Rising plant-mediated methane emissions from arctic wetlands.

Plant-mediated CH4 flux is an important pathway for land-atmosphere CH4 emissions, but the magnitude, timing, and environmental controls, spanning scales of space and time, remain poorly understood in arctic tundra wetlands, particularly under the long-term effects of climate change. CH4 fluxes were measured in situ during peak growing season for the dominant aquatic emergent plants in the Alaskan arctic coastal plain, Carex aquatilis and Arctophila fulva, to assess the magnitude and species-specific controls on CH4 flux. Plant biomass was a strong predictor of A. fulva CH4 flux while water depth and thaw depth were copredictors for C. aquatilis CH4 flux. We used plant and environmental data from 1971 to 1972 from the historic International Biological Program (IBP) research site near Barrow, Alaska, which we resampled in 2010-2013, to quantify changes in plant biomass and thaw depth, and used these to estimate species-specific decadal-scale changes in CH4 fluxes. A ~60% increase in CH4 flux was estimated from the observed plant biomass and thaw depth increases in tundra ponds over the past 40 years. Despite covering only ~5% of the landscape, we estimate that aquatic C. aquatilis and A. fulva account for two-thirds of the total regional CH4 flux of the Barrow Peninsula. The regionally observed increases in plant biomass and active layer thickening over the past 40 years not only have major implications for energy and water balance, but also have significantly altered land-atmosphere CH4 emissions for this region, potentially acting as a positive feedback to climate warming.