Air Date: Week of November 19, 1999
With the help of some high-tech satellite imaging that color-codes soil types, scientists have recently discovered one source of some of the excess nutrients choking Lake Victoria, Africa’s largest lake. Pedro Sanchez, director-general of the Kenya-based International Center for Research in Agroforest, discusses this discovery with host Steve Curwood.
CURWOOD: From space, Lake Victoria appears to be a giant jewel of Africa, a glittering sapphire the size of Ireland set in Kenya, Tanzania, and Uganda. The lake is an important trade route and source of food and livelihood. And like so many other bodies of water today, Lake Victoria is in trouble. Excess nutrients are feeding toxic algae blooms. Fish are dying off. And a carpet of water hyacinths is spreading across the lake, blocking boat traffic. Small farms around the lake have often been cited as the source for the nutrient pollution, but now new research shows that farmers might be taking too much of the blame. The scientists studying soil erosion at Kenya's International Center for Research and Agroforestry were reviewing satellite photos that color-code soil types. Dr. Pedro Sanchez, the center's Director General, says they were startled by what they saw in the water.
SANCHEZ: What I saw, and I'm looking at the picture right now, it's a green shadow against a black background of a lake satellite. And it's quite remarkable; it's very, very clear.
CURWOOD: So, where is that sediment coming from, and what does that mean?
SANCHEZ: We have found out that sediment comes from rivers and two watersheds as far away as about 150 miles from Lake Victoria. And that most of that sediment does not come from farms, but it comes from open land or common property. In other words, areas that are grazed by the village cattle or roadsides and gullies and so on.
CURWOOD: What is the activity, exactly, that leads to all these nutrients going into the water, you say, from common areas? What happens there?
SANCHEZ: Any time a soil is left uncovered, it doesn't have vegetation on top of it. And if you are on any kind of a slope at all, which is the case here, when the rains come there is runoff, and that water literally runs off into the lake carrying the sediments. Normally, it would be stopped by what we call the riparian areas, or the areas around the lake shore or near a river, where there usually are a lot of trees that physically stop the movement of those sediments into the water, and also take advantage of those nutrients and grow very happily.
CURWOOD: What happened to the trees around Lake Victoria?
SANCHEZ: The trees around Lake Victoria are being cut off mainly by small-holder farmers and people who live in the villages, for firewood.
CURWOOD: Well, what's the follow-up here? What's to be done?
SANCHEZ: Okay. What's to be done, now, is to plant trees or grass barriers to stop the sediments from flowing into the rivers, and into Lake Victoria. And the soil and water conservation branch of Kenya is a very active institution that works together with farming communities, and they have told us now that we know where the problem is. We're going to start working with these farmer communities to start growing trees around these common areas, and begin to plant trees close to these riparian areas or these river shore or lake shore areas as well.
CURWOOD: What about the other countries that border on Lake Victoria? I'm thinking of Uganda and Tanzania -- and my geography is weak from there.
SANCHEZ: No, no, you're correct. Actually, most of Lake Victoria belongs to Tanzania and Uganda. Kenya has only about ten percent of it. The problem is the same.
CURWOOD: How applicable is this to other lakes suffering from similar problems?
SANCHEZ: It would be very applicable. This is sort of a generic situation. Our contribution is a small contribution to identifying what the problem is. But our contribution, in terms of having the techniques that identify where sediments come from, through satellites, and in an exact way, is something that is applicable all over the world.
CURWOOD: Well, I want to thank you for taking this time with us today.
SANCHEZ: Thank you, sir. It's a pleasure to be with you.
CURWOOD: Pedro Sanchez is Director General of the Kenya-based International Center for Research in Agroforestry.
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