DURHAM, N.C. – In the ongoing process of climate change, one of the most important variables is methane flux, the rate at which the greenhouse gas methane (CH4) flows between the Earth’s surface and the atmosphere.
Depending on the types of plants growing in a particular ecosystem and other natural and anthropogenic factors, the ecosystem may be a “methane sink” absorbing more methane from the atmosphere than it emits, or “methane source” emitting more methane than it absorbs.
Determining which category the vast tropical wetlands of South America fall into has been particularly tricky. Not only is the precise extent of wetlands in this region still unknown, but rates of CH4 emission can vary with different types of vegetation.
Now, however, a research team from Duke University’s Nicholas School of the Environment has succeeded in filling in some of the blanks.
The researchers measured methane emissions from a peatland in southeastern Peru and found major differences in the level of methane flux from different zones of vegetation growing there.
Their on-the-ground analysis showed that one type of landscape, dominated by the aguaje palm tree (Mauritia flexuosa), represents a major methane source, emitting roughly three times as much CH4 as a second type, which is mostly open and dominated by sedges.
Heading the research team were 2017 PhD graduate R. Scott Winton and faculty member Curtis J. Richardson, John O. Blackburn Distinguished Professor of Resource Ecology, who is studying the Peruvian site as part of a larger project for the Department of Energy’s Office of Science.
They published their peer-reviewed study Oct. 20 in the journal PLOS ONE.
Researchers have long suspected that the peatlands of the Amazon basin might be a significant source of methane, but have struggled to collect data from the inhospitable landscape, Winton explained. “This is a super-vast, wild place, really difficult for scientists to reach,” he said.
“One shortcut for estimating methane emissions from a large area is to measure gravitational anomalies via satellite,” Winton explained. “The pull of gravity is stronger above areas with quantities of standing water, and flooded areas are methane sources.”
But he noted that this shortcut doesn’t apply in areas like the Amazon basin, where annual floods of up to 35 feet can distort the results of the usual calculations from gravitational signals.
For this reason, the Duke team decided to conduct their investigation of methane fluxes of the Amazon basin on foot.
Winton, who is now a postdoctoral fellow at the Swiss Federal Institute of Technology (ETH) Zurich, said the peatlands of Peru were “a very rich and beautiful place” but contained their share of hazards: steep cliffs and perennial flooding, hordes of stinging insects, plants with razor-sharp spikes, and the occasional anaconda.
“We had budgeted four or five days for our fieldwork, but it took two days of hacking through the bush with machetes just to get to our first site,” he said.
The data they collected may be subject to “geographic bias”—that is, the sites they sampled may eventually turn out not to be representative of the entire Amazon basin—but at least they offer a starting point for further studies, Winton said.
Neil Flanagan, of the Duke University Wetland Center, co-authored the new paper.
Funding for the study came from the Office of Science, Terrestrial Ecosystem Sciences, at the US Department of Energy, and from the Duke University Wetland Center Endowment.
The research was conducted in accordance with the regulations of Peru’s Servicios Forestales and in collaboration with the Amazon Conservation Association. Winton earned a doctoral degree from the Nicholas School in 2016, where Richardson directs the Duke University Wetland Center.
CITATION: “Neotropical peatland methane emissions along a vegetation and biogeochemical gradient,” R. Scott Winton, Neal Flanagan, Curtis J. Richardson, Oct. 20, 2017. https://doi.org/10.1371/journal.pone.0187019
Note: This story was written by Sandra Ackerman, a freelance science writer based in Durham, N.C.