Water Pollution
- Fertilisers and untreated sewage can be washed into water bodies such as lakes and streams, resulting in a process known as eutrophication
- The following events occur with the continued run-off of fertilisers and sewage into water bodies:
- These pollutants are high in nitrogen, an essential mineral for plant growth, so this can result in the overgrowth of aquatic plants and algae at the water surface
- Light is blocked and aquatic plants below the surface die and are broken down by decomposers, e.g. bacteria and fungi
- Decomposers increase in number, and the increased respiration of these organisms uses up oxygen in the water, reducing dissolved oxygen levels
- The water no longer contains enough oxygen to support other organisms, so many aquatic organisms die
Water pollution from fertiliser run-off diagram
Fertiliser and sewage run-off can result in the suffocation of aquatic organisms
Examiner Tip
Note that the term 'eutrophication' is not required to gain marks in questions relating to this process. You must instead show understanding by describing the sequence of events that results from fertiliser run-off.
