Download A-level Environmental Studies Teacher guide Teacher guide

hij
Teacher Resource Bank
GCE Environmental Studies
Unit 2 ENVS2 The Physical Environment
• Teachers notes
Copyright © 2009 AQA and its licensors. All rights reserved.
The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee registered in England and Wales (company number 3644723) and a registered
charity (registered charity number 1073334). Registered address: AQA, Devas Street, Manchester M15 6EX.
Dr Michael Cresswell, Director General.
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
Unit 2 ENVS2 The Physical Environment
Introduction
These Teachers’ Notes are intended to expand upon Unit 2: The Physical
Environment by providing greater detail of the topics to be covered and how these
should be developed.
Examples included in the specification must be covered. Where specific examples are
not given, suitable examples should be chosen to illustrate the principles and issues
that are included in the specification. This guide includes suitable examples that may
be used (in italics) but others may be used if preferred eg if the candidates or teachers
have particular experience or knowledge.
It is anticipated that the use of carefully selected examples may reduce total teaching
effort by enabling a number of issues to be covered in a single situation. This will also
help candidates to appreciate the holistic, inter-connected nature of the subject and
prepare them for the study of broader issues such as sustainability in A2.
The emphasis should be placed on the environmental significance of aspects on the
features of the physical environment. ie how they affect the survival of life on Earth,
human exploitation of the Earth’s resources, the problems caused by human activities
and the possible solutions to these problems.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
1
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
UNIT 2 – The Physical Environment
The Atmosphere, Hydrosphere and Energy Resources
Physical resources such as atmospheric gases, water and mineral nutrients are essential for life on
Earth.
Humans exploit and manage physical resources to provide higher material living standards.
The use of many of these resources is unsustainable.
3.2.1 The
3.2.1
TheAtmosphere
Atmosphere
Study of the atmosphere involves consideration of the composition of the atmosphere and the
processes which influence life on Earth. Global climate change and ozone depletion are considered
in greater depth.
The composition of the atmosphere
The atmosphere is a mixture of gases that may be contaminated by varying levels of pollutants.
Candidates should know the normal percentages of the main gases in the atmosphere.
Gas
Nitrogen
Oxygen
Carbon dioxide
Rare gases
(combined)
Water vapour
Ozone
Normal atmospheric
concentration/%
78 %
21 %
0.038 %
1%
Variable
0.000007 %
A range of processes may cause the composition of the atmosphere to fluctuate .
eg photosynthesis/respiration on daily and annual cycles, evapotranspiration
The atmosphere is a turbulent, gaseous envelope that surrounds the planet and consists of several
layers, the most significant for life on Earth being the troposphere and the stratosphere. These are
also the layers which are affected by human activities.
2
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
Changes with altitude
Composition. More ozone naturally occurs in the stratosphere where UV interacts with oxygen.
Temperature declines with increasing altitude in the troposphere due to heating by IR from the
ground, but it increases with altitude in the stratosphere due to heating by UV from the sun.
Atmospheric pressure decreases with increasing altitude.
The importance of the atmosphere as a life-support system, a source of oxygen, carbon dioxide
and nitrogen for living organisms, and water vapour for the hydrological cycle.
The ozone ‘layer’ provides protection from ultraviolet light
Monatomic, diatomic and triatomic oxygen form a dispersed layer in the stratosphere. They absorb
ultraviolet light which produces a dynamic equilibrium of chemical reactions forming and
destroying ozone. The ozone layer prevents most UV from reaching the Earth’s surface.
Solar radiation and the atmosphere
The process of nuclear fusion as it occurs in the sun. The nuclei of hydrogen atoms join at high
temperatures causing the release of energy.
The wave nature of electromagnetic radiation and the electromagnetic spectrum, including its
wavelength characteristics, and the environmental importance of ultraviolet, visible and infrared
light.
The characteristics of radiation:
•
•
•
•
at outer limits of the atmosphere: mainly visible light and ultraviolet light
as it passes through the atmosphere: ultraviolet light is absorbed by ozone layer, some visible
light scattered, reflected or absorbed by clouds and particulate matter
some visible light is absorbed or reflected by particulate matter and clouds
when it reaches the Earth’s surface: remaining visible light reflected or absorbed, to be radiated
as infra red radiation.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
3
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
Global climate change
The Greenhouse Effect
The importance of the Greenhouse Effect as a natural phenomenon in controlling the energy and
heat balance of the atmosphere and Earth’s surface.
The infra red radiation emitted by the Earth’s surface is partly absorbed by gases in the atmosphere.
The atmosphere becomes warmer until the surplus heat energy is radiated into space.
Enhanced Greenhouse Effect and global climate change
The role of the gases in the atmosphere in maintaining the heat balance and global climate of the
Earth. How an increase in certain gases may result in heat being retained for longer and hence
global climate change.
The gases which may contribute to global climate change include:
carbon dioxide, methane, chlorofluorocarbons (CFCs), oxides of nitrogen and low level
(tropospheric) ozone.
The major anthropogenic sources of these gases:
•
Carbon dioxide
Combustion of fossil fuels, deforestation.
•
Methane
Livestock, padi fields, landfill sites (all due to anaerobic bacteria).
Produced during formation of fossil fuels and released by the ventilation of coalmines,
leaks from natural gas fields and pipelines.
•
Oxides of nitrogen
Reaction of oxygen and nitrogen in air at high temperatures in vehicle engines and
power stations.
•
Chlorofluorocarbons
Aerosol propellants, fire extinguishers, refrigerants, solvents, expanded foam plastics.
•
Tropospheric ozone
Produced by the photochemical breakdown of NO2 and subsequent reaction with
oxygen.
•
The changing concentrations caused by human activities.
Concentrations of some gases continue to rise while the concentrations of others, such
as methane, seem to have peaked, possibly due to attempts to control emissions.
4
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
The relative effects of these gases
Gas
Carbon dioxide
Methane
Tropospheric ozone
Nitrous oxide
CFCs
Approximate relative
effect per molecule
1
30
2000
160
25 000
The likely consequences of global climate change
Sea level rise:
• increased temperatures cause water to expand
• Increased temperatures cause land ice to melt, flow into the sea and increase the volume of the
sea.
Change in climate,
Most climate systems are driven by energy from the sun. Retention of more energy in the
atmosphere may change these systems:
• wind patterns – winds may change in velocity, frequency and direction
• precipitation – higher temperatures increase evaporation rates which will increase
precipitation rates. The water vapour will be transported by winds and result in
precipitation when the air cools sufficiently. Changed wind patterns may result in areas
getting more or less rain.
Ocean current changes.
El Niňo changes in the Peruvian current may become more frequent.
Increased amounts of cold freshwater in the North Atlantic from melting glaciers may cause the
Gulf Stream to slow and have less of a warming effect on NW Europe.
Ecological changes.
Temperature rise may cause plant growth rates to increase.
Precipitation changes may cause wetlands to enlarge or shrink.
Oak trees have deeper roots than beech trees and can survive droughts better.
Dormouse hibernation may be disturbed by warmer winters, causing them to use up stored fat and
have a reduced chance of survival.
The timing of ecological events such as flowering, migration and nesting may change. Survival of
interdependent species may be reduced eg if pollinating insects are not present when flowers are
produced.
There will be consequential changes in species distribution and extinction of species that cannot
colonise suitable new habitats.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
5
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
Difficulties of predicting global climate change
Some processes fluctuate naturally or have multiple causes;
there are limited historical records of climate data;
there are many positive and negative feedback mechanisms;
different processes may combine to increase or reduce effects;
changes may be slow;
changes may differ in different areas;
we have an incomplete understanding of how the climate and related processes are regulated.
Feedback mechanisms
Negative and positive feedback mechanisms could decrease or increase the rate and pattern of
global climate change.
Positive feedback mechanisms
A positive feedback mechanism occurs where an environmental change causes other changes which
increase the rate or amount of the initial change and therefore increase its effect.
eg raised temperatures cause the following:
increased rates of decomposition cause more carbon dioxide to be released;
reduced areas of ice and snow reduces the albedo of land and sea so less sunlight is reflected and
solar heating is increased;
methane released from methane hydrate in marine sediments;
melting permafrost releases methane gas that was trapped in the ice.
These either increase temperatures directly or increase the concentrations of the gases which will
cause further temperature rise.
Negative feedback mechanisms
A negative feedback mechanism occurs where an environmental change causes other changes which
decrease the rate or amount of the initial change and therefore reduce its effect and help to reestablish the original equilibrium.
eg higher temperatures cause increased rates of photosynthesis which stores more carbon in
biomass, increased low-level cloud may increase albedo and reflect away sunlight which will
reduce solar heating.
6
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
Control of global climate change
The need to reduce emissions of greenhouse gases with reference to recent
relevant international conventions
The Kyoto Protocol (1997)
MEDCs that sign up to the treaty are legally bound to reduce their emissions of six greenhouse
gases (collectively) by an average of 5.2 % below their 1990 levels by the period 2008–2012.
Countries that fail to achieve this will be punished by having their permitted emissions for the next
period cut by a further 30 %.
Each country has developed its own method to meet its target. The EU has identified
12 000 factories and power stations which have been given a carbon dioxide quota. If they exceed
this they can purchase extra allowances or pay a financial penalty. If they fall below the amount
they can sell the extra quota.
LEDCs do not have legally binding emission limits.
Methods of preventing the release of greenhouse gases
Candidates should be able to describe methods of reducing levels of the following greenhouse
gases:
Carbon dioxide
eg energy conservation, increased combustion efficiency, reduced use of fossil
fuels (by using other energy resources), ‘carbon sequestration’ by planting more trees, underground
storage of carbon dioxide released by power stations.
Methane
eg reduced use of landfill sites, collection and use of methane from landfill
sites, reducing livestock production, better collection of gas from coalmines and gas and oil
facilities.
Oxides of nitrogen
eg reduced use of internal combustion engines, removal of NOx by the
addition of urea to power station effluent gases, catalytic converters in vehicle exhaust systems.
CFCs
eg reduced use of CFCs by using alternative materials or methods –
hydrocarbons in aerosol cans, HFCs and HCFCs refrigerators trigger / pump action sprays instead
of aerosol cans.
Tropospheric ozone
eg reduced emissions of NOx will reduce tropospheric ozone levels.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
7
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
Strategies to cope with climate change
Climate change may require changes in lifestyle, infrastructure service and land use.
eg changes in building design to cope with temperature change or increase in storms;
changes in agriculture to cope with increased water demand for irrigation;
crop changes as temperatures rise;
land use changes and defences to deal with flooding by sea or rivers.
Ozone depletion
Ultraviolet (UV) light absorption
UV is categorized by its wavelength:
UVA: 320–400nm this is not absorbed by ozone
UVB: 280–320nm is almost fully absorbed by ozone
UVC: <280nm is completely absorbed by ozone and normal oxygen
The UV light considered in studying ozone depletion is UVB.
The effects of UVB light on the gases in the atmosphere
The chemical reactions producing a dynamic equilibrium of monatomic, diatomic and triatomic
oxygen. UVB is absorbed by both diatomic and triatomic oxygen. A dynamic equilibrium of
photolysis and subsequent molecule formation produces the ‘ozone layer’. The absorption of the
UVB prevents it reaching the Earth’s surface.
Summary of reactions
UV
O3
O2 + O
UV
The effects of UVB light on living organisms
When UVB is absorbed by living cells it can break up biological molecules causing skin damage,
DNA damage, skin cancer, cataracts and damage to plant tissue.
The role of pollutant gases
Halogens,especially chlorine in the stratosphere cause ozone depletion in a number of possible
reactions.
Ozone destruction
Cl + O3
ClO + O2
Reaction with monatomic oxygen (prevents formation of ozone)
Cl + O
ClO
ClO + O
ClO2
The ClO2 breaks down to release the chlorine which may repeat these reactions thousands of times.
ClO2
Cl + O2
8
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.1 cont…
CFCs
CFCs do not reduce ozone depletion but they break down in the stratosphere to release chlorine.
Past uses of CFCs: aerosol propellants, refrigerants, solvents, expanded plastic blowing agents.
Properties of CFCs: boiling point just below ambient so can be liquefied easily, solvent, not
flammable, most are not toxic.
CFC emission reduction:
• International agreements
The ‘Montreal Protocol (1987) which phased out manufacture and use of CFCs and
other ozone-depleting substances.
•
Replacement materials
HCFCs in refrigerators
Hydrocarbons eg propane and butane in aerosols
•
Alternative processes or methods
Trigger / pump action sprays.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
9
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2
TheHydrosphere
Hydrosphere
3.2.2 The
The Hydrosphere contains water in all its forms (solid, liquid and vapour) which may be found on,
in and around the Earth.
Environmentally significant properties of water
Changes of state (including hydrogen bonding)
These occur within a narrow temperature range, which allows the hydrological cycle to occur.
Anomalous expansion near freezing point
Ice floats and prevents lakes from freezing solid.
Solvent
Physiological solvent – most reactions occur with solutes dissolved in water, plant nutrients must be
dissolved, dissolved oxygen allows aquatic life to survive.
High heat capacity
Helps climatic stability by moderating temperature change.
The hydrological cycle
The locations of reservoirs of water in the hydrological cycle and proportion of
water stored in these reservoirs
Reservoir
Quantity of water/
% of total
Oceans
Land ice
Groundwater
Lakes & rivers
Soil moisture
Atmosphere
Living organisms
97
2
0.7
0.01
0.005
0.001
0.00004
Residence times and transfers between reservoirs
Candidates should be able to calculate residence times using the formula:
RT = Vol/mean transfer rate
An understanding of these helps in the management of water resources which are renewable, but
where individual reservoirs can still be depleted.
10
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2 cont…
Reservoir
Groundwater
Lakes
Soil moisture
Atmosphere
Average residence time
100 – 10 000 yrs
50 – 100 yrs
1 – 2 months
9 days
Some sources of water are abundant but are replaced slowly eg groundwater
The main process involved in the hydrological cycle
The processes and human activities affecting them should be studied.
Inputs
• precipitation – global climate change, deforestation
Transfers
• interception – amount and type of vegetation cover
• infiltration – soil compaction, ground cover eg urbanisation
• percolation – soil compaction
• throughflow – the flow of water through the pore spaces in the ground above the water table
• groundwater flow – abstraction, artificial recharge
• runoff – ground cover eg vegetation, urbanisation
Outputs
• evaporation – exposed surfaces eg reservoirs, global climate change
• transpiration – type of vegetation
• river channel discharge – abstraction
Sources of energy driving the hydrological cycle: solar insolation and gravity/potential energy.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
11
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2 cont…
Water as a resource
Uses of water
Abstractive uses
Domestic
eg washing, flushing toilets, food preparation, watering plants, drinking, recreation
Industrial
eg cooling, heating, washing, transport, steam generation for electricity generation, transport,
solvent
Agricultural
eg irrigation, washing, livestock drinking
Physical, chemical and biological criteria for assessing water quality for public supply and their
relative merits:
to include turbidity, pH, calcium content, pesticide and heavy metal concentrations, dissolved O2,
Cl2 retention and E. coli abundance.
Non-abstractive uses
Recreation
eg swimming, sport fishing, boating
Wildlife conservation in wetlands
eg wetlands/flooded gravel/clay pits/reservoirs
Energy
eg HEP reservoirs
Transport
eg canals
Study of these uses should include the associated problems and conflicts of interest and methods
used to resolve these conflicts.
eg Prohibition, restrictions, time zoning, space zoning
12
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2 cont…
Sources of water
The availability of water has a major effect on many aspects of life: domestic, agricultural and
industrial.
The major possible sources are: rivers, reservoirs, seawater, aquifers.
Rivers
Factors affecting the suitability of a river as a source of water.
eg annual flow, fluctuations in flow rate, level of contamination, turbidity
Reservoirs
The best hydrological sites for reservoirs are often those that have greatest value for scenery and
wildlife. This makes the decision-making process difficult.
eg Devon – increasing demand, highest demand in Summer when rainfall is lowest, no significant
aquifers, no large rivers, best reservoir sites within National Parks
Factors affecting the siting of reservoirs
Topography
Basin with large volume and small surface area.
Geology
Impermeable rock with no unstable faults, fissures or seismic activity.
Catchment area
Large catchment area to increase water volume.
Water supply
Reliable, regular rainfall and/or river flow, low evaporation rate
Existing land use
No more important existing land uses.
Pollution risk
No high risk activities within the catchment area.
Sedimentation
Low sediment load in inflow water.
Infrastructure
Availability of workers, building materials, equipment, closeness to area of demand.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
13
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2 cont…
Environmental effects of reservoirs
Sedimentation
Sediments deposited in reservoir and therefore do not flow further downstream.
Microclimate
Smaller temperature fluctuations, higher windspeed, higher humidity downwind.
River regime downstream of dams
Change in flow fluctuations, temperature, turbidity, fluvial features. eg meanders.
Habitat change
Flooding of reservoir site, division of river length producing a barrier to migration/dispersal.
Aquifers
Aquifers: suitable rock types
Porous, permeable rocks.
eg chalk, limestone, sandstone.
Porosity
A measure of the proportion of the volume of a rock which is space and therefore may hold fluids.
Permeability
A measure of the ease with which fluids may flow through a rock because of the interconnections
between the spaces and their size.
Suitable geological structures
The rock below the water-bearing rock must be impermeable to prevent the escape of the water.
eg granite, clay.
Some of the rock above must be permeable to allow recharge of the aquifer with water from above.
Consequences of aquifer overuse
The effects of over-abstraction, including:
•
Reduced supplies
If the extraction rate exceeds the recharge rate then the volume of water available for
abstraction will be reduced.
•
Subsidence
Water no longer present in interstitial spaces to support rock particles.
14
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2 cont…
•
Lowered water table causing changes to the surface hydrology:
reduced groundwater flow into rivers
•
Drying up of wetlands
eg marshes
•
Wildlife change
as plants with a higher water requirement die or fail to compete with plants with a lower
requirement.
Death of aquatic or semi-aquatic animals.
Loss of species that do not require high water levels, but rely on those species that do.
•
Salinisation
as seawater in the rock under the sea flows sideways into the aquifer to replace the freshwater
which has been removed. The salt makes the water unsuitable for irrigation as it may kill crops
by osmotic dehydration.
Seawater
Desalination of sea water is very energy intensive and expensive and is only used in countries with
inadequate freshwater supplies where sea water is available.
Water treatment
Processes involved in water treatment
Candidates should be able to outline the treatment processes used to supply water of potable
(drinkable) quality.
Freshwater treatment
Screening
using grilles or meshes to remove vegetation, plastic, paper etc
Sedimentation
allowing water to remain static to allow suspended solids such as silt to settle.
Aeration
using air bubbles or sprays to destroy odours such as hydrogen sulphide and to make some metals
insoluble.
Flocculation/coagulation and clarification
the addition of flocculants such as alum or polyelectrolytes to allow suspended solids with repelling
surface charges, eg clay to coagulate and settle.
Filtration
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
15
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
to remove suspended solids and bacteria.
3.2.2 cont…
Activated carbon filters
to remove organic chemicals.
eg pesticides
Sterilisation
The addition of chlorine, ozone, ultraviolet light
to sterilise the water and kill pathogens.
Fluoridation
to improve the dental health of people drinking the water .
Seawater
Desalination of seawater by:
• Reverse osmosis
The filtration at high pressure through a partially permeable membrane followed by the
collection of freshwater and rejection of very saline water.
Distillation
Water is boiled by heating and/or reducing the pressure. The steam produced is condensed and
collected.
Demand for water
The demand for water changes as changes occur in the society.
The causes of changes in demand:
• change in population size
• changing living standards
• industrialization – amount and type of industry
The spatial and temporal mismatch of supply of and demand for water in the
British Isles
Future demand for water
Regional changes in:
• amount of industry
eg industrial decline in North West England and South Wales
•
types of industry
eg less heavy water demanding industry in the U.K., more service industries
•
population growth rates
eg slow population growth in the U.K.
•
migrations for employment and retirement.
16
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
eg from N. England to S.E. England for Employment; from all areas to South coast for retirement
3.2.2 cont…
A comparison of per capita demand for water in More Developed and Less Developed
countries and the problems caused by water shortages
eg crop and livestock losses, less productive agriculture, restrictions on industrial development,
shortages causing time wastage in collecting water and the problems caused by the use of
contaminated sources
The difficulties involved in meeting the demand for water.
Water conservation and management
An outline of the strategies for providing adequate supplies to include the decision-making
processes and relative merits of the following:
•
Increase abstraction
•
Reduce use
•
Increase availability by reducing pollution of potential sources.
Details of how each strategy can increase supplies or increase usability of existing supplies
Surface storage reservoirs
to store surplus river flow for later use.
Aquifer recharge
to replenish partially depleted aquifers during periods of surplus surface water.
Desalination plants
to provide (expensive) freshwater from abundant sea water.
Estuarine barrages creating a freshwater lake
to create a reservoir with few land-use conflicts, but a high pollution risk.
Interbasin transfer
from areas of surplus to areas of shortage.
Catchment management
The prevention of pollution upstream of water abstraction points makes purification easier.
Reservoirs can be used to maintain river water levels in times of low natural flow and to store water
during periods of flood risk.
Conservation and recycling of water including the value of recycling of water.
Details of advantages and disadvantages of each method.
Grey water use
for uses where non-potable water is adequate.
eg flushing toilets
Metering
to discourage wasteful use.
Domestic appliances with lower water consumption.
eg washing machines
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
17
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.2 cont…
Leakage control.
Better maintenance of supply pipes, taps, appliances.
18
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3
TheLithosphere
Lithosphere
3.2.3 The
The natural processes affecting the distribution and availability of exploitable rocks, minerals and
elements in biogeochemical cycles are investigated and are developed further through a study of
their human use and the strategies to maximise their future availability.
The composition and formation of soils are considered to allow an understanding of their properties
and how they may be analysed. The importance of soils is expanded in Unit 4.
The importance of the Lithosphere
The Lithosphere provides resources for life on Earth and consists of the various components of the
Earth’s crust: rocks, soils, minerals and the land. Unsustainable exploitation of these resources can
result in:
•
•
•
•
the exhaustion of reserves
the increased production of harmful waste
land degradation
a lower quality of life for current and future generations.
Mineral Resources
The most important mineral resources:
Fossil fuels
Metal ores
Non-metal-ore minerals
The geological origins of economically important minerals
If all the minerals in the crust were evenly mixed then none of them would be sufficiently
concentrated to allow exploitation. Geological processes have provided local concentrations that can
be exploited.
Igneous processes
Granite produced in intrusive batholiths as molten magma cools slowly and minerals crystallize.
Hydrothermal metal ore deposits where mineral-rich hot solutions travel along fissures. They are
redeposited in a predictable order according to their solubilities.
eg ores of tin, copper, lead
Sedimentary processes
Existing rocks are broken down and removed (denudation: weathered and eroded)
Alluvial/placer deposits – sand, gravel, tin ore
Evaporites - salt
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
19
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Biological deposits – fossil fuels, limestone
Chemical precipitates – deep-sea manganese nodules
Metamorphic processes
Existing rock is exposed to extreme heat and pressure so its form changes but does not melt.
Slate is formed from sedimentary shale.
Resources, reserves and exploitation
Minerals are non-renewable resources because the amounts that exist are finite although most are
very abundant. Economically recoverable resources account for a tiny proportion of the total that
exists.
The main limitations on mineral availability are the locations, chemical form and purity of the
deposits, and the availability of technologies to exploit them.
Their exploitation is economically important but can cause environmental damage.
Resources and reserves
It is important to understand the difference between the terms ‘resource’ and ‘reserve’.
Resources include all the material which is theoretically available for exploitation. This includes
deposits that cannot be exploited now.
eg too deep, low grade, unusable chemical form, prohibitive land use conflict
Reserves include that portion of the resource which can be exploited now, economically, using
existing technology.
The size of a resource is finite but the quantity included in the reserves can change.
eg the reserves will increase if there is an increase in market price or if new extraction technologies
are developed. If market prices drop then reserves may decrease
Sources and demand
Factors affecting the viability of exploiting mineral deposits
Extraction costs
Affected by depth, overburden quality, drainage problems, size of deposit.
Processing costs: the chemical form of mineral.
The cost of extracting a metal depends upon the other elements with which it is combined.
eg aluminium is most abundant in clay but can only be economically extracted from bauxite
Purity
The financial cost, energy required and quantity of ore-bearing rock extracted all increase rapidly as
ore purity decreases.
20
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Land conflicts
Competing land uses may be considered more important or valuable than mining
eg urban areas, conservation of landscape or wildlife
Transport costs
These are affected by the distance to market, the ease of bulk transport and the presence of a suitable
existing transport infrastructure.
Market economics
The market demand and sale value of the minerals control the economic viability of exploiting a
particular mineral deposit.
The cut-off ore grade is the lowest ore purity that can be exploited economically.
The environmental impacts of mineral exploitation
Exploration, extraction and processing all cause significant environmental damage. A range of
methods may be used to reduce these.
Exploration
Marine seismic surveys affecting whales; exploration on land causing vegetation loss.
Land take
Extraction may cause conflicts with existing land uses.
Minerals can only be exploited where they are found. This makes land use conflicts more likely as
there is a limited choice of locations that can be exploited.
Habitat loss
The loss of the species where the mineral is to be extracted is unavoidable.
Removing the wildlife by capturing the animals and transplanting the plants to move them to
unthreatened habitats has been attempted but is rarely completely successful.
Habitat restoration when mining has ended is often carried out.
Loss of amenity
Mining may cause aesthetic problems for local communities.
This may be reduced by landscaping and tree planting.
Air and water pollution
Dust, reduced by water sprays.
Noise, reduced by baffle mounds and restricted times for blasting.
Turbid drainage water, reduced by sedimentation lagoons and filtration.
Toxic leachate, reduced by chemical treatment and containment.
Spoil disposal
Spoil instability can cause landslides or erosion.
It can be reduced by drainage, compaction and landscaping.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
21
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Transport nuisance
Mineral transportation can produce noise, fumes, dust and cause traffic accidents.
These can be reduced by water sprays and careful route choices.
Flooding can be caused by drainage water
The risk can be reduced by containment in lagoons behind well-constructed dams with carefully
timed releases.
Subsidence
This is caused by poor spoil compaction or undermining.
It can be reduced by compaction of spoil and leaving support pillars in deep mines
Turbid drainage water
Drainage water from mines or ore processing can smother aquatic plants and silt up rivers.
This can be reduced by building sedimentation lagoons.
Toxic leachate
Water draining from spoil heaps may contain toxic metals.
This may be reduced by collection and chemical treatment.
The future of mineral supplies
Reserves of exploitable minerals are finite. They are non-renewable resources. A range of methods
may be used to extend the time period in which they may be exploited.
More exploration
In previously unexplored areas, eg remote areas/areas with difficult conditions.
eg Antarctic; deep ocean floor for manganese nodules
Better exploratory techniques
Remote sensing
eg Satellite surveys – allow rapid aerial photography of large areas of land
Geophysical techniques
seismic surveys – echoes of surface vibrations provide information on depth, angle, density and
thickness of rock strata.
Gravimetry – the strength of gravity provides information on the density of rocks. Igneous rocks are
usually more dense than sedimentary rocks.
Magnetometry – the strength of magnetism helps to detect magnetic rocks, eg iron ores.
Better/more mechanised mining techniques
eg larger excavators which can dig deeper into the ground
Use of low-grade ores
eg electrolysis of spoil heap leachate to remove copper; bacterial recovery from disused mine spoil
22
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Recycling
to make used materials into a new resource.
eg melting of scrap metals and glass;
crushing of used concrete
Substitution
The use of alternative more abundant materials.
eg plastic pipes instead of copper;
fibre-optics instead of copper for telecommunications
Biogeochemical Cycles
The common features of biogeochemical cycles
The concept that the cycling of elements, including plant nutrients, occurs between the gaseous,
hydrological, sedimentary and biological reservoirs with varying residence times. They are driven
directly or indirectly by solar energy.
An understanding of these cycles aids the management of nutrient supply systems and the control of
human activities.
eg agricultural nutrient management;
control of eutrophication;
predicting global climate change
The carbon cycle
The main reservoirs of the carbon cycle
Candidates should know the principal reservoirs of carbon in the carbon cycle:
In the atmosphere: mainly as carbon dioxide.
In water: mainly as salts of carbonic acid (hydrogen carbonate ions) and dissolved carbon dioxide
In plants, animals and dead organic matter: mainly as carbohydrates, lipids and proteins.
In carbonaceous rocks (eg limestone): mainly as calcium carbonate.
In fossil fuels: mainly as carbon and hydrocarbons.
The main processes in the carbon cycle
Candidates should know the physical, chemical and biological processes involved in moving carbon
between the reservoirs in the carbon cycle.
Photosynthesis
The capture of light energy by pigments such as chlorophyll and the conversion of low-energy
substances such as carbon dioxide and water into high-energy carbohydrates which can be stored if
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
23
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
necessary. Oxygen is a by-product.
3.2.3 cont…
Respiration
The release of energy from high-energy substances, such as
carbohydrates, to drive metabolic processes.
Aerobic respiration can break down organic compounds more fully and release much more energy
than anaerobic respiration.
Anaerobic respiration allows some organisms to survive and use food sources in oxygen-deficient
environments.
Food chains
The passage of organic compounds as food between organisms.
Fossilisation
The incomplete decomposition of organisms, often under anaerobic conditions, leading to the
deposition of fossil fuels.
The absorption of carbon dioxide by marine organisms, its storage in their skeleton and subsequent
sedimentation of limestone and chalk on the seabed.
Combustion
The release of carbon dioxide by the burning of organic substances such as wood and fossil fuels.
Decomposition
The breakdown of organic matter by microorganisms, releasing gases such as carbon dioxide under
aerobic conditions and methane under anaerobic conditions.
Dynamic equilibria in the carbon cycle and factors affecting them
The concept of dynamic equilibria produced by active processes which produce an overall balance
by cancelling out the changes they cause.
eg photosynthesis and respiration normally form a dynamic equilibrium
The Gaia hypothesis considers the planet as a self-regulating system which resists change.
The effects of human activities on the carbon cycle and the environmental
significance of these changes
Fossil fuel exploitation
Combustion increases atmospheric carbon dioxide levels.
Coalmine and gas and oil processing all release methane.
Deforestation
Combustion reduces carbon stored in biomass and increases atmospheric carbon dioxide levels.
Reduced photosynthesis increases atmospheric carbon dioxide levels by reducing the fixation of
carbon in biomass.
24
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Agriculture
Livestock release methane into the atmosphere which may be subsequently oxidised to carbon
dioxide.
Soil disturbance increases the rate of decomposition which releases more carbon dioxide into the
atmosphere.
Rice padi fields release methane.
Global climate change
This increases the rate of decomposition which releases more carbon dioxide into the atmosphere. It
also increases the rate of photosynthesis which absorbs more carbon dioxide from the atmosphere.
The nitrogen cycle
The main reservoirs of nitrogen
In the atmosphere: mainly as gaseous nitrogen, with some oxides of nitrogen.
In plants: mainly as proteins.
In animals: mainly as proteins.
In dead organic matter: mainly as proteins which break down to release ammonium compounds.
In soil: as nitrates, nitrites and ammonium compounds
In water: as dissolved nitrates and ammonium compounds.
In rocks: in minerals containing nitrogen.
The main processes in the nitrogen cycle
The physical, chemical and biological processes involved in moving nitrogen between the reservoirs
of the nitrogen cycle.
Ionisation
The events that provide the energy for atmospheric nitrogen and oxygen to react and produce
oxides of nitrogen.
eg lightning and meteor trails (ionising phenomena)
Fixation
The chemical reduction of nitrogen to ammonia by some micro-organisms.
eg free-living in the soil, or in the root nodules of legumes.
Food chains
The passage of nitrogen between organisms as amino acids and proteins in food.
Nitrification
The oxidation of ammonium ions to nitrites then to nitrates by nitrifying bacteria in the soil.
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
25
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Denitrification
The chemical reduction of nitrates in soil to nitrogen and nitrogen oxide gases by denitrifying
bacteria in the soil.
Leaching
The loss of soluble substances such as nitrates from the surface layers of the soil as it is carried
away by water.
Absorption by roots
As soluble ions such as nitrates, nitrites and ammonium compounds.
The effects of human activities on the nitrogen cycle
Haber process
Artificial fixation of atmospheric nitrogen by converting it to ammonia using large amounts of
energy. details of chemical processes are not required.
Agriculture
The use of nitrate fertilizers may increase the problems caused by leaching, especially if application
is followed by heavy rain.
Drainage increases the numbers of nitrifying bacteria and reduces
the numbers of denitrifying bacteria.
Soil disturbance by ploughing increases the rate of decomposition which releases more nitrogen
oxides into the atmosphere.
Soil disturbance, changes in moisture content and aeration all change the abundance of the various
groups of bacteria in the nitrogen cycle. Nitrifying bacteria are often aerobic while anaerobic
bacteria are often anaerobic.
Legumes, eg peas and beans, may be grown to increase the levels of nitrogen compounds in the soil,
which crops can subsequently use.
Pollution
NOx are released into the atmosphere by combustion processes and may subsequently increase the
amount of nitrates washed into the soil by rain.
26
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.4.3 cont…
The phosphorus cycle
The reservoirs involved in the phosphorus cycle
Plants and animals
eg in bones, ATP and DNA
Sediments and rocks
eg apatite, calcium phosphate
Water
As dissolved phosphates produced by the weathering of rock
(most are relatively insoluble).
The main processes involved in the phosphorus cycle
Candidates should have a general understanding of the physical, chemical and biological processes
involved in moving phosphorus between the reservoirs in the phosphorus cycle.
Absorption by roots, food chains, decomposition, sedimentation, mountain building.
Candidates should be able to explain how the low solubility of phosphates and the absence of a
gaseous reservoir often makes the availability of phosphorus the limiting factor on plant growth.
eg in the open oceans
The effects of human activities on the phosphorus cycle
Use of phosphate fertilisers to increase yields
The rapid growth and subsequent decay of aquatic vegetation caused by effluents rich in phosphates
and nitrates.
eg fertiliser runoff and sewage effluent
klm
Copyright © 2008 AQA and its licensors. All rights reserved.
27
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
3.2.3 cont…
Soils
Soil and its properties have a major impact on plant survival in both natural and
agricultural habitats. All nutrients in biogeochemical cycles pass through the soil
The components of soil
Soil consists of :
Mineral skeleton (sand, silt, clay): soil texture
This affects nutrient levels, water content, aeration and drainage of the soil.
Air
This is found in the spaces between the solid particles which are not occupied by water.
The air affects the ease with which aerobic processes occur such as decomposition.
Water
This is found in the spaces between the solid particles. Nutrients can only be absorbed by
plants if they are dissolved in water.
Living organisms
These are responsible for decomposition, nutrient recycling and drainage.
Organic matter including humus
This is important as a source of nutrients and food for soil organisms. Humus is the complex
mixture of organic materials, including organic acids and the breakdown products of lignin.
Humus helps to hold soil together, retains water, aids drainage and acts as a thermal insulator.
The effect of soil properties on soil fertility and productivity
Aeration
Well aerated soil enables aerobic processes to occur rapidly such as decomposition and microbial
nutrient cycling. A high air content reduces the thermal capacity of the soil.
Water drainage, infiltration and retention
Some water is essential to enable nutrient absorption. If crops are short of water then stomata will
close to prevent dehydration. This will prevent carbon dioxide being absorbed so photosynthesis,
and therefore growth, would stop.
Thermal capacity
The composition of the soil affects its ability to retain heat and therefore the rate at which it heats up
and cool down. This affects how soon growth can occur in spring and the rates of chemical and
biological reactions in the soil.
Soil structure (crumb, blocky, platy peds)
The aggregation of soil into peds affects the ease of movement of air, water and roots through the
soil.
28
Copyright © 2008 AQA and its licensors. All rights reserved.
klm
Teacher Resource Bank / GCE Environmental Studies / Teachers’ Notes Unit 2 / Version 1.1
Practical Skills
Practical skills
klm
Candidates should have firsthand experience of soil
analysis methods
Soil analysis including texture (particle size of
sand, silt, clay), organisms, pH, water content and
organic matter. Candidates should be able to
identify soil types using a soil triangle
Copyright © 2008 AQA and its licensors. All rights reserved.
29