Garbage Soil Helps Trees Grow in the Desert

Egypt's Lake Nasser is the world's largest man-made lake. The lake's sediment can be used to reforest areas of desert.
Egypt’s Lake Nasser is the world’s largest man-made lake. The lake’s sediment can be used to reforest areas of desert. Photo: A. Vergani/De Agostini/Getty Images

According to the U.N., about 12 million hectares of land are lost to desertification each year, an area a little smaller than New York State. Desertification has many causes, but it’s usually used to describe a relatively dry area that becomes drier and drier, losing water, arable land, and plant and animal life. Fighting desertification has become a global cause — the U.N. has its own convention specifically to address it — with thousands of people taking up the cause. One NGO has a novel approach: just use garbage dirt.

Serbian-born Vesela Tanaskovic got her Ph.D. in geoengineering from the Technical University of Vienna. Her focus during that time was on desertification, and a process she came up with there became the basis of Afforest4Future, a nongovernmental organization that’s tackling desertification all over the world.

To explain what Afforest4Future does, we have to first look at man-made lakes. Throughout the world, but especially in drier areas, man-made lakes support whole populations, sometimes the vast majority of the population in a region. “Wherever you have deserts and people, in North Africa or Central Asia or wherever, there are man-made lakes because this is how we survive,” says Tanaskovic. Those lakes are often made by damming rivers. All very ordinary stuff.

The problem lies with the way those lakes are maintained. All rivers contain large amounts of sediment; they pick it up along their routes. Ordinarily, that’s not a problem because the velocity of the river, its carrying power, just carts that sediment along, maybe dropping it into a delta or the ocean eventually. But when you dam up a river, its velocity slows down or stops, and that sediment drifts to the bottom. There’s a huge industry in dredging, hauling up sediment (or other stuff, but often sediment) from the bottoms of lakes to keep them working properly. If that sediment isn’t removed, the capacity of the lake slowly shrinks as the bottom literally rises upward. They can lose 20 percent or more of their capacity, or even overflow.

But in the world’s developing countries, many of which are in quickly desertifying areas, it can be expensive to regularly dredge. Dredging can be seen as a low-priority expense, compared with the vast infrastructure needs of countries in, say, Central Asia or around the Sahara. So these countries sometimes don’t bother. It’s estimated that 68 dams fail in China each year.

Dredging might be a pain, but that sediment is far from useless. This is good, virtuous silt, cleansed by a river and containing excellent quantities of minerals and nutrients. “The moment you take it out, it’s viable topsoil,” says Tanaskovic. So that’s exactly what Afforest4Future does. It uses existing dredging companies to haul out the lake sediment and process it only minimally; there’s no need, says Tanaskovic, to treat it or add anything to it. The processing is simply to remove any larger objects that might clog pipelines, which are sometimes used to transport the sediment.

That sediment can then be spread over land. A depth of five centimeters, for example, is enough to enable people to plant all kinds of local forestry crops, like moringa, a drought-tolerant plant native to South Asia and East Africa that is often touted as a superfood. Plenty of other plants and crops can thrive in this lake-garbage topsoil: legumes, some native cereal grains, date palms, or clover, which replenishes nitrogen back into the soil and is also a beloved food by grazing animals.

This is potentially a solution with much broader possibilities than it sounds; there are millions of these lakes, some of which are enormous. Lake Nasser, in Egypt, is one of the largest man-made lakes in the world, at over 2,000 square miles. Tanaskovic says it contains about 7 billion tons of silt, which if you removed and covered to a depth of five centimeters would cover an area about the size of Latvia. The entire country of Latvia.

This topsoil isn’t just useful for agriculture; soil as a sink for carbon sequestration is tremendously promising. Soil, when treated the right way with nutrient-injecting plants like clover or legumes, can store vast amounts of carbon dioxide, keeping it out of the atmosphere, where it contributes to climate change. The silt from that one Egyptian lake, says Tanaskovic, would store about 1.2 billion tons of carbon — about the same amount emitted by the whole nation of Russia in a year.

Afforest4Future works with the U.N. and various governments — it’s working on a pilot program in Dubai right now — to implement its technology, which includes machine learning to adapt to changing conditions in newly greened deserts. It makes money, Tanaskovic says, but as an NGO, it filters that money back into the business to expand. And there’s no shortage of lakes to dredge, or deserts to green.

‘Garbage Soil’ Can Help Trees Grow in the Desert