Back in the 1970's, Lake Erie was considered dead. Too many nutrients were flowing into the lake, causing algae blooms that used up the oxygen. Massive fish kills were one result. Until recently, scientists thought they had the problem licked. But a few years ago, researchers began to realize those conditions were returning. Zebra mussels could be one culprit, but scientists aren't sure. So the U.S. EPA has launched a research ship to gather data that might help to unravel the mystery. The Great Lakes Radio Consortium's Karen Schaefer reports:

For years, scientists believed the water quality of Lake Erie was steadily improving, thanks in large part to a discovery made in the 1970's. That's when researchers discovered that too much of the nutrient phosphorus was making its way into the lake from farm fertilizers, sewage treatment plants, and cleaning agents. The extra nutrients fed toxic blue-green algae blooms that - in summer - often used up all the oxygen in the colder water at the bottom of the lake, creating anoxic - or 'dead' - zones. New limits were set on how much phosphorus could be discharged into Erie and other Great Lakes and millions of dollars were spent to improve wastewater treatment systems. By the 1990's it was clear that efforts to reduce phosphorus loads had been successful and until recently scientists believed that dead zones were a thing of the past. But a few years ago, the U.S. Environmental Protection Agency began to observe that levels of phosphorus were once again rising, even though the same amount of the nutrient was entering the lake.

"And then in 1995, there was a big bloom of toxic blue-green algae again. The increased phosphorus in the lake was a surprise and it corresponds to the bloom of the blue-green algae."

Dave Culver is a biologist with Ohio State University who's been studying Lake Erie since 1977. He says last summer a new dead zone appeared in the lake's central basin. In looking for the cause of the unexpected changes, Culver and other researchers are turning their suspicions to Lake Erie's most recent immigrant - the zebra mussel.

"One of the possibilities is that zebra mussels are processing organic matter and instead of allowing the phosphorus to settle out in the sediments, they squirt it out their excurrent siphon up into the water column where it can then used over and over and over again."

Zebra mussels invaded the Great Lakes in the late 1980's and spread rapidly. But Culver believes zebra mussels may be just one of many possible sources for the recent changes. He says it could be anything from farm run-off to political policies.

"The questions is, given that we observe an increase, what are the relative roles of external loading, internal recycling by zebra mussels, changing water levels, global warming, a Republican governor... I don't know what all these things are."

This summer Culver and some 30 other scientists from the U.S. and Canada will be working to gather new data they hope will help solve the mystery. It's one of the biggest research investigations the U.S. EPA has launched in the Great Lakes. The agency has brought in its research ship, the 180-foot Lake Guardian. It's equipped as a floating laboratory and scientists will work and live on board, gathering samples of water, plankton and other material from the lake's Central Basin. On the back deck of the ship one crew is working with Niagra University biologist Bill Edwards to program a probe that will measure minute changes in water temperature.

"That'll give us all kinds of information about what the transport of things like the phosphorus and the oxygen and those things that the EPA is very concerned about."

What researchers find out this summer could have implications far beyond Lake Erie. Zebra mussels are now well-established throughout the Great Lakes. They're also been found in the Mississippi and, most recently, in the Tennessee River. Meredith Carr is a graduate student in engineering studying fluid mechanics at the University of Illinois.

"One of the rivers we're studying is the Illinois River of Lake Michigan, which is another one of the Great Lakes. It serves as a source to allow zebra mussel larva into the river, so understanding better what happens in the lake, we can understand better what happens in the river."

But finding out what's happening in Lake Erie might not solve the problem. If zebra mussels are the chief culprit, it might be difficult, even impossible, to reduce manmade sources of phosphorus enough to restore a healthy lake.

For the Great Lakes Radio Consortium, I'm Karen Schaefer.

© 2002 Great Lakes Radio Consortium