What is soil erosion?

Soil erosion is the process in which the topmost layer of the land or soil wears away due to several factors including topography, climate, soil structure and composition and vegetation present. Basically, there are two main causes of soil erosion – wind and water. When the topmost layer of the soil is loose, it becomes vulnerable to the natural forces of wind and water to blow the soil particle away. This loss of topsoil particles is soil erosion, as it is an almost irreversible loss.

The blown soil particles can get deposited elsewhere by wind. Still, it beats the purpose as we know that it takes hundreds and thousands of years for one inch of topsoil to form. Therefore, we do not want the topsoil to be loose, instead, we want to use conservation practices like reducing tillage and vegetative cover to keep the integrity of the topsoil. Soil erosion is, at its core a natural process. There are those who argue that soil erosion is caused by weather events, not by human activities. To some extent it holds true as weather events are the proximate cause of much of if not all soil erosion. The part played by human activities in contributing to soil erosion is in making the terrain susceptible to soil erosion and in removing natural barriers and impediments to soil erosion. In the absence of human activities, soil erosion is moderated, impeded, tempered, blocked by vegetation. Plants have roots that hold soil in place whilst their stems and leaves impede and slow the movement of the fluids that transport eroded material. In this article we approach soil erosion through evaluation the following:

  • What are the causes of soil erosion? 
  • What are the impacts of soil erosion?
  • What are the types of soil erosion and their examples?

What are the causes of soil erosion?

The main causes of soil erosion are:

  • Water (in its liquid and solid states)
  • Wind
  • Gravity
  • Topography 
  • Human activities

Water and wind are dependent on gravity to provide the friction needed to move soil particles, both slowly (rain runoff) and abruptly (stream bank cutting). Topography factors in the aspect of the land that determines how much gravity acts on it. Human activities are the non-natural but powerful agent that helps initiate the others. A typical example would human vegetation harvesting that leaves the topsoil bare and susceptible to the direct effects of wind and water.

Vegetative cover of plants or crop residues protects the soil. The less vegetation cover, the more erosion can occur. Topsoil is the top later of soil and is the most fertile because it contains organic, nutrient rich materials. If the rain falls, water gathers on the ground, causing water flow on the land surface. It carries soil away and deposits it elsewhere. The impact of raindrops will break up the soil and water build-up will create runoff, taking sediment with it. The steeper the slope, the greater the amount of soil that can be lost. As the soil erodes downwards, it increases the slope degree, which in turn, creates further erosion. 

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What are the impacts of soil erosion?

There are several impacts of soil erosion. These include:

  • Nutrient loss
  • Water related effects 
  • Aquatic habitat disruption
  • More aquatic plants 

During the erosion process, topsoil generally erodes first. As the nutrient-rich topsoil erodes, the soil that becomes exposed is less likely to contain enough nutrients to sustain plant life. As the topsoil erodes, the process exposes deeper soil at the land’s surface. This deeper soil often does not hold water well, is very compact and has reduced drainage capacity. Therefore, runoff increases in these areas. The loss of organic matter in the topsoil is the largest contributor to the reduction of water retention in the soil. Soil erosion causes sediment to accumulate in nearby lakes, rivers and oceans. Sedimentation in water bodies affects the ability of fish and wildlife to feed by making the water cloudy. Murky water makes it difficult for fish and wildlife to see well and find food. Some fish also intake the soil particles through their gills, which can affect their breathing. In addition to the change in water quality, soil particles that accumulate along riverbeds can destroy the areas that fish and insects use to lay their eggs. The nutrients loss from the land surface as the soil erodes moves to the water bodies when the sediment accumulates. Some of these nutrients promote the growth of aquatic plants that are detrimental to the overall health of the water body. For example, increased concentration of phosphorus promotes growth of algae. As algae proliferates, they can cover the surface of the water, changing the appearance of the area and making life more difficult for other plants, fish and insects. 


What are the types of soil erosion and their examples?         

The types of soil erosion and their examples include

  1. Sheet erosion
  2. Rill erosion
  3. Gully erosion

Hill slopes are prone to sheet erosion and rill erosion. The amount of hillslope erosion largely depends on how the land is used. Sheet erosion occurs when a thing layer of topsoil is removed over a whole hillside paddock and may not be readily noticed. Rill erosion occurs when runoff water forms small channels as it concentrates down a slope. These rills can be up to 0.3 m deep. If they become any deeper than 0.3 m they are referred to as gully erosion. Gully erosion happens when runoff concentrates and flows strongly enough to detach and move soil particles. For example, a waterfall may form, with runoff picking up energy as it plunges over the gully head. Splash back at the base of the gully head erodes the subsoil and the gully eats its way up the slope. Gullies may develop in watercourses or other places where runoff concentrates. In cultivation or pastures, advanced rill erosion can develop into gully erosion. This type of erosion is visible and affects soil productivity, restricts land use, and can damage roads, fences and buildings. Gully depth is often limited by the depth of the underlying rock which means gullies are normally less than 2 m deep. However, gullies may reach depths of 10-15m on deep alluvial and colluvial soils. 

Getting excited about dirt!

The soil erosion discussion is summed up with a definition of soil erosion. It is a physical process that detaches and transports materials on earth through soil mass decomposition to single particles through erosion forces such as water flow and wind. The loose particles are moved off by wind or water quickly than they can undergo chemical change. There is actual loss of soil, by volume in the process of soil erosion. The soil quality, structure, stability, and texture are affected which in turn affect the holding capacity of the soil. Eroded soil can inhibit growth of seeds, bury seedlings, contribute to road damage, and even contaminate water sources and recreational areas. In conclusion we quote Professor David Pimentel, “Soil erosion is second only to population growth as the biggest environmental problem the world faces,” he goes on to sum it up saying “Yet, the problem, which is growing ever more critical, is being ignored because who gets excited about dirt?”

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Pimentel. D. 2006. Soil Erosion: A Food and Environmental Threat. Journal of the Environment, Development and Sustainability. 8. 

Soil Erodibility retrieved 21/05/21

Types of erosion retrieved 21/05/21