# Eutrophication is a process that can reduce biodiversity in a freshwater lake. Explain how the use of fertilisers on nearby farmland leads to eutrophication and results in the death of animal species living in the lake.

> Pearson Edexcel International GCSE Biology (4BI1) — 4.1 The organism in the environment · Explain · 4 marks

> Farmers often apply nitrate and phosphate fertilisers to their fields to increase crop yields. After heavy rainfall, some of these minerals are washed from the soil into a nearby freshwater lake.

## Mark scheme (4 marks)

1. Fertilisers are leached/washed from the land into the lake, causing excessive growth of algae at the water surface.
2. The algae at the surface block/prevent light from reaching aquatic plants below.
3. Aquatic plants can no longer photosynthesise and die.
4. Decomposers break down the dead plant material and use up oxygen, reducing the amount of oxygen available for animal species, which die.

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/eutrophication-is-a-process-that-can-39aad780) · Published by Druglandscape Ltd.