Article published May 27, 2007
Lake Erie's 'dead zone' plays possum, study hints
The term "dead zone," when applied to central Lake Erie in the summertime, always has been sorely misleading but it is even moreso in light of new research about what goes on down there, down deep.
Three Ohio Sea Grant researchers have discovered that a layer of active, abundant microscopic plankton is at work above the oxygen-depleted layer during summer in the central basin. These plant-like organisms, called picoplankton, actually interact with it and contribute oxygen to the surrounding waters.
It all means a new way of thinking about a portion of the lake - the "dead zone," a term which makes sexy headlines or sound-bytes on the 11 o'clock news and horribly misleads public and political opinion about the state of the lake.
Though they are micro-microscopic - 100 of them could fit across the width of a human hair - these small organisms are massive in total. "These picoplankton outweigh everything else in the lake," says George Bullerjahn. That includes all the fish.
Bullerjahn is a biologist at Bowling Green State University, who with his colleague there, Michael McKay, and biologist Steve Wilhelm, of the University of Tennessee, are collaborating on the Sea Grant work.
Before going further into their work, however, form a correct picture of the central basin's oxygen-depleted zone. Sensationalized accounts of it every summer have created an image in the public mind of a great black hole in the middle of Lake Erie that is devoid of life from top to bottom. Wrong, very wrong.The zone actually is a layer of deep water which, because of the geology of the basin, becomes depleted in oxygen most summers. What happens is, the upper water in the basin is heated while the lower water remains cold and dense, with little oxygen. The layer in between, called the thermocline, is the home of the tiny blue-green algae.
The deep low or no-oxygen zone has formed historically, even before man's industrial-grade interferences, which can contribute to the size and extent of the zone. Fish simply swim away from it, much as you would seek fresh air if you were cooped up in a stuffy room.
So, though the oxygen-depleted zone lacks visible life it by no means is lifeless. Because Lake Erie contains three basins that look -if seen from the side geologically - like steps, different water conditions exist in each. The western basin does not form a low-oxygen zone in summer because it is so shallow, and the eastern basin does not because it is so deep. Only in the central basin, which is separated from the other basins by underwater ridges or sills that prevent mixing, are conditions just right.
The researchers make a point that the picoplankton - or picocyanobacteria, a subset of the blue-green algae family - are not new. They have been there pretty much all along. It is just that no one was looking for them. The little stuff, however, plays a big role in chlorophyll and photosynthesis, which is the process that powers the plant food machine that feeds so much life on earth, one way or another.
Bullerjahn previously had done laboratory studies on cyanobacteria and found that lots of species actually may benefit from low or no-oxygen environments. So, he explains, "I didn't go into this thinking that the [central] basin is a dead zone and the lake is going to die.We've identified an abundant amount of biomass that we don't understand, and until we understand how it works we can't make informed predictions about the impacts or contributions of their production to the food chain.
"It is the base of the base of the food chain that leads right up to walleye and yellow perch." Those fishy words alone should get everyone's attention.
Adds McKay: "This particular picoplankton, Synechococcus, comprises upward of 50 percent of the total cholophyll in the Great Lakes and can also be performing up to half the photosynthesis that occurs offshore. It appears to be regulating the oxygen levels in the deep waters of the lake."
In short, thanks to the activity and presence of the large mass of picoplankton, Bullerjahn said, "there may be more nutrient recycling to other organisms going on in the central basin than we previously believed." It's all going on in a part of the lake that was not considered very productive, he added, and "they've been there all along."
In the summer of 2002, Bullerjahn and Wilhelm were collecting water samples in the central basin north of Cleveland en route to making chlorophyll measurements. One sample from about 50 feet down turned their filter red instead of green or brown. The researchers took more, similar samples in 2004 and 2005 before the late-summer set-up of the oxygen-depleted zone. That led to discovering the picoplankton.
Bullerjahn previously had done laboratory studies on cynaobacteria and found that lots of them actually may benefit from low or no-oxygen environments.
He and McKay have done some of their work in winter on a Canadian icebreaker, and among their findings is that the lake "is very photosynthetically active in the winter." Just like the aquatic plants in a farm pond will grow and thrive under an ice blanket.
"Long-term [lake] models now will have to account for that." Bullerjahn said that patchy areas with lots of algae exist in winter having photosynthetic rates comparably high to those of midsummer.
That could mean more food for fish than previously thought, or it also could mean more plant material to decay and fall to the bottom and use up oxygen. So the research, while tantalizing in the way it promises to reform basic thinking about the lake's food web, must go further.
Perhaps, McKay theorizes, that area of the lake cycles back and forth between an oxygen and low/no-oxygen regime. That phenomenon may promote the natural degradation of toxic organic materials that man has dumped into the lake and which may require both oxygen and no-oxygen cycles for breakdown.
In an article in last winter's edition of Twine Line, a Ohio Sea Grant publication, Bullerjahn noted the need for far more detailed study of the lake's picoplankton. "Until 20 years ago, these cyanobacteria hadn't even been documented. When you generally think of blue-green algae, you tend to think of the bad guys, such as poisonous Microcystis. What we've discovered are the good guys who are doing a great deal of photosynthesis in the lake."Potential record fish likely is a hybrid
A potential state record white bass of 4 pounds, 10 ounces, and 22 1/2 inches long, taken a week ago from the Maumee River below Grand Rapids Dam, tentatively has been identified instead as a hybrid of a white bass and a striped bass, or wiper, a few of which have been known in the river.
Mike Wilkerson, a biologist with Ohio Wildlife District 2 at Findlay, examined the fish, taken by angler Tim Spurgeon, of Napoleon, on Friday. He said he is sending the fish to Ohio State University for final confirmation. The record white bass, 4 pounds and 21 inches, was taken in 1983 from a gravel pit near Cincinnati.
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