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Examine how human activities can accelerate soil erosion and methods used to prevent this.
Outline main human activities that accelerate soil erosion
Examine two in detail with examples (three discussed below)
Examine two in detail with examples (three discussed below)
Examine how human activities can accelerate soil erosion and methods used to prevent this
Soil is a non-renewable resource that once it is eroded it is not renewed. Soil erosion is the permanent change of the main characteristics of soil that could see it lose its fertility, pH, colour, humus content or structure. Soil erosion occurs naturally by wind or harsh climatic conditions but human activities include overgrazing, overcropping and deforestation.
Overgrazing occurs when farmers stock too many animals such as sheep, cattle or goats on their land. The animals damage the soil surface by eating the vegetation and either digging into wet soil or compacting dry soil with their hooves. This can prevent grass growing and slow down the percolation of water through the soil. This leads to the damaging of the soil structure as the level of nutrients is removed and the air between peds is compressed out. This then can reduce the amount of water between the soil crumbs as the weight and movement of the animals flattens and compresses the soil. Soils with less vegetation become exposed, drier and prone to further erosion by the wind and rain. Soils that become drier tend to be vulnerable to the winds blowing the top soil away. The Sahel region of Africa is an example of soil erosion caused both by overgrazing and population growth. In the West of Ireland additional funding from the EU in the 1990’s saw an increase in the sheep population. However, areas of West Mayo suffered soil erosion by the additional hooves and further funding was needed to sort this problem.
Overcropping is when the land is being continuously under cultivation and is not allowed to lie fallow between crops. This constant farming of the land reduces the soils ability to produce valuable humus for soil fertility as it is constantly being ploughed or stripped for crop growth. The soil becomes drier and less fertile. While humus is primarily needed for the addition of nutrients and minerals it is also a valuable source of air and water needed by soil to keep it moist and aerated. With less humus the soil dries out and is open for wind and rain erosion. Usually over cropping occurs in areas where there is a demand for crops either for market or a large local population. Many farmers attempt to restore soil fertility by adding fertilizers or artificial nutrients but some countries do not have this opportunity due to poverty or lack of education. In South America soya is a quick-growing and valuable crop. The leading producers of soya in this region are Brazil and Argentina. Despite some artificial fertilisers being added the soil is not allowed enough time to recover its fertility or structure and is ultimately being eroded by this human activity.
Deforestation is the cutting down of large areas of forests leaving an open, exposed landscape. Deforestation occurs for many reasons such as the sale of wood, charcoal or as a source of fuel, while cleared land is used as pasture for livestock, plantations of commodities, and settlements. The removal of trees without sufficient reforestation has resulted in damage to habitat. biodiversity loss and aridity (drying of soil). This human activity quickly accelerates natural erosion in two ways. Firstly the removal of trees is a removal of nutrients and minerals from the soil as the source of humus is greatly reduced. The natural dead organic material that supplies the soil with its humus is generally leaves that have fallen from the trees, animal droppings, tree fruit or decaying trees in the soil. Secondly, deforestation accelerates soil erosion by leaving large areas exposed to heavy rainfall (which can cause leaching or flash floods) or wind erosion. Without the roots of the trees to keep the soil structure in place the soil is loose and easier to erode. The tropical rainforests of Brazil are seeing huge areas of forest being cut down each day. Each year about 13 million hectares of the world’s forests are lost due to deforestation.
In Brazil large area of the country have been deforested to create route ways, increase farmlands and to supply the American and European market with hardwoods.
Overgrazing, over cropping and or deforestation can lead to desertification – the spread of desert like lands due to these human activities accelerating natural erosion of soil.
However, while soil erosion can be accelerated by human activities it can also be conserved by methods such as windbreaks, reforestation, farm techniques and stone walls.
Windbreaks are natural wind barriers created by planting trees that produce many branches and leaves. This method is used at the edges of large farmland areas (or individual fields) to stop the wind from blowing soil away which can damage or destroy the soil. One area of a windbreak can have an immediate effect on a much larger area as the power of the winds are greatly reduced. While it is important to break the strong winds it is also important to allow a certain amount of wind through this barrier as it controls the flow of the wind without creating a complete block which could result in swirling winds or strong gusts near the barrier. In West Africa large countries like Mali have seen that tree windbreaks can increase the yield of protected fields by up to 20%.
Reforestation is the deliberate planting of trees. This may occur in areas of deforestation, mountain slopes or as a general practice to plant a seedling for each tree cut down. EU legislation now controls the minimum height and age of tree that can be cut and also offers incentives to farmers to turn part of their land over for forestry. In areas like the Apennines in Italy or the mountainous terrain of the West of Ireland this is seen as a valuable alternative to crop or animal farming. The EU forestry grant aid is the initiative to attract farmers to grow and maintain areas of forestry. In the 1900’s only half of one percent of Ireland was classified as under forests but due to a change in laws and funds this has risen to over twelve percent. The policy of ‘cut one, plant two’ is hoping to see an increase in this figure and, in turn, the slowing down of the rate of soil erosion.
Farming techniques such as contour ploughing, stubble planting and time of ploughing can also be useful methods of soil conservation. Contour ploughing is the ploughing of the land following the natural contours of the land instead of the usual practice of going up and down the slopes in lines. If farmers follow the natural contours it can reduce the amount of soil creep or mass movement along the slope as the soil is not destabilised and more vulnerable to erosion. The grooves between ploughed lines allows rainwater to find its way naturally downslope again reducing the possibility of valuable top soil being carried downhill. Stubble planting is something that is practiced in Ireland in areas where grains and cereal crops are produced. As the wheat or barley is harvested by the combine harvester it leaves short stubble of stalks left in the ground. Over time these stubbles decompose becoming valuable humus. The stubble also act as anchors to keep the soil in place until the next crop is planted. Then when the next crop is being planted a technique known as ‘slitting’ is used. This is where small slits are cut into the soil for seeding for the next batch of crops. By not reploughing the soil the structure is maintained and the possibility of erosion is reduced or removed. Finally farmers have changed their planting times to reduce the possibility of soil erosion. This now takes place in wetter conditions when the soil is not likely to become windborne in warm, dry conditions.
Stone walls work like simple versions of windbreaks. These walls of stone are built following the contours of the soil to prevent soil erosion down slope and to allow the rain water to percolate down through the soil rather than straight down the slope.