Download Higher Geography Biosphere For this unit you should be able to

Higher Geography
Biosphere
For this unit you should be able to:
• Draw and annotate a soil profile for the following soils:
Podzol, Brown Earth Soil and Gley.
• Describe and explain the processes which have created a
Podzol, Brown Earth Soil and Gley.
Biosphere
The term Biosphere refers to the biotic response to specific climatic and other
environmental conditions such as relief and soils, which results in a variety of different types
of vegetation. The various plants which exist on the earth’s surface inter-react within a
system called an ecosystem.
Soil Content
Water – from atmosphere (22.5%)
Mineral matter – minerals derived from parent material by weathering. (40%)
Air – in ever changing amounts. Fills pore spaces. (22.5%)
Organic matter – from decaying roots, leaves. (10%)
Biota – life forms such as worms and moles found in soil that help to break it down. (5%)
Soil Formation Factors
Climate - Rainfall v Evaporation
(leaching/capillary rise). Temperature –
affects weathering and decomposition
rates and presence of organisms within
the soil.
Time – takes 3,000-12,000 years to
develop deep enough for farming.
Vegetation – Impacts on humus content,
soil acidity and soil fertility.
Relief – affects depth of soil (thicker at
base of slope) and drainage (soils are
better drained on slopes than flat areas).
Poor drainage leads to waterlogging.
Organisms – animals mix and aerate
soil. Plants stabilize and provide
organic material.
Parent Material – affects colour and
nature of soil.
Soil Profiles
Soils can be examined by looking at a vertical section through the soil from topsoil (most
recently deposited) to parent material (weathered bedrock). Soils develop a series of
distinct layers called horizons. These horizons are identifiable by colour and texture and
having different material composition and mineral content. By examining these horizons, it
is possible to work out the type of soil.
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The O horizon is the layer of humus that is found on the surface. It forms from the
leaves/pine needles/pine cones that fall from the vegetation on the surface.
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The A horizon and B horizon are where nutrients from the humus and the minerals from
the C horizon are mixed.
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Mixing occurs because of water.
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Wet conditions: water flows down through the soil, removing nutrients and minerals
from the humus. This is known as leaching. It involves:
Eluviation – washing out of A horizon.
Illuviation – washing into B horizon.
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Dry conditions: evaporation is greater than precipitation, and as a result water moves up
through the soil bringing minerals up from the C horizon. This is known as capillary
action.
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Plant roots create passages through which material from the humus can percolate into
the A and B horizons.
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Animals - worms and moles can assist in taking materials from humus and depositing it
further down. They can also help to mix the soil.
Soil Profiles
O horizon - Humus
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Present at the surface.
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Essentially decaying vegetation.
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Consists of litter (leaves etc.), fermentation (organic
matter decomposes) and humus (decomposed vegetation,
animals and bacteria).
A horizon (Topsoil)
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Mixture of organic and inorganic material.
B horizon (Subsoil)
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Less organic matter.
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Coarser in texture, reflecting the importance of
weathering.
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Soluable soil material containing nutrients may be leached
out of A into B.
C horizon (Weathered Rock)
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Large particles which sit on underlying bedrock.
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Formed by the decay of the parent rock with minerals being released.
D horizon (underlying parent material/solid rock)
Task
Define the follow key soil terms:
Soil Profile
Horizon
Humus
Decomposition
Leaching
Capillary action/rise
Eluviation
Illuviation
Gleying
Soil Formation Factors
The 3 soils that you will study are Podzols, Brown Earths and Gley soils.
The key features that you should refer to when describing and explaining how each soil is
formed are:
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Climate
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Relief
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Organisms
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Parent Material
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Vegetation
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Time
Task
Explain how each of the factors listed above can affect soil formation.
Podzol Soils
Location of podzol soils
Podzols occupy approximately 4% of the earth's total land mass.
Task
Study the map above and the copy on the whiteboard and complete the following:
1.
2.
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Describe the location of podzol soils.
How might the climate of these areas affecting the following:
Vegetation.
Humus content.
Organisms.
Soil processes.
Podzol Soil Profile
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Location - northern coniferous forests with associated cold, wet climates.
Coniferous trees have shallow roots.
O horizon consists of decaying plant litter (pine needles, cones).
Cold climate means slow decay of organic matter to form an acidic mor humus of pH 3.5
– 4.0.
Precipitation is greater than evaporation.
Clearly defined horizons due to the process of podsolisation. This involves leaching of
iron, aluminium and humus from surface layers to lower layers.
Leaching produces an ash coloured, bleached A horizon.
Lower down, iron, aluminium, clay and humus are washed in (illuviated) and redeposited
in B. The presence of iron and aluminium explain the reddish brown colour of B.
If iron accumulates over a long period, a rust coloured iron pan can from. This can
prevent free drainage and result in waterlogging.
C horizon is parent material, generally weathered rock or glacial or fluvio-glacial
material.
Clear horizons encouraged by lack of organisms esp. worms.
Not naturally fertile. Lime added to combat acidity.
Brown Earth Soil Profile
Brown earths are mostly located between 35° and 55° north of the Equator. The largest
expanses cover western and central Europe, large areas of western and Russia, the east
coast of America and eastern Asia. Brown earths cover 45% of the land in England and
Wales.
Task
Study the information above on the location of brown earth soils and complete the following:
1.
2.
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Describe in detail the location of brown earth soils.
How might the climate of these areas affecting the following:
Vegetation.
Humus content.
Organisms.
Soil processes.
Brown Earth Soil Profile
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Location - broadleaved deciduous forests of Western Europe.
Trees have deep roots.
Leaching is less pronounced.
O horizon rich in nutrients due to input of decaying fleshy deciduous leaves in Autumn.
Litter decomposes relatively quickly due to milder climate. Result is a less acidic mull
humus.
Deep tree roots penetrate down to C horizon and extract minerals to ensure nutrient
cycling. This allows chemicals lost by leaching to be brought back up. Extensively used
for agriculture.
Brown earth forms on gently sloping and low lands. Land is well drained and allows
biological activity
Indistinct horizon boundaries – Soil is well mixed due to earthworm and soil bacteria
activity.
A horizon – well aerated, humus enriched mineral soil (pH 5.8). Dark brown in colour
because humus replaces minerals that are leached out.
B horizon not so distinct as in podzol but is usually lighter brown in colour due to less
humus.
C horizon derived from varied parent material ranging from limestone to schist.
Gley Soil Profile
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Location - Most extensive soil cover in Scotland.
Grasses/shrubs with short roots or grasses
Climate – relatively warm. Precipitation greater than evaporation so some leaching.
Found on gentler slopes where the water does not drain away readily. Gley soil is
waterlogged for all or most of the year. Drainage giving anaerobic conditions.
Waterlogging creates a chemical reaction and ferrous iron is formed due to the lack of
oxygen, creating a bluish grey colour in the B horizon.
Waterlogging denies the soil the oxygen that the soil organisms need to survive.
The organisms left in the soil extract the oxygen they need to survive from the iron
compounds and the soil gradually turns grey, blue or green as the oxygen is depleted.
Horizons – well defined Ao, A and B horizons.
A horizon, dark brown/grey colour – B horizon, blue-grey with red mottling (iron
compounds).
Parent Material – coastal sand, glacial till, impermeable clay.