As we consider our relationship to nature this Earth Day, let's consider humanity's vital need for fresh water. The most valuable resource to humankind exists in extremely concentrated areas. Did you know that about two-thirds of Earth's accessible fresh water lies in just 20 lakes, which, altogether, make up just 0.2 percent of all continental area? These important bodies of water can teach us important lessons about environmental stewardship.

Robert Sterner
Robert Sterner
These glistening planetary jewels, the largest of all lakes, include Baikal in Siberia, the five Laurentian Great Lakes of North America, and the Great Rift Valley Lakes of Africa. They are scattered across the globe from the Arctic to the tropics, from remote locations to densely populated ones, and in regions that are among the world's richest to among the world's poorest.

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People benefit from these huge freshwater resources in countless ways. More than one out of 10 of all fish species count large lakes as home and would disappear without them. Large lakes provide more than 1 million tons of seafood harvest to hungry people around the world per year, much of which occurs great distances from ocean coasts, so is an especially important source of protein. These huge lakes generate billions of dollars of the world's economy from activities such as fisheries, transportation, recreation, and the cooling of power plants.

Visible from space, our freshwater seas are truly immense on our own human scale. Some of these large lakes constitute international boundaries; others define the culture and economy of a region. One cannot see all the way across many of them, and waves are often so high they pose great risk to those attempting to cross.

Yet, in my own professional lifetime, the list of Earth's largest 20 lakes has changed twice. How can such immense features come and go?

One of them, the Aral Sea (the words sea and lake are sometime interchangeable), has dropped completely off the list. Located in an arid region, the Aral Sea's inflowing rivers were diverted beginning in the 1960s for irrigation to increase the production of cotton. This produced a quick economic boom for the former Soviet Union. Sadly, the increased evaporation caused by spraying huge volumes of water on the arid landscape greatly reduced inflow to the lake, which shrunk its area by 90 percent. It eventually decimated an inland fishery that had been feeding people for centuries, if not millennia. What was once one of the largest lakes on Earth today is but a vestige of its former self. Images of Aral Sea fishing boats stranded on a vast desert, a symptom of a rapidly dwindling freshwater resource, are haunting.

Through its near demise, the Aral Sea bears witness to the immensity of human action on Earth and its sometimes dire consequences.

At the same time that the Aral Sea was shrinking its way off the list of Earth's largest lakes, a new lake appeared. It was capped by hundreds of meters of ice and was unexposed to the Earth's atmosphere for millions of years. Today we recognize this new lake as Lake Vostok of Antarctica, the fifth largest lake on Earth by volume. It has found its way onto our list of Earth's largest lakes not by growing but rather by revealing its frozen secrets. Indications of a large sub-ice lake in the Vostok basin go back to about 1950, but it is only since the 1990s that science was up to the challenge of properly mapping it and ascertaining its actual volume. Earth's fifth largest reservoir of liquid fresh water was only recently discovered.

Where the Aral Sea offers sobering lessons, Lake Vostok should give us hope in showing how we are constantly learning new and sometimes unexpected things. We can't count on finding huge new freshwater reservoirs time and again, but if we are still learning such big things about our Earth, what other new discoveries await us? What else will we find to help us live today without jeopardizing our children's future?

While there surely is degradation there also is discovery.

Earth's largest lakes epitomize the yin and the yang of Earth Day. We confront human footprints while at the same time learn more about our planetary support systems so we can manage them better. That is the most important lesson of all.

Earth Day reminds us that while we can and do do harm, our future is in our hands, and the more we know the better.

 

Robert Sterner is director of the Large Lakes Observatory in Duluth (https://scse.d.umn.edu/large-lakes-observatory) and is a biology professor at the University of Minnesota Duluth.