Active layer variability and change in the Mackenzie Valley, Northwest Territories between 1991-2014: An ecoregional assessment

ABSTRACT

Active layer thicknesses (ALTs) from sites along a transect through the Mackenzie Valley, Northwest Territories, Canada, were analyzed to explore variation in thickness within and between ecoregions. At an ecoregional scale the relation between ALT, latitude, freezing and thawing degree-days, and snowfall were examined to determine the presence of trends. Site-specific variables including dominant vegetation and substrate were explored to explain spatial variability in ALT within ecoregions. Generally, average ALT increases moving southward through the comprising ecoregions (68 cm to 126 cm), following the increase in air temperature. Spatial variability in ALT within ecoregions was greater than that between ecoregions (up to 145 cm), which may be attributed to site-specific conditions (vegetation and snow cover). Most notable, sites with shrubs had thicker than average active layers likely because of increased snow retention leading to warmer overall ground conditions. Despite a warming trend in air temperatures, only one northern ecoregion showed a corresponding thickening trend in ALT. Sites located in southern ecoregions with mature forests showed limited response to changes in air temperature. For these locations, disturbance, specifically changes in thermally protective vegetation cover, rather than changing air temperature could potentially have a larger impact on ALT into the future.

KEYWORDS:

• permafrost
• active layer
• ecoregion
• Mackenzie Valley

Acknowledgments

Logistical support was provided by Polar Continental Shelf Program and Inuvik Research Institute. We are thankful for the support and assistance provided by communities in the Northwest Territories. Numerous colleagues have contributed to data collection over the years. We also thank A. Leblanc for review prior to submission. Data management and processing support was provided by J. Chartrand.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Government of Canada, Natural Sciences and Engineering Research Council of Canada.