Soil erosion in the Ithala Game Reserve, KwaZulu/Natal, South AfricaSoil erosion is the wearing away of topsoil by the natural forces of water and wind, or through farming activities. It has become one of the most serious environmental problems worldwide. Through the loss of the nutrient-rich upper soil layers, soil erosion reduces agricultural productivity and threatens the survival of whole ecosystems. Sediments—the eroded soil particles carried away by water or wind and deposited elsewhere—may choke rivers, lakes and wetlands over wide areas. Human activities have greatly increased the rate at which erosion is occurring. Intensive agriculture, deforestation, climate change and urban sprawl all have an effect.
Rainfall produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion and gully erosion. In splash erosion, falling raindrops create small craters in the soil from which soil particles are ejected. This can be considerable during high-intensity storms.
If rainfall is greater than the rate at which the water can percolate (seep down) into the soil, run-off occurs. Loosened soil particles are carried by the surface water down the slope. This is known as sheet erosion.
Rills and gullies
Each year, about 75 billion tons of soil is eroded from the land. Human activities are responsible for most of this. Scientists estimate that erosion is occurring at up to 40 times faster than it would do so naturally.
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