The Impacts of Permafrost Disturbances on Vegetation and Growing Season Carbon Dioxide Exchange in a High Arctic Tundra Ecosystem

Abstract:

Permafrost disturbances are widespread across the Fosheim Peninsula, Ellesmere Island, Canada, where they take the form of active layer detachment slides and retrogressive thaw slumps. This project analyzes the impacts of these disturbances on ecosystem structure and function. Eddy covariance and static chamber measurements were used during the 2013 growing season to determine net ecosystem exchange (NEE) and ecosystem respiration (ER) from multiple retrogressive thaw slumps located in areas with different vegetation types. Two eddy covariance towers were established at the beginning of the growing season and ran continuously throughout the summer. Flux partitioning based on wind direction allowed us to determine NEE fluxes from disturbed tundra, which were compared with fluxes from surrounding undisturbed tundra. A static chamber system was utilized throughout the season to measure ER from corresponding disturbed and undisturbed tundra. Vegetation composition and environmental variables were determined across multiple disturbances. NEE and ER were separated throughout the season into three periods of analysis based on temperature, precipitation, and vegetation development.

Eddy covariance measurements indicate decreases in NEE in disturbed areas. In one site, this decrease shifted the system from a net sink to a net source of carbon over the entire growing season. Vegetation community composition determines the overall impact of disturbance on carbon dioxide fluxes. Seasonal shifts in fluxes are also apparent. Disturbances increased ER in sedge tundra and decreased ER in dwarf shrub communities. Analysis of vegetation indicates a decrease in overall vegetation cover within two active disturbances when compared with undisturbed surrounding areas. This corresponds with differing dominant vegetation types in these zones. We determined the impacts of permafrost disturbances on ecosystem structure and function by quantitatively measuring vegetation composition and carbon dioxide fluxes from disturbed and undisturbed tundra.