Peatlands face rising threat as carbon loss accelerates during extreme droughts
A recent study published in Science demonstrates that extreme droughts, combined with elevated temperatures and higher atmospheric carbon dioxide levels, significantly increase carbon emissions from peatland ecosystems. According to the findings, future droughts could quickly convert peatlands from carbon sinks to sources, potentially eliminating as many as 250 years' worth of stored carbon in mere months.
"As temperatures increase, drought events become more frequent and severe, making peatlands more vulnerable than before," said Yiqi Luo, senior author and Liberty Hyde Bailey Professor at Cornell University's College of Agriculture and Life Sciences. "We add new evidence to show that with peatlands, the stakes are high. We observed that these extreme drought events can wipe out hundreds of years of accumulated carbon, so this has a huge implication."
Previous research highlighted reductions in ecosystem productivity and surges in peatland carbon release during drought, but this investigation is the first to detail how warming climate conditions can amplify these losses. The Intergovernmental Panel on Climate Change estimates that the risk of extreme drought events could multiply by up to 7.2 times in the near future. Luo emphasized the urgent need to address the climate crisis and draw greater attention to peatlands due to their critical role in carbon storage.
"It's a huge reservoir of carbon compared to any other ecosystem," Luo noted. "We need to find a way to mitigate climate change and bend the warming curve."
The research team analyzed data from the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment, based in a boreal spruce bog in northern Minnesota. At this site, Oak Ridge National Laboratory runs large-scale climate manipulation studies using chambers where both temperature and carbon dioxide levels are controlled. The study focused on carbon loss during a severe drought in July and August of 2021 across 10 projected climate change scenarios.
Findings revealed that reduced water tables during drought took longer to stabilize at higher temperatures and elevated carbon dioxide, intensifying carbon release. Luo anticipated greater losses under heat, but discovered that elevated carbon dioxide also heightened emissions. Notably, while high carbon dioxide usually helps plants and buffers drought in upland areas, in peatlands it triggered additional dissolved carbon and substrate buildup, ultimately releasing more carbon dioxide when exposed to oxygen.
"Previous studies indicated that elevated carbon dioxide can usually make extreme events less impactful, but our results indicate the opposite," Luo stated.
With raised carbon dioxide levels alone, ecosystem productivity improved slightly, but the combination of high temperatures and carbon dioxide led to a dramatic surge in carbon emissions during the drought. Further analysis showed that dissolved carbon concentrations increased within the peat bog, leading to accelerated atmospheric release when dried.
Alongside Luo, contributors included several postdoctoral researchers, senior associates, and scientists from Oak Ridge National Laboratory, Florida State University, USDA, Georgia Institute of Technology, ETH Zurich, Northern Arizona University, Australian National University, University of Western Ontario, and Duke University. The investigation was supported by funding from the U.S. Department of Energy, the National Science Foundation, USDA, New York State Department of Environmental Conservation, and New York State Department of Agriculture and Markets.
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