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Great Lakes Article:

Lake's 'dead zones' perplex scientists, but tiny invader may be partly to blame

Chicago Tribune and The Baltimore Sun
10/21/2002
Lake Erie, once so polluted and putrid that it was irreverently called "the place where fish go to die," is now often cited as a model for ecosystem recovery.

But on the 30th anniversary of the Clean Water Act, legislation inspired in part by Lake Erie's near-death in the 1960s, scientists say parts of the Great Lake are dying once again.

Mysterious dead zones, or areas without oxygen, have returned to about half of the lake's central basin. Yellow perch and prized walleye populations declined in the 1990s. Meanwhile, avian botulism, also present in the 1960s, has killed thousands of water birds, including common loons and ring-billed gulls.

Decades ago, the problem was chemical pollution, primarily phosphorus from sewage, detergent and fertilizer. Today, despite controls, the phosphorus is back and scientists suspect the culprit is biological pollution, due in part to changes wrought by invasive species such as the zebra mussel.

The dead zones in Lake Erie are a bit counterintuitive - they occur because there is too much life. When too many nutrients like phosphorus are in the water, algae grow maniacally. Algae blooms are followed by a die-off, and as the material decays, it consumes oxygen like a forest fire. No fish, plants or insects can live in oxygen-free zones.

Located in depths below 40 feet, the dead zones are ominously spreading east in the middle of the lake from the Lake Erie Islands toward Erie, Pa., during the summer months.

Lake Erie's central basin has been running out of oxygen more rapidly than ever, partly because of its flat geography and average depth of 60 to 80 feet.

The fish that can leave the area do. Everything else eventually suffocates.

The Clean Water Act, which limited phosphates and supplied more than $80 billion to upgrade sewage-treatment plants, largely solved the problem of chemical pollution.

But in the mid-1990s, the U.S. EPA's Great Lakes National Program office discovered that phosphorus levels and dead zones had both increased.

To figure out why, a team of researchers led by Gerry Matisoff, chairman of the department of geological sciences at Case Western Reserve University, and Jan Ciborowski of the University of Windsor began a two-year, $2 million study in June.

Their working theory is that zebra mussels and the related quagga mussels, which have a maddeningly efficient ability to filter debris and extract zooplankton, use phosphorus in a different way from other species.

"We think (invasives) might have interrupted the natural process of carbon and phosphorus cycling (in Lake Erie) and how the ecosystem interacts with their chemistry," said Matisoff, who spent most of the summer on the EPA's research vessel, the Lake Guardian.

Tiny but prolific, zebra mussels quickly can take over a body of water, clogging power-plant intake pipes, stealing food and oxygen from other species and even suffocating native mussels that they attach themselves to and eventually encrust.

In the Mississippi, they have pushed a species of native mussel closer to extinction. In Lake St. Clair on the Michigan-Ontario border, they might be poisoning a kind of duck known to eat them.

Native to the Caspian Sea, zebra mussels were detected in North America in 1988, apparently having made their way over in the ballast tanks of oceangoing freighters. Within a few years, the species had established itself throughout the Great Lakes and the Mississippi River and its tributaries, and now is found in waters from Minnesota to Louisiana.

Zebra mussels have been found in the upper reaches of the Chesapeake Bay watershed, in parts of the Susquehanna River in New York, increasing fears that they could pose a threat to municipal water systems and power facilities in Maryland such as the Conowingo Dam.

Once a colony begins, it can grow rapidly - one female zebra mussel can lay more than 1 million eggs in a single spawning season. Power plants around the world have spent millions of dollars unclogging pipes where zebra mussels have settled.

Unlike native freshwater species, zebra mussels have Velcro-like threads that enable them to attach themselves to seemingly anything hard in a river - rocks, boats, pipes, mussels. This ability has allowed zebra mussels to spread far and wide, hitching barnacle-like onto boats and moving greater distances than they could on their own.

In Lake Erie, as mussels vacuum organic matter out of the water, they expel the phosphorus their food contained and it sinks to the bottom. This helps the algae grow, and the algae drain the oxygen from the deep water. As material decomposes, it consumes oxygen and is not replenished until fall, when temperature changes cause the lake water to mix.

But the lake's variability from year to year is a major problem for scientists trying to understand the processes at play. Round gobies, a newer invasive species, are now eating zebra mussels, and no one is sure what impact that will have. In addition, underreported phosphorus levels and climatic change could be exacerbating the situation.

Phosphorus loads are supposed to remain below 11,000 metric tons per year to keep Lake Erie healthy, but scientists, thinking Lake Erie was rebounding, relaxed their monitoring efforts in the 1990s as funding dwindled.

David Dolan, a professor of natural and applied sciences at the University of Wisconsin Green Bay, determined that phosphorus levels spiked in 1997 at 17,000 metric tons but are now below the target level.

The phosphorus increases are probably related to the amount of rainfall the basin receives and how much fertilizer makes its way from sewers and farms to streams and into lakes, said Dolan, an environmental statistics expert.

Climate change might be another factor. When the lake was recovering, water levels were rising, but since 1997 the water level has dropped by 3 to 4 feet, reducing the oxygen reservoir, said Jeffrey Reutter, director of the Ohio Sea Grant Program. With less water, it's more difficult to keep the phosphorus level down.

Should Lake Erie grow worse, the effects on the region and its billion-dollar fishery could be huge.

The lake also supplies drinking water to 11 million people. When blooms of algae die and sink to the bottom, they release chemicals that smell foul, taste musty and can be detected in tap water.

"We know Cleveland is the poster child of what goes wrong when you don't pay attention to the lakes and rivers," Mayor Jane Campbell told Great Lakes commissioners at their annual meeting this week, as she called for help with a billion-dollar sewer-improvement project.

"Now we're trying to turn it around to be the poster child for the solution."

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