For Great Lakes' Sakes, continued

Some problems are unique to certain systems. Baikal and the African lakes have few problems with accidentally introduced species because they are not very connected to other lakes (if at all) and don’t support shipping from other lakes and foreign seas. But invading nonnative species have colonized North American Great Lakes, with sometimes disastrous effects. Sea lampreys entered through the Welland Canal in the early 1900s and decimated lake trout populations within years. Zebra and quagga mussels hitchhiked aboard the ballast tanks of ocean-going vessels. The filter feeders have helped clean up the waters, but have also disrupted food webs, leading to skinny, poorly conditioned whitefish, a valuable native species.

Dobiesz says her research has helped develop profiles of lake health based on commonly available metrics. These profiles will guide management and research and provide a good picture of changes in lake ecosystems over time.

Heat Wave

Arkady Kalikhman, a scientist who has kayaked Lake Baikal, says that for centuries the big lake has been an icon of “beauty, purity, grandeur and inaccessibility” to those who live around it.

“To my knowledge there’s no other natural resource in any other country for which an anthem has been written and all people in that country know or recognize that song,” says Marianne Moore, aquatic ecologist at Wellesley College and authority on Baikal. “The lake is a powerful symbol for Russians. It represents for them the unspoiled beauty of the Russian motherland—pristine wilderness.”

The sense of untrammeled nature, however, is belied by data emerging today from a remarkable trove of painstaking field observations gathered by three generations of a Russian family.

Limnologist Mikhail Kozhov directed the Baikal Biological Station at Irkutsk State University when he began sampling water in 1946. Taking a boat in summer and trudging over the ice in winter, he recorded water temperature and clarity and gathered samples from as deep as 2,600 feet. He laboriously identified hundreds of plankton species. Eventually, he was joined by his daughter, Olga Kozhova, and later by granddaughter Lyubov Izmestyeva.

The family’s records became known to non-Russian scientists only recently. “It’s extraordinary,” says Moore. “They sampled so frequently, every 10 to 14 days through all seasons of the year since 1946.”

The Kozhov data show Baikal has warmed, especially in summer. Ice covers the lake fewer days than in years past. And that does not bode well for the big lake. Earlier melting might threaten both endemic diatoms that proliferate under the early spring ice and the freshwater seal, which gives birth and shelters pups in ice caves on the lake. A warming climate is expected to increase melting of permafrost in the watershed, releasing nutrients and increasing eutrophication.

Higher temperatures will cause different problems in Africa’s great lakes. Warmer surface temperatures will intensify stratification. As a result, the oxygenated surface waters will become shallower; the anoxic depths, even deeper. The zone suitable for crucial fisheries will shrink.

It’s fair to say concern over the world’s great lakes won’t drive solutions to climate change. But concern over a changing climate makes other stewardship all the more important. “Climate change is likely to exacerbate some of the other environmental stressors facing that lake,” says Moore. So managers should try to minimize the others, such as reducing industrial pollution or eutrophication.

Razor Thin

Among the challenges that could magnify the threat posed to great lakes threatened by climate change is the growing—and sometimes conflicting—demand for the finite ecosystem services they provide.

Lakes maintain levels by a balance of inflow, evaporation and outflow. In Lake Malawi, the difference is razor thin: 85 percent of the inflow evaporates, leaving 15 percent to exit as the Shire River, tributary to the Zambezi. A little more evaporation, a little less rain, and the outflow ceases, says Johnson. Under such circumstances, he says, “the alkalinity of the lake goes up, the ecosystem changes dramatically because of that change in chemistry.” If climate change creates such alterations, Malawi, with the most diverse fish community on Earth, could lose some of its more than 1,000 species of sunfishlike cichlids.

The Greatest of the Great - By Volume

1) Baikal (Russia) - 23,600 KM3

1) Tanganyika (Burundi, Congo, Tanzania and Zambia) - 19,000 KM3

3) Superior (U.S. and Canada) - 12,100 KM3

4) Malawi (Malawi, Mozambique and Tanzania) - 7,775 KM3

5) Michigan (U.S.) - 4,920 KM3

6) Huron (U.S. and Canada) - 3,540 KM3

7) Victoria (Kenya, Tanzania and Uganda) - 2,760 KM3

8) Great Bear (Canada) - 2,292 KM3

9) Great Slave (Canada) - 2,088 KM3

10) Ontario (U.S. and Canada) - 1,640 KM3


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