Water pollution and eutrophication
Water pollution
- Untreated sewage and excess fertiliser washed into rivers and lakes damage water ecosystems.
Practice
Which commonly pollute rivers and lakes?
Sewage and excess fertiliser running off the land damage freshwater ecosystems.
Eutrophication (Supplement)
- Excess fertiliser causes eutrophication:
- fertiliser adds nitrate ions and other ions to the water,
- producers such as algae grow very fast,
- they soon die, so decomposition increases,
- decomposers use up the oxygen in aerobic respiration,
- the dissolved oxygen falls, so fish die.
Practice
Put the steps of eutrophication in order.
Nitrate enrichment → algal bloom dies → decomposers use up oxygen → organisms die.
Practice
In eutrophication, organisms die because the dissolved oxygen falls too low.
Decomposers respiring aerobically use up the dissolved oxygen, suffocating fish and other organisms.
You've got it
Key idea
- sewage and excess fertiliser pollute fresh water
- eutrophication (Supplement): fertiliser → algae bloom → they die → decomposers use up the oxygen → fish die
- the key killer is the fall in dissolved oxygen