Biosphere

Question 1

Explain how brown soils are formed

Answer 1

brown earth soils are found in temperate areas of the world. The thick humus layer is formed by decaying leaves, for example from deciduous trees like chestnut and oak (1)
which shed their leaves in the autumn. (1)

organic material decays well in warm climates thus adding humus to the soil. (1)

long tree roots go deep into the soil allowing minerals to be moved about. (1)

there is a little leaching of the soil. Leaching of minerals can cause an iron pan to develop. (1)

the iron pan hinders soil drainage. (1) worms and moles help to mix the decaying litter which in turn helps to maintain fertility. (1)

worms and moles also help to aerate the soil and therefore prevent the formation of distinct layers in the soil (1)

Question 2

Draw a fully annotated soil profile of a podzol soil to describe its main characteristics (including horizons, colour, texture and drainage), and associated vegetation

Answer 2

• coniferous woodland/heather moorland (1 mark)
• layer of needles and cones (1 mark)
• black humus (1 mark), mor/acidic humus (1 mark)
• some darker staining in upper A horizon (1 mark)
• shallow spreading roots (1 mark)
• ash grey lower A horizon (1 mark) with sandy texture (1 mark)
• iron pan develops in lower A / B horizon (1 mark) impeding drainage (1 mark)

Well defined horizons (1 mark), few soil biota (1 mark)

• B horizon is reddish brown (1 mark) with denser texture (1 mark)
• downward movement of water (1 mark)
• C horizon is generally glacial or fluvioglacial material (1 mark)
• partially/not well weathered parental material.

Question 3

Explain the main conditions and processes which lead to the formation of a gley soil.

Answer 3

limited vegetation produces a thin acidic organic layer/mor humus (1 mark)

low temperatures cause a slow rate of decomposition (1 mark)

• heavy precipitation/snow melt causes waterlogging. (1 mark) Found on flat surfaces as relief can cause drainage problems. (1 mark)

Impermeable clays can impede drainage (1 mark)

• waterlogged soil creates anaerobic conditions (1 mark), meaning iron compounds are changed from red brown to blue (1 mark), due to oxygen being extracted by microorganisms (1 mark)
• cold temperatures/waterlogged conditions mean few organisms can survive (1 mark)
• limited biota reduces mixing causing clearly defined layers (1 mark)
• burrowing animals/soil drying out in summer leave oxygen pockets (1 mark) this allows re-oxygenation of the iron (1 mark) in the soil causing a red mottling effect (1 mark)
• shallow roots limit the recycling of minerals. (1 mark)
• Freeze-thaw takes place causing vertical mixing (1 mark) causing large chunks of angular rock to be brought up to the A and B horizons. (1 mark)

Question 4

Explain the main conditions and processes involved in the formation of a podzol soil

Answer 4

· low temperatures lead to slow decomposition (1 mark)

· coniferous needles and cones produce acidic (mor) humus (1 mark)

· high precipitation leads to leaching (1 mark) which is the downward movement of the aluminium and iron oxides (1 mark), this leads to formation of an iron pan between the A/B horizons (1 mark)

· this iron pan may impede drainage causing water logging (1 mark)

· eluviation leaves an ash grey A horizon (1 mark)

· illuviation leads to a reddish brown B horizon (1 mark)

· limited soil biota leads to well defined horizons (1 mark)

· found on steep slopes, this further encourages leaching (1 mark)

· shallow roots mean limited absorption of deep leached minerals (1 mark)

· shallow roots also mean limited nutrient recycling. (1 mark)

Question 5

Explain the main conditions and processes involved in the formation of a brown earth soil.

Answer 5

natural vegetation — deciduous forest vegetation provides deep leaf litter, which is broken down rapidly in mild/warm climate (1 mark)

· trees have long roots which penetrate deep into the soil, accessing nutrients from lower layers which are recycled to leaves (1 mark)

· soil organisms — they ensure the mixing of the soil, aerating it and preventing the formation of distinct layers within the soil (1 mark)

· climate — precipitation slightly exceeds evaporation, giving downward leaching of the most soluble minerals and the possibility of an iron pan forming, impeding drainage (1 mark)

· aspect — south-facing slopes in northern hemisphere with a greater amount of sunshine and higher temperatures increase the rate decomposition resulting in humus layer (1 mark)

· rock type — determines the rate of weathering, with hard rocks such as schist taking longer to weather, producing thinner soils.

Softer rocks, such as shale, weather more quickly (1 mark)

· relief — tend to be found on gentler slopes leading to lower rates of erosions so thicker soils (1 mark)