Lake Superior has dropped nearly a foot this year to its lowest late-autumn water level in eight decades, a startling decline that is raising worries about shipping, shorelines and fish populations.
The rapid fall of the world's broadest freshwater lake is largely the result of six months of regional drought, authorities say.
For shipping, an economic force in Duluth and Superior, the drop means freighters carrying iron ore, coal and limestone are loading less in order to navigate locks, channels and harbors.
Ken Gerasimos, port captain for Great Lakes Fleet/Key Lakes Inc., which has eight freighters sailing the Great Lakes out of Duluth, said that with less cargo on board, boat operators have to charge more to some customers. "You and I pay for that," he said.
"That coal goes to heat homes," he said. "The iron ore goes into Tonka toys and automobiles."
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On the North Shore, the combination of receding lake water and little runoff has allowed sandbars to form in the mouths of small feeder streams, cutting off trout and salmon from spawning beds and possibly reducing future populations, said Don Schreiner, area fisheries supervisor for the Minnesota DNR.
At the Apostle Islands National Lakeshore, some docks are now sitting so high above the water that they're going to be fitted with extra guards next spring to keep boats from sliding under them. Park officials are also considering dredging some bays ahead of schedule to maintain boat access; dredging might also be needed to help ferries navigate between Bayfield and Madeline Island, said Bayfield Mayor Larry MacDonald.
"We're seeing sandbars we haven't seen in a long time," MacDonald said.
Decline may continue
Fluctuations are normal for the Great Lakes; Lake Superior has varied 4 feet in more than a century of record-keeping, and oscillates 1 foot in a normal year. What has stunned observers this year is that instead of rising through the spring and summer, as is customary, the lake fell from near normal in spring to almost a foot below normal in fall, brushing the November low set in 1925.
The U.S. Army Corps of Engineers predicts it will drop another 3 inches in the next three weeks. Minnesota state climatologist Jim Zandlo, who's been studying the lake as part of ongoing North Shore snow research, says it will drop 5 inches or more by the end of February.
That means levels will continue to hug the monthly record lows set in the winter of 1925-26, in the dry years that preceded the Dust Bowl.
The main cause? The extreme shortage of rainfall across the Lake Superior basin since May, Zandlo said.
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Much of the lake's watershed has been ranked in "extreme" drought, the next-to-worst category, by the National Drought Mitigation Center for much of the last six months. Areas of northern Minnesota have been at or near all-time rainfall lows since mid-May.
While farmers had surprisingly good harvests, that was attributed to moisture in the soil from 2005. And though other effects of the drought may have appeared minimal, the drop of Lake Superior puts an exclamation point on it.
"For it to go down that fast on Superior is a strong indicator that this is a very extreme drought," Zandlo said.
Without rain falling, the lake is more vulnerable to evaporation. Because of its size, the lake rarely takes on significant ice cover, freezing over perhaps once a decade and then for only short periods.
The surface's contact with cold air, which is drier than summer air, causes the lake to lose more water to evaporation in the winter than in the summer. Minnesota's inland lakes will stop losing volume as soon as they freeze, Zandlo notes.
If the drought extends into spring, Lake Superior could drop below its lowest recorded level.
Is it global warming?
Several people interviewed for this article, without being asked, made a connection between the drought's impact on Lake Superior's level and global warming. The drought has been extremely sudden, however, and global warming scholars don't agree on whether climate trends for the Great Lakes region are moving drier or wetter, or to a troublesome alteration between extremes.
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"The jury's out," said Lucinda Johnson, associate director of the Natural Resources Research Institute at the University of Minnesota-Duluth.
Long-term lower levels on Lake Superior, as on any lake, would be a problem for shorelines, where vegetation might change and then be disrupted by a quick rise, and where people might be tempted to build new structures, Johnson said. She and others said that wetlands, like those along the south shore, would lose water, reducing habitat for wildlife and underwater organisms, and eliminating the water-filtration role that wetlands play.
"If this trend continues, that's going to be of great concern," said Bob Krunemaker, superintendent of the Apostle Islands National Lakeshore.
-- Copyright © 2006, Minneapolis Star Tribune/Distributed by McClatchy-Tribune Business
