Arctic lake a laboratory for studying climate change's effects on ecosystem

[cedric]

http://www.guardian.co.uk/science/2008/jul/22/scienceofclimatechange.climatechange

Scientist Anne Hershey paddled a small inflatable raft across an arctic lake, pausing in her stroke to consider how the melting permafrost caused a landslide of mud and sediment spilling down the bank into the water.

Since the bank collapsed two years ago, the water has grown cloudy with sediment, providing scientists a natural laboratory for studying how warmer temperatures may play out in ecosystems far and near.

Global air and water temperatures are inching up, causing seas to warm and expand, and polar ice to melt. Alaska is warming more quickly than lower latitudes of the United States, so scientists can observe changes from global warming here first. The average annual temperature in arctic Alaska has increased about 4 degrees Fahrenheit in 50 years, according to the Alaska Climate Research Center.

Hershey, an aquatic ecologist at the University of North Carolina-Greensboro, heads a team of researchers who are studying arctic lakes and how the surrounding landscapes affect what lives in them. Increasingly, a focus of their research is the effects of climate change.

"As time has gone on, it's become more and more important," Hershey said. "The Arctic is very sensitive to climate change. We're experiencing that."

Hershey, 55, has spent parts of nearly every summer at Toolik Field Station in northern Alaska since she was a graduate student at North Carolina State University in the late 1970s.

Toolik - its name is the Eskimo word for "loon," the water bird whose tremulous cries provide a summer evening soundtrack - houses scientists trying to develop a blueprint of the Arctic ecosystem. A hodgepodge of large tents and drab-green laboratory trailers sits beside the research outpost about 150 miles south of the Arctic Ocean.

The surrounding grassy tundra is pocked with thousands of pristine glacial lakes undisturbed by development and beyond the reach of roads. As a result, the lakes are accessible only by foot or aircraft such as a helicopter.

Such unspoiled ecosystems are ideal laboratories for Hershey and other scientists.

"We can really understand basic science because the lakes are not affected by many aspects of human activity," said Hershey, who has studied about 200 lakes in the region.

One of the things researchers might expect to see is that the sediment from the collapsing lake banks could add more organic matter to the lakes. That would affect what grows in them, including algae and the creatures that feed on algae. So far, Hershey said, they haven't observed that, but they're still studying it.

"It could be the lakes are changing as a result of climate change, but not in ways that were expected," she said.

While Hershey collected water samples from different depths of the lake for analysis, graduate student Matt Bostick of Greensboro lowered a heavy steel tube into a different part of the lake to collect cores of sediment.

Bostick, 27, is comparing differences in methane gas levels between undisturbed arctic lakes and lakes where melting permafrost is dumping extra organic matter from decomposed plants.

Methane is a powerful greenhouse gas, more than 20 times as potent at trapping heat in the atmosphere as carbon dioxide. Any methane that is not consumed by microorganisms in the lake would go up in the atmosphere and contribute to climate change.

"The thermokarsts are getting bigger in the lakes," Bostick said, referring to the phenomenon of collapsing banks along rivers and lakes. "This is something I can see. It seems to be such a rapid process."

Hershey said it appears that methane is becoming a more important part of the diet of bacteria and animals that eat bacteria in the lakes, but they're studying how climate change is contributing.

"That's science," Hershey said. "That's what we're doing up here, trying to find answers to these questions."