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, despite efforts to reduce nutrient pollution. Zebra mussels could be one culprit, but scientists aren't sure. So the U.S. EPA has launched its research ship, the Lake Guardian, on a summer-long project to gather data that may help to unravel the mystery. 90.3 WCPN's Karen Schaefer reports.
Karen Schaefer: 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 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 waste water 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.
Dave Culver: And then in 1995, there was a big bloom of toxic blue-green algae again. The increased phosphorus in the lake was surprise and it corresponds to the bloom of the blue-green algae.
KS: 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.
DC: 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.
KS: 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.
DC: 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.
KS: 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. In its biggest research investigation since the 1970's the U.S. EPA is putting more than half-a-million dollars into the project. It's also donating the use of 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. Today a class of graduate students and local teachers is sailing with scientists on a shakedown cruise to get ready for the season of sampling. The ship has cruised to a sampling station just south of West Sister Island. U.S. EPA researcher Dave Rockwell is helping a crew of two gather its first water samples.
Dave Rockwell: This is going to be a drill just to learn how to go through the procedures. There's going to be about two students to each operation and I've volunteered to work with the rosette sampling. And then they're going to be doing chemistry in the lab after collecting all these samples. So there's some pretty busy operations. It's going to take about two hoours to go through this procedure at the first station.
KS: On the back deck of the ship two more crews are preparing other sampling equipment. A winch operator lowers a long, fine-mesh net into the water to gather plankton. A second crew is working with Niagra University biologist Bill Edwards to program a probe that will measure minute changes in water temperature.
Bill Edwards: Temperature-gradient micro-structure profiler, which basically uses little minute variations in temperature in the water column to measure how much turbulence has gone on in the last few minutes. And so we're measuring what the rate of mixing is. 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.
KS: 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.
Meredith Carr: One of the rivers we're studying is the Illlinois 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.
KS: But finding out what's happening in Lake Erie may not solve the problem. If zebra mussels are the chief culprit, it may be difficult, even impossible, to reduce manmade sources of phosphorus enough to recapture the balance that's needed for a healthy lake. And it will be at least next March before these researchers can analyze their data and present their preliminary findings. On the Lake Guardian, I'm Karen Schaefer, 90.3 WCPN News.