September 22, 2016

Aquatic Plants Accelerate Arctic Methane Emissions

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.

Principal Investigator

Christian Andresen
Los Alamos National Laboratory
candresen@lanl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

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).

References

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). https://doi.org/10.1111/gcb.13469.