# Describe the process of eutrophication, including how it leads to a reduction in the biodiversity of a river.

> Cambridge International IGCSE Biology (0610) — 20.3 Pollution · Describe · 4 marks

## Mark scheme (4 marks)

1. Fertilisers are washed from fields into the river, providing an excess of nutrients
2. Algae / aquatic plants grow rapidly, forming an algal bloom that covers the water surface and blocks sunlight
3. Aquatic plants below the surface cannot photosynthesise and die; decomposers break down the dead plants and use up oxygen
4. The decrease in dissolved oxygen causes organisms such as fish to die, reducing biodiversity

## Key terms

- [eutrophication](https://www.gradenine.co.uk/glossary/eutrophication)
- [biodiversity](https://www.gradenine.co.uk/glossary/biodiversity)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-process-of-eutrophication-including-69f46436) · Published by Druglandscape Ltd.