Environmental Science: Soil Conservation

slumping

fast downhill movement of soil

sheet erosion

type of erosion that occurs when large sheets of water flow over the land and carry soil particles away

gully erosion

type of soil erosion that develops when water carves away the soil until deep gullies are formed

rill erosion

type of soil erosion that occurs when water runs over land, carving out small channels as it flows

saltation

type of wind erosion that occurs when particles are blown into the air, travel a short distance, and then fall back to the ground, dislodging other particles as they hit the ground

runoff

water that does not enter the ground or get used by plants, but instead runs over the land's surface

surface creep

when large soil particles bounce around on the ground's surface as a result of wind erosion

suspension

when soil particles are blown into the air by wind and travel long distances

Desertification

Desertification is a condition that develops when an area becomes so damaged by soil erosion and long periods of drought that nothing can grow there. It is characterized as a growing area of desert in a geographical area. One place in the world where this is occurring is in China. China has more than 1 million square miles of desert, but this was not always the case. The deserts in China, such as the Gobi, have been expanding more than 200 square miles per year. The reason they are expanding? You guessed it, desertification. Most of the desertification in China is due to the cutting down of trees and vegetation and the overgrazing of land by cattle. When land is exposed to weathering and vegetation is removed, the water begins to dry up, the soil becomes salty, and the land is no longer able to support life. It has become a desert! In China, the government is making efforts to build what is known as the "Green Wall of China." Massive efforts are underway to replant much of the land that was once destroyed. The hope is that the new vegetation will create a natural barrier to wind and erosion, and the land will once again be able to support plant growth.

Gravity

Finally, soil is also eroded simply by gravity, which is the force that pulls objects on Earth toward the surface. Gravity causes objects to move downhill from areas of high elevation to areas of low elevation. One example of this is slumping, which is the rapid falling of materials downhill. Slumps most often occur when steeply sloped land is saturated with water after heavy rainfalls. Another example is soil creep, which is a slow downhill movement. We cannot observe soil creep in action, but we can see the aftereffects as in this soil creep diagram. Notice the bent trees and leaning poles that result from the soil underneath them slowly drifting downhill. This picture shows you an extreme example of soil slumping. It is hard to imagine that this house once sat on top of the hill and was not covered in six feet of mud, rocks, and dirt!

WHAT CAUSED THE DUST BOWL STORMS?

In 1939, American novelist John Steinbeck first published his famous novel The Grapes of Wrath. It detailed the life story of a family affected by the Dust Bowl storms. This story brought to light the human side of the Dust Bowl, but how was it caused? In the early 1930s, much of the prairie land in Oklahoma, Texas, Kansas, Colorado, and New Mexico was converted into cropland to meet the needs of the growing population and the war efforts. The land was plowed, and crops such as corn and wheat were grown. The problem was, however, that the native prairie grasses, which once held the fragile soil in place, were no longer present to protect the soil. When the winds blew in times of drought, so did the soil. In 1934, there were many wind storms that stirred up the soil and caused great clouds of dust and debris. This dust destroyed the crops and pasture land, and most of the plants died. Many people lost everything that they owned when the crops died, and many abandoned their land and their homes and migrated west.

The Dust Bowl

In this lesson, we will learn about the events of the Dust Bowl and the environmental factors that contributed to it. Then we will discuss how problems like this continue to take place all over the world today, and how we can help prevent such disasters.

LET'S REVIEW!

In this lesson, you have covered the following points: Soil erosion is the movement of soil from one place to another, by water, wind, or gravity. Soil erosion causes loss of topsoil and damage to property. Also, the soil that gets eroded away often ends up in streams, clogging up waterways with sediment and carrying agricultural chemicals to surface waters. Agricultural runoff is a leading factor in the development of In this lesson, you have covered the following points: Soil erosion is the movement of soil from one place to another, by water, wind, or gravity. Soil erosion causes loss of topsoil and damage to property. Also, the soil that gets eroded away often ends up in streams, clogging up waterways with sediment and carrying agricultural chemicals to surface waters. Agricultural runoff is a leading factor in the development of hypoxic dead zones in surface waters. Human activities that accelerate soil erosion include agriculture, grazing, logging, construction, and recreation. Farmers can use best management practices to conserve soil and prevent soil erosion. dead zones in surface waters. Human activities that accelerate soil erosion include agriculture, grazing, logging, construction, and recreation. Farmers can use best management practices to conserve soil and prevent soil erosion.

What You Should Know Before you begin, you should: understand the composition and importance of soil as discussed in the previous lesson.

OBJECTIVES Define and give examples of erosion. Identify and describe problems associated with soil erosion. Explain ways in which human activities accelerate erosion. Describe ways to prevent erosion and conserve soil resources. Explain the relationship between soil erosion and runoff and how these affect water quality.

Water

Running water is the leading cause of erosion because it can easily take soil with it as the water flows downhill or moves across the land. Also, as you see in the diagram, raindrops do cause damage to the soil. A drop of rain falls at about 20 miles per hour. Upon impact with the soil, it breaks apart clumps of soil into individual particles that are then easily blown or carried away by rainwater.

Agricultural Best Management Practices

Since agriculture is a leading contributor to soil erosion, let's look more in depth at some agricultural practices that can reduce soil erosion, which were briefly mentioned in the video on agricultural best management practices (BMPs). This publication from Iowa State University gives you more information on these BMPs. Notice the box of BMPs on page 2 and the table on page 3 that shows the effects of vegetative cover on soil erosion.

CONSEQUENCES OF SOIL EROSION

Soil erosion can cause major consequences, like those seen during the Dust Bowl years in the central section of the United States. Below is the description of the main problems associated with soil erosion. 1. Loss of topsoil is the number one problem of soil erosion. When topsoil is lost, so are valuable soil nutrients necessary for plant growth. 2. Property damage occurs when soil moves down slope and buries roads, homes, and other structures. 3. Loss of productive land occurs as gullies take over fields and forests. 4. When soil is removed from the land by erosion, it often ends up in water. Water that moves over the land is called runoff, and it runs over the land, eventually making its way to a larger stream or the ocean. Runoff water can carry huge amounts of soil and chemicals, which ultimately pollutes streams like this one.

Contributing Factors

Soil erosion, or the removal of soil, is a serious problem because it takes away a valuable resource that we need to grow food. The Dust Bowl storms were America's most severe examples of soil erosion. As you have just learned, the loss of productive land forced thousands of families to leave their homes. Many faced poverty and hunger as a result. There were several factors that contributed to the Dust Bowl storms. First, farmers in the central U.S. had plowed grasslands to grow food crops to feed the increasing human population. They left the fields plowed and bare in the winter months when crops were not grown, and this left the soil exposed to wind. Next, a long drought in the 1930s left the exposed soil especially dry due to the lack of precipitation. When the spring winds began blowing, the dry, exposed soil was easily picked up and blown away. So in other words, plowing the land to plant food crops eventually made the land unsuitable for crops because all the topsoil had blown away. Topsoil is the most fertile part of the soil, so when it was wiped away, plants could no longer grow on the land, which created a dilemma. How can farmers continue producing crops and conserve the soil at the same time? It can be done, and to see how, let's first take a look at some causes of soil erosion, which are water, wind, and gravity.

Soil Erosion Prevention

Soil is especially vulnerable to erosion if it is bare or exposed. Plants serve a tremendous role in preventing soil erosion. If the soil is covered with plants, erosion is slowed down. But when soil is bare, the rate of erosion speeds up tremendously.

Wind

Wind is the next leading cause of erosion. Just as in the Dust Bowl storms of the 1930s, wind can blow soil many hundreds of kilometers away. Wind erosion occurs by three main processes: Saltation—Sand-sized particles are blown into the air, travel a short distance, and then dislodge more soil as they fall back to the ground. Suspension—Very fine particles are lifted into the air by the effects of saltation. They can remain suspended high in the air for long periods of time and travel great distances. Surface creep—Large soil particles move along the ground's surface after being loosened by the effects of saltation. This animation shows you a close-up of wind erosion. Notice how the larger particles stay near the ground. The other particles bounce around, dislodging soil as the wind carries them along.

Runoff

You just saw that runoff water carries soil particles to streams and rivers, making them muddy and brown. The sediment load itself can harm the wildlife in the streams. Another problem with runoff is that agricultural sediments often have pesticides and fertilizers on them. These chemicals can be especially harmful to wildlife and people who depend on the stream water. In urban settings, soils become mixed with oil spills and other chemicals from cars and factories. These contribute to urban runoff, which is equally damaging to streams. We can decrease the negative impact of agricultural runoff by preventing soil erosion from farms and by reducing the use of chemical fertilizers and pesticides. One approach to this is integrated pest management (IPM), which relies on chemical pesticides as a last resort and depends more on using natural pest control methods.

desertification

expansion of desert lands caused by human activities and drought that accelerate soil erosion

soil creep

slow downhill movement of soil