Soil erosion
What is Soil Erosion?
Soil erosion is a process that involves the wearing away of the topsoil. The process involves the loosening of the soil particles, blowing or washing away of the soil particles, and either ends up in the valley and faraway lands or washed away to the oceans by rivers and streams. Soil erosion is a natural process which has increasingly been exacerbated by human activities such as agriculture and deforestation.
The wearing away of the topsoil is driven by erosion agents including the natural physical forces of wind and water, each contributing a substantial quantity of soil loss annually. Farming activities such as tillage also significantly contribute to soil erosion.
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Thus, soil erosion is a continuous process and may occur either at a relatively unnoticed rate or an alarming rate contributing to copious loss of the topsoil. The outcomes of soil erosion are reduced agricultural productivity, ecological collapse, soil degradation, and the possibility of desertification.
Causes of Soil Erosion
All soils undergo soil erosion, but some are more vulnerable than others due to human activities and other natural causal factors. The severity of soil erosion is also dependent on the soil type and the presence of vegetation cover. Here are few of the major causes of soil erosion.
- Rainfall and Flooding
Greater duration and intensity of rainstorm means greater potential for soil erosion. Rainstorm produces four major types of soil erosion including rill erosion, gully erosion, sheet erosion, and splash erosion. These types of erosions are caused by the impacts of raindrops on the soil surface that break down and disperse the soil particles, which are then washed away by the
runoff.
Over time, repeated rainfall can lead to significant amounts of soil loss. Rapidly moving stormwater, flashfloods, and flooding may also occur because of excess surface water runoff, thus, causing extreme local erosion by plucking bed rocks, forming rock cut-basins, creating potholes, and washing away the loosened soil particles.
- Rivers and Streams
The flow of rivers and streams causes valley erosion. The water flowing in the rivers and streams tend to eat away the soils along the water systems leading to a V-shaped erosive activity. When the rivers and streams are full of soil deposits due to sedimentation and the valley levels up with the surface, the water ways begin to wash away the soils at the banks.
This erosive activity is termed as lateral erosion which extends the valley floor and brings about a narrow floodplain. This erosive activity is evident in most rivers or streams especially during heavy rainfall and rapid river channel movement.
3. High Winds
High winds can contribute to soil erosion, particularly in dry weather periods or in the arid and semi-arid (ASAL) regions. The wind picks up the loose soil particles with its natural force and carries them away to far lands, leaving the soil sculptured and denudated. It is severe during the times of drought in the ASAL regions. Hence, wind erosion is a major source of soil degradation and desertification.
- Overgrazing, Overstocking and Tillage Practices
The transformation of natu
ral ecosystems to pasture lands has largely contributed to increased rates of soil erosion and the loss of soil nutrients and the top soil. Overstocking and overgrazing has led to reduced ground cover and break down of the soil particles, giving room for erosion and accelerating the erosive effects by wind and rain. This reduces soil quality and agricultural productivity.
Agricultural tillage depending on the machinery used also breaks down the soil particles, making the soils vulnerable to erosion by water. Up and down field tillage practices as well create pathways for surface water runoff and can speed up the soil erosion process.
- Deforestation, Reduced Vegetation Cover, and Urbanization
Deforestation and urbanization destroy the vegetation land cover. Agricultural practices such as burning and clearing of vegetation also reduce the overall vegetation cover. As a result, the lack of land cover causes increased rates of soil erosion.
Trees and vegetation cover help to hold the soil particles together thereby reduces the erosive effects of erosion caused by rainfall and flooding. Deforestation and urbanization are some of the human actions that have continued the cycle of soil loss.
- Mass Movements and Soil Structure/Composition
The outward and downward movements of sediments and rocks on slanting or slope surfaces due to gravitational pull qualify as an important aspect of the erosion process. This is because mass movements aids in the breakdown of the soil particles that makes them venerable to water and wind erosion. Soil structure and composition is another factor that determines erosivity of wind or rainfall.
For instance, clay soils tend to be more resistant to soil erosion compared to sandy or loose silt soils. Soil moisture content and organic matter make up are some of the soil component aspects that determine erosivity of wind or rainfall.
