Soil Erosion and Degradation
Goats will often overgraze areas, removing all vegetation and leaving bare earth.

Soil Erosion and Degradation

One of the topics studied in GCSE Geography is soil erosion and degradation. This quiz looks not only at the causes of soil erosion, but also the effects - such as how it damages ecosystems.

In the past 150 years half the topsoil on the planet has been lost. In addition compaction, loss of soil structure, loss of nutrients and an increase of salinity are damaging other parts of soil, destroying its ecosystems and the chances for plants to reclaim the land and begin to form a new ecosystem.

This loss of soil also damages other environments. It increases the pollution in the waterways and the sedimentation in streams and rivers. Blocking these waterways reduces the drainage and so removes the possibility of fish and other aquatic life breeding and occupying these valuable resources.

When you are studying soil erosion and degradation you start to think about how something as seemingly insignificant as soil is the foundation of all the living things. The nutrients that the plants need to grow and begin the food chain are found in the soil. And most of the nutrient cycles that return these valuable compounds into the food chain take place in the ecosystems that are hidden within the soil.

Whilst natural ecosystems support and are supported by the soil, agriculture often damages it and is the cause of soil loss. Farming practices increase the process of soil run-off. Huge areas of rainforest are being cut down to provide land for coffee, cotton, palm oil, soya beans and wheat. These crops are unable to trap the soil as the forest did and so run-off increases. In places of high rainfall, as the former rainforest is, a single season can be enough to leave the soil completely unable to support plant growth.

Have a go at this quiz and test your knowledge of the causes and the effects of soil erosion and degradation.

Nomadic tribespeople are becoming more sedentary, leading to over cultivation. How is over cultivation defined?
Not planting enough crops to allow the soil to be protected from the rain
Planting more crops than can be watered, leading to death of some of the crops
The excessive use of farmland to the point where productivity falls due to soil exhaustion or land degradation
Adding too much fertiliser, leading to eutrophication of the streams and waterways.
Nomadic populations are being encouraged to settle down in fixed areas by the increase in land ownership and facilities such as stand pipes
Which of the following is not a method of soil conservation?
Planting hedges
Contour ploughing
Slash and burn agriculture
Slash and burn agriculture removes all of the plant life from the surface exposing the soil to erosion
When a field is ploughed, why is it best to plough at right angles to the slope?
Ploughing parallel can lead to machines toppling over
Ploughing at right angles to the slope improves plants' chances at getting equal sunlight
Ploughing parallel to the slope draws the soil downhill
Ploughing parallel to the slope can increase gully erosion
Ploughing leaves behind ridges and furrows. If these are across the slope they trap water and runoff, but if they are down slope they encourage the water to run downhill and carry soil away with it
What type of erosion occurs when moderate rainfall on bare soil removes the topsoil down-slope?
Sheet Erosion
Gully Erosion
Wind Erosion
Sheet erosion is worse in areas with steep slopes, often removing the soil down to bare rock
What form of erosion occurs when intense rainfall cuts small streams into slopes in areas with little or no vegetation cover?
Sheet Erosion
Gully Erosion
Wind Erosion
Tropical storms can cut gullies into slopes. These can become deep channels that flood in the wet seasons
Where do most nutrients in soils come from?
Broken down rocks
Decaying organic matter
Rain fall
Volcanic eruptions
Since the nutrients come from decaying organic matter, they tend to be concentrated in the top layer of the soil
On many islands and in some nature reserves, goats are being removed and banned. How does removing goats and similar grazing animals reduce soil erosion?
Goats tend to move around a lot, stirring up soil and leaving it open to erosion
Goats will often overgraze areas and remove all vegetation, leaving bare earth
The excess organic matter from the goats' droppings leads to pockets of rapid plant growth
Goats discourage other animals that may help the plants to grow
The roots of plants bind soil together, so, without vegetation, soil is more susceptible to erosion. Goats will even climb trees and strip leaves, thus reducing leaf litter
What is the danger of soil being left bare in hot, dry zones?
Desertification as the soil blows away, leaving only the heavier sand grains
Weeds will grow rampant, preventing crops from growing
Build up of dry soils as the bare patch spreads
The nutrients will be leached away by the Sun
Bare soils can be caused by overgrazing or extreme droughts
What happens to the soil when salinisation occurs?
During storms, sea water washes in and contaminates plants
Salts and other minerals are washed out of the soil during heavy rains
Water evaporates in high temperatures drawing salts from the soil to the surface
Flood water removes all the other soil particles except salt
Salt is toxic to many plants, so the soil ends up being bare and therefore more easily subjected to erosion. Irrigation can lead to salinisation. As water is brought in, it evaporates, drawing the salt up to the surface and leaving a layer that is dense in salt
Heavy machinery often leads to soil compaction. How does soil compaction lead to soil erosion?
The solid soil is removed in blocks rather than in small amounts
The solid soil prevents water from percolating into the soil and increases surface runoff
The compacted soils will be lower and encourage water to pool and soil to be washed away
The machines remove large amounts of soil on their tyre treads
Surface runoff causes soil erosion. Soil structure is a delicate balance and can be destroyed by compaction. Protecting the soil structure is a key method of reducing soil erosion
Author:  Ruth M

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