Impacts of active retrogressive thaw slumps on vegetation, soil, and net ecosystem exchange of carbon dioxide in the Canadian High Arctic

• Published in: Arctic Science
• Main Authors: Cassidy, Alison E., Christen, Andreas, Henry, Greg H.R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2017
• Subjects: Arctic; Ellesmere Island; Fosheim Peninsula; permafrost; Tundra
• Online Access: http://dx.doi.org/10.1139/as-2016-0034; https://cdnsciencepub.com/doi/full-xml/10.1139/as-2016-0034; https://cdnsciencepub.com/doi/pdf/10.1139/as-2016-0034

Retrogressive thaw slumps (RTS) are permafrost disturbances common on the Fosheim Peninsula, Ellesmere Island, Canada. During the 2013 growing season, three different RTS were studied to investigate the impact on vegetation composition, soil, and growing season net ecosystem exchange (NEE) of CO 2 by comparing to the adjacent undisturbed tundra. Eddy covariance and static chamber measurements were used to determine NEE and ecosystem respiration (R e ), respectively. Vegetation cover was significantly lower in all active disturbances, relative to the surrounding tundra, and this affected the overall impact of disturbance on CO 2 fluxes. Disturbances were characterized by greater R e compared to surrounding undisturbed tundra. Over the mid-growing season (34 days), eddy covariance NEE measurements indicated that there was greater net CO 2 uptake in undisturbed versus disturbed tundra. At one site, the undisturbed tundra was a weak net sink (−0.05 ± 0.02 g C m −2 day −1 ), while the disturbed tundra acted as a weak net source (+0.07 ± 0.04 g C m −2 day −1 ). At the other site, the NEE of the undisturbed tundra was −0.20 ± 0.03 g C m −2 day −1 (sink), while the disturbed tundra still sequestered CO 2 , but less than the undisturbed tundra (NEE = −0.05 ± 0.04 g C m −2 day −1 ). Two of the RTS exhibited average soil temperatures that were greater compared to the surrounding undisturbed tundra. In one case, the opposite effect was observed. All RTS exhibited elevated soil moisture (+14%) and nutrient availability (specifically nitrogen) relative to the undisturbed tundra. We conclude that RTS, although limited in space, have profound environmental impacts by reducing vegetation coverage, increasing wet soil conditions, and altering NEE during the growing season in the High Arctic.