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Great Lakes Article:

Underwater forest remains in peril
By Gary Wisby
Chicago Sun Times
09/03/03

A cluster of about 50 stumps, rooted on the bottom of Lake Michigan, is all that's left of a grove of trees that was swamped by the rising lake 8,300 years ago.

Now the prehistoric stumps themselves are threatened--by zebra mussels, the pesky little shellfish best known for clogging water intakes.

The striped mollusks attach to the soft wood and have formed a growing colony.

"Eventually the weight is going to potentially break off pieces of the wood," said Michael Chrzastowski, a coastal geologist for the Illinois State Geological Survey.

The stump grove is the only one discovered so far, but many others doubtless lie on the lake bottom along the banks of ancient rivers. Carbon dating of the wood would tell researchers when water levels rose, killing the trees.

"Different elevations and different times the trees died would give us more data points on the history of lake-level change," Chrzastowski said.

The grove is about 15 miles east-southeast of Navy Pier, in 80 feet of water.

Salvage divers using sonar accidentally found the underwater woodland in 1989. They were looking for planes that crashed and sank while being flown by pilots learning how to land on aircraft carriers during World War II.

Trees on the Olson Site, named after lead diver Alan Olson, are oak and ash. Carbon dating showed their age at 8,300 years.

That told researchers when water covered the area again after an absence of some 1,700 years. In the meantime, one could walk the land--and trees could grow--between what is now Chicago and the state of Michigan.

Protecting lake-bottom forest remains from zebra mussels' depredations won't be easy.

First order of business would be to find the stumps before the mussels whittle them down to nothing.

"The problem with that is, this is a needle-in-a-haystack-type thing," Chrzastowski said. "We would need to map all of southern Lake Michigan, and that would be time- and money-intensive."

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