GSLM - Threats to Soil (Lesson)

Threats to Soil

 

Why do we study soil?

We study soil because it’s a(n) great integrator, a snapshot of geologic, climatic, biological, and human history, waste decomposer, the source material for construction, medicine, art, etc., essential natural resource, home to organisms, plants, animals, and others, medium for plant growth, producer and absorber of gases, medium of crop production

Introduction

Before we move into the next lesson in this module, read over the following questions and be certain you are able to answer all of these before moving on to the next lesson.

  • Why is soil such an important resource?
  • What is needed in soil for it to be fertile and productive?
  • What are naturally occurring pollutants found in soil that can hinder plant growth?
  • Would soil mature faster from unaltered bedrock or from transported materials?
  • If soil erosion is happening at a greater rate than new soil can form, what will eventually happen to the soil in that region?
  • What are some kinds of pollutants that could not easily be removed from the soil?

Click here to watch the video Oh Gully, Where is the Soil Part 3 Links to an external site. to review the three types of water erosion that lead to soil loss and the use of vegetative cover to help stop the loss.

Erosion

Please watch the videos, Oh Gully, Where is the Soil Part 1 Links to an external site. and Erosion and Soil Links to an external site. about the types of erosion.

Then, complete the matching activity below to see if you are able to identify the three types of erosion.

Desertification

Desertification is the rapidly increasing amount of formerly fertile land turning into desert. The formation of deserts normally occurs due to climatic factors related to latitude and precipitation in a region. Desertification is impacting semi-arid regions secondary to human activity. Areas susceptible to desertification tend to have sparser vegetation, irregular precipitation patterns. These characteristics in combination with overgrazing, poor agricultural techniques such as over-cultivation, overgrazing, and deforestation have damaged and exposed sensitive soils, leading to further degradation and soil loss. Climate change and extended droughts increase the sensitivity of these areas, as well.

Click here to please watch the PBS Desertification video. Links to an external site.

Overgrazing and Soil Compaction

Soil compaction occurs when soil loses the normal amount of pore space for the soil type, which decreases water permeability. Decreased permeability leads to additional erosion and loss of topsoil. This becomes an example of a positive feedback loop since, as topsoil is lost, the soil becomes more and more compacted with erosion eventually leading to exposure of subsoil layers.

Human causes of soil compactions include the moving of heavy equipment over the land, farming, and logging. Another significant cause of compaction is the grazing of farm animals, especially when soil is wet as it compresses far more easily.

Overgrazing is a significant cause of soil compaction, particularly in semi-arid regions in developing countries. Sensitive soils that are not allowed to recover from grazing lose the vegetation that anchors the soil and becomes more and more compacted by repeated use. Accelerated erosion results and compaction limits the ability of plant regrowth by the diminished ability to both hold water and allow root growth.

Waterlogging

Waterlogging occurs when the soil has so much water filling its pore space, it is unable to hold oxygen. This lack of oxygen, although dependent on plant species, leads to anaerobic conditions and the decomposition of root tissue. Waterlogged soil can also produce nitrous oxide, a greenhouse gas.

Improper irrigation of crops, inadequate drainage of farmlands, and soils high in clay are vulnerable to waterlogging.

Deforestation

Photo of Haiti deforestationSoils in forests are the foundation for the health of the forest. Characteristics of soil are as unique as the forests that grow in them and they depend on each other. For example, as dense as tropical rain forests are with plant life, the soil is thin and nutrient-poor due to the constant leaching from heavy rainfall and the demands of plants growing in them. Removal of trees, deforestation, exposes soil that was protected by the plants to wind and rain accelerating erosion causing soil loss, and filling local surface waters with sediment. Organic material is lost first, then topsoil follows losing soil fertility and quantity.  

Deforestation of slopes increases soil loss and can be a significant trigger to mass wasting events. Deforestation in developing countries due to wood used for heating and cooking, has led to increased flooding, landslides, and loss of arable land. Both countries on the island of Hispaniola, Haiti, and the Dominican Republic have significant land quality. Early on the Dominican Republic realized the need to replace trees to maintain both the soil and the climate, while unmonitored deforestation has left much of Haiti's soil poor and susceptible to flooding. The picture to the right shows the difference conservation has made. Haiti is on the left side of the picture, the Dominican Republic is to the right.

Soil Pollution

Pollutants in the soil can be organic or inorganic, water-soluble or insoluble, naturally occurring or anthropogenic but all impact the functionality of soil. Mining activities, industrial, domestic and agricultural waste dumping, and pesticide and fertilizer use can all impact soil health. Soil contaminants can enter water supplies, ground, and surface, and prevent or impact soil fertility. Further, many soil pollutants can be picked up by plants or cattle eating the plants impacting the quality of food produced.

 

RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.