Professors find clue to dead zone in lake

11/10/2009

For decades if not centuries, a portion of Lake Erie's central basin has been so depleted of oxygen that it has not supported life.

Two Bowling Green State University researchers believe they have uncovered cold-weather diatoms, or microscopic pieces, of algae that contribute to the lake's infamous dead zone.

The research that Michael Mc-

Kay and George Bullerjahn have done into Aulacoseira islandica (pronounced All-LE-sa-SY-ruh Eye-LAND-icka) is not likely to solve the dead zone's mystery.

But they said it could explain one of the many factors behind it.

Mr. McKay and Mr. Bullerjahn, both professors of biological sciences, said they first noticed the diatoms of algae in brownish pockets floating under Lake Erie ice in February, 2007, while they were aboard a Canadian Coast Guard icebreaker.

The tiny bits of algae made up 80 to 90 percent of some collected samples, Mr. McKay said.

Unlike microcystis, a toxic, free-floating algae that has blanketed the lake's western basin between Monroe and Sandusky almost annually each summer since 1996, Aulacoseira islandica isn't harmful.

It's just hardy. It thrives in cold water while most other types of algae dissipate.

The diatoms sink to the lake bottom as the water temperature rises in late winter and early spring, Mr. McKay said.

They form a large source of carbon for bacteria to decompose, which consumes oxygen.

"When they sink and die, that's when we have the oxygen depletion occurring," Mr. McKay said.

Mr. Bullerjahn agreed.

"This is a cold adapted algae. It's pretty much gone when spring comes," he said. "It's likely contributing to the dead zone."

Lake Erie's dead zone is known to shift locations from year to year, varying in size and shape. One day, it may be found in the lake's midpoint, northeast of Cleveland. Then, before long, in another locale. It is almost always within the central basin.

Limnologists - scientists who specialize in lake research - have said at least some of it is likely the result of Lake Erie's physical attributes.

The lake's three basins vary greatly in depth, from the shallowness of western Lake Erie to the large drop-off near Buffalo. Consequently, water recirculates differently in each basin.

"The jury's still out on what is causing the dead zone. I'm of the belief there are multiple factors," Mr. McKay said.

Although Aulacoseira islandica is one of many naturally occurring forms of algae, it is like others in that it depends on a steady diet of phosphorus and nitrogen. Both are land-based fertilizers and waste products that trickle into lake tributaries after heavy rain.

The algae may thrive in spite of pollution controls because of how zebra mussels have changed the lake biology. Native forms of algae, most of which the public never sees, are "not as abundant in the past as they have been since zebra mussels invaded," Mr. McKay said.

"The zebra mussels created some conditions in the water chemistry that might have allowed this species [of algae] to emerge as a dominant type," he said.

The professors' research has been funded for at least the next two years.

By better understanding how the lake functions during the winter, scientists will be able to make better predictions about its future. "This helps complete our predictions about carbon functions in the lake," Mr. Bullerjahn said. "If you don't know what the lake's doing on its own, it's hard to target it for protection."

Contact Tom Henry at:

thenry@theblade.com

or 419-724-6079.