Download Biosphere model answers

Higher Geography
Paper one
Physical and Human
environment
Biosphere
Model answers
Soil profile model answer – Podzol
Past paper question
Select one of the following soil types:
1. Podzol
2. Brown Earth
3. Gley
With the aid of an annotated diagram of a soil profile, explain how the
major soil forming factors have contributed to its formation.
Past papers – ’91, ’93, ’95, ’98, ’99, ’02, ’04, ’06, ’07, ‘09
Climate
Podzols are found in a belt of the Northern Hemisphere associated with
coniferous forests. Cold, cool climates lead to a lack of soil biota and slow
decomposition of leaf-litter. Spring snow-melt and precipitation, although low,
exceeds evapotranspiration.
Coniferous forests create small amounts of pine cone and needle litter. Thin,
acidic humus (mor) develops from needle litter.
Natural vegetation
Precipitation and snow melt leads to a rapid leaching of iron and aluminium
oxides (eluviation) from the A horizon which leaves it rich in silica and ash-grey
in colour. The decomposition of iron oxides into the B – horizon (illuviation)
which then creates a red-brown colouring which may concentrate to form a thin
solid layer called an iron pan. This can impede drainage and can cause water
logging in the topsoil.
Soil Biota
Clearly defined horizons are created, by limited soil biota and slow activity due
to the cold climate which restricts soil mixing.
Parent materialWeathering of parent material contributes only slightly to soil
forming processes.
Soil profile model answer – Brown Earth
Past paper question
Select one of the following soil types:
1. Podzol
2. Brown Earth
3. Gley
With the aid of an annotated diagram of a soil profile, explain how the
major soil forming factors have contributed to its formation.
Past papers – ’91, ’93, ’95, ’98, ’99, ’02, ’04, ’06, ‘09
Climate
Brown Earths are found in the areas to the south of Podzols, in deciduous
forest. Although precipitation levels and spring snowmelt are less than podzol
areas, precipitation still exceeds evaporation (pedalfer). Due to the warm/cool
climate it encourages abundant soil biota and activity.
Natural Vegetation Deciduous forests provide plentiful supplies of broad leafed
litter. The resulting humus is very deep and only slightly acidic (mull). The annual
leaf fall returns bases to the soil.
Relief and Drainage
The A horizons texture may be quite greasy due to the high organic content.
The light brown colour as humus replaces leaching minerals. Leaching is a
significant process, but is moderate compared to Podzols. The iron pan may
develop where leaching is more active and iron and aluminium oxides are
deposited in the B horizon. The B horizon deepens when developing.
Soil Biota
More of the biota results in rapid decomposition of leaf-litter. This then leads
to the less distinctive soil horizons due to the mixing and aeration by biota.
Parent Material
The weathering of the parent material contributes to the soil forming process.
Soil profile model answer – Gley
Past paper question
Select one of the following soil types:
1. Podzol
2. Brown Earth
3. Gley
With the aid of an annotated diagram of a soil profile, explain how the
major soil forming factors have contributed to its formation.
Past papers – ’91, ’93, ’95, ’98, ’99, ’02, ’04, ‘07
Climate
The brief, mild summers and severe winter temperatures restrict the soil biota
activity. With the continual seasonal freezing and thawing with consequent
expansion and contraction leads to vertical mixing of the soil particles and
poorly defined horizons. The permafrost impedes drainage.
Natural Vegetation
There is limited variety of tough grasses ad ground hugging plants (e.g. mosses
and lichens) due to cold climate. This then produces dark, acidic humus (mor).
Relief and Drainage
Poor drainage is the key soil forming factor. The damp, waterlogging soils is due
to the poor drainage from permafrost layer a short distance below the surface.
The waterlogging removes the oxygen from the soil which creates anaerobic
(absence of free oxygen) conditions. This then leads to gleying, as the iron
compounds turn blue-grey in colour. The texture is greasy to touch.
Soil Biota
The soil biota activity is restricted due to waterlogging and climatic factors.
Little soil mixing and slow rates of humus decomposition result.
Parent Material
Weathered fragments of parent material are pushed up by freeze thaw into
blue-grey and peaty clays of B horizon.
Climax vegetation Model answer.
Past paper question
“Explain fully what is meant by the term climax vegetation?”
Past papers – ’92, ’94, ’97, ’99, ’05, ‘11
ü Pioneer plants (mosses, lichens) colonize bare ground e.g. sand dune,
mudflats, derelict sites
ü The pioneers weather the surface, retain water in their roots and bind
the soil. This gradually alters the area’s environmental conditions.
ü Pioneers die and decay to form a richer, deeper soil suitable for more
complex plant species to colonize.
ü Succession begins when environmental conditions begin to favour certain
plant species. These species can compete more effectively for available
nutrients, light, space and water. They shade out the ground from
sunlight, thus succeeding (replacing) the pioneers which are now less well
equipped to compete and survive.
ü When the ecosystem becomes stable and relatively unchanging the climax
stage is reached. This is the final stage of succession and the plant
community is in a state of dynamic equilibrium (i.e. continuous small
changes occur but overall stability is maintained.)
ü The climax vegetation is the most complex group of plants in an area and
develops over a long period of time.
Sand dunes model answer
Past paper question
“Describe and explain the changes in vegetation along a coastal sand dune”
Past papers – ’92, ’94, ’96, ’98, ’00, ’01, ’03, ’05, ’08, ’10, ‘11
Strandline/embryo dune
ü Sea Twitch/ Sea Rocket dominant species close to water’s edge as they
can withstand the –
o Desiccating (drying) effect of on-shore winds.
o High salinity
o Lack of humus
o High alkalinity levels (from calcium carbonate in shell fragments)
o
ü Some species e.g. sea couch grass can withstand short periods of
immersion in salt water.
ü These early colonisers help stabilise the embryo dune and decay to
provide humus for the next stage.
Fore Dune
ü Salinity decreases with increasing distance from the sea.
ü Humus content increases slightly from colonisers.
ü Soil acidity increases slightly due to less calcium carbonate.
ü
Plants e.g. Sea Holly continue to stabilise the dune, allowing the key
establishment of marram grass.
ü Marram grass succeeds Couch grass. It thrives on fresh supplies of sand
and its long roots stabilise the dune further and help the dune build up.
Yellow Dune/Main Dune
ü Alkalinity decreasing further and fresh water increasing both due to
increasing humus content from decay of vegetation on the fore dune.
ü Salinity continuing to decrease with increasing distance from sea.
ü As a result, marram grass now thriving together with wider variety of
plants e.g. Ragwort, Sea Bindweed.
Semi-fixed Dune
ü Once yellow dune over 10m high, less sand builds up behind it. Marram
grass dies out and forms thin humus layer.
ü Other plants able to grow here e.g. Dandelions.
Dune Slacks
ü Behind dunes, water collects in damp, sheltered hollows called dune
slacks.
ü The water table is near the surface which encourages the establishment
of cotton grass, reeds, creeping willow.
Grey dune/fixed dune
ü Damper soils with higher humus content
ü More acidic due to leaching of carbonates by rain
ü Shelter increases, so sand and salinity decreases
ü Wider variety of plants develop e.g. healthier, grasses, lichens
Climax vegetation
ü Grassland develops on alkaline soils, heathland on more acidic soils
ü High humus and water content allows these plants to succeed previous
vegetation.
ü Eventually, tree species e.g. oak, spruce are establish to give the climax
vegetation.