Transcript Human Impact

Human Impact on the
environment
AH Biology
Unit 2 Environmental Biology
Changes to ecosystems
Human Impact on the environment
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i Changes in complexity.
ii Effects of intensive food production.
iii Effects of increased energy production.
iv Pollution.
Succession - Arrangements
• Autogenic succession (primary and
secondary succession).
• The increase in complexity of ecosystems from
pioneer through to climax communities.
• Facilitation of change in early stages.
• Increase in complexity shown by increase in
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diversity of species,
variety of habitats and niches,
complexity of food webs.
Changes in stability and productivity through
succession.
Changes in complexity
Arrangements
• Reference to effects of external factors in
allogenic succession and relatively short-term
nature of degradative (heterotrophic)
successions.
• Loss of complexity through human activity as
illustrated by
– monoculture,
– eutrophication (algal bloom and its
consequences),
– toxic pollution,
– habitat destruction.
Succession
• This is the non-seasonal, directional and
continuous pattern of colonisation and
extinction at a site by populations of species.
• Pioneers
r-strategists
Rapidly changing
Climax community
K-strategists
stable communities
Categories of succession
• Autogenic succession – natural sequence
– Primary succession
– Secondary succession
• Allogenic succession
• Degradative succession
Changes in complexity
• Limited complexity is typical of naturally
stressed communities
• Loss of complexity is also typical of stressed
communities associated with polluted
habitats that may result from
– Eutrophication
– Toxic
• Reduction in complexity can also be a result
of
– Monoculture
– Habitat destruction
Eutrophication
• “Enrichment of waters by inorganic plant
nutrients, usually nitrogen and phosphorous,
which increases primary production”
• Freshwater ecosystems are classified by the
status of nutrients in their waters.
– Oligotrophic = nutrient poor and unproductive
– Eutrophic = rich in nutrients and productive
– Mesotrophic = waters that fall in between
Factors which influence the rate
of eutrophication
• Natural eutrophication is caused by natural features
of a lakes catchment, e.g. a lakes nutrient content
rises with age.
• Cultural eutrophication – anthropogenic influences.
• Most important factors in temperate lakes are:
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Fertility of drainage basin
Seasonal behaviour of the water
Depth of a lake
Temperature of the water
Rate of turnover of the water
Cultural eutrophication
Cultural Eutrophication of lakes
and rivers
• Areas of concern for lakes and rivers
– Acidification of lake water associated with acid rain
– Introduction of toxic wastes
– Eutrophication
• Effects of cultural eutrophication
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Species diversity decreases and the dominant biota change
Turbidity increases
Rate of sedimentation increases
Anoxic conditions may occur
Further problems caused by
eutrophication
• Difficulties in the treatment of drinking water
• Growth of algae may leave unacceptable
tastes or odours in the water supply
• Water may be injurious to health
• Amenity value is reduced
• Growth of plants may inhibit water flow and
navigation
• Loss of salmonids and coregonids from water
may have economic consequences for
fisheries
Causes of Cultural
Eutrophication
• Soil erosion may increase phosphate levels in
the water
• Nitrates from inorganic fertilizers or from
sewage treatment facilities
• Phosphate from animal waste; sewage or
manure
• Possible solution to eutrophication is to limit
the amount of phosphorous going into
watercourses, as it is cheaper to remove at
sewage treatment plants.
Stages of Eutrophication
• Algal bloom – caused by the effect of
fertilizers on the growth of microscopic green
algae
• Rapid growth of algae causes death of higher
plants
• Flow rate of river slows down
• Older algae decompose, bacterial
populations increase (BOD increases)
• Fish are killed and the entire food web of the
river is disrupted.
Toxic pollution
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E.g. pesticides, insecticides or heavy metals
Loss of diversity
Reduction in species richness
Species present in large numbers due to lack
of interspecific competition in polluted
habitats
Toxic pollution
• Problems with pesticides
– Kill non-target species
– target species evolve resistance to the insecticide
– some insecticides become concentrated up food
chains
• PCB’s and heavy metals
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Egg shell thinning
Interference with mammalian reproduction
Damage to the immune system
Carcinogenic
Monoculture
• Loss of diversity by modern agricultural
practices
• A single crop species is grown over a large
area, reducing the complexity of the
ecosystem to a single species.
• Unstable ecosystem, at risk from interspecific
competition.
Habitat destruction
• Britain's wild orchids
disappearing habitats
• Annual
deforestation
estimates
Essay question
Give an account of the
types of succession and
the changes in complexity
of ecosystems as a result
of succession.
Effects of intensive food
production.
• Monoculture and its effect on
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soil condition,
field size,
shelter
habitats.
• Environmental impact of increased use of
pesticides and chemical fertilisers in relation to
species diversity and loss of stability.
Development of Farming in
Britain
• 14, 000 y.a
– domestication of dogs from semi-wild animals
• 9,000 – 10,000 y.a
– domestication of cattle, sheep and goats
– gatherer-hunters
• 5,000 – 6,000 y.a
– Agriculture develops
– lowland deforestation for crop growing
Intensive farming
• This is an open system; there is a net loss of nutrients
as large yields are being exported from the farms,
which then has to be replaced by fertilisers.
• Animals are farmed at high densities, which increase
the chance of catching diseases due to stress, and
overcrowding, this leads to antibiotics being added
to their food.
Pupil Activity
• With the use of a highlighter, read the
handout on intensive farming – advantages
and disadvantages.
Monoculture
• Single species cultivated over a large area for
economic efficiency
• Disadvantages
– Replacement of naturally diverse communities
with a single species
– Removal of nutrients (open system)
– Leaching of nutrients from soil
– Soil erosion
– Invasions by pests
• Weeds, insects and animal pests, pathogenic fungi,
bacteria and viruses.
Hedgerow Destruction
• Hedgerow
– narrow belt of vegetation dominated by shrubs
and occasional trees.
• Traditionally hedgerows served two functions
– A barrier to the movement of livestock.
– Marking property boundaries.
Hedgerows have a high landscape and
conservation value
• They are a traditional feature of the landscape and
add diversity to it.
• Provide foraging, roosting and nesting sites for birds.
• Rich in plant and animal species.
• Act as a source of beneficial insects.
• Act as wildlife corridors through an increasingly hostile
agricultural landscape.
Hedgerow losses
• Estimated that between 1945 and 1970 there
was an annual loss of about 8,000km year-1 in
the U.K.
• In the 1990’s it is estimated that the U.K. was
still losing 5,000 – 6,000 Km year-1.
Advantages of Hedgerow
removal to the farmer
• Hedgerows act as a refuge for weeds,
diseases and crop pests.
• Reduce the loss of crop yields adjacent to the
hedge
• Bigger field sizes – decreases the amount of
land needed for turning machinery.
Disadvantages of Hedgerow
removal to the farmer
• Increases soil erosion
• Reduce crop yields through the loss of
beneficial insect species
– Predators for pest control
– Pollinators
Pollution from farm wastes
• Fertilisers
– Nitrogen from fertilisers can build up in the soil.
– Soil bacteria then convert this to nitrates.
– The nitrates then get into stream and river
systems through surface run off.
• Pesticides
– Bioaccumulation in food chains
– Non specific
Major changes in agricultural activity in
the U.K. since the 1940’s
• Increasing levels of farm mechanisation,
energy inputs and decline in the labour force
• Development of highly productive strains of
crops and livestock
• Increasing use of fertilisers and pesticides.
• Changes in farm sizes.
• Changes in farming practices and
significance of different crops.
• Financial returns.
Pupil Activity
• Diagram – consequences of modernisation of
agriculture on ecology and wildlife interests of
farmland.
– Stick the diagram into your book
– Write out a paragraph discussing the diagram,
including any comments that you can draw form
the diagram.
Essay question
Discuss the
advantages and
disadvantages of
intensive food
production
Effects of increased energy
production.
• Fossil fuels as finite energy resources.
• Need for conservation and use of alternative sources
of energy.
• Air pollution from fossil fuels:
– acidic gases (sulphur dioxide, nitrous oxide, carbon dioxide)
and greenhouse gases (carbon dioxide and water)
produced.
– Other greenhouse gases include methane and CFCs.
• Enhanced greenhouse effect and effects of global
warming on abundance and distribution of species
– E.g. zooxanthellae and 'coral bleaching'.
Fossil fuels
Alternative energy sources
Atmospheric Pollution
• Atmospheric pollution can be attributed to
anthropogenic causes; it causes harm to
humans and other living organisms in the
environment.
• By the late 20th C. atmospheric pollution
effects can be seen in all nations of the world.
• Air pollution is a global problem as it ignores
international boundaries, as does the wind
that carries it. This had led to international cooperation and global legislation for air
pollution.
Atmospheric Pollution
• The increase in pollution over the last 150
years can be attributed to the increasing
human population and increases in urban
and industrialised societies.
• There are 3 main concerns of atmospheric
pollution
– Acid rain
– Greenhouse effect
– Climate change / global warming
Acid Rain
• Explain the production of acid rain and it’s
effect on lakes and forests
• 1872 - The Scottish chemist, Robert Angus
Smith, first used the term “Acid rain”.
• Acid rain is used to describe the acidity of wet
and dry deposition
– Wet deposition
fog
– Dry deposition
= rain, snow, hail, sleet, mist or
= gases and particles
Acid Rain
• Natural precipitation is weakly acidic (pH 5.6),
as carbon dioxide dissolves in rainwater it
forms weak carbonic acid.
– In Britain, Europe and North America, often find pH
of 4 or 4.5
– 10th April 1974 – Rainstorm in Pitlochry, Scotland, pH
2.4
• The increasing acidity of rainwater has been
attributed to the production of sulphur dioxide
(SO2) and nitrogen oxides (NOX) during the
burning of fossil fuels.
Pupil Activity
• Read the Aric Fact sheet “What is Acid Rain?
• Answer the following questions
– What are the natural sources of sulphur dioxide
and nitrogen oxides?
– Compare the quantities of natural sources of these
gases, and those released from emissions.
Formation and Deposition of
Acid Rain
Formation and Deposition of
Acid Rain
• Washout – when acids present below the
clouds are taken up by the falling rain or
snow.
• Rainout – when cloud water droplets or ice
crystals containing acids grow to sufficient size
to fall.
Effects of Acid Rain
Terrestrial Ecosystems
• The most noticeable symptom of acid rain in
terrestrial ecosystems is in trees
– Conifers most at risk, as they do not shed there
pines all at once.
– Deciduous trees only have a few months to
intercept acid rain, so only a seasons growth is
damaged
• As a result trees need extra energy to grow
extra leaves, which can lead to a failure to
reproduce, increasing susceptibility to
disease, pests, drought and frosts.
The Effects of Acid
Rain on Trees
Effects on trees include
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Poor growth
Lower productivity
Discolouration of needles
Shallow roots
Dieback of crown
• In Europe, deterioration can be seen in Norway
spruce, Scots pine and beech.
• In areas affected by acid rain populations of wildlife
have declined (h/out impacts of air pollution and
acid rain on wildlife)
Pollution of the Air
Structure of the atmosphere, and absorption of
ultraviolet and infrared light
Carbon Dioxide
The Greenhouse Effects
• Outline roles of carbon dioxide and methane
in enhanced greenhouse effect and global
warming.
• Appreciate international efforts to reduce
carbon dioxide emissions.
Carbon Dioxide
• Carbon dioxide is naturally occurring in the
atmosphere at a concentration of less than
0.05%.
• CO2 Levels
– Constant 2,500 – 200 ya 270ppm
– Since industrial revolution risen to 360ppm
• Since 1960 levels have been slowly rising
Carbon dioxide concentrations in
the Northern Hemisphere
Seasonal variations in CO2
concentrations
• Spring & summer – CO2 levels fall, as plants
make new leaves and grow
• Autumn & winter – CO2 levels rise as leaves
fall and decay, producing CO2
• 2 reasons for overall rise in CO2 levels
– Global use of fossil fuels as energy source; fossil
fuels act as sinks in the carbon cycle, carbon
would not naturally escape.
– Increase in the destruction of the world’s forests.
Trees act as carbon reservoirs
Rate of CO2 fixation by trees
• Tropical rainforest
– between 1-2 kg/m2 carbon per year
• Deciduous forest
– 0.2 – 0.4kg/m2/year
• Increasing CO2 levels caused by deforestation
is reversible. As regrowth of forests would use
CO2 and release O2
• Forests can be renewable energy resources if
allowed to grow.
Greenhouse Effect
• The presence of the atmosphere increases
the Earth’s surface temperature by an
average of about 33oC.
• Sun’s energy travels through the atmosphere
and warms the Earth’s surface.
• Some heat is radiated back into the
atmosphere where the gases prevent heat
energy from escaping into outer space.
Sources of Greenhouse Gases
Greenhouse gas
Water vapour
(H2O)
Carbon Dioxide
(CO2)
Source or origin
Evaporation and transpiration
Combustion of fossil fuels, wood
CFC’s
Refrigerators, aerosol sprays
Methane
Cattle, rice fields, bogs and
rubbish tips
(CH4)
Nitrous oxide
(N2O)
Ozone
(O3)
Denitrification
Secondary pollutant from car
exhausts
Carbon dioxide and Methane
• Due to human activity CO2 and CH4 are increasing
in abundance. This may be causing global
warming by enhancing the natural greenhouse
effect of the atmosphere.
• Methane (CH4)
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Primarily from the breakdown of cellulose
Animal emissions exceed 100 million tonnes
10 times more effective as a greenhouse gas than CO2
Concentration in the atmosphere is lower than carbon
dioxide
– Increase 800ppbv to 1720ppbv in last 200 years
• Carbon dioxide contributes about 60% to the
greenhouse effect, methane contributes about
15%.
Climatic Effects
• Climate in naturally variable, last 100 years
seen an average world temperature rise of
0.5oC
– Predicted a 1oC – 5oC rise in the next 50 years
• What evidence?
– The effects of global warming are not known, and
many scientists remain unconvinced that it is
occurring.
Present Situation
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Oceans surface is warmer at the equator
More water evaporates
Warm air rises faster causing stronger winds
Moisture laden air is carried further from the tropics
Less rain in the tropics
Floods in temperate regions
• Last 30 years seen more extremes of weather
and more droughts in the tropics
El Nino
• Warms surface waters off the coast of South
America
• Causing drought and conditions in Australia
and Indonesia
• Torrential rain in Peru and Ecuador.
• If El Nino lasts for 12 months or longer, it
severely disrupts populations of plankton, fish
and seabirds in upwelling areas and can
trigger extreme weather changes over much
of the globe.
Normal Conditions
El Nino Conditions
Future
• Death and destruction from hurricanes and
floods
• Ice caps melt – rise in sea levels
• Polar meltdown would switch the path of the
Gulf Stream
– colder climate in the North Atlantic and UK.
Effects of Global Warming on
British Flora
• Increasing the northwards range of rare
orchids
• Plants adapted to the cold would suffer e.g.
bluebells rely on a cool spring
• Due to the complexity of ecosystems it is very
difficult to predict how changes in climate will
affect biodiversity. However the combination
of this and habitat loss is not looking good for
biodiversity.
International efforts to reduce carbon dioxide
emissions
• 1998 –
international panel on climate change
formed to report on the global situation
• 1992 –
climate change convention was signed
at the Rio Earth Summit in 1992 (greenhouse gas
emissions to go back to 1990 levels by 2000)
• 1997 Kyoto Protocol
• Recognised this was unachievable
• Targeted CO2, methane, nitrous oxide, some
fluorocarbons and sulphur hexafluoride.
• Aim to cut emissions to 5% below 1990 by 2010
• Each nation given a specific target – allowing countries to
trade in carbon emissions
Montreal vs. Kyoto Protocol
Montreal Protocol
Kyoto Protocol
Ozone depletion was evident
Uncertainty about the actual
consequences of global
warming.
Technology existed to replace
CFC’s with less damaging
products
Developed world is reliant on
fossil fuels, no easy alternative
energy source.
- Developed countries need
to make the major
contribution to lowering
greenhouse gas emissions.
• Another reason for lack of success is the
current political climate.
• To stabilise atmospheric CO2 at 560ppm
(which is two time the natural level), requires a
reduction to 60% below 1990 levels.
Approaches to reducing
Emissions
• Less reliance on fossil fuels, switch to renewable
energy resources
• Energy saving measures – insulating houses
• Lower expectations about the standard of living
• Plant more trees (CO2 sink)
• Alternatives to petrol and diesel for a fuel – “clean
sources of energy”
• Pump CO2 underground or down to ocean floor
• Encourage massive oceanic algal blooms to trap
CO2 in organic matter.
Example
– zooxanthellae and “coral bleaching”
• Communities of coral polyps in a symbiotic
relationship with a single celled algae called
zooxanthellae.
• Corals can only tolerate a narrow range of
temperatures
Temperature rise and coral
bleaching
• Rising water temperatures block the photosynthetic
reaction that converts carbon dioxide into sugar.
• This results in a build-up of products that poison the
zooxanthellae.
• To save itself, the coral spits out the zooxanthellae
and some of its own tissue, leaving the coral a
bleached white.
• The bleached coral can recover, but only if cooler
water temperatures return and the algae are able
to grow again.
• Without the zooxanthellae, the coral slowly starves
to death.
Essay question
Give an account of the
need for conservation and
use of alternative energy
sources, including the
greenhouse effect and
global warming.
Pollution.
• Biodegradable organic pollutants and changes in
biochemical oxygen demand (BOD).
• Major types of toxic pollutants and their sources
– DDT
– heavy metals.
• Bioaccumulation.
– Consequences of biological magnification in food chains.
– Biotransformation.
– Toxicity and persistent/non-biodegradable nature of DDT.
• Susceptible and favoured species
– the use of indicators in the monitoring of quality of fresh
water ecosystems.
Biodegradable organic
pollutants
• Biodegradable organic pollutants include:
– Sewage
– Farm waste
– Industrial waste
• Problems arise when the system becomes
overloaded and eutrophication ocurs.
Biological Oxygen Demand
(BOD)
• Definition
– The mass of dissolved oxygen, in grams per cubic
metre or milligrams per cubic decimetre, taken out
of solution by a water sample incubated in
darkness at 20oC for five days.
Biological Oxygen Demand
• BOD is a common measure of organic
pollution
• Calculation of BOD
– How much oxygen is taken up by a sample of
water when it is kept in the dark for 5 days at 20oC.
– Kept in the dark to prevent photosynthesis.
– Therefore the oxygen used up is by the microorganisms breaking down organic matter.
The table below shows the BOD of some organic pollutants, the figures are
for before the pollutants enter a river (once in a river the pollutant will
become diluted).
Indicator Species of Water
Pollution
• In order to use indicator species as a measure
of organic pollution you must first understand
the tolerance levels of different species to
pollution.
• A level for pollution is estimated depending
on the presence or absence of certain
organisms from a habitat.
• Biological monitoring gives a summary of the
recent history of the environment.
Indicator Species of Water
Pollution
• In 1964, Trent River Authority devised a recording
system for monitoring the pollution of watercourses.
• BMWP Score Sheet – points are allocated on the
presence of invertebrate families. The score is
totalled them divided by the number of groups
present. The lower the score, the more polluted the
river.
• Aquatic plants and invertebrates complement each
other as biological indicators, as they have different
tolerance levels to certain chemicals.
Pupil Activity
• Explain why the use of biochemical oxygen
demand and indicator species may give
different measures of water pollution.
The effects of an organic effluent on a river at different
distances downstream from the outfall
A + B = physical and
chemical changes
C
= changes in microorganisms
D
= changes in larger
animals
(based on Hynes, 1960)
Events affecting quality of water
in a river
• In a given stretch of river, there is continual
exchange of water, so that events at some
distance upstream can affect the river much
lower down.
Pupil Activity
• Sewage – inadequate treatment leading to
pollution
– Using the information given in the handout, in the
table and in the graphs, explain as fully as possible
the changes of water quality, and plant and
animal populations in a river after the introduction
of sewage
Pesticides and Toxins
• Appreciate the need for pesticides and explain the
consequences of pollution by DDT.
• Pesticides are an important group of agricultural
chemicals, which are designed to kill organisms,
therefore their use has health and environmental
concerns.
• Need for pesticides
– Necessary in intensive farming regimes to;
• prevent damage of crops whilst growing
• give a longer shelf life to fruits and vegetables by reducing
decay from surface micro-organisms
• reduce the infection of farm animals
The Ideal Pesticide
• effective at low dosage against its specific
target
• inexpensive to manufacture
• non-polluting
• Plentiful
• easy to apply
• breakdown products should be harmless to
non-target organisms in air, soil and water
Problems associated with
certain pesticides
• pose a risk to human health
• herbicides have a rapid breakdown and are
only toxic when absorbed or ingested in high
concentrations
• fungicides not known to have environmental
effects?!
Insecticides
• Early insecticides include:
– stomach poisons
– tar oils
– plant extracts
• Since 1940’s 3 main types of insecticides come into
use
– Organochlorines (chlorinated hydrocarbon compounds)
• Examples – DDT, Dieldrin
• Ecological effects of DDT, accumulation of toxin in food
chains
– Organophosphate compounds
• Examples – malathion and diazion
• Very toxic to insects and humans
Insecticides
– Carbamates
• Examples – carboxyl, aldicarb
• Do not leave long lasting residues in environment
• Lethal to non-target organisms
• Problems with pesticides
– Kill non-target species
– target species evolve resistance to the insecticide
– some insecticides become concentrated up food
chains
Bioconcentration
• Materials are absorbed whilst being used for
feeding or respiration/
• Materials then may move to storage sites
within the body where it can accumulate and
concentrate.
Biomagnification
• Materials are concentrated through ingestion,
and incorporation into the body of the
consumer (aquatic food chains)
• Substances which are harmless at original
environmental concentrations may
concentrate to levels at which toxic effects
are significant.
• E.g. The DDT story and its warnings
Case Study: DDT
• The story of dichlorodiphenyltrichloroethane
(DDT to its friends)
• In 1939 DDT was first used as an insecticide.
– DDT and other Organochlorines last for 10-25 years
in the environment.
– As they are more soluble in fat than water, once
they have been ingested they remain in fatty
tissues (lipids).
• DDT and Organochlorines have been found
to accumulate in food chains.
Case Study: DDT
• In the 1950’s the numbers of peregrine falcons in Europe halved
over 20 years, this was traced to DDT dressing put on seeds,
eaten by pigeons, eaten by the Falcons.
• The DDT caused the falcons to lay eggs with thinner shells, so
when they were sat on they were smashed.
• In the 1980’s, after restrictions on the use of DDT, falcon
numbers returned to normal.
Pupil Activity
• Read through the information, answer the
questions on “pesticides and
Bioaccumulation”.
Case Study: Clear Lake, California
• The earliest example of Bioaccumulation comes
from Clear Lake in California.
– 1949
• lake was sprayed with DDD, 99% of non-biting phantom
midge larva died.
– 1951
• swarms of midge recover
– 1954
• second dose of DDD, this time more concentrated
• 100 Western Grebes dead on lake (bioconc. X 30 000)
– 1957
• population fell 30 000 to 30 pairs, most of which were
sterile
– 1960’s
• switch to substitute organophosphorous insecticide and
Grebe populations are slowly recovering.
Transfer of an organochlorine pesticide through
the food chain of Clear Lake.
PCB’s and Heavy Metals
• Outline the sources of polychlorinated
biphenyls (PCBs) and heavy metals and the
consequences of their release on the
environment.
• PCBs
– There are over 200 different types of PCB; they
were first released in the US in 1929.
– Their use includes electrical insulators and the
manufacture of paint, ink and plastics.
– Effects of PCBs were first noticed in the 1960’s and
their use was banned in the 1970’s.
Environmental Concerns
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Egg shell thinning
Interference with mammalian reproduction
Damage to the immune system
Carcinogenic
• Since 1988, over 20 000 seals in the North Sea have
died of viral infections, these are thought to have
been enhanced by PCB poisoning.
• In Canada, Inuit nursing mothers have five times
more PCB in their milk than mothers in southern
Canada.
Heavy Metals
• Heavy metals become pollutants when found in high
concentrations in water and soils.
• There has been an increase in heavy metal
concentrations since the industrial revolution, but
they have been around for over 3000 years.
• Effects at high Concentrations
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Toxic to animals
Developmental defects
Cancers
Kidney failure
Immune system failure
Biotransformation
• Biotransformation occurs during the
degradative metabolic processes of
organisms.
• This process is vital to the sustainability of life if
part of natural degradation.
• It can be deleterious
– Example – mercury
• Inorganic mercurial ions with low toxicity can be
transformed into the highly toxic methyl mercury ions
by microbial activities.
• Minimata bay, Japan
Case Study: Mercury Poisoning
• Mercury is a serious pollutant in the Amazon Basin,
where it is used to extract gold.
• In the 1950’s in Minimata Bay in Japan, high
concentrations of Methyl Mercury was released into
the river, this concentrated in the marine food chain.
– The Japanese ate fish and shellfish; over 1000 people were
killed or disabled between 1950 and 1970.
• Some plants can develop tolerance to heavy metals,
for example Leadwort near the abandoned lead
mines in Yorkshire and Derbyshire.
Differential sensitivity
• Not all species respond in the same way to a
pollutant, and it is important to recognise that
for any particular pollutant there will be very
sensitive and less sensitive species.
• TBT (organic tin) has devastating effects on
oysters and other molluscs (dog whelk) whilst
having negligible effects on most other
species.
Essay Question
• Give an account of
monitoring water quality
particularly the uses of
indicator species and
biological oxygen demand.