- promote all aspects of large lakes research; and
- communicate research findings through publications and meetings.
On their web page, I searched specifically for information about Lake Superior.
Seasonal changes in Lake Superior’s water level have been thought to be related to changes in evaporation, but until recently, evaporation was only estimated or modeled. A researcher directly measured evaporation from the Stannard Rock light located 24 miles north of Marquette, MI (39 km), which is the farthest offshore of any lighthouse in the U.S. Evaporation measurements were taken continuously for over two years. Surprisingly, during the summertime there was virtually no evaporation; all of the strong summertime solar energy was used to warm the large volume of Lake Superior’s water. In the winter, when solar energy was weak, evaporation was large with the energy supplied from the lake itself. Since evaporation cools the water surface, this promotes ice cover (especially near-shore). Though a better understanding of these physical controls, we will be in a better position to predict evaporation with climate change, and therefore better predict changes in water levels.
Toxins in Lake Superior Lake Trout
Toxaphene is a major contaminant in Lake Superior fish, even though this substitute for DDT was banned as an agricultural insecticide in 1985 in Canada and 1990 in the United States.
Scientists from both countries collaborated to examine how this chemical, which enters the lake mainly from atmospheric deposition, accumulates from lake water and sediments in top predator fish.
Toxaphene is a mix of up to 1,400 possible compounds, making it a challenge to measure. The study, funded by the U.S. Environmental Protection Agency, found that certain components of toxaphene become more and more concentrated as they are passed along the food chain from water to lake trout, magnified 10 million to 5 billion times.
Similar biomagnification occurs for toxaphene in other nearby lakes, such as the remote Siskiwit Lake on Isle Royale, an island in Lake Superior, although absolute levels in the lake trout from Siskwit Lake are about 15 times lower than in Lake Superior. This may be because Lake Superior lake trout rely on forage fish as food, placing them higher up the food chain. Another possible factor is that the chemical may last longer in the cold, deep waters of Lake Superior.
Pollution Level Decrease Improves Eagle Population
In the 1970s, DDT decimated bald eagle reproduction along the shores of Lake Superior. In the 1980s, although conditions improved, DDT and PCBs still depressed these eagles' chances of successfully raising eaglets. But no more.
In the 1990s contaminant levels finally dropped to nearly insignificant amounts. Researchers believe that ecological factors such as food and weather are now more important than contaminants in determining how successful eagles are at reproducing.
Contaminant levels and reproductive rates were studied in eagles along the Wisconsin coast of Lake Superior in the 1990s. They measured concentrations of total PCBs and DDE (a metabolite of DDT) in the blood of nestling eagles, and monitored the number of eagle nests and eaglets produced.
They discovered that the contaminant levels in eaglets were similar to the levels found in other normal, healthy populations. The number of eagle nests along the Lake Superior shore in Wisconsin increased steadily from 15 to 24 per year throughout the study period, and the eagles' reproductive rate averaged 1.0 young produced per pair, which is typical of healthy eagle populations.
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