For Great Lakes' Sakes

Tanganyika

International collaboration helps the world’s largest sources of freshwater face the challenge of human-induced change.

The first time aloft over the Canadian North offers an unforgettable sight: Thousands of lakes filling the raw scars of recent glaciers, shimmering in the slanting subarctic light. It’s an astounding abundance of water.

Yet if you were to add these hundreds of thousands of lakes to hundreds of thousands of other lakes in northern Europe and Asia, and combine them with the millions of miles of streams and rivers in the world (even the Amazon and Nile and Mississippi), and all the glacial meltwaters and every wetland—if you were to add up all that liquid freshwater, it would only be half the amount contained in the world’s 10 largest lakes. 

These great lakes—Baikal in Asia; Superior, Michigan, Huron, Ontario, Great Bear and Great Slave in North America; and Tanganyika, Malawi and Victoria in Africa—contain the vast volume of the freshwater on Earth. And they provide for the needs of millions of people.

“Large lakes of the world are magnets for human population. We’re drawn to the lakes for easy access to freshwater, we’re drawn to them for their aesthetic beauty, we’re drawn to them for their fish, we are drawn to them for their transportation services,” says Tom Johnson, founder of the Large Lakes Observatory at the University of Minnesota Duluth.

Big as they are, these lakes are not immune to harm. Many have already suffered overfishing, the introduction of exotic species, industrial pollution and algae blooms and other signs of nutrient inflow from deforestation, agriculture and sewage disposal. And, of course, climate change. All these influences stand to impair the gifts these large lakes provide.

Fortunately, as human pressures increase, our understanding of large lakes is increasing as well. And lessons learned on one continent can help solve problems on another. Researchers studying large lakes around the world share insights pertinent to management, whether it is mitigating the damage of invasive species in U.S. Great Lakes, protecting a rare freshwater seal from industrial contamination of Lake Baikal, or balancing concerns of biodiversity with the needs of African fishermen.

What’s So Special?

The world’s largest lakes work much like its smallest. The same laws of physics, the same rules of chemistry apply. Sunlight penetrates surface waters, stimulating the growth of rooted plants and free-floating plankton. These are eaten by zooplankton and other tiny herbivores, which are eaten by larger invertebrates and fish. Lakes are warmed by sun, cooled by evaporation. Wind and waves mix their waters and impart currents. Inputs of nutrients increase productivity and turbidity.

From a great lake to a small pond, the processes are remarkably similar, says Sally MacIntyre, a physical limnologist and oceanographer at the University of California, Santa Barbara. “You can use those little lakes as laboratories to understand the big ones.”

As size increases, however, so does time. “Residence time”—the time it takes for inflow and outflow to theoretically replace all water in a basin—can run to four centuries in a huge, deep lake such as Baikal or Tanganyika. An oil spill in Baikal, with no known oil-eating microbes, would linger for decades.

Yet scientists are sometimes surprised. 

“We used to think that in large lakes changes happen more slowly because they were such large systems. We’re finding that that is not always the case,” says Norine Dobiesz, research associate with the LLO. The proliferation of nonnative filter-feeding zebra and quagga mussels in Lake Huron has apparently undermined the food chain, causing a swift crash of exotic alewives and Chinook salmon. “So it’s making people rethink how fast these large lakes can react,” says Dobiesz.

The world’s great lakes have large size in common. But they also have important differences.

Podcast: Global Great Lakes

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Project lead Robert Hecky explains how the Global Great Lakes project aims to improve management of large lakes around the world by improving our ability to acquire, interpret and share data.


Videos: Lake Superior & Climate Change







Scientists at the Large Lakes Observatory in Duluth explore the implications of climate change and other human activities for Lake Superior and the African great lakes.


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