prepared by: sarah & pqah

Wednesday, December 3, 2008

CHAPTER 9 : Endangered Ecosystem




  • Burning of fossil fuels is the main source of air pollution.they are burnt in coal,petroleum n gas-fired power stations in domestic n industrial boilers n in the internal combustion engines of cars,lorries,buses and trains.

What is Acid Rain?
Acid rain is a result of air pollution. When any type of fuel is burnt, lots of different chemicals are produced. The smoke that comes from a fire or the fumes that come out of a car exhaust don't just contain the sooty grey particles that you can see - they also contains lots of invisible gases that can be even more harmful to our environment.
Power stations, factories and cars all burn fuels and therefore they all produce polluting gases. Some of these gases (especially nitrogen oxides and sulphur dioxide) react with the tiny droplets of water in clouds to form sulphuric and nitric acids. The rain from these clouds then falls as very weak acid - which is why it is known as "acid rain".
How acidic is acid rain?
Acidity is measured using a scale called the pH scale. This scale goes from 0 to 14. 0 is the most acidic and 14 is the most alkaline (opposite of acidic). Something with a pH value of 7, we call neutral, this means that it is neither acidic nor alkaline.
Very strong acids will burn if they touch your skin and can even destroy metals. Acid rain is much, much weaker than this, never acidic enough to burn your skin.
Rain is always slightly acidic because it mixes with naturally occurring oxides in the air. Unpolluted rain would have a pH value of between 5 and 6. When the air becomes more polluted with nitrogen oxides and sulphur dioxide the acidity can increase to a pH value of 4. Some rain has even been recorded as being pH2.
Vinegar has a pH value of 2.2 and lemon juice has a value of pH2.3. Even the strongest recorded acid rain is only about as acidic as lemon juice or vinegar and we know that these don't harm us - so why do we worry about acid rain?
The Effects of Acid Rain
Acid rain can be carried great distances in the atmosphere, not just between countries but also from continent to continent. The acid can also take the form of snow, mists and dry dusts. The rain sometimes falls many miles from the source of pollution but wherever it falls it can have a serious effect on soil, trees, buildings and water.
Forests all over the world are dying, fish are dying. In Scandinavia there are dead lakes, which are crystal clear and contain no living creatures or plant life. Many of Britain's freshwater fish are threatened, there have been reports of deformed fish being hatched. This leads to fish-eating birds and animals being affected also. Is acid rain responsible for all this? Scientists have been doing a lot of research into how acid rain affects the environment.

It is thought that acid rain can cause trees to grow more slowly or even to die but scientists have found that it is not the only cause. The same amount of acid rain seems to have more effect in some areas than it does in others.
As acid rain falls on a forest it trickles through the leaves of the trees and runs down into the soil below. Some of it finds its way into streams and then on into rivers and lakes. Some types of soil can help to neutralise the acid - they have what is called a "buffering capacity".
Other soils are already slightly acidic and these are particularly susceptible to the effects of acid rain.
Acid rain can effect trees in several different ways, it may:
• dissolve and wash away the nutrients and minerals in the soil which help the trees to grow.
• cause the release of harmful substances such as aluminium into the soil.
• wear away the waxy protective coating of leaves, damaging them and preventing them from being able to photosynthesise properly.


  • They are the most affected by human activities.
  • Industries n domestic n agricultural pratices produce waste that pollutes the water.

What is BOD?
BIOCHEMICAL OXYGEN DEMAND(BOD) refers to the amount of oxygen that is utilised when all the organic matter in one litre of water is oxidised by living organisms in the water. The measurement of BOD can provide an indication of the level of water pollution. If there is a large amount of organic waste in the water supply, the number of aerobic bacteria working to decompose this waste will also be great. In this case, the biochemical demand for oxygen (BOD) value will be high and subsequently, the dissolved oxygen levels in the water will decline rapidly.Generally, an increase in BOD levels corresponds with decrease in dissolved oxygen levels. The dissolved oxygen level is an indication of the level of water pollution. It also shows how well the water can support aquatic plant and animal life. A higher dissolved oxygen level or lower oxygen level indicates better water quality. A lower dissolved oxygen level or higher BOD level indicates poor water quality.A BOD level 1-2 ppm ( parts per million) is considered very good.There is not much organic waste present in the water. A water body with a BOD level of 3-5 ppm is considered moderately clean. A BOD level of 6-9 ppm means the water is considered mildy polluted since organic matter is present and decomposition of organic waste can take place.At BOD levels of 10 ppm or greater, the water supply is considered very polluted with organic waste.

Oil pollution is one example of how human activities can lead to the death of organisms in an entire food chain and cause extensive damage to an ecosystem. Oil spills occur at sea when oil tankers either accidentally or deliberately, during the cleaning of their storage tanks, spill crude oil into the sea. Crude oil contains volatile components which are highly toxic and affect marine life. Many sea birds and marine mammals die because the oil which coats their bodies makes their feathers or fur lose their insulating capacity. Many fish are poisoned while the larger sea animals are killed when they eat poisoned food. the layer of oil an the surface reduces the exchange of oxygen between the water and the air by preventing oxygen from dissolving in the sea water. This effects organisms which come to the surface of the water to breathe and take oxygen. besides, oil pollution also causes a loss of income from tourism. Chemical dispersants and detergents can be used to breaks up oil slick. However, these chemicals may end up causing more damages to the living organisms than the oil itself. A more suitable technique, the polluted area is deliberately seeded with bacteria (for example, Pseudomonas sp.) can break down the complex hydrocarbon compunds in oil simpler, non-polluting substances.


1. IS caused by the discharged of heat or warm water from power stations or industrial fields in excess heat in the environment.

2. GLASS buildings also contribute to thermal pollution.

3. MANY industries use water as a coolling agent. HENCE the temperature of the water is increased.

4. AQUATIC organisms will die due to high temperature and less oxygen.


1. IS the occurence of excessive noise in the environment that disturbs the tranquility of life.

2. SOURCES: vehicles, air crafts, machines, construction sites, traffic & others.

3. EFFECTS: a) Hearing problems b) Ear injury c) Headaches d) Emotional & Mental disturbances e) High blood pressure f) deafness


a) ENFORCEMENT of the environment laws

1. Environmental Quality Act, 1974.

- Controls and Prevents the pollution of the environment.

- Controls the type of licensing, content and quality of environment.

- Tests and Examines the samples of substances and disposal of smoke and gas from industries.

2. Other Acts : - Factories and Machinery Act, 1967 /1983

- Pesticides Act, 1974

- National Forestry Act,1984

b) USE of technology

1. Use expensive modern equipments and chemicals to control oil spills

2. Recycle rubbish

3. To look for methods to do research

4. Change organic rubbish to biogas

5. Use Less polluting and Clean fuels in motor vehicles

6. Control and Treat the toxic and dangerous waste before disposing


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