| Thanks!  贴个背景资料吧 3. SOIL EROSION In the United States 30% is natural erosion, while 70%
 is because of human intervention. Suspended sediment
 from erosion is one of the world’s greatest
 pollutants. Sediment can fill reservoirs and navigable
 waterways, impair wildlife habitats, increase flooding
 and water treatment costs, and deplete valuable
 topsoil. It can also concentrate harmful chemicals and
 bacteria. Among the methods of preventing soil erosion
 are reforestation, maintenance of fallow strips,
 terracing, underdraining, ditching, deep plowing, and
 plowing across slopes rather than up and down.
 
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