BIOSPHERE

Summary of What You Must Know

You should be able to:

describe and explain the effect of physical factors – climate, relief, drainage, parent material, soil biota and vegetation on soil formation.

draw annotated diagrams to describe the properties of podzols, brown earth soils and gley soils, referring to horizons, colour and texture.

recognise the type of soil shown in a profile diagram, and describe the features which help to identify the soil type.

compare and contrast the appearance and soil forming factors of two of the three soil types.

explain the series of soils found in a soil catena.

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The Biosphere Core

The Living environment

This consists of plants, animals, insects, micro-organisms and people.

The Non-living environment

This consists of

Water (rain or stored in the soil). Air – provides oxygen and carbon dioxide which is essential

for life. Solar energy – provides heat and light. Rocks – the lithosphere – provides nutrients Soil – varies in depth, acidity, nutrients and fertility

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The Biosphere – where life is found 3m below to 30m above the ground. It comprises water areas, both salt and fresh and all land. An Ecosystem – a natural system in which life of plants and animals are clearly linked to one another and to the non-living environment through food chains.

Ecosystems vary in size from extensive areas of rainforest to a micro system under a stone.

All ecosystems depend on two basic processes:

• A flow of energy (heat and light)• The recycling of nutrients within the system

Ecosystems will remain in balance unless conditions change such as climate or through human interference.

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Soils

Soil is the function of climate (water and temperature), organisms (bacteria, insects, plants etc.), parent material (rock under the soil), relief (steepness) and time.

Factors affecting soil formation

Soil Formation

Climate

Drainage

Relief

Vegetation

Soil Biota

Parent Material

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Classification of soils:

When precipitation exceeds evaporation water washes down through the soils carrying minerals with it. These soils are called pedalfers and include podzols and brown earth soils.

Hard pan – a resistant layer in the soil at or below the surface. Usually caused by illuviation (deposition of minerals, humus and other materials) after leaching of the upper horizons. Hard pans can be formed of clay humus or a compound of Calcium, iron and silicon.

Soil formation – a profile

A

B

C

Horizons

Organic matter Humus

Translocation

Hard pan

Bed rock

When describing any soil you must mention the impact of climate, vegetation, parent material, soil biota, drainage and relief on its development

Brown Forest Soils

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Natural vegetation — deciduous forest vegetation provides deep leaf litter, which is broken down rapidly in mild/warm climate providing nutrients.Trees have roots which penetrate deep into the soil, ensuring the recycling of minerals back to the vegetation.Moderate leaching occurs leading to a thin iron pan whenever leaching is more active. In lower rainfall areas no iron pan can form.soil biota break down leaf litter producing mildly acidic mull humus. They also ensure the mixing of the soil, aerating it and preventing the formation of distinct layers within the soil.

South-facing slopes with a greater amount of sunshine and higher temperatures increase the rate of humus production.Soil colour varies from dark brown in A horizon to lighterbrown in B horizon where humus content is less obvious. Texture is loamy and well-aerated in the A horizon but lighter in the B horizon.The C horizon is derived from a range of parent material, with limestone producing lighter-coloured alkaline soils, clay producing dark coloured soils.

This is the most fertile of the three soils we study and it can support agriculture which allows greater human development and higher population density.

Podzol Slide 32

High levels of precipitation plus spring snowmelts leads to a great deal of water flushing through the soil causing rapid leaching of minerals and the formation of a thick iron pan.

Yellowish/ grey colour in the top soil due to leaching and a the lack of minerals from the parent material.

The Iron pan impedes drainage causing waterlogging and reduced bioactivity in the top soil.

• Pine cones and needles and a lack of other vegetation result in a very thin acidic humus (mor).

Soil horizons more clearly defined as there is little mixing due to restricted action of soil biota (this is a result of the cold climate).

Cold climate also leads to slow breakdown of plant materials, thin acidic humus.

greater altitude results in temperatures and the growing season being reduced and an increase in precipitation. This high precipitation and short growing season restricts the bioactivity (soil biota) to a short period of the year.

Steeper slopes tend to produce thinner soils due to gravity. These steeper slopes mean more downward movement of water which increases leaching forming an iron pan.

Parent material – may be fluvioglacial sands or till or acidic parent rock which determines the nature of the C horizon

Tundra/Gley Soils

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Gleys have damp waterlogged soils due to inadequate drainage resulting from permafrost layer found below the surface. Because of this waterlogging there is a lack of oxygen in the soil.

There is a lot of partially decomposed material due to the restricted level of biotic action. This is the result of a very short summer with low temperatures and the waterlogged soils.

Horizons are poorly defined due the movement caused by constant freezing and thawing.

Parent material is obvious within the B horizon. The vegetation is dominated by mosses and lichens

which produce acidic humus. Large areas of flat land in addition to the permafrost

increase the drainage problems and form large tundra ponds in summer .

REMINDER:

When describing any soil you must mention the climate, vegetation, soil biota, relief and the impact of each on

the development of the soil.

Soil catena showing variations in soil processes and effects along a slope

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Brown EarthBrown Earth Podzol Podzol GleyGley

Climate Climate Milder warmer Milder warmer climate leads to climate leads to increased biotic increased biotic activity and activity and decomposition.decomposition.

Moderate Moderate leaching occurs leaching occurs leading to thin iron leading to thin iron pan in some pan in some places where places where leaching is more leaching is more active.active.

High levels of High levels of precipitation and precipitation and spring snow melt spring snow melt leads to downward leads to downward movement of water movement of water and consequent and consequent leaching of mineralsleaching of minerals

Hard iron pan forms Hard iron pan forms and impedes and impedes drainage.drainage.

Cold temps. result Cold temps. result in slow breakdown of in slow breakdown of plant materials and plant materials and leads to a thin black leads to a thin black humus.humus.

Soils are waterlogged Soils are waterlogged due to inadequate due to inadequate drainage resulting from drainage resulting from permafrost. permafrost. Waterlogging leads to Waterlogging leads to lack of oxygen in soils.lack of oxygen in soils.

Constant freeze thaw Constant freeze thaw means horizons are means horizons are poorly defined and poorly defined and parent material is found parent material is found in the B horizon. in the B horizon.

VegetationVegetation A plentiful supply A plentiful supply of plant material of plant material (esp. from (esp. from deciduous leaves) deciduous leaves) leads to slightly leads to slightly acidic humus acidic humus

Acidic humus Acidic humus caused by nature caused by nature of the needles and of the needles and cones from pine cones from pine trees. trees.

Mosses and lichens Mosses and lichens dominate vegetation dominate vegetation leading to acidic humus leading to acidic humus

Summary Notes

Brown EarthBrown Earth Podzol Podzol GleyGley

Bio activity Bio activity (organisms) (organisms)

Horizons merge Horizons merge more gradually due more gradually due to increased action to increased action of biota. Leads to a of biota. Leads to a thick humus and thick humus and more minerals more minerals brought from the brought from the parent material.parent material.

Climate severely Climate severely limits soil bio limits soil bio activity so horizons activity so horizons are clearly defined. are clearly defined. Little influence of Little influence of parent material. parent material.

Because summer Because summer is so short and cold is so short and cold there is a very there is a very restricted biotic restricted biotic action. This results action. This results in lots of partially in lots of partially decomposed decomposed material in the soil. material in the soil.

Relief and Relief and drainagedrainage

Gentle slopes Gentle slopes lead to good lead to good drainage and drainage and restricts leaching.restricts leaching.

Less likelihood of Less likelihood of hard pan so soil is hard pan so soil is free draining free draining

Higher areas have Higher areas have more precipitation more precipitation and a shorter and a shorter growing season.growing season.

Steep slopes Steep slopes cause downward cause downward flushing of water flushing of water and increases and increases leaching and hard leaching and hard pan formation. pan formation.

Much flat land Much flat land which increases which increases drainage problems. drainage problems.

Summary Notes

As they burrow through the soil, earthworms drag dead leaves and other organic matter down to the

lower levels, and break them down into humus

This earwig and her babies are among the thousands of insects and other

small animals that live in soil.

Dung beetle feeding on animal dung and so help to

break down plant and animal matter.

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Soil

TIME

• 400 yrs for 10mm of soil to form

• 1000 yrs for 1mm in extreme conditions

• 3,000 – 12,000 yrs for farming soil

• Horizons develop when soil reaches maturity

PARENT MATERIAL

• Depth

• Texture (coarse or fine)

• Drainage (permeability)

• Nutrient content

• Colour

CLIMATE

• Determines rate of weathering

• Precipitation affect type of vegetation

• Dictates leaching or capillary action

• Temperature determines length of growing season and humus supply

SOIL BIOTA

• Nutrient cycle/recycling

• Bacteria and fungi decompose dead plants and animals

• Worms and termites aerate the soil

RELIEF/TOPOGRAPHY

• Altitude: soils are thinner higher up

• Aspect: Northern Hemisphere south-facing slopes are warmer and drier.

• Slope angle affects drainage and soil depth

HUMAN INFLUENCE

Affects soil development by

• Adding fertiliser

• Breaking up horizons by ploughing, draining or irrigating land

• Accelerating or controlling soil erosion

determines soil

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Equator

Tropic of Cancer

Tropic of Capricorn

Arctic Circle

Podzol

Podzol

Brown Earth Brown Earth

Gley Soil Gley Soil

Distribution of 3 Major Soil Types: Brown Earths, Podzols and Gleys.

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Brown Earth Profile

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Podzol Profile

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Gley Soil Profile

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Gley Soil Profile

Waterlogged Tundra in summer

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AB

C

Which soil type is which?

Simplified stages in

soil formation

HYPOTHESES: The sequence of soil profiles found in western Britain

1. Soil depth will decrease as gradient increases.

2. Soil moisture will decrease as gradient increases.

3. Soil acidity will be highest where gradient is lowest and leaching predominates.

4. Soil texture will be sandier where slope gradient is greatest and clay particles have been washed down-slope.

5. Organic content will be highest where slope gradient is lowest and soil depth greatest.

6. Soil acidity will be positively related to vegetation density.

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