Impact of Land Cover Disturbances on Permafrost Landscapes in Yukon, Case Studies

English Abstract:

The impacts of rising temperatures in permafrost regions are already being observed in many communities. Environmental changes can be exacerbated by human intervention and most of the time these operations (e.g. road installation, logging) can impact on the environment at a faster pace than those induced by climatic changes. When combined, climatic and anthropogenic changes can result in important hazards for community planning. From a project managed by the Northern Climate ExChange, case studies from Yukon were selected to illustrate the impacts of land cover changes on permafrost landscapes.

Under a FireSmart zone where trees are still present, the stability of the permafrost has been maintained with an active layer depth of 0.65 m. Illustrating how surface disturbance can impact the ground thermal regime, an adjacent cleared area has developed a near-surface talik (unfrozen zone over the permafrost) that reaches 8 m in depth.

To access gold bearing material, placer mining operations strip the first meters of soil and vegetation. A land plot shows early signs of permafrost degradation in a stripped area. By removing the insulating organic cover, the active layer has thickened to a depth greater than 1.6 m in just under 10 years. In comparison, an adjacent forested zone is showing a 52 cm thick active layer, underlain by ice-rich permafrost.

Removing vegetation and stripping the ground can also lead to the accelerated degradation of ice wedges, such as occurred at a residential area where a forest was cleared in the 90’s for agricultural purposes. In a little over 20 years, degradation of ice wedges created linear subsidence and water ponding where the terrain was previously flat and polygonal network of ice wedges progressively appeared and are now clearly visible.

Our results indicate that land-use changes, especially those affecting the vegetation cover, can impact permafrost geosystems much more rapidly than changes induced by atmospheric warming only.