Effect of permafrost thaw on methane and carbon dioxide exchange in two western Alaska peatlands

• Main Author: Johnston, Carmel Eliise
• Other Authors: Chairperson, Graduate Committee: Stephanie A. Ewing, Stephanie A. Ewing, Jennifer W. Harden, Paul C. Stoy, Ruth K. Varner, Kimberly P. Wickland, Joshua Koch, Christopher Fuller and Mark T. Jorgenson were co-authors of the article, '2.0 effect of permafrost thaw on CO 2 and CH 4 exchange in a western Alaska peatland chronosequence' submitted to the journal 'Environmental research letters' which is contained within this thesis., Stephanie A. Ewing, Merritt R. Turetsky, Jennifer W. Harden, A. David McGuire and Miriam Jones were co-authors of the article, '3.0 effect of recent permafrost thaw on the spatial distribution of CO 2 and CH 4 exchange in a western Alaska peatland' submitted to the journal 'Environmental research letters' which is contained within this thesis.
• Format: Thesis
• Language: English
• Published: Montana State University - Bozeman, College of Agriculture 2013
• Subjects: Methane; Carbon dioxide; Permafrost; Thawing; Climatic changes; Bonanza; Fairbanks; permafrost; Alaska
• Online Access: https://scholarworks.montana.edu/xmlui/handle/1/9099

Methane (CH 4) causes about 20% of greenhouse gas radiative forcing despite its relatively short lifetime (~10 y) and low concentration (1800 ppb) in the atmosphere. Wetlands are the largest natural source of CH 4, amounting to 22% of CH 4 production globally, with emission of CH 4-C by both diffusion and ebullition pathways. Permafrost peatlands store about 10% of permafrost C and 5% of global belowground C; hence CH 4- C emission with peatland permafrost thaw is of concern. We quantified temporal and spatial aspects of CH 4 and CO 2 emissions from northern peatlands using two approaches: (1) a ~1000 y thaw chronosequence in remote western Alaska (Innoko Flats Wildlife Refuge; May-September, 2011), and (2) lateral transects in intermediate age (~20-500 y) collapse-scar bog features at a well-instrumented site near Fairbanks, Alaska (Alaska Peatland Experiment (APEX)/Bonanza Creek Long Term Experimental Research site; June-September, 2012). At Innoko Flats, peak CH 4 production was observed in features aged 30-590 y since thaw, which had warmer soils than younger sites and shallower water tables than older sites. Average surface flux at these 30-590 y sites (+2.52 ± 0.98 mg CH 4-C m -2 hr -1) was greater than estimated ebullition flux (0.13 ± 0.05 mg CH 4-C m -2 hr -1) based on an observed rate of 0.78 ± 0.33 mL m -2 hr -1. Net ecosystem exchange of CO 2-C (NEE) did not differ among chronosequence features, and offset CH 4-C emissions by a factor of 2 to 400 when considered as 100-y global warming potential. At APEX, bogs reflecting <100 y since most recent thaw showed high variability in CH 4 exchange, but rates were generally consistent with levels at the Innoko 30-590 y sites (mean of 5.42 ± 1.16 mg CH 4-C m -2 hr -1). APEX bogs showed greater balance between CH 4-C efflux and CO 2-C influx, with CH 4-C fluxes offsetting 80-140% of NEE during the growing season when considered as 100-y global warming potential. We argue that CH 4 contributes most significantly to post-thaw C loss over timescales of decades ...