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

 

 

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