Abstract
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 CO2 by comparing to the adjacent undisturbed tundra. Eddy covariance and static chamber measurements were used to determine NEE and ecosystem respiration (Re), respectively. Vegetation cover was significantly lower in all active disturbances, relative to the surrounding tundra, and this affected the overall impact of disturbance on CO2 fluxes. Disturbances were characterized by greater Re compared to surrounding undisturbed tundra. Over the mid-growing season (34 days), eddy covariance NEE measurements indicated that there was greater net CO2 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 CO2, 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.
Highlights
Permafrost disturbances are expected to increase in frequency and magnitude with predicted climate change (ACIA 2005; Vincent et al 2011; Kokelj and Jorgenson 2013; Segal et al 2016)
Landscape mosaics were evident on the Fosheim Peninsula as a result of permafrost disturbances
Site characteristics that result from morphological modifications following retrogressive thaw slumping are dependent on initial site characteristics
Summary
Permafrost disturbances are expected to increase in frequency and magnitude with predicted climate change (ACIA 2005; Vincent et al 2011; Kokelj and Jorgenson 2013; Segal et al 2016). In the High Arctic, common permafrost disturbances include active layer detachment slides (ALDS) and retrogressive thaw slumps (RTS). RTS remain active until ground ice is depleted or further thaw is prevented by falling blocks of soil and vegetation, which act as insulation (Burn and Friele 1989). Ecosystem responses to these permafrost disturbances have focused on hydrological impacts (Kokelj and Lewkowicz 1998, 1999; Lamoureux and Lafrenière 2009). Thaw slumps modify vegetation communities with changes persisting for centuries (Cray and Pollard 2015)
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