Beavers are running amok in the Arctic, taking advantage of climate change and likely exacerbating its impact.
Studies show they are now able to move into many tundra regions where they’ve never been seen before, and once there are building dams and creating new water bodies.
This is changing the landscape and could accelerate the thawing of the permafrost soils, releasing massive quantities of greenhouse gases, according to research by a US-German team reported in the journal Environmental Research Letters.
Two years ago, a team from the University of Alaska (UA) and Germany’s Alfred Wegener Institute (AWI) calculated that North American beavers living in an 18,000-square-kilometre section of northwest Alaska had created 56 new lakes in just five years.
In the new study, they and colleagues from the University of Minnesota used satellite data and extended time series to track beaver activity in two other regions in Alaska – and were surprised by what they found.
In a 100-square-kilometre area near the town of Kotzebue there were two dams in 2002 and 98 by 2019, with more than five new dams being constructed per year. The same trend emerged in a larger survey area covering the entire northern Baldwin Peninsula.
“We’re seeing exponential growth there,” says AWI’s Ingmar Nitze. “The number of these structures doubles roughly every four years.”
This has already affected the water balance, the researchers say. Beavers appear to work in those parts of the landscape that they can most easily flood. Sometimes they dam small streams, and sometimes the outlets of existing lakes, which expand as a result.
“The animals have intuitively found that damming the outlet drainage channels at the sites of former lakes is an efficient way to create habitat,” says UA’s Benjamin Jones, the study’s lead author. “So a new lake is formed which degrades ice-rich permafrost in the basin, adding to the effect of increasing the depth of the engineered water body.”
Over the 17-year study period the overall water area in the Kotzebue region grew by 8.3%, and roughly two-thirds of that growth was due to the beavers, the researchers believe. They also suspect there have been similar construction booms in other regions of the Arctic.
“The growth in Canada, for example, is most likely even more extreme,” says Nitze. “And each additional lake thaws the permafrost below it and on its banks.
“Granted, the frozen soil could theoretically bounce back after a few years, when the beaver dams break; but whether or not the conditions will be sufficiently cold for that to happen is anyone’s guess.”
cosmosmagazine.com, 1 July 2020
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