Water Pollution (Cambridge (CIE) IGCSE Biology): Revision Note
Exam code: 0610 & 0970
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Untreated Sewage & Excess Fertiliser
Human activities have led to the pollution of land, water and air
Pollution comes from a variety of sources, including industry and manufacturing processes, waste and discarded rubbish, chemicals from farming practices, nuclear fall-out, and untreated sewage
Pollutant | Source / Cause | Effect |
|---|---|---|
Untreated sewage | Lack of sewage treatment (poor infrastructure/funding) means sewage enters rivers or streams. | Increases bacteria → reduces oxygen in water → kills aquatic life. This process is known as eutrophication. |
Fertilisers | Runoff from farmland when used in excess. | Causes algal blooms → bacteria feed → oxygen depletion → death of aquatic organisms. Another case of eutrophication. |
Methane | Released by cattle farming, rice paddies, and landfills. | Potent greenhouse gas, contributes to climate change. |
Carbon dioxide | Produced by burning fossil fuels or trees (land clearance). | Also a greenhouse gas, contributing to global warming and climate change. |
Eutrophication: Extended
Runoff of fertiliser from farmland enters the water and causes increased growth of algae and water plants
The resulting ‘algal bloom’ blocks sunlight so water plants on the bottom start to die, as does the algae when competition for nutrients becomes too intense
As water plants and algae die in greater numbers, decomposing bacteria increase in number and use up the dissolved oxygen whilst respiring aerobically
As a result there is less oxygen dissolved in water, so aquatic organisms such as fish and insects may be unable to breathe and would die
Sequence of events causing eutrophication in lakes and rivers
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