Water pollution and eutrophication
Introduced| English | Meaning |
|---|---|
| eutrophication/ˌjuːtrəfɪˈkeɪʃn/ | Nutrient enrichment of water that can cause excessive plant or algal growth and oxygen depletion as organic matter decomposes. |
| nitrates/ˈnaɪtreɪts/ | A compound containing the nitrate ion, NO₃ with a single negative charge. |
| algae/ˈælɡiː/ | A diverse group of mainly aquatic photosynthetic organisms that lack the true roots, stems and leaves of plants. |
| algal bloom/ˈælɡl bluːm/ | A rapid increase in the abundance of algae or similar photosynthetic microorganisms in a body of water. |
When fertiliser poisons a river
- Fertilisers help crops grow — but washed into rivers and lakes, they can kill the life there.
- This damaging chain of events is eutrophication 富营养化.
Eutrophication sequence
Follow fertiliser runoff from nutrient input to fish death.
Eutrophication is usually started by:
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Extra nitrates trigger the process.
The extra nutrients cause a rapid growth of:
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Nitrates feed an algal bloom.
A rapid surface growth of algae from excess nutrients is an algal ______.
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The bloom blocks light and starts the harm.
The cause
- Fertiliser (or sewage) runs off into water, adding lots of nitrates 硝酸盐.
- These nutrients make algae 藻类 grow rapidly, covering the surface — an algal bloom 藻华.
Eutrophication: extra fertiliser makes algae bloom, then the water loses its oxygen and fish die
Fish die in eutrophication because the water loses its:
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Decomposers use up the oxygen.
Put the eutrophication steps in order.
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Nitrates → bloom → plants die → oxygen used up → fish die.
The chain of harm
- The algal bloom blocks light, so plants below die.
- Decomposers break down the dead plants, and their respiration uses up the oxygen.
The result
- With little oxygen left, fish and other animals die.
- This is eutrophication — fertiliser pollution suffocating a waterway.
Worked example. Fertiliser washes into a lake → nitrates feed an algal bloom → light is blocked, plants die → decomposers use up the oxygen → fish suffocate. Each step follows from the last.
You've got it
- eutrophication: nitrates (fertiliser/sewage) cause an algal bloom
- the bloom blocks light (plants die); decomposers then use up oxygen
- with no oxygen, fish and animals die — the water is polluted
Write from an algal bloom
- Nitrate fertiliser washes into a river.
- Algae cover the surface and then die.
What uses up the oxygen, and what happens to the fish?
The oxygen crash comes after the microbes feed on the dead algae.
After an algal bloom dies, why do fish die?
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Decay of the bloom spends the dissolved oxygen.