Geoecology – Three Essays in Section – Choose One – Each essay 80 marks Sample Geography Paper

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Soil Profiles

A soil profile is a vertical section through the soil from surface to bedrock

The Soil profile usually shows different layers in the soils

These layers are called horizons are there are usually four horizons in a soil profile.

The O horizon is on the surface which usually has – A large amount of organic matter, micro-organisms and humus in the lower part.
The A horizon is topsoil which has a mixture of minerals and organic matter, large amount of roots from vegetation and is dark in colour.
The B horizon called subsoil with percolating rain water, leached materials
The C horizon (regolith) with weathered parent materials (minerals).
General Classification of Soils
World soils maps do not always show the soils as they exist in reality – they show the soils as it is most likely to occur.
As climate is the most important factor in soil formation as they affect the soil forming processes and influence the amount of biological activity in soil – world soils are classified firstly according to climate.
The soils which develop in response to climatic conditions are called zonal soils they are found in particular climatic regions.

In climatic zones there are local differences due to differences in relief either upland or lowland

local climates (micro-climates), drainage, parent rock materials these produce local soils called intrazonal soils.

Example of a zonal soil – Brown Earth – Divided into Three Distinct Areas
Part One Soil Characteristics

  1. Brown earths are a zonal soil. They are found in temperate latitudes 40˚-60˚ North of the Equator

  2. The climate is normally cool temperate oceanic, they are a common soil in Ireland. Eg. NE Ulster and SE Leinster.

  3. Most brown earths have a crumb texture and this means that pore spaces are provided for air and water.

  4. The PH of brown earth can vary from slightly alkaline to slightly acidic (ranging from 5-7 on PH readings) and as acidity levels control which plants and animals will live in the soil there are local variations of plant/animal life.

  5. Brown earths usually have a dark brown colour throughout their soils profile as they contact a large amount of humus.

  6. Brown earths are usually very fertile as humus is composed of dead plants and animals and rainfall washes the humus into the soil and it is used by plant roots as nutrients.

  7. Brown earths are well drained and water can pass through them. The humus content ensures that they can hold moisture.

  8. Structurally, brown earths are a loam soil equally composed of sand silt and clay. It remains free from waterlogging and is good for agriculture.

Part Two The Processes/Factors that influence the characteristics of soil

  1. The factors or causes of the characteristics of brown earths are the usual ones for zonal soils.

  2. The cool temperate climate allowed the growth of dense deciduous forests. The trees (oak, beech) and the dense undergrowth provided larger amounts of plant litter for the development of humus in the soil.

  3. The cool temperare climate is warm enough for biological activity and micro-organisms (bacteria and fungi) and animals such as earthworms are present for activity to occur for more than nine months of the year.

  4. The microorganisms break down the plant litter to form humus which gives the soils its crumb texture, brown colour and fertility.

  5. The crumb texture and the burrowing animals provide pore spaces for water and air to help plant growth and fertility.

  6. There is enough rainfall all year round to provide a little leaching and this limited leaching mixes the soil and washes nutrients into the soil.

  7. Irish brown earths can vary from slightly alkaline to slightly acidic and this helps the activities of earthworms, fungi and bacteria to decompose the humus and mix the nutrients.

  8. The parent materials for Irish brown earths range from limestone, granite, and glacial boulder clay.

  9. Usually brown earths develop in relief areas with gentle slopes allowing the free draining of water in the soil. Combined with the warmer temperatures this helps the development of humus.

Part Three Soil Profile
Homework, use the information below to create 8 SRP’s referring to the four horizons, referring the colour of the soil. Remember the SRP’s need to hold together to create a cohesive and well written piece.

Human Influences affecting Soil

Example of Sahel – Africa

Human Influences in the Sahel region have led to desertification of the land. There are reports to suggest that the Sahara Desert is advancing southwards by between 5-10 km per year. The Sahel is a band of land that is traditionally covered by grassland and supports a nomadic society that followed the rains. It is semi arid, wet season from June to September.
Refer to page 163 – Fig 7-1-13

  • Over-cropping occurs when people use the land year after year without

  • In the Sahel region of Africa (Mali, Chad) increasing population pressure and the need to repay loans has increased over-cropping because all the land is needed year after year and the soild cannot be left fallow to regain nutrients

  • People are so poor they cannot afford to purchase and use artificial fertilizers to improve soil fertility.

  • The development of plantation farming for cash crops (cotton, nuts) to repay debts has led to mono culture growing the same crop each year on the same piece of land. This uses up the same soil nutrients each year.

  • The repeated deep ploughing needed to allow planting of the crops destroys the soil structure by breaking up the peds and burying organic matter too deep for plant use.

  • Deep ploughing also loosens the topsoil for future water and wind erosion – loose dry topsoil is blown away by the wind as happens in Mali.

  • The need for large amounts of irrigation water each year to keep the land famed continuously has led to the problem of salinisation in the hot, dry climates of Mali and Ethiopia. Salinisation is the accumulation of soluble mineral salts near the surface of the soil. Evaporation of water leaves soluble salts close to the surface of the soil. The excess water from irrigation raises the water table and brings salt to the surface. The hard, white crust prevents nutrients entering the soils.

  • Over-cultivation causes the soils to become so lacking in minerals that the soils soil is :


  • Over-Grazing occurs when the farmers allow too many animals to graze an area of land. So much vegetation cover is removed that the animals:

    • Remove vegetation exposing the soil

    • Destroy the soil structure

  • The need for an assured water supply attracts many migrant people and their animals. Around many new water-wells sunk in the 1980’s in Kenya overgrazing has occurred due to increased numbers of cattle removing trees and grass, thus exposing the soil to erosion.

  • In many African countries, eg. Kenya people measure their wealth in terms of the numbers of animals (cattle and goats) no the quality. So as the human population grows the number of farm animals increases also. This leads to the removal of grass and exposes the soil to soil erosion.

  • The lack of vegetation of grass means that there is no interception of raindrops. This means that heavy rain falls directly onto the soil and loosens it.

  • This leads to sheet erosion on slopes as the whole topsoil layer can be washed evenly down a slope. Eg. Ethiopian Highlands

  • When new shoots of grass appear after the rains they are eaten immediately and when rain alls again there is no vegetation to absorb it and gully erosion occurs (small streams remove soil and cut into the soil surface)

  • Grass roots bind the soil together but with no vegetation to bind it together soil is loosened and can be blown away (dry season) or washed away (wet season)

Final section refer to page 164
Write 8 SRP’s on Deforestation and you can mention Shelter belts as positive option
SRP 1___________________________________________________

SRP 2___________________________________________________

SRP 3___________________________________________________

SRP 4___________________________________________________

SRP 5___________________________________________________

SRP 6___________________________________________________

SRP 7___________________________________________________

SRP 8___________________________________________________

Name _________________________________ Date Received _________________________

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