Eutrophication and fertiliser run-off

Overview

How nitrate applied to a field reaches a nearby river, algal bloom and why leaving soil bare over winter increases nutrient loss.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Define eutrophication.

   Model answer

   Eutrophication is the enrichment of a body of water with mineral nutrients, which triggers excessive growth of algae and a subsequent loss of oxygen and biodiversity.

2. 2

   Which two mineral ions from fertilisers are chiefly responsible for eutrophication?

   Model answer

   Nitrate ions and phosphate ions are chiefly responsible.

3. 3

   Explain how nitrate applied to a field reaches a nearby river.

   Model answer

   Nitrate is very soluble and is not held by soil particles, so rain washes it down through the soil and into drains and groundwater feeding the river.

4. 4

   What is an algal bloom?

   Model answer

   An algal bloom is a dense growth of algae that forms a layer over the surface of a body of water.

5. 5

   Explain why mineral enrichment causes an algal bloom.

   Model answer

   The growth of algae is normally limited by the supply of nitrate and phosphate, so adding these nutrients allows them to reproduce very rapidly.

6. 6

   Explain how an algal bloom causes the death of submerged plants.

   Model answer

   The dense surface layer blocks the light, so the plants beneath cannot photosynthesise enough to survive.

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