Impacts of active retrogressive thaw slumps on vegetation, soil, and net ecosystem exchange of carbon dioxide in the Canadian High Arctic
Cassidy, A.E. A. Christen and G. Henry. 2017.
Abstract
Retrogressive thaw slumps (RTS) are permafrost disturbances common on the
Fosheim Peninsula, Ellesmere Island, Canada. During the 2013 growing season, three differ-
ent 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.
Key Words
eddy covariance, Ellesmere Island, Fosheim Peninsula, net ecosystem exchange, permafrost disturbance, retrogressive thaw slump, tundra ecosystem
