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The impacts of High Arctic permafrost disturbances on vegetation and carbon flux dynamics

Cassidy, A. E.. 2016.

Abstract

Changing climate and disturbance regimes can have widespread ecosystem impacts, especially in the Arctic. Vegetation recovery and carbon flux dynamics were examined to determine the impacts of thermokarst disturbance on patterns and processes in High Arctic tundra ecosystems. Ecosystem responses to two forms of permafrost disturbance, active layer detachment slides and retrogressive thaw slumps, were studied on the Fosheim Peninsula, Ellesmere Island, Canada during the 2012, 2013, and 2014 growing seasons. The impacts of disturbance on vegetation and recovery were determined by sampling active retrogressive thaw slumps and recovered active layer detachment slides that were investigated nearly 20 years ago. Comparison of historic and modern data indicates distinct vegetation communities exist in differently aged disturbances with unique vascular plant species defining various zones and ages of disturbance. Differences were also found in site characteristics (including soil moisture, temperature, active layer depth, and soil nutrient concentrations) indicating the impacts of permafrost disturbance on the landscape. In addition, four active layer detachment slides measured in 1994 had transitioned to active retrogressive thaw slumps, which may be a response to the progressively warming climate. Carbon dioxide fluxes between the surface and the atmosphere were measured using a static chamber system and the eddy covariance technique at three sites on the Fosheim Peninsula. Over the studied growing seasons, disturbed landscapes sequestered significantly less carbon than their surrounding undisturbed tundra. In some sites, this resulted in the shift of the system from a net sink of CO%u2082 to a net source. A dual eddy covariance sampling approach was found to be preferable over a single tower setup with separation of fluxes based on wind partitioning as disturbed and undisturbed fluxes were simultaneously measured throughout the growing season using this method. Overall, active layer detachments and retrogressive thaw slumps alter vegetation and carbon flux dynamics, and these changes may persist over many years. With predicted increases in the frequency and magnitude of these permafrost disturbances, impacts on tundra ecosystems will be evident at the landscape scale.