By Dave Dempsey

            Already challenged by water pollution and invasive species, the Great Lakes and those who care about them face what may be an even more formidable problem – preserving them from water uses and outside forces such as climate change that could affect their levels. These threats have the potential to affect spawning habitat for valuable sportfish species, drain biologically significant wetlands, thwart commercial navigation, alter lakeshore property owners’ land values, and degrade water quality. Adapted to natural fluctuations in water levels, the Lakes are at risk from variations that could go well out of the normal range.           

The most significant threat may be climate change. There is evidence that it is already menacing water levels. Reduced ice cover is believed to cause increased evaporation, and thus lower lake levels. Average ice cover has declined on all Great Lakes since 1973, with a 73% decrease between 1973 and 2002. A more recent analysis covering the period 1973 to 2008 found a continued decline, with three of the four lowest ice cover years occurring on Lakes Superior, Michigan, Huron and Erie between 1998 and 2008.            

Further complicating matters, the Lakes are warming – rapidly, in the case of Lake Superior. The lake’s summer (July-September) surface water temperatures increased about 4.5 degrees F between 1979 and 2006. This is significantly more than observed regional atmospheric warming.            

Warmer temperatures don’t just affect lake levels; they can also change the Great Lakes fishery. Increased temperatures in the water column associated with increases in surface water temperatures can threaten native fish communities most vulnerable to climate-driven invasive species. Changes in temperatures may be lethal to, or cause redistribution of native species. Warmer water temperatures can also move the southernmost range of coldwater fishes such as brook trout and lake trout to the north while promoting the number of warmwater fish species not native to the Great Lakes in southern Great Lakes habitat.           

Warmer lakes can also threaten the health of people who come into contact with water, like swimmers, because of algae blooms. Blooms of cyanobacteria, particularly toxin-producing species, are increasing in the Great Lakes. Summer 2011’s massive algae blooms in Lake Erie were the largest since the 1970s.  

The most significant cyanobacteria bloom species in the Great Lakes, Microcystis aeruginosa, produces a toxin (microcystin) that has both chronic and acute effects. In late July 2011, a large Microcystis bloom in western Lake Erie had toxin concentrations exceeding 1000 ug/l. The World Health Organization recommends levels of microcystin concentration not exceed 1 ug/l for drinking water and 20 ug/l for recreational exposure during swimming, boating, and fishing.           

The exact amount by which water levels will decline as a result of climate change is a guesstimate, even for scientists. The dynamics of Great Lakes levels are not yet precisely understood, so the experts rely on models. Because of regional changes in precipitation caused by climate change, some of the models even forecast increased levels, although that’s not considered likely.           

Whatever the exact impact, industries and individuals will feel the difference as levels fluctuate beyond historical levels. For every inch that lake levels go down, a cargo ship must reduce its load by 99 to 127 tons. The ability of wetlands to capture and naturally filter and clean up nutrients like phosphorus and human and agricultural wastes will be greatly reduced. Higher levels can threaten lakeshore properties, as happened in 1985 when scores of Michigan homes fell into the lakes after erosion by winds and waves.           

Although water withdrawals and uses can also diminish water quantity, there’s some good news. The 2008 Great Lakes Compact, agreed to by the eight Great Lakes states and approved by Congress, calls for water conservation by large industrial and municipal users in addition to tightening restrictions on diversions of water out of the Great Lakes basin. Although implementation has been slow, in part because of government budget problems, states seem to be making some effort to comply with the Compact requirements. Ohio Governor John Kasich vetoed a bill that would have allowed up to 5 million gallons of water a day to be withdrawn from Lake Erie, 2 million gallons a day from rivers, and 300,000 gallons a day without a state permit. Kasich proposed his own legislation reducing the numbers that can be taken without state approval.           

Great Lakes residents have long feared that politically powerful states and regions far from here could ship Great Lakes water hundreds or even thousands of miles away in pipelines and vessels. To forestall that, the Compact limits new diversions to cities and counties that straddle the edges of the Great Lakes watershed, shutting down schemes to transfer water to the parched Southwest. But its exemption for Great Lakes water in small containers, like bottled water, has raised concerns that the water will be captured, exported, and sold for profit far from the Great Lakes, potentially setting up a market for speculators. Since many observers expect water to become “the oil of the 21^st Century,” such a market could lead to large draws on the Great Lakes.           

Perhaps the key to address these risks to the quantity of Great Lakes water is a combination of prudent policies and energized citizens. Climate change is already underway, and there is little individuals can do to hold it off in the short run. But adaptation strategies can soften the effects of climate change, including conserving water and better protecting the most valuable coastal wetlands and restoring or creating new ones.            

The Great Lakes region is doing a pretty good job of keeping water uses from damaging the lakes. But it will have to become smarter and swifter in dealing with new threats in order to preserve the health of habitats, fish and wildlife, and people.  

Information for Dave Dempsey’s book “On the Brink: The Great Lakes in the 21^st Century,” published by Michigan State University, including ordering information, can be found at http://msupress.msu.edu/bookTemplate.php?bookID=2210

[Return to Newsletter Index]