As the Arctic warms up and the landscape thaws and shifts, scientists have zeroed in on a potentially potent source of greenhouse gases: lakes and other bodies of water.
Thawing permafrost and increasing plant growth are both consequences of rising temperatures in the chilly Arctic—and both are full of carbon-rich organic materials. Researchers have suggested that more and more of this organic carbon may be winding up in the Arctic lakes that dot the landscape.
And these lakes may be spewing large quantities of that carbon back out into the atmosphere.
“This has been a really active area of research for lake scientists, or limnologists—and they’ve kind of come to the conclusion that lakes and rivers and streams and kind of aquatic ecosystems in land do actually emit a lot of greenhouse gases to the atmosphere,” said Matthew Bogard, a postdoctoral researcher at the University of Washington. “And it’s like a piece of the global carbon cycle that had been missing or not considered until maybe a decade ago.”
Much of the recent research on lake carbon has focused on far-north regions in Siberia and Alaska, where lakes are closely connected with large tracts of thawing permafrost. As a result, it’s not necessarily safe to say that Arctic lakes across the board are all big greenhouse gas emitters, Bogard pointed out.
And now, new research suggests that lakes across significant swaths of the Arctic landscape may be emitting much less carbon dioxide than previously suspected.
A survey of lakes across the Yukon River Basin in Alaska found that “many of these lakes are kind of hydrologically isolated from the landscape,” said Bogard, who led the research. In other words, almost all of the carbon measured in the lakes originated from inside the lakes themselves.
“Because this landscape is very flat and arid, there’s less delivery of material from the land—from the trees and soils—into the lakes, and they basically have less fuel to produce greenhouse gas emissions,” Bogard said.
This type of landscape makes up about a quarter of all the lake-occupied area in the Arctic, the researchers suggest. But Bogard estimates that only about 1 percent of existing data have been collected from it.
The findings would seem to suggest that overall estimates of lake emissions from across the Arctic should be revised down. But it’s not necessarily that simple, Bogard warned.
For one thing, the research only focused on carbon dioxide and did not measure methane—a greenhouse gas that persists for much shorter periods of time in the atmosphere than carbon dioxide, but has a much stronger warming effect while it lasts. Some research suggests that Arctic lakes may be strong emitters of methane, as well, in some places, and it’s unclear how this kind of landscape may fit in with that idea.
But the study also raises the question: If the organic matter in the plants and the soil on this landscape isn’t ending up in the lakes, where is it going? And is it ending up back in the atmosphere or getting stored someplace else?
It’s also unclear how continued warming in the region may affect the carbon cycling in these lakes. For instance, some scientists have warned that the area could become increasingly prone to wildfires in the coming decades. That would burn up vegetation and allow more dead organic material to fall into the lakes.
These kinds of measurements are important to climate scientists, who are working to figure out how the natural landscape may affect the amount of carbon that goes into or comes out of the atmosphere.
In general, the terrestrial landscape—plants and soils—serves as a massive carbon sink, soaking up perhaps as much as a quarter of all the carbon that goes into the atmosphere, according to some estimates. In this way, it helps serve as a buffer against the climate-warming greenhouse gases that humans emit.
But as landscapes shift, including under the influence of climate change, some places may soak up less carbon or emit more carbon into the atmosphere. That can affect the speed at which scientists expect the climate to warm in the future. Determining where greenhouse gas hot spots exist, and what kinds of factors affect them, can help scientists make better estimates for the global carbon cycle as a whole.
For now, the new research provides a snapshot in time—one that would suggest that the carbon cycle in one part of the Arctic isn’t necessarily representative of the carbon cycle in another part. And determining exactly where carbon is and isn’t ending up will help scientists keep tabs on how the area changes in the future.
“Our point was really to look at landscapes that people aren’t really paying as much attention to,” Bogard said.
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.