Erosion:
On the Move

So WHAT About Soil?

Erosion is an important concept for students to learn about because the loss of soil/land affects their lives in many ways:

• loss of productive land to grow food, timber, fiber for clothing.
• runoff into water bodies degrading water quality for fishing and swimming.
• loss of coastal land as habitat and for recreation.
• loss of a future resource.

Soil is formed by the weathering of rocks over long periods of time. Weathering is the mechanical (physical disintegration) and chemical (decomposition) wearing away of rocks by air and water. Soil is a mixture of tiny particles of inorganic minerals and rocks, decaying organic matter, water, air, and living organisms.

The soil profile is composed of different layers called soil horizons. See Figure 1.

The thin layer of soil – ranging up to several feet thick – on the Earth’s surface helps provide the food most living things depend on for their survival, the natural fibers used to make clothes, the paper used for writing and packaging, and the lumber used to build houses and furniture.

While soil is technically a renewable resource, the average rate of erosion throughout the world greatly exceeds the rate at which soil is being formed. Erosion is caused by air and water moving over weathered material. After the material is loosened and moved, it is deposited when the air and water lose their carrying power. For example, when a river slows down as it meets the sea, the sand it carries is deposited near the mouth, becoming part of a layer of sediment. Because of flooding, the Mississippi River has been leveed so it no longer overflows its banks. This also prevents sediment from the river being deposited to replenish soils and build coastal lands. Instead the sediment is being dumped off the continental shelf at the Gulf of Mexico. Forces of air and water that erode soil include flooding, waves, wind, and ice. During the 1930’s wind erosion caused the Dust Bowl in the Great Plains region of the United States. Soil erosion was so extensive that farmers lost their lands and had to relocate. Over 9 million acres of farmland were destroyed and 80 million acres were severely damaged.

Other causes of erosion are human-induced, such as clearing away vegetation to build houses or other structures, farming, and overgrazing. When vegetation is removed, the soil is left exposed to rain and wind. This causes sedimentation runoff, a type of nonpoint source pollution that gets washed into water bodies, clogs them and adds excess nutrients leading to eutrophication (the process by which a body of water becomes either naturally or by pollution rich in dissolved nutrients, such as nitrates and phosphates, causing a deficiency in dissolved oxygen).

• Conservation tillage farming techniques - instead of plowing and leaving the soil exposed, the soil is disturbed as little as possible (ex. the no-till method plants seeds and adds fertilizers and weed killers at the same time with almost no disturbance of the soil).
  
• stream bank restoration – ex. stabilizing the stream slope with terraced banks and revegetating the banks to hold the soil in place.
  
• revegetation of coastal areas – planting marsh grasses on areas of the coast that have been damaged by waves.
  
• Best Management Practices (BMPs) for new residential and commercial developments – using sediment fences, bales of hay or grassed-swales to collect any sediment that would runoff from a construction site into local water bodies.
  
• Local sediment ordinances that developers must follow to eliminate sediment runoff – developers must implement prescribed BMPs such as the ones stated above.
  
• Join the NRCS’s Earth Team, a student volunteer program.

The importance of soil in our everyday lives is not recognized by many people. Because it takes so long to create soil, humans must find ways to conserve the soil that is left. Students can play a role by being “soil-aware” and getting involved in their local areas.