Human influences on the environment
Make a list!
The Earth's population reached 6 billion in September, 1999. It will increase this
decade by another billion, the fastest population growth in history.
Every second, three people are added to the world; every day a quarter of a million
are added.
Estimates suggest that:
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an area the size of England is disappearing from tropical forests every year.
we have increased atmospheric CO2 concentration by 30%.
over 50% of terrestrial nitrogen fixation is caused by human activity (use of
nitrogen fertilizer, planting of nitrogen-fixing crops, release of reactive
nitrogen from fossil fuels into the atmosphere).
about 20% of bird species have become extinct in the past 200 years, almost
all of them because of human activity.
by the year 2030 there could be a global warming of between 1.5 and 4.5 C
1. Atmospheric pollution
This refers to changes in the atmosphere brought about by human activities.
Acid rain (read page 153-156)
Describes precipitation (……………………………… or ……………………………) with a pH of ………………
or lower. It is due to the production of …………………………………………………………………………………
and ……………………………………………………………………………… during the burning of
……………………………………………………………
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Effects on fish
Effects on trees
Effects on humans
1) Sulphur dioxide is one of the gases which contributes to the formation of acid
rain. The table gives data about sulphur dioxide emissions from fossil fuel
burning.
Year
1980
1990
1995
2000
2010
Europe
59
42
31
26
18
Sulphur dioxide / million tons
U.S.
24
20
16
15
14
Asia
15
34
40
53
79
a) Plot a graph of this data and describe the trend shown by each of these
graphs.
b) Suggest reasons for the differences in the trend shown by Europe and that
shown by Asia.
Greenhouse effect (read page 157-161)
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Explain the natural greenhouse effect
Greenhouse gases (top of page 158)
These contribute to the enhanced greenhouse effect.
Name of gas
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Sources of gas
carbon dioxide levels are maintained by…
they are increasing because…
what is global warming?
what can we do about it?
2. Water pollution
Eutrophication
Eutrophication refers to the effects of nutrients on aquatic ecosystems, usually a
sudden and dramatic increase in nutrients due to human activity, which disturbs and
eventually destroys the food chain.
The main causes are fertilisers leaching off farm fields into the surrounding water
course, and sewage (liquid waste from houses and factories). These both contain
dissolved minerals, such as nitrates and phosphates, which enrich the water.
Since producer growth is generally limited by availability of minerals, a sudden
increase in these causes a sudden increase in producer growth – referred to as an
algal bloom. Algae produce oxygen, so at this point the ecosystem is well oxygenated
and fish will thrive.
However, the fast-growing algae will out-compete larger plants for light, causing the
plants to die. The algae also grow faster than their consumers, so many will die
without being consumed, which is not normal. These both lead to a sudden increase in
detritus. Sewage may also contain organic matter, which adds to the detritus.
Decomposing microbes can multiply quickly in response to this, and being aerobic they
use up oxygen faster than it can be replaced by photosynthesis or diffusion from the
air. The decreased oxygen concentration kills larger aerobic animals and encourages
the growth of anaerobic bacteria, which release toxic waste products.
Biochemical Oxygen Demand (BOD)
This measures the rate of oxygen consumption by a sample of water, and therefore
gives a good indication of eutrophication. A high BOD means lots of organic material
and aerobic microbes, i.e. eutrophication.
BOD is measured by:
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collecting two water samples from the same site;
measuring the oxygen concentration of one sample with an oxygen meter;
sealing the second sample in an air-free container and incubating it in darkness at
20C for five days;
measuring the oxygen concentration of the second sample at the end of this
incubation period.
the difference in oxygen concentration is the standard measure of BOD.
clean water
polluted water
cleaned sewage
raw sewage
BOD (mg/dm3)
3
10
20 (legal max)
300
Read about water pollution in Jones and Jones pages 457 - 460
Biodiversity
The population of animal species vary according to the level of oxygen in the water.
Most tolerant of low oxygen are worms (Tubifex) whose haemoglobin has a
particularly high affinity for oxygen. These worms can therefore survive close to a
sewage outfall and as competition is reduced because other species cannot survive
their numbers increase greatly.
Further downstream as oxygen levels rise larvae of the midge Chironomus are able to
survive. These compete with the Tubifex for the small amount of oxygen and the
worm population is reduced.
A continuing rise in oxygen levels downstream results in the appearance of species
like the water louse Asellus. This increases competition further.
Finally as the sewage is completely decomposed, oxygen levels return to normal and
clean water species like the freshwater shrimp Gammarus are present.
These organisms act as indicator species for polluted water.
Find out what “fish kill” is.
Sewage effluent
Most human sewage is treated in sewage works, but these also discharge organic
matter into rivers. In winter this may cause little problem, because the river
contains a lot of fast-flowing cold water. In summer, however, there may be less
water, a slower current and warm water. These three factors can significantly
increase BOD in the river.
Complete the following:
Sewage contains mineral ions such as nitrates and ……………………………………… and also
suspended solids. If raw sewage flows into a river, the suspended solids are broken
down by ……………………………………………, resulting in a decrease in the concentration of
dissolved oxygen in the water. The volume of oxygen used by a sample of water is
known as the ……………………………………………, which steadily ………………………………………… as the
organic solids start to be broken down. Mineral ions stimulate the growth of algae
which can reduce the growth of submerged plants by reducing the amount of
………………………………………………… reaching them.
3. Changes in land use
Deforestation (read page 144-150)
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This means…
People do it because…
Immediate effects are…
Possible long term effects on the environment are…
Effects on biodiversity are…
Strategies of sustainable management are…
2. Forests all over the world are being cut down for timber and to provide land for
agriculture.
(a) Explain how this deforestation will lead to an increase in the amount of
carbon dioxide in the atmosphere.
(2)
(b) Carbon dioxide and methane are "greenhouse gases". Give two reasons why
the amount of methane in the atmosphere is increasing.
(2)
(c) What long-term effects will these gases have on the earth's climate?
(2)
(d) Some forests are managed instead of being cleared. As soon as trees have
been cut down, new trees are planted to replace them. How will this system
affect the amount of carbon dioxide in the atmosphere? Explain your answer.
(2)
8 marks
Desertification (read page 150-153)
 A desert is…
 Desertification means…
 This happens because…
 Effects on the soil are…
 Strategies for restoring the land are…
Pollution, people and politics
Read page 174 and 175. You are supposed to “be aware of European legislation to
control air and water quality”.