THAWING PERMAFROST IN PEATLANDS OF NORTHWESTERN CANADA

The presence or absence of permafrost in discontinuously frozen peatlands of the Canadian subarctic can be determined from historical aerial photographs and high-resolution satellite images. In these images, permafrost-affected peat lands (e.g. peat plateaus) appear in dark shades owing to the dense cover of black spruce. Areas without permafrost (e.g. fens and bogs) lack a significant forest cover and appear in lighter tones. These visual differences in frozen and unfrozen peat lands allow the determination of changes in permafrost distribution over time.

A total of eight study sites within six regions in the Mackenzie Valley, northwestern Canada, were studied for permafrost thaw rates over approximately the past 50 years, using historic aerial photographs and Ikonos satellite images. Sites ranged from Zama (AB) at 59oN to Big Smith Lake (NWT) at almost 65oN. Results indicate that permafrost in peatlands has declined at all sites, with the greatest rates of thaw found in the Liard River valley near 61.5oN, where an up to 41% decrease in permafrost extent was observed over the time span 1947-2000. Sites further north and higher elevation sites to the south showed a greater proportion of peatland area to be permafrost-affected, and these sites showed lesser thaw rates over the past (approx.) 50 years. Sites in the Liard valley also showed the greatest rate of lateral thaw (mean of 20 m over about 50 years). Peatlands in the Liard River area have also developed a high degree of interconnected hydrology over the past 50 years, resulting in improved drainage and an increase in shrub dominance in peatlands. In contrast, sites other than the Liard River area are still permafrost-dominated, although the trend is certainly towards ongoing thaw, the coalescence of thaw features, the development of an integrated drainage basin, and a landscape becoming more dominated by unfrozen peatlands. These dramatic changes in permafrost distribution have significant impacts upon hydrology and carbon sequestration.