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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Aquatic Plants Accelerate Arctic Methane Emissions

Christian G. Andresen

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22 September 2016

Climate change has caused a boom in aquatic plant biomass on the Arctic tundra in recent decades. Those plants, in turn, are releasing increasing amounts of methane into the atmosphere.

The Science
Researchers measured methane (CH4) fluxes of aquatic vegetation during 2010–2013 at sites characterized in the 1970s at the International Biological Program (IBP) research site near Barrow, Alaska. They then developed statistical models to determine the major environmental factors associated with CH4 emissions such as plant biomass and active-layer depth. They used the IBP historic datasets to model changes in CH4 fluxes between the 1970s and 2010s. Next, using high-resolution imagery, the researchers mapped aquatic vegetation and applied their model to estimate regional changes in CH4 emissions.

The Impact
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.

Summary
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 the 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. The researchers used plant and environmental data from 1971 to 1972 from the historic IBP research site near Barrow, Alaska, which they resampled in 2010-2013, to quantify changes in plant biomass and thaw depth. They used these data 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, the researchers 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.

Contacts
BER Program Managers
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)
Jared.DeForest@science.doe.gov (301-903-1678)

Principal Investigator
Christian G. Andresen
Los Alamos National Laboratory, Los Alamos, NM
candresen@lanl.gov (505-665-7661)

Funding
This research is supported by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project of the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, and by the National Science Foundation (NSF) Graduate Research Fellowship Program to CGA (NSF-1110312).

Publications
Andresen, C.G., M.J. Lara, C.T. Tweedie, and V.L. Lougheed. "Rising plant-mediated methane emissions from Arctic wetlands." Global Change Biology 23(3), 1128–1139 (2016). [DOI:10.1111/gcb.13469]

Related Links
EOS article

This research is supported by the DOE Office of Science, Office of Biological and Environmental Research, Next Generation Ecosystem Experiment, NGEE-Arctic project and by the National Science Foundation (NSF) Graduate Research Fellowship Program to CGA (NSF-1110312)

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