According to the World Wildlife Fund, the world has lost a staggering 50% of all of its topsoil in the last 150 years. In this guide, we’ll take a close look at the causes and effects of soil erosion, why it matters, and what we can do about the issue.
What is soil erosion?
In essence, soil erosion is when soil is relocated from one place to another, usually by wind or water. As part of this process, the soil is removed, or eroded, from its original position.
This can strip the ground of fertile topsoil and even reshape the landscape. Over time, soil erosion can make the land less able to support vegetation and crops, impacting the environment and humans alike, as well as causing pollution and contributing to water scarcity and climate change.
The erosion process has three stages:
- Detachment: the soil is loosened or removed from its original location.
- Movement: the earth is then moved by one of a variety of forces, most commonly wind or water.
- Deposition: the soil is deposited in another location, whether on the ground or in waterways.
This cycle of detachment, movement, and deposition may happen so slowly that it barely impacts the environment or may occur rapidly with dramatic effects.
There are various types of soil erosion, which include:
- Wind erosion: wind erosion is one of the most common and severe forms of erosion. As the name suggests, the wind blows topsoil away, eroding the earth over time.
- Rill erosion: in this form of erosion, heavy rains and flowing surface water form rills, or shallow channels, across the surface, eroding the soil.
- Gully erosion: gullies are formed by water flow, when water runoff shifts the soil along drainage lines, often deepening natural depressions, which can dramatically reshape the landscape.
- Ephemeral erosion: this is a similar process to gully erosion, but the depressions formed are typically more shallow.
- Bank erosion: when the water flow erodes the banks of a river or stream. This can occur in nature, changing the course of rivers over time.
- Sheet erosion: sheet erosion occurs when soil is moved by runoff water or raindrop splash, usually evenly across the same slope, and may be so subtle that it doesn’t become obvious until the majority of the rich topsoil has disappeared.
What are the main causes of soil erosion?
In the early stages of soil erosion, wind, water, or other forces remove the lighter, finer particles found in the topsoil. Over time, once these particles are gone, larger and heavier materials found in the deeper soil layers may also erode.
Erosion has occurred in nature almost since the earth was formed, shaping and reforming the landscape over time. However, human activity is, directly and indirectly contributing to soil erosion, greatly accelerating the process on a wide scale.
Deforestation and land clearing
Clearing forests and other vegetation is one of the major causes of soil erosion. When trees and plants are removed, their roots no longer hold the earth in place, leaving this soil vulnerable to water and wind erosion.
Even residual roots from plants that are no longer there can create channels for water to infiltrate the soil rather than running off the surface, which could cause erosion.
Additionally, when soil is covered with vegetation, its organic matter is continually being replenished as leaves, fruits, and animal droppings fall to the ground and are broken down by microorganisms.
In the absence of these processes, the soil composition changes over time, and its organic component is depleted, making it vulnerable to erosion.
As large areas are left bare and open to the elements, the process of erosion accelerates. If there are no trees, shrubs, or organic matter to act as windbreaks, soil particles can be carried much further by wind or water.
Vegetative cover and organic residues protect the soil from raindrop and splash impact, as well as slowing down the movement of water, preventing sediment from moving too far and giving moisture more time to be absorbed into the ground.
While crops offer some level of protection, native vegetation such as forests and permanent grasses are most effective in covering the soil and helping to prevent erosion.
Conventional agricultural practices can damage the structure of the soil and lead to erosion in other ways. Agricultural regions in the USA are affected by erosion at a rate of 1,500 feet per million years, compared to 60 feet per million years in the case of natural erosion.
In particular, conventional tillage loosens the soil and often leaves it bare for months of the year, creating a perfect storm for erosion.
An Intergovernmental Panel on Climate Change (IPCC) report found that in the absence of conservation practices, cultivation causes soil to erode 100 times quicker than it is replaced.
Additionally, both crop farming and overgrazing can deplete the soil of organic materials, making it more vulnerable to erosion. Organic particles are more resistant to erosion than many inorganic components, so when these materials are removed through grazing or agriculture practices, the soil is more likely to erode.
Finally, when smaller fields are combined into larger ones in an effort to maximize profits, this frequently increases the slope length of the land. Longer slopes mean water can pick up speed and flow faster, and this increased force makes it more likely to cause erosion.
The mining industry is another big culprit when it comes to soil erosion. Open-cut mines, in particular, not only dig into large tracts of ground, they also expose the remaining soil to the elements, making it vulnerable to erosion.
This problem is compounded by the fact that mining activities often contaminate the soil with heavy metals and other toxic pollutants. Therefore, as the soil erodes, it can pollute surrounding habitats, waterways, and the underground water table.
Soil erosion can happen because of a number of natural causes. Although these factors have been causing erosion for hundreds of thousands, if not millions of years, human activities have exponentially increased the pace and severity of soil erosion.
Water and wind
Rain and water runoff can easily erode the soil, especially in the case of heavy rains, but even in more mild conditions. Typically, lighter soil types such as silt, fine sand, and organic matter are most vulnerable to being washed away, but heavier soil and mineral particles can also be removed by harsher weather and severe floods.
Even mild winds can cause soil erosion over time, reducing soil quality. Just as strong flowing water washes the soil away, more severe winds are more likely to cause greater erosion, and lighter soil materials are more susceptible as they are easier to pick up and blow away.
A prominent example of this was the infamous American dust bowl during the 1930s, when loose, dry soils were blown away after years of drought and over-cultivation. This further compounded the impacts of the drought and the Great Depression, and the clouds of earth reportedly blacked out the sun across vast regions of the Southern USA.
Natural properties of the soil and the landscape
The individual natural properties of the soil determine its erodibility factor, or its ability to resist erosion. These properties include the texture and structure of the soil, as well as how able it is to retain and transmit water, also known as permeability.
The presence and proportion of certain materials, such as organic matter and clay minerals, can also influence how likely the soil is to erode, with soils with higher concentrations of organic matter being more resistant to erosion.
The natural geography of the land can also make land more vulnerable to soil erosion. Most notably, the slope, gradient, shape, and aspect of the landscape can impact how severely the soil is eroded, or whether it is eroded at all.
For example, in hilly areas with a higher degree of slope, water will move more quickly across the surface, increasing the severity of erosion.
While soil erosion can occur naturally, the severity and scale of erosion is greatly increased by human activities. Furthermore, even when natural factors are the direct cause of soil erosion, human intervention is often the underlying cause.
Researchers estimate that human intervention is responsible for ten times more soil erosion than all natural factors combined. This is not new: farming and other human activities have contributed to soil erosion for thousands of years.
Additionally, climate change due to human activity has made certain conditions that contribute to soil erosion – such as extreme weather, flooding, and drought. Therefore, it’s important to understand how soil erosion can affect people and the environment, as well as what we can do to prevent it.
How does soil erosion affect us and the environment?
Although soil erosion is a natural process, it can have a range of negative effects, especially when it is accelerated by human activity. The increasingly severe and rapid soil erosion caused by factors such as agriculture, mining, and deforestation is already having devastating impacts on people and the environment.
It contributes to soil degradation
Soil erosion affects soil quality in a range of ways. Most obviously, this process removes the topsoil, impacts the volume and composition of the soil, and makes it less fertile.
Erosion also typically compacts the soil by removing the lighter, looser particles on the upper layers. In turn, soil compaction can have various effects, such as reducing the earth’s ability to absorb water, making it less suitable for crops and vegetation, disrupting the water cycle, and increasing the risk of natural disasters.
Erosion and degradation can increase soil acidity by changing the soil composition, making it less suitable for plant life.
As the soil degrades and becomes less able to support crops and other plant life, less and less organic matter is returned to the soil, further degrading the soil in a vicious cycle.
In extreme cases, this may eventually lead to desertification, when rich fertile soils turn into arid desert.
It impacts the agricultural industry
Soil erosion almost always involves a loss of topsoil; in some cases, the fertile topsoil may disappear altogether. This can significantly damage crop yields and could make the ground utterly unsuitable for cultivation.
Erosion can also shape the landscape, leading to the loss of productive farmland as well as damaging infrastructure. For example, bank erosion can carve away fertile farmland while causing damage to fence rows and undermining bridges.
All of this can greatly compromise the agricultural industry, damaging the local economy and threatening communities’ way of life.
It leads to food insecurity
Along with the economic and social effects, food production also suffers when the agricultural industry struggles. In extreme cases, this can cause food insecurity or even famine.
It contributes to water scarcity
Soil erosion and degradation can play havoc with the water cycle, leading to droughts, flooding, and water scarcity.
As the fine topsoil and organic matter erodes, this can leave only rock ground that is less able to absorb water, leading to drought, failing crops, and even desertification. Water runoff, in these cases, can also cause devastating floods.
It causes pollution
Soil erosion can also cause problems in the wider environment. When particles are washed into waterways, this can lead to water pollution and sedimentation.
Because eroded ground is less able to absorb moisture, this leads to increased water runoff. In agricultural areas, this can wash fertilizers and pesticides into rivers and streams, causing further water pollution that may poison aquatic plants and animals.
This can devastate aquatic ecosystems, make rivers and canals unnavigable, and cause large-scale natural disasters. Water pollution caused by soil erosion can also contaminate drinking water, threatening communities’ water supply and potentially making people sick.
It contributes to climate change
Soil erosion and degradation can lead to deforestation over the long term. Forests act as important carbon sinks; therefore their destruction releases greenhouse gases into the atmosphere and increases the rate of climate change.
Additionally, soil itself can sequester carbon, effectively acting as carbon sinks. Top soil rich in organic matter that contains carbon, which can be released into the atmosphere as the ground erodes.
According to the United Nations, there is a direct link between soil degradation and how much carbon it can store. As global temperatures rise, killing off vegetation and driving more soil erosion, this is set to become another vicious cycle.
It can put human life at risk
The effects of soil pollution can put people at risk not only through food insecurity but because of various other dangers.
Soil erosion can cause flooding: erosion decreases rivers’ ability to absorb large volumes of water, and sedimentation build up in waterways preventing water flow. In Indonesia in 2020, silt build-up in rivers and canals caused devastating floods that killed hundreds of people.
When the earth behind seawalls erodes away, this threatens the structural integrity of the sea wall. In extreme cases, this can cause the sea wall to fail completely, putting properties and human lives at risk through flooding and storm damage.
Why is the soil erodibility factor important?
Every soil can be classified in terms of its erodibility, which is its ability to resist erosion, and this will depend on its physical characteristics. Texture, structure, permeability, and organic matter content all contribute to how well the soil will resist erosion.
Texture is the most influential factor in determining soil erodibility:
- The most erosion-resistant (therefore least likely to erode) are sand, sandy loam, and loam-textured soils
- Very fine sand and some clay-textured soils are more likely to erode
Soils that infiltrate water more quickly are more resistant to erosion, because moisture is more readily absorbed and filters through the ground, rather than running off at the risk of causing erosion. Conversely, compacted soils, or those with a hard crust, are less able to absorb water and more likely to be eroded through water runoff.
Conventional agriculture can impact the texture of the soil, for example compacting it through the use of farming machinery or because of grazing animals. Farming and grazing can also lower the levels of organic materials in the soil, reducing its erodibility factor.
When the soil erodibility factor is reduced through human activities such as agriculture, this makes the ground more vulnerable to forces such as rainfall-runoff, flooding, and wind. In turn, this means that erosion is more likely to occur.
Erosion itself can also reduce the soil’s erodibility factor. As the soil erodes and loses its organic-rich topsoil, this often results in poorer structure and lower composition of organic matter, making it more susceptible to erosion.
As the level of organic matter drops, this also reduces the concentration of nutrients and crop yields suffer, meaning poor crop cover which further damages the soil erodibility factor.
What can we do to combat soil erosion?
Given the close relationship between human activity and soil erosion, we can do plenty of things at a political and individual level to prevent erosion and mitigate its effects.
Protect our forests and support reforestation
Deforestation is one of the major causes of soil erosion, so protecting our forests and supporting reforestation efforts is a powerful way to prevent erosion.
At a political level, necessary actions include tighter controls on logging, agriculture, and mining, introducing sustainable forestry policies, encouraging tree-free products, and funding tree-planting efforts.
As an individual, here are just some of the things you can do to protect our forests:
- Buy certified wood products or wood alternatives, and avoid tree-sourced items wherever possible
- Avoid using paper, disposable plates and food containers, and switch out disposable napkins, toilet paper, and diapers for sustainable alternatives
- Join tree-planting groups or plant trees in your garden
- Get your news and magazines online, get an e-reader, and join your local library
- Buy organic produce and products
- Reduce the amount of waste you produce and recycle everything you can
Build infrastructure to prevent erosion
Building terraces into slopes can also stabilize the soil and protect plant life, helping to avoid soil erosion. Planting robust plant species in areas prone to erosion can also help to stabilize the soil.
We can also control water erosion by building infrastructure like walls, protective barriers, or drainages such as pipes and canals.
Encourage sustainable farming practices
Sustainable farming practices can go a long way to protect soils from erosion. Perhaps most importantly, conservation tillage farming doesn’t leave the soil vulnerable to being washed or blown away.
The impact of tillage on the soil erodibility factor depends on how it is conducted: specifically, how deep the soil is tilled, in which direction, and at what time of year, as well as ensuring to leave as much vegetation or crop residues on the surface as possible at all times.
Conservation tillage involves managing all of these factors and tilling the land in such a way as it will have minimal risk of causing erosion or otherwise degrading the soil. These include minimum-till and no-till techniques, as well as ridge-till and mulch-till approaches, which maintain soil integrity and cover.
Cropping practices that cover the land year-round, either with living vegetation or crop residues, can also protect the soil from water runoff and wind damage.
As a consumer, you can support sustainable farming practices and help fight soil erosion by buying organic produce and products.
Soil erosion is a significant environmental issue affecting the broader ecosystem and human economic interests, food security, and safety. However, despite this, the problem doesn’t receive much attention, so it’s essential to understand the causes and effects of soil erosion.
You can do your part to prevent soil erosion through responsible consumer and lifestyle choices, such as looking for organic and forest-friendly products.
If you’d like to go even further, you could lobby your local representatives to take action on soil erosion, or join campaigns to support the cause.