Photo of Lake Michigan waves in Grand Haven on 10/26/10.
MADISON, Wisc. (DETROIT FREE PRESS)-- Facing multiple threats -- from zebra mussels to toxins to light pollution from brightly lit shoreline cities -- Lakes Erie and Ontario are the most threatened of the five Great Lakes, while the depths of Lake Superior remain the most pristine, according to an analysis of 34 stressors to the world's largest supply of fresh water.
• RELATED: Map: Where the Great Lakes are most threatened
The threats, rather than a single problem, underscore the need to approach restoration efforts more strategically, rather than a single threat at a time, the study's authors say.
"It's almost a death-by-a-thousand-cuts syndrome," said Peter McIntyre, a coauthor of the study and a professor at the University of Wisconsin-Madison's Center for Limnology.
Among the biggest threats: Invasive mussels and lamprey that threaten the food chain, climate change that can affect water temperature and water levels, ballast water from ships that may introduce more uninvited species, a buildup of urban areas along the coast that sweeps auto and human waste into the waters during rainfall, and a continual runoff of phosphorous from farmlands.
In contrast, mining and a dwindling ice cover in the winter remain a threat to Lake Superior, said David Allan, the project's lead researcher and a professor of aquatic sciences at the University of Michigan's School of Natural Resources and Environment.
"There are many environmental stressors that affect an ecosystem, and the Great Lakes is a poster child for that," he said.
The study, published Monday in the scientific journal Proceedings of the National Academy of Sciences, charts out the "cumulative stress" on the lakes, which provide 1.5 million jobs and $62 billion in paychecks annually, according to a 2010 study. In addition, there is the fun for swimmers, anglers, boaters and other outdoor enthusiasts.
For three years, a team of 22 scientists from across the U.S. and Canada collected, then layered, data and reports and satellite images -- previously available only piecemeal -- to compile a single map that charts humans' impact on the Great Lakes.
Additionally, 161 of North America's Great Lakes researchers and natural resources managers filled out a lengthy questionnaire that ranked what they felt were the most damaging threats.
"(But) none of the things we addressed had zero impact," said McIntyre, who began working on the study as a postdoctoral fellow at U-M.
Even light pollution -- ranked low in the survey -- can disrupt fish foraging for food sources, fish reproduction and bird migration.
The result of the three-year effort: A multicolored map in which red highlights areas of the lakes facing a multiplicity of problems and blue in which fewer threats exist.
The map offers details as small as just a half-mile long and can be found at www.greatlakesmapping.org.
The work underscores that a restoration effort focusing on a single, high-profile threat -- trying to battle zebra mussels, for example -- may have minimal effect unless other threats are addressed, too.
McIntyre likened the lakes' red zones to a sick patient with multiple organ failure: "It's not going to do a lot of good to have a heart transplant if their kidneys and liver aren't working."
Many of the reddest areas, in fact, hug the shoreline of urban areas, including Detroit -- little surprise given industry and man's physical destruction of the natural shoreline.
But there's another reason that a wide swath of red runs along the southern Lake Erie shoreline beginning near the Pennsylvania-New York border, continues westward through Ohio and curls northerly to the Detroit area: It's agriculture and the runoff of fertilizer.
Those are "some of the heaviest loads of phosphorous in North America," said U-M's Allan.
The map confirms that the more than $1-billion federal Great Lakes Restoration Initiative is correctly targeting the most acutely threatened regions, Allan and McIntyre said.
But the lesser-threatened areas of the Great Lakes -- highlighted on the map as blue -- offer a lesson, too, the authors said. In those areas, less-extensive, less-expensive restoration efforts can have a wide impact given the interconnectedness of the Lakes.
While most resources understandably are aimed at the most acutely threatened areas, "the point is that there are low-hanging fruit at both ends of the spectrum," McIntyre said.
Contact Robin Erb: 313-222-2708 or firstname.lastname@example.org