A study of satellite imagery indicates that 90 percent of 6.7 million acres at eight tropical peatland sites in Southeast Asia are sinking at almost an inch a year, “a speed an order of magnitude greater than rising sea level in the region,” says a University of Oregon researcher.
The findings, published in Nature Geosciences, unveil the effects of deforestation and drainage to convert pristine peatland, especially in the last 20 years, for human uses. Just 40 years ago, the region had 25 million hectares of peatland. The peatland study sites on Sumatra and Borneo cover as much land as the state of Vermont.
Subsidence, or sinking land, is a challenge for Southeast Asia. With most of its peatlands already at sea level, the sinking threatens productivity, and frequent flooding or complete inundation and saltwater intrusion are possible in coming decades, the four-member research team concluded.
Peatlands consist of partially decayed organic matter that normally absorb carbon dioxide. Draining water and burning ground cover to use the land for plantations and agriculture, however, open the soil to oxidation, which releases carbon dioxide into the air. The study revised 2015 estimates on emissions to about 155 metric tons a year, toward the higher end of a previous range, by incorporating data gathered from all land use sources.
“CO2 emissions from these degrading peatlands are of similar magnitude as both regional fossil fuel emissions and CO2 emissions from peat fires,” said study co-author Estelle Chaussard, an assistant professor in the UO’s Department of Earth Sciences. “Another way to put it is that these degrading peatlands, which occupy a relatively small extent of the region, produce more CO2 each year than landfills and waste management in the United States.”
An analysis of remotely sensed maps, built from data compiled in 2007-11 using interferometric synthetic aperture radar, or InSAR, showed that drainage is the primary driver of the sinking on all the peatlands, regardless of usage.
Before the study, subsidence was primarily tracked by elevation changes using measuring poles anchored in clay and only monitored on plantations. InSAR uses microwave pulses sent from satellites at regular intervals. The data, which is not affected by day or night, clouds or vegetation, can show centimeter- to millimeter-scale changes to land elevation.
“In our work, we utilized a novel method to characterize elevation changes across all disturbed peatlands of Southeast Asia to shed light on variables that control degradation rates and to quantify the role of peat degradation in climate change,” Chaussard said.
Such data, she added, should be part of climate modeling and could help efforts focused on biodiversity and ecosystem preservation or restoration.
“Satellite data can help us make informed decisions about environmental challenges faced in the short and long term and do so across disciplines,” she said. “This type of data could help us understand at what rate 20,000 years of accumulated peat carbon will be released to the atmosphere and on what time scale the land will become permanently flooded.”
The research was inspired by a conversation Chaussard had at an American Geophysical Union meeting with the study’s lead author, Alison M. Hoyt, then a doctoral student at the Massachusetts Institute of Technology, who asked if InSAR could work on peatlands. Hoyt is now a postdoctoral researcher at the Max Planck Institute for Biochemistry in Germany.
The study was pursued with funding secured by Hoyt’s doctoral adviser, Charles F. Harvey, from the National Science Foundation and MIT sources. Sandra Seppalainen, also an MIT doctoral student, was a co-author.
Chaussard joined the UO in spring 2019 as a member of the Oregon Center for Volcanology. She heads the Tectonic, Geohazards & Environmental Remote sensing Lab, which studies the sustainability of natural resources and hazards posed by geological processes. One of Chaussard’s graduate students is using InSAR to detect volcanic changes at Mount St. Helens, while another is tracking groundwater use in California’s Central Valley.
The satellite data is fed into UO’s Talapas supercomputer, part of a cluster of high-speed computational tools available through Research Advanced Computing Services.
“The UO and Talapas provided me with critical resources to process the InSAR data presented in this study,” Chaussard said. “My lab and I are working to develop a state-of-the-art InSAR processing system hosted on Talapas, which will hopefully soon allow us to do similar surveys on a much greater scale.”
—By Jim Barlow, University Communications