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.
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 stormwater 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.
- 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 natural 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.
Effects of Soil Erosion
The consequences of soil erosion are primarily centered on reduced agricultural productivity as well as soil quality. Water ways may also be blocked, and it may affect water quality. This means most of the environmental problems the world face today arises from soil erosion. The effects of soil erosion include:
- Loss of Arable Land
Lands used for crop production have been substantially affected by soil erosion. Soil erosion eats away the top soil which is the fertile layer of the land and also the component that supports the soil’s essential microorganisms and organic matter. In this view, soil erosion has severely threatened the productivity of fertile cropping areas as they are continually degraded.
Because of soil erosion, most of the soil characteristics that support agriculture have been lost, causing ecological collapse and mass starvation. It is likely that most of the cultivated areas around the globe are vulnerable to soil erosion.
- Water Pollution and Clogging of Waterways
Soils eroded from agricultural lands carry pesticides, heavy metals, and fertilizers which are washed into streams and major water ways. This leads to water pollution and damage to marine and freshwater habitats. Accumulated sediments can also cause clogging of water ways and raises the water level leading to flooding.
The water quality of various streams, rivers, and coastal areas has also been deteriorated as a result of soil erosion, eventually affecting the health of the local communities.
- Sedimentation and Threat to Aquatic Systems
Apart from polluting the water systems, high soil sedimentation can be catastrophic to the survival of aquatic life forms. Silt can smother the breeding grounds of fish and equally lessens their food supply since the siltation reduces the biodiversity of algal life and beneficial aquatic plants. Sediments may also enter the fish gills, affecting their respiratory functions.
- Air Pollution
Wind erosion picks up dust particles of the soil and throws them into the air, causing air pollution. Some of the dust particles may contain harmful and toxic particles such as petroleum and pesticides that can pose a severe health hazard when inhaled or ingested.
Dust plumes from the deserts or dry areas can cause large and widespread air pollution as the winds move. Such a case is evident in North America where dust winds from the Gobi desert have recurrently been a serious problem.
- Destruction of Infrastructure
Soil erosion can affect infrastructural projects such as dams, drainages, and embankments. The accumulation of soil sediments in dams/drainages and along embankments can reduce their operational lifetime and efficiency. Also, the silt up can support plant life that can, in turn, cause cracks and weaken the structures. Soil erosion from surface water runoff often causes serious damage to roads and tracks, especially if stabilizing techniques are not used.
Soil erosion is a major driver of desertification. It gradually transforms a habitable land and the ASAL regions into deserts. The transformations are worsened by the destructive use of the land and deforestation that leaves the soil naked and open to erosion. This usually leads to loss of biodiversity, alteration of ecosystems, land degradation, and huge economic losses.