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

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

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

Soil Profile Soil Horizons

Water cycle & Weathering

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

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.

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

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

The dust bowl http://www.youtube.com/watch?v=guTek7ipD4U

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

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

Guess the main cause of erosion

Guess the main cause of erosion

Guess the main cause of erosion

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

Other forms of degradation Acidification Salinisation Vegetation loss

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.

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?

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

Why is Peak Soil significant?

Removal of vegetation and topsoil results in…

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

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.

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.

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)