Warming May Be Drying Up Alaska's Lakes, Photo Study Says

Richard A. Lovett
for National Geographic News
October 17, 2006
Thousands of Alaska's lakes have shrunk and many others have dried up
over the past 50 years, scientists have discovered.

During this period the 49th U.S. state has been experiencing a steady warming trend, which suggests that global climate change will continue to shrink lakes that are critical habitat for millions of migratory waterfowl.

In a new study published last week in the Journal of Geophysical Research - Biogeosciences, researchers from the University of Alaska, Fairbanks, compared modern satellite photos to aerial photos from the 1950s.

The scientists also examined another set of aerial photos taken between 1978 and 1982.

The photos document changes in water levels in nine lake-strewn tracts ranging from the shores of the Arctic Ocean to Talkeetna, a region not far north of Anchorage (Alaska map).

The biggest changes, the study revealed, occurred in interior Alaska's boreal forest, which sprawls across two million square miles (five million square kilometers), says Brian Riordan, lead author of the study.

In this region, Riordan says, lakes have shrunk by 14 to 31 percent.

In the colder reaches of the Arctic and in Talkeetna, which enjoys a cooler maritime climate, there was very little change.

Receding Shores

The team's findings document a trend that has also been observed by Native Americans.

"When I started the project, there was much speculation," Riordan said. "You would have village elders saying, My family's hunted ducks at this pond for 150 years, and in the past 20 years the shore has been receding each year.

"One of the most important results from our study is to put a number to it," Riordan said.

Interior Alaska may be particularly vulnerable to drying lakes.

That's because it's a semi-arid region with extremely cold winters and relatively warm, dry summers, says David Verbyla, one of the study co-authors.

But nobody is sure about the mechanisms that are causing the region's lakes to disappear.

"It's probably a combination of factors," Verbyla says. "One is that the permafrost [in this region] is thin and discontinuous."

(Related news: "Thawing Permafrost Could Supercharge Warming, Study Says" [June 15, 2006].)

As global warming makes that permafrost even thinner, he said, "you could basically have leaks through [it]" and lake water would sink far below ground.

Another possibility is that warmer, longer summers are triggering more evaporation, he says.

Or climate warming could be accelerating the rate at which marsh plants such as cattails, bulrushes, and sedges invade ponds and convert them to meadows.

Increased forest fires could also play a role, Verbyla says.

By burning off the layer of twigs, pine needles, and other organic matter on top of the soil, fires reduce the soil's ability to insulate the underlying permafrost from summer thawing.

Up to 25 percent of the acreage in some areas has burned in the past 50 years, Verbyla says.

"Two-thousand four was our biggest fire year ever. … Wildfire is a big deal in the boreal forest."

Hunting Losses

In addition to supporting migratory birds, Alaska's interior ponds provide moose habitat as well as fishing and bird-hunting areas for native villages.

"In a lot of villages, spring duck hunting is a major subsistence activity," Verbyla said.

Riordan adds that some villages also make substantial revenue through guided tours for visiting hunters.

In addition, he notes, Alaska law grants water rights to the native villages.

"What happens when the water they were given is reduced by 30 percent?" he asks. "Are they entitled to more acreage? That's something for the folks down in Juneau [the state capital] to hash out, I'm sure."

But nobody knows exactly how receding lakes will affect birds and other animals.

Diving ducks, for example, may be harmed by a loss of deep water in shrinking ponds, while dabbling ducks might find increased habitat.

"It could be beneficial to some species and detrimental to others," Verbyla said.

Nor are the effects likely to be uniform throughout the region.

"I've seen a lot of fluctuation in water levels over the years," says Mark Bertram, a wildlife biologist who's been with the U.S. Fish and Wildlife Service's Yukon Flats National Wildlife Refuge for 13 years.

"There are obviously wetlands that are actively drying up, but I've also observed quite a few water bodies that are flooded that weren't flooded 13 years ago."

But Bertram agrees with the "general consensus" that, overall, interior Alaska is in a drying trend.

Research soon to be conducted at Yukon Flats, he adds, will follow up on Riordan's study in an effort to understand exactly what is happening to the region's ponds.

"Our biggest concern, at least from the Yukon Flats perspective, is waterfowl," he said.

"We have very high densities of breeding waterfowl here, so if we have changes that are going to affect the wetlands, it's going to affect the waterfowl."

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