Invasive species pose biggest lake challenge

May 22, 2008

By Gitte Laasby Post-Tribune staff writer

There's mixed news for Lake Michigan and its future, according to experts.

The good news is that some of the most dangerous chemicals in the lake are on the decline.

The bad news is that invasive species pose a threat to the lake in the coming years because they can cause harm to native plants and animals and human health. Officials hope sturgeon and lake trout can help solve the problem.

A comparison of 1994-1995 data from the U.S. Environmental Protection Agency with more recent data from Michigan showed that levels of PCBs, polychlorinated biphenyls, have declined, said Gary Kohlhepp with the Michigan Department of Environmental Quality.

Most of the PCBs that still enter the lake come from the air, especially in the Chicago area. PCBs seem to be evaporating out of the lake at a faster pace than it's coming in, he said.

Data and modeling show much of the pollution that enters the lake comes from air deposition, contaminated sediment and tributaries such as the Fox River in Wisconsin and various tributaries in Michigan. Contaminated sediment from the Grand Calumet River also contributes to the pollution, but on a smaller scale.

Mercury levels still exceed EPA guidelines in most trout and salmon. Most of it comes from air pollution, but some comes from solids in the water that settle. The challenge is that many of the pollutants keep cycling through the ecosystem and never completely disappear, Kohlhepp said.

"Once a contaminant is there, it tends to stay there," he said.

Officials said invasive species, such as quagga mussels and zebra mussels and Asian carp, may pose the biggest challenge to the lake. The mussels enter the lake through ballast water and boating. They help filter the water, but also provide nutrients with their fecal matter, which contributes to algae growth, and they compete with fish for other food.

The spread of invasive species is hard to control. But sturgeon naturally reproduce in eight Lake Michigan tributaries, and are now being re-introduced into Lake Michigan. That could help control invasive species like mussels, said Judy Beck, a Lake Michigan team manager of the Great Lakes National Program Office under the U.S. Environmental Protection Agency.

"For some reason, they think invasives are tasty, so that might solve a lot of problems," Beck said.

Lake trout, which spawn in the tributaries and parts of Lake Michigan, also eat mussels.

Cleanup of contaminated hotspots are important for sustaining fishery, Beck said. Congress is considering funding for the Great Lakes Legacy Act, which would provide up to $150 million a year to do that.

Efforts to control the spread of Asian carp are also under way.

"What can be done? In the short term, completing the electrical barrier system" to prevent the carp from entering the lake, said Michael Hoff with the U.S. Fish and Wildlife Fisheries.

In the long term, he said, better education and more effective measures are needed.