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Great Lakes Article:

Scientists puzzled by Erie's developing dead zone

London Free Press

Thursday, July 18, 2002

 A dead zone, an oxygen-deprived area unable to support life, is developing this summer in Lake Erie and a large-scale scientific effort is underway to find out why.

After rebounding from being declared dead in the 1960s, Lake Erie is again a growing concern as puzzling changes threaten decades of improving water quality.

The U.S. Environmental Protection Agency is investing $500,000 US in a two-year study involving 25 Canadian and American scientists.

Scientists in eight vessels will criss-cross the lake's central basin this summer, collecting thousands of water samples to map the extent of the problem.

Some scientists are declaring it the start of the second environmental war to save Lake Erie.

The first was waged after plant-nurturing pollutants, mainly phosphorus and nitrogen from agricultural runoff and inadequate sew-age treatment, caused huge algae blooms in the 1950s and 1960s.

This plant matter absorbed oxygen from the water as it decayed, creating large lifeless zones.

But a massive cleanup effort that saw hundreds of millions of dollars spent on improved sewage treatment and other pollution controls returned the lake to what appeared to be robust health.

Now, scientists are seeing an increase in anoxia, or lack of oxygen, said Tim Johnson, a Ministry of Natural Resources researcher in Wheatley.

Important fish species such as walleye may be at risk.

Scientists are concerned because the change can't be explained by increases in nutrients or algae, said Johnson, one of the scientists involved in the study.

"So it's puzzling to us what is causing the low oxygen," Johnson said.

One top theory is zebra mussels, invaders introduced in the 1980s, have changed Erie's ecosystem, said Gerald Matisoff of Case Western Reserve University in Cleveland.

"Zebra mussels have . . . taken the algae and organic matter that used to be up in the water column and put it down at the bottom of the lake," said Matisoff, who heads the U.S. side of the study. "When that stuff decomposes during the summer, the bottom water oxygen gets used up."

The changes brought by such invaders make scientists aware the lake's ecosystem is more complex than it seemed 15 years ago, said Murray Charlton of the National Water Research Institute in Burlington.

"There needs to be more effort put into understanding it and whether further changes are needed in managing fisheries and nutrient sources."
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