation immediately decreased soil moisture and thaw front depth of breached polygons – as found by Godin et al. (2016) – and the environmental conditions of disturbed polygons thus got closer to those of mesic environments. Consequently, we observed a gradual but marked shift in vascular plant community composition within ten years after disturbance, characterized by the emergence of Arctagrostis latifolia and Salix spp. at the expense of hydrophilic species such as Carex aquatilis, Eriophorum scheuchzeri and Dupontia fisheri.

High Arctic wetlands are therefore highly sensitive to thermo-erosion processes, which can rapidly drive the transformation of low-centered wet polygon landscape. The transition towards mesic environments could soon impact food resources of herbivores – which are fond of hydrophilic species – and modify emissions of greenhouse gases.

Interestingly, the latest observations showed that, ten years after disturbance inception, hydrology and thaw regimes of breached polygons have not reached equilibrium with new conditions yet whilst cover of mesic bryophytes and dominant shrubs are still lower than in adjacent intact mesic environments. This paves the way for long-term monitoring studies of permafrost disturbance and recovery of its associated vegetation.

 

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The full story is available here:

Perreault, N., Lévesque, E., Fortier, D. and Lamarque L. J.: Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation, Biogeosciences, 13, 1237-1253, 2016.

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by Godin.E

New paper in Biogeosciences: Nonlinear thermal and moisture response of ice-wedge polygons to permafrost disturbance increases heterogeneity of high Arctic wetland

March 10, 2016 in Article, post by Godin.E

The floor of the Qalikturvik valley (Bylot Island, NU) is a mosaic ice-wedges polygons. A subtype of polygons named wet polygons are bowl like shaped, which enable moisture from snowmelt and precipitation to concentrate in their centers. These fields of wet polygons can support productive ecological environments, particularly when considering the usually arid nature of the High-Arctic.

Thermal erosion gullying erode and breach the contour (rims) of the bowl-shaped polygons, therefore affecting their capacity to retain moisture and possibly changing the near-surface thermal regime. One gully can breach the rims of hundreds of polygons: at the study site, three dozen gullies were located.

Nearby polygons located near a gully were identified and instrumented; reference and intact polygon characteristics were compared against eroded polygons during 2012-2013. The intact polygon center was saturated following snowmelt and during precipitation events later in summer. The moisture diminished following the thickening of the active-layer and its overall moisture was significantly higher than any disturbed polygons. The thermal regime during 2012-13 for this polygon was similar to another intact polygon. The vegetation in its center was well distributed and relatively uniform (ex: Carex sp.).

On the other hand, disturbed polygons were characterized by varying state for their moisture, ground temperature and vegetation cover. A disturbed polygon could simultaneously be partially dry, partially wet, depending on the severity of the rims breach. The active layer evolution could be similar to an intact polygon or could be significantly thinner. Dry tussocks were present in the centers, underlining the changing moisture state of the polygon, where plants better adapted to the new conditions settled. Therefore in the eroded polygon centers, there was an intra-polygonal variability as there was an heterogeneity in the moisture levels and plant distributions and an inter-polygonal variability (as in not all disturbed polygon were affected in the same way), depending on the severity of the breach, the recharge capability and proximity to the gully.

At the scale of the decade, gullying cause heterogeneity in the landscape with a tendency toward a dryer environment than pre-gullying. Further, gullying affect polygons rims thus the area affected by the erosion exceeds the gully as it affects an entire disturbed polygon.

The paper is available here:

Godin, E.; Fortier, D. & Lévesque, E.
Nonlinear thermal and moisture response of ice-wedge polygons to permafrost disturbance increases heterogeneity of high Arctic wetland
Biogeosciences, 2016, 13, 1439-1452

 

 

by Godin.E

M.Sc. thesis successfully completed for Gautier Davesne!

March 5, 2016 in post by Godin.E

Congratulation to Gautier Davesne who successfully completed his M.Sc.’s thesis under the supervision of Daniel Fortier! His research project deals with the spatio-temporal evolution of the marginal mountain permafrost on the summit of Mont Jacques-Cartier. This work has been a basis to write a paper entitled “The thermal regime of mountain permafrost at the summit of Mont Jacques Cartier in the Gaspé Peninsula, Québec, Canada: a 37-year record of fluctuations showing an overall warming trend” (authors: J. Gray; G. Davesne; D. Fortier; E. Godin) submitted to the journal Permafrost and Periglacial Processes and accepted with minor corrections. A second paper entitled “Snow conditions control the occurrence of contemporary marginal mountain permafrost of the Chic-Chocs mountains, south-eastern Canada – a case study from Mont Jacques-Cartier” (authors: G. Davesne; D. Fortier; J. Gray) is presently in the process of writing and will be soon submitted to the journal The Cryosphere.

To consult his M.Sc. thesis, please click here!