1. Soil – its dirty and muddy, so who cares?
(Why is soil important?)

2. Soil degradation - A severe reduction in the quality of soils
Soil degradation - A severe reduction in the quality of soils. The term includes soil erosion, salinization and soil exhaustion (loss of fertility).
Soil and soil erosion

3. Soil formation What is Soil?
Soil is formed from organic matter and eroded rocks over time
Is it the same all over the world?
No, different bedrock + different plants = different soil types
Is it all the same if we dig down?
Mature soil will have a number of layers (parallel) called soil horizons, they show the movement of water and minerals up and down
How can we see these?
We can see a profile of the soil if we find a piece of land that has fallen away or by digging a soil core

4. Soil Profile
Soil Horizons

5. Water cycle & Weathering

7. So, if soil is constantly developing, how does soil degradation occur?

8. Normal erosion Soil erodes naturally and this is called normal erosion
It is a slow process and one which affects the top layer of soil only
The speed of this erosion is affected by the following:
Factors affecting the rate of erosion
Rainfall (duration, amount, intensity)
Vegetation (nature and amount of cover)
Length and angle of the slope
The soils texture, structure and dispersability
Make a table listing each of these factors and in the other 2
Columns; a) rank each factor in terms of its potential for erosion,
then b) state how each affects the speed of erosion.

9. Accelerated erosion Human activity can cause erosion to Increase, this
is called
accelerated
erosion

10. Causes of accelerated erosion
Vegetation cover is removed. This will expose soil to wind and water erosion
Cultivation of soil. This removes weeds which help to hold the soil together and ploughing breaks up the soil profile making it more susceptible to erosion
Over grazing can lead to desertification

11. The dust bowl

12. Rural soil erosion
In rural areas erosion usually occurs due to loss of vegetation cover
This can lead to lower crop yields
Soil erosion is considered a hazard as potentially it could lead to starvation if communities cannot cultivate enough for them to eat

13. Urban soil erosion
This occurs when rural areas are converted to urban areas
Trees are removed
Soil is compacted by machinery bought in to build the urban area
Topsoil removed in leveling process
Construction can lead to massive erosion around the area, once built the erosion rate slows again but much of the soil is covered up or already lost

14. Guess the main cause of erosion

15. Guess the main cause of erosion

16. Guess the
main cause
of erosion

17. Two processes of soil erosion
Wind erosion
Soil is bound loosely together allowing wind to pick it up
Soil more vulnerable when it is dry and particles are lighter
Desertification can occur (extension of the desert)
Water erosion
Erosion caused by water from rainfall, usually heavy rain or for an extended period
Sheet erosion: even removal of soil across a large area
Gully erosion: gullies are formed usually through heavy rainfall

19. Other forms of degradation
Acidification
Salinisation
Vegetation loss

20. Describe the global distribution of soil degradation
Compare this map with the map on p163 of Patterns and Change textbook. Explain the reasons for soil degradation for each continent.

21. What causes degradation
Reduction of natural vegetation cover – what does this mean?
The soil becomes more susceptible to erosion – why?
e.g: Deforestation for logging, farming or fuel – where?
Unsustainable land use practices – what does this mean?
e.g. Over-irrigation, overgrazing, incorrect use of fertilisers – how could each of these affect the soil?
Groundwater over abstraction – what does this mean?
Dries out soil – why is this a problem?
Atmospheric deposition – what does this mean?
Heavy metals and pollutants deposited – how does this affect the soil?

22. This is 20% of the worlds pasture and grazing land
Today there are more than 20 million square km of degraded land in the world.
This is 20% of the worlds pasture and grazing land
The effects are worldwide but degradation is most severe in Africa and Asia

23. Why is Peak Soil significant?

24. Removal of vegetation and topsoil results in…

25. Increased surface run off and stream discharge
Reduction of seed germination of native plants
Reduction of water infiltration and groundwater recharge
Removal of vegetation and topsoil results in…
Change in the surface microclimate that enhances aridity
Development of erosional gullies and sand dunes
Drying up of wells and springs

26. Socio-economic Impacts
Lack of farm productivity
Rural unemployment
Migration
Silting of dams and reservoirs
Hunger and malnutrition
Although it is most severe in Asia and Africa, soil degradation is not limited to poor countries. Australia and the USA also suffer. Therefore it is not totally linked to level of development.

28. Consequences of soil degradation
Soil buffering capacity: (the ability of the soil to absorb contaminants) Direct impact on the carbon cycle. Less soil = increased release of Co2 into the atmosphere.
Loss of Biological Diversity: Soil degradation = reduction of climax vegetation = decrease in available habitats = reduced biodiversity of extinction.
Mudflows & Flooding: Soil degradation = reduction in infiltration capacity of soil = greater surface run off = increased potential for flooding.

29. Consequences of soil degradation
Impact in water bodies
Large delivery of soil, nutrients and contaminants delivered to water bodies
Eutrophication is an increasing problem
Blocking and increasing the potential of flooding
Silt up reservoirs and harbours
UK estimated contamination from agricultural pollutants is GBP203M per annum (NT$9.3B)