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Boreal lake offers preview of warming.

Boreal lake offers preview of warming

While scientists remain uncertain whether the expected global warming has begun, a lake in the boreal forest of Ontario offers a disturbing glimpse of ecological changes that may lurk around the century's corner.

The portentous findings emerge from a unique, long-term project in which researchers have been monitoring conditions within many small lakes in northwestern Ontario over the past 20 years. Because the region has warmed considerably during that time, the project provides an in-depth look at the kinds of changes that could accompany a global greenhouse warming, assert David W. Schindler of the University of Alberta in Edmonton and his colleagues at the Canadian Department of Fisheries and Oceans in Winnipeg, Manitoba. They discuss their observations of one particular lake, known simply as #239, in the Nov. 16 SCIENCE.

"This is going to be an absolutely vital data set for looking at the effects of global warming on aquatic ecosystems in lakes. I don't know of any other region where they have that kind of long-term record," says Eville Gorham, an ecologist and lake expert at the University of Minnesota in Minneapolis.

The Canadian team found that the average air and lake temperatures in this part of Ontario have risen a significant 2[degrees]C since 1970. Snowfall and rainfall have dwindled slightly and evaporation has increased dramatically, causing a general drying of the watershed. In the driest years, large fires have swept through the region. The scientists also note that winter ice on Lake 239 now melts several weeks earlier in the springtime than it did at the beginning of the project.

In shallow northern lakes, the temperature increase already recorded could kill off species of fish and invertebrates that cannot tolerate warm water, the researchers say. These cold-loving species, called glacial relicts, have inhabited the lakes since the retreat of the glacial sheets at the end of the most recent ice age, some 10,000 years ago.

Deeper boreal lakes, such as #239, have long provided a haven for such glacial leftovers because these lakes are stratified with a region of cold water beneath a warmer surface layer. But complex ecological changes in the last 20 years have deepened Lake 239's temperature boundary by several meters, squeezing the habitat of the cold-requiring animals and threatening their survival, Schindler says.

Because of evaporation and precipitation changes, the amount of runoff pouring into Lake 239 declined sharply over the study period, slowing the rate of water replacement. "Whereas that lake flushed itself completely every four to six years at the beginning of our experiment, it's now taking 20 years," Schindler says.

That effect, along with an increase in forest fires, can concentrate chemicals in lakes and deepen the temperature boundary in stratified waters--two shifts that would stress the ecosystem, say the Canadian researchers.

Some scientists, noting that lakes in warmer regions to the south generally harbor more wildlife than boreal lakes, have suggested that global warming will increase the biological productivity of these northern lakes. Schindler challenges that assumption, calling it too simplistic. If certain species go extinct, he and his colleagues say, "it is by no means certain that fisheries of comparable value or ecosystems of comparable diversity would be reestablished quickly."

Major research programs on climate change have largely failed to study the effects on freshwater habitats, they add. "But when you look at what resources are probably going to limit human activity or ecosystems, the first one we're going to come up against is fresh water," Schindler warns.
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Title Annotation:ecological changes affecting a lake in Ontario and global warming
Author:Monastersky, Richard
Publication:Science News
Date:Nov 24, 1990
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