Biosphere

Question 1

Formation of podzol soil

Answer 1

• layers AO, A, B, C
• found in upland areas of the UK
• coniferous forest (Christmas trees)
• partial, slow decay of vegetation due to cold climate
• short tree roots so don’t brung up any materials from weathered rock further down the profile
• pine needles decompose to form an infertile MOR humus
• high precipitation and snowmelt means leaving takes place. Minerals eg iron and aluminium are washed from the topsoil leaving it infertile and grey in colour
• re deposition of minerals leaves a hard pan layer which can sometimes impede drainage and make top soil wet (illuviation)
• reddish brown layer due to leached materials being redeposited
• distinct layers as cool conditions mean organisms can’t survive so no mixing occurs
• all this leads to an infertile acidic soil that can’t support life
• nothing grows so cycle is self perpetuating

Question 2

Formation of brown earth soil

Answer 2

• layers A, B, C
• found in moderate climates such as the UK
• deciduous woodland
• deep lead litter decays in warm climate to provide a rich, fertile humus. Moderate rainfall helps this process
• produce a less acidic MULL humus
• long tree roots bring up materials from weathered regolith, producing a fertile top soil
• precipitation > evaporation so some leaching occurs but most minerals remain in topsoil leaving it dark in colour
• the subsoil is also brown due to some leaching of minerals eg iron and aluminium from topsoil being redeposited
• underlying rock type is often sedimentary which weathers easily releasing minerals into the soil
• there are no distinct layers due to the presence of biota/organisms eg earthworms in the soil, causing mixing
• all this leads to a basic fertile soil which encourages plant growth and produces fertile humus enriching soil

Question 3

Formation of gley soil

Answer 3

• layers AO, A, B, C
• found in tundra zones
• heaths
• partially decayed black peat like MOR humus due to cold climate so slow decay of shrubs and heaths
• heavy rainfall and snowmelt leaches minerals out of the topsoil leaving it infertile and grey in colour
• GLEYING occurs which is when pore spaces fill with water so there is a lack of oxygen from iron compounds turning them from a red ferric colour to a blue ferrous colour
• may be some red flecks (mottling) where iron compounds haven’t been fully broken down due to small air pockets where re-oxygenation has taken place or when the soil dries out in summer
• frozen subsoil/permafrost means water can’t drain away leading to water logging
• distinct layers as cool, anaerobic conditions means few organisms present to mix layers
• all this leads to a poor, infertile soil that cannot support more than grass and small shrubs or heaths