PARENT SESSION
Organized Oral Session 21: Implications of disturbance on boreal peatland carbon cycling: From sites to to landscape-scale carbon budgets
Organizer(s): RK Wieder, KD Scott, and DH Vitt
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 511a, Level 5, Palais des congrès de Montréal
Post-fire carbon fluxes from boreal peatlands in Alberta, Canada.
Wieder, R. Kelman1, Scott, Kimberli1, Kamminga, Katherine1, 1 Villanova University, Villanova, PA
ABSTRACT- Peatlands of continental, western Canada (Alberta, Saskatchewan, Manitoba) cover 365,160 km2 and store 42 Pg of C as peat and another 6 Pg of C in aboveground vegetation. If these peatlands are functioning as a net sink for atmospheric CO2-C of 24.5 g/m2/yr, a commonly accepted value, they would represent a net sink of 8.9 Tg/yr. However, across this region, on average, wildfire burns 1,470 km2 of peatland annually, directly releasing about 4.7 Tg of CO2-C into the atmosphere. We used a peatland chronosequence of 10 sites spanning 1 to 102 years since fire to assess post-fire C fluxes. Chamber-based measurements of CO2 fluxes were made at different light intensities and temperatures, characterizing the CO2 flux response to light intensity with a rectangular hyperbolic function and the dark respiration response to temperature using the Arrhenius equation. Based on these fitted relationships and on hourly climate data from a weather station at one of the peatland chronosequence sites, we estimate that one year after fire, peatlands are a net source of CO2-C of about 134 g/m2/yr, and at 102 years after fire, peatlands are a net sink of CO2-C of about 60 g/m2/yr. The recovery trajectory over the 102 year chronosequence is linear, such that peatlands switch from functioning as a net source to a net sink of C at about 70 years after fire. We estimate regional post-fire C losses from peatlands that burned within the past 102 years to be 5.3 Tg/yr such that regional C losses from both direct combustion and post-fire fluxes are 10 Tg/yr. Assuming that at 102 years after fire, net C fluxes from peatlands have reached a steady state net sink value of 60 g/m2/yr, and assuming a fire return interval of 250 years (365,160 km2 divided by annual burn are of 1470 km2), the C sink for the 218,160 km2 of peatlands at steady state within the entire region is 13 Tg/yr. Considerable C fluxes occur during and after fire from peatlands of continental western Canada. However, these losses do not exceed the larger than previously estimated sink strength of "old" peatlands, such that across this entire region, peatlands today may represent a net sink for atmospheric C of about 3 Tg/yr.
Key words: Peatland, Fire, Carbon Cycling, Climate Change