Erosion

Erosion is the breaking down and wearing away of any part of Earth's surface by water, wind, ice, or gravity. Here, we will focus mainly on water erosion, as it pertains most closely to our topic.

Types of Erosion

There are two types of erosion: normal and accelerated. Normal erosion occurs as land surfaces are worn away gradually under normal environmental conditions. It helps the soil retain its natural fertility by removing materials no longer useful for nutrients, and because it occurs very slowly over time, it does not result in a net loss of surface soil. Accelerated erosion, on the other hand, exceeds the rate of soil profile maintenance and is thus destructive. It may result from the alterations man has made to vegetative or soil conditions, and it is worse in areas without plant cover. Accelerated erosion occurs as rain beats on compacted soil. Because the soil is compacted, it can absorb less water, and soon excess water accumulates on the surface. This water, or run-off, removes rich surface soil, humus (decayed organic matter), and dissolved minerals. It may also destroy any remaining plant cover.

The degree of normal erosion in a particular area depends on local landscape and climatic conditions. The coastal plain of the southeastern United States, for example, demonstrates a very low rate of normal erosion, while the Grand Canyon demonstrates a high one. Accelerated erosion results almost entirely from human activities, including land cultivation, deforestation, overgrazing, surface mining, and industrial development. In can be worsened, however, by natural causes such as fires or dust storms. Because fires often destroy vegetation, they may trigger accelerated erosion.

Sheet Erosion

Sheet erosion is a specific case of accelerated erosion. It occurs when a layer of soil over an entire area is washed away. The soil is eroded evenly, often leading to the formation of gullies or landslides. Sheet erosion also increases water run-off, the accumulation and subsequent washing away of water on the surface of soil. Soil that contains few plants is especially susceptible to this type of erosion. Because the soil is not protected by plant cover and plant roots, rainfall can easily remove soil particles, humus, and minerals. As this rainfall continues, the soil becomes increasingly compacted, and water accumulates on the surface instead of being absorbed. The fewer air spaces that remain inside the soil, the less water it can absorb. Ultimately, erosion produces a bare expanse of soil that contains few nutrients and as such is unable to sustain plant and animal life.

Effects of Erosion

The effects of erosion on an ecosystem are surprisingly far-reaching. Because erosion destroys plant cover, less photosynthesis occurs, and the ecosystem contains less total energy and biomass. This leads to competition among other species for scarce nutrients, and many organisms are unable to survive. Those that do survive are often forced to make significant adaptations in order to endure in an ecosystem with few plants. Erosion also affects the cycling of matter, as plants enable these cycles to occur efficiently. Without plants, other species have a hard time obtaining nutrients such as carbon, oxygen, and nitrogen, nutrients that are essential for survival.

Erosion Case Studies

The Costa Rican stream valley is eroding as a result of deforestation. With fewer trees, there are fewer roots to hold the soil, and few decaying plants to replenish nutrients. Eventually, this area may resemble a desert.

In Maryland's Chesapeake Bay, wind, rain, and extreme temperature cycles are continually eroding the land. Shown is a picture of a house on an eroded cliff. Residents of the area are planting grass and trees or using netting in the effort to stem this erosion.

Erosion Solutions

Fortunately, many methods of erosion control and prevention exist. One such method is reforestation, or the intentional growth of plants in order to improve the soil and reduce erosion. Added vegetation stabilizes the soil, minimizing erosion. It also enhances the natural beauty of the landscape, and is effective in virtually any location. Finally, reforestation is relatively inexpensive, and it can provide food, nesting sites, and protective cover for animals. On the other hand, however, it is the most fragile form of erosion control, as it does not protect against storms and is sensitive to human intervention.

Breakwaters and beach fills represent two potential solutions to the problem of shoreline erosion. Breakwaters are structures that are placed offshore to deflect strong currents and protect a beach from the energy of incoming waves. They usually consist of a long mound of stone rubble and rubber tires, and they may be fixed or floating in the ocean. Breakwaters protect the shore and promote sedimentation, or accumulation, of sand on the beach. Beach fills, however, provide a more direct approach of reducing shoreline erosion. “Fill,” or sand resembling original beach material, is added to the shore, increasing its width. Beach fills represent an effective short-term solution to shoreline erosion, but refilling soon becomes necessary at regular intervals. The effectiveness of beach fills is highest when they are used in conjunction with breakwaters.

Strip planting can also be used to control erosion. It involves altering rows of regular crops, such as corn, wheat, and cotton, with cover crops, including grass, alfalfa, and clover. Strip planting prevents rain from eroding soil, as cover crops hold soil in place with their extensive roots. While this method is very inexpensive, it leaves less room for cultivated crops and as such may lower a farm's profits. In the long run, however, this sacrifice proves valuable, as soil productivity is maintained instead of being diminished by erosion.

Finally, contouring, or the planting of crops in rows along hills, prevents the formation of gullies by erosion, as the contoured land retains more water than flat terrain.

Thinkquest Team "Fish," March 2005, Disclaimer and copyright information