December marks the end of east Africa’s rainy season, and typically a time of growth and plenty. But for the fish living in east Africa’s Lake Victoria, the rainy season is one more factor which could lead to their extinction. I’m Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.
Lake Victoria is the largest tropical freshwater lake in the world, and a textbook example of what happens when the balance of an ecosystem is altered. Ichthyologist Melanie Stiassny:
“OK. What’s happened in Lake Victoria over the last twenty years is really a microcosm of what we’re seeing happening to fresh water ecosystems throughout the planet. I guess it really comes down to one major factor which is the growth of human populations. As the people living around Lake Victoria have been increasing in numbers throughout the century, we’ve seen increasing fishing pressure on the lake. So more and more fish have been pulled out of the lake. At the same time, to support those people in addition to fish, agriculture has been developed around the lake. And to develop agriculture, you have to cut down trees. So trees have been cut down all around the lake.”
Tree roots help hold soil in place. Take away the trees, and soil is washed right into the lake during the rainy season.
“Soil and agricultural waste that wash into the lake bring nutrients. Now to bring nutrients sounds like a good idea, but in fact it’s a very bad idea. Because you bring nutrients into the lake and what we see are blooms of algae. These algae are able to utilize the nutrients. The algae bloom. The place becomes like a pea soup and all of the oxygen is extracted from the lake by the algae. So the lake literally suffocates.”
We’ll hear more on Lake Victoria in future programs. Pulse of the Planet is presented by the American Museum of Natural History. I’m Jim Metzner.