Massive Peatland Carbon Banks Vulnerable to Rising Temperatures

Deep peat destabilization increases greenhouse gas emissions from peatlands.

The Science

To investigate the effects of long-term climate change on peatland carbon stability, the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment warmed the air and soil (to >2 m deep) of a Minnesota bog up to +9°C above ambient temperatures with a subset additionally subjected to doubled atmospheric carbon dioxide (CO2) concentrations. Following five years of warming, both surface and deeply buried peat served as carbon sources contributing to large increases in methane (CH4) and CO2 emissions, suggesting that the massive carbon banks stored as peat are vulnerable to climate change.

The Impact

While soil carbon has accumulated over millennia in peatlands, these results demonstrate that the vast deep carbon stores become destabilized under prolonged warmer conditions (>1 year), providing important insights into climate-peatland interactions.

Summary

Northern peatlands contain one half of Earth’s soil organic carbon due to their cold, water-saturated, acidic conditions that slow decomposition. The investigators at the University of Oregon working with the Oak Ridge National Laboratory whole-ecosystem manipulation SPRUCE project hypothesized that warmer temperatures—due to changing climate—would increase emissions of the greenhouse gases carbon dioxide (CO2) and methane (CH4). To test this hypothesis, air and peat (to >2 m deep) at SPRUCE were warmed to five temperatures (0°C, +2.25°C, +4.5°C, +6.25°C, and +9°C above ambient), with and without elevated air CO2 concentrations. Previous results after more than 1 year of treatment showed that the exponential increase in CH4 emissions with warming was solely due to surface processes. After 5 years of treatment, large increases in both CH4 and CO2 emissions were observed in response to warming. Further, radiocarbon dating and laboratory incubations revealed that the increased emissions resulted from both surface peat and destabilization of deep ancient peat. Decomposition has become more methanogenic with warming as indicated by a decrease in the CO2:CH4 ratio in anaerobic respiration, which is particularly concerning given the large global warming potential of CH4. Elevated air CO2 concentrations to date have only had small effects on CH4 processes. These results highlight the vulnerability of massive peatland carbon banks to a warmer climate and suggest a positive feedback that is expected to exacerbate climate warming.

Principal Investigator

Scott Bridgham
University of Oregon
bridgham@uoregon.eduv

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 material is based upon work supported by the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for DOE. Funding was provided by the DOE under DE-SC0014416, DE-SC00008092, DE-AC05-00OR22725, DE-SC0007144, and DE-SC0012088. Radiocarbon samples were run at the National Ocean Sciences Accelerator Mass Spectrometry Facility (Falmouth, Massachusetts).

References

Hopple, A. M., R. M. Wilson, M. Kolton, and C. A. Zalman, et al. "Massive peatland carbon banks vulnerable to rising temperatures". Nature Communications 11 (2373), (2020). https://doi.org/10.1038/s41467-020-16311-8.

Wilson, R. M., A. M. Hopple, M. M. Tfaily, and S. D. Sebestyen, et al. "Stability of peatland carbon to rising temperatures". Nature Communications 7 (13723), (2016). https://doi.org/10.1038/ncomms13723.