Eroded, bright-red soils in Betsiboka Estuary, Madagascar. (Photo courtesy of NASA/JSC)
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EROSION AND ITS EFFECTS
The loss of trees, which anchor the soil with their roots, causes widespread erosion throughout the tropics. Only
a minority of areas have good soils, which after clearing are quickly washed away by the heavy rains. Thus crop
yields decline and the people must spend income to import foreign fertilizers or clear additional forest. Costa
Rica loses about 860 million tons of valuable topsoil every year, while the Great Red Island, Madagascar, loses
so much soil to erosion (400 tons/ha) that its rivers run blood-red, staining the surrounding Indian Ocean. Astronauts
have remarked that it looks like Madagascar is bleeding to death, an apt description of a country with grave environmental
degradation and an ever-declining agricultural economy that depends on its soils. The rate of increase for soil
loss after forest clearing is astonishing; a study in Ivory Coast (Cote d'Ivoire) found that forested slope areas lost 0.03 tons
of soil per year per hectare; cultivated slopes annually lost 90 tons per hectare, while bare slopes lost 138 tons
per hectare.
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Plane view of deforestation-induced erosion in Madagascar
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After heavy tropical rains fall on cleared forest lands, the run-off carries soil into local creeks and rivers.
The rivers carry the eroded soils downstream, causing significant problems. Hydroelectric projects and irrigation
infrastructure lose productivity from siltation, while industrial installations suspend operations due to lack
of water. Siltation also raises river beds, increasing the severity of floods, and creates shoals and sandbars
that make river navigation far more troublesome. The increased sediment load of rivers smothers fish eggs, causing
lower hatch rates. As the suspended particles reach the ocean, the water becomes cloudy, causing regional declines in coral
reefs, and affecting coastal fisheries. The loss of coral reefs worldwide, often labeled the rainforests of the sea, is especially
distressing to scientists because of their tremendous diversity and the important services they provide. Coastal
fisheries are affected not just by the loss of coral reefs and their communities, but by the damage inflicted on
mangrove forests by heavy siltation.
Besides damaging the fisheries industry, deforestation-induced erosion destroys infrastructure of roads and highways
that cross through the forest. The government does not shut down the roads, but must rebuild them repeatedly, using
money that could be used more productively elsewhere.
Erosion is extremely costly for developing countries. Besides the damage to infrastructure, fisheries, and
property, erosion of precious topsoils costs tens of billions of dollars worldwide each year. For example, in the
late 1980s the Indonesian island of Java was losing 770 million metric tons of topsoil every year at an estimated
cost of 1.5 million tons of rice, enough to fulfill the needs of 11.5-15 million people.
ENVIRONMENTAL REFUGEES
Environmental deterioration can leave people as "environmental refugees"—people who are displaced due to environmental degradation. The United Nations says that as many as 50 million people could be considered environmental refugees by 2010 due to deforestation, sea-level rise, expanding deserts, and catastrophic weather events. Red Cross research shows more people are now displaced by environmental disasters than by war.
Review questions:
- Why do rainforests help prevent erosion?
- Why is erosion a problem?
- What are environmental refugees?
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Continued: Species Loss, Extinction and Disease
This article was written by Rhett A. Butler [bibliographic citation for this page] and was last updated on the most recent date listed in the column on the right side.
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WEEKLY NEWSLETTER
INTERACT
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Recent news
Panama canal drives forest conservation, offers insight on value of ecosystems
(09/26/2011) As demonstrated by growing enthusiasm for conserving forests and the rise of the Reducing Emissions from Deforestation and Degradation (REDD+) program, the public is increasingly aware of the role forests play in delivering ecosystems services — like clean air and water — that benefit mankind. Yet, science still lags conventional wisdom — researchers have yet to fully quantify much of what healthy forests provide. Bridging this gap is key to unlocking the full value of protecting and restoring tropical forests. The ambitious Agua Salud Project in Panama is attempting to do just that.
Reforestation program in China preventing future disasters
(05/13/2011) China's response to large-scale erosion with reforestation is paying off according to a study in the Proceedings of the National Academy of Science (PNAS). The 10-year program, known as Sloping Land Conversion Program (SLCP), is working to turn some 37 million acres back into forest or grasslands after farming on steep slopes in the Yangtze and Yellow River basins had made them perilously susceptible to erosion and flooding.
What does Nature give us? A special Earth Day article
(04/22/2011) There is no question that Earth has been a giving planet. Everything humans have needed to survive, and thrive, was provided by the natural world around us: food, water, medicine, materials for shelter, and even natural cycles such as climate and nutrients. Scientists have come to term such gifts 'ecosystem services', however the recognition of such services goes back thousands of years, and perhaps even farther if one accepts the caves paintings at Lascaux as evidence. Yet we have so disconnected ourselves from the natural world that it is easy—and often convenient—to forget that nature remains as giving as ever, even as it vanishes bit-by-bit. The rise of technology and industry may have distanced us superficially from nature, but it has not changed our reliance on the natural world: most of what we use and consume on a daily basis remains the product of multitudes of interactions within nature, and many of those interactions are imperiled. Beyond such physical goods, the natural world provides less tangible, but just as important, gifts in terms of beauty, art, and spirituality.
Climate change doubles coastal erosion in Alaska over 5-year period
(02/18/2009) Coastal erosion along a 64-kilometer (40-mile) stretch of Alaska's Beaufort Sea doubled between 2002 and 2007, report researchers, who link the development to "declining sea ice extent, increasing summertime sea-surface temperature, rising sea level, and increases in storm power and corresponding wave action."
Destruction of wetlands worsens global warming
(07/20/2008) Destruction of wetland ecosystems will generate massive greenhouse gas emissions in coming years, warn experts convening at an international wetlands conference in Brazil.
More news on erosion
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