Field Notes

For the Love of Lakes - Nitrogen pollution is reaching even the pristine "big lake."

It's larger than the Czech Republic. It holds ten percent of the planet's fresh water. And, it's right in our back yard. Yet, says Professor Bob Sterner (Ecology, Evolution, and Behavior), "We know more about the large, remote lakes of Africa and Asia than we do about Lake Superior. It's a scandal that we don't know more about it."

Bob Sterner is studying the effects of rising nitrogen levels in Lake Superior.

That's one reason much of his current research focuses on Superior, yet what he's learning isn't such good news. Superior is "still fairly pristine by most measures," says Sterner. "Unlike the lower Great Lakes, there are no large urban centers around it and there is virtually no agriculture to provide chemical runoff." So, he was surprised when his research showed that nitrates are building up in the lake at an inexplicably fast rate. The nitrogen level has increased six-fold in the last 100 years, he says.

If not from farms or factories, how is nitrogen reaching the lake? High temperature combustion in factories and cars releases certain forms of nitrogen that waft through the atmosphere and fall into Superior and other bodies of water when it rains or snows. As a result of human activities, the lake now receives an extra four million kilograms, or eight to ten million pounds, of this form of nitrogen per year.

Sterner stresses that Superior's nitrogen levels are still well below the EPA's limits for safe drinking water. Yet, nitrogen is a major cause of oxygen depletion in other bodies of water. The symptoms include blooms of algae (both toxic and non-toxic), declines in the health of fish and shellfish, loss of sea grass beds and coral reefs in oceans, and ecological changes in food webs. Now, with funding from the National Science Foundation, he's studying the "bio-geo-chemistry" that is taking place in Superior as a result of the increasing nitrogen levels.

Sterner became a limnologist because of his wide-ranging scientific interests. "It allows me a huge amount of freedom to study intriguing things, be they chemical, physical or biological, and I may utilize many different approaches to solving questions."

That perspective led to the publication of his book Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere (Princeton University Press, 2002), coauthored by his long-time colleague from Arizona State University, James Elser. The book, about the balance of chemical elements in ecological interactions, has received high praise in the most prestigious journals such as Nature and Science. "I believe that this is one of the most important books written on ecology in the last 10 years," said a reviewer in Ecology. The book has been adopted as a textbook at some universities and, Sterner jokingly points out that it has reached the status of number 5,000 on Amazon.

Sterner's research and his book offer greater understanding of how human behavior affects the environment and he hopes we'll take some corrective action. "Lake Superior is like the canary in a coal mine, sending a strong signal about the condition of all the world's lakes. It's a treasure and we need to take care of it."

-Terri Peterson Smith