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Great perils of the Great Lakes

Invasive species, sinking water levels, and pollution are worrisome trends. But there’s also grandeur to be seen aboard a bulk freighter.

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“The US Army Corps of Engineers estimate they have a backlog of 17 million cubic yards of sediment in virtually every US port on the Great Lakes,” says Mr. Neksavil. “That would cost $230 million to dredge. The Harbor Maintenance Trust Fund is funded by a tax on cargoes, and currently has a surplus of $4.8 billion, which I think the government is using to balance its books.”

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Drinking-water safety an issue

The Canadian Leader slows at Am­­bas­­sador Bridge, on the Detroit River between Lake Erie and Lake St. Clair, long enough to pick up mail for the crew. Tundra swans and snow geese laze on the sparkling water.

Detroit draws its drinking water from the river, and the concentration of ships, steel mills, and car plants here reminds one how dependent Great Lakes communities are on freshwater resources.

“Drinking water from the Great Lakes is the envy of the world,” Davis says.

But a series of scientific reports has raised concerns about drinking water in Detroit and other communities. Trace amounts of pharmaceuticals flushed down toilets have found their way into river water. Byproducts of chlorine treatment and disinfection, coliform bacteria, and lead also pose health risks. Canadian petrochemical plants at Sarnia on the St. Clair River are also a concern.

Sewage overflows are a major problem. “During heavy rainstorms,” Davis says, “it’s easy for treatment plants to risk being overwhelmed. There are two things we can do to help: conserve water, so that we’re not using as much, and use ‘green infrastructure,’ like rooftop gardens, to cut the amount of stormwater that needs to be treated.”

On to Thunder Bay, Ontario

Under cover of night, the Canadian Leader transits the Soo lock on the St. Mary’s River between Michigan and Ontario, passing a huge windfarm on the Canadian side. Then it’s 18 hours of steaming out of sight of land, across glittering Lake Superior, before docking at a grain elevator in Thunder Bay to pick up a 28,000-ton load of durum wheat.

Lake Superior’s temperature is rising, says Jay Austin, an oceanographer at the Large Lakes Observatory of the University of Minnesota at Duluth. “Temperature is the most important environmental variable” in a lake, he says. It determines “the chemical reaction rates, the metabolism rates of fish, phytoplankton, and zooplankton, and the spawning rates of fish.”

Mr. Austin and his colleague Steve Colman are deploying an array of moorings at different depths in Lake Superior, from just below the surface to some 1,300 feet down, just above the lake bottom. “Surface water in Lake Superior is warming faster than the air temperature,” he says. “Lakes Michigan and Huron also seem to be experiencing the accelerated warming phenomenon, although not Lake Erie.”

Less ice cover in winter means more evaporation, which in turn lowers water levels, stressing ecosystems. Austin says change on this scale is hard to ima­gine, much less control. The warming of the Great Lakes is its latest challenge, he says – perhaps its most serious one.