Excess nitrates (SQA National 5 Biology): Revision Note

Fertilisers can leach into water bodies such as lakes and streams, adding extra, unwanted nitrates

• Leaching is the process by which soluble substances, e.g. nitrates, are washed out of the soil by rainwater

The following events can occur as a result:

1. Fertilisers provide nitrates to aquatic plants

2. There is overgrowth of aquatic plants and algae at the water surface; algae overgrowth is known as an algal bloom

3. Light is blocked, and aquatic plants below the surface die

4. dead plant matter becomes food for decomposers, e.g. bacteria and fungi, which increase in number

5. The increased respiration of these organisms uses up oxygen in the water, reducing dissolved oxygen levels

6. The water no longer contains enough oxygen to support other organisms, so many aquatic organisms die

Overusing fertilisers raises costs for farmers and leads to environmental problems, such as leaching and algal blooms

Genetically modified (GM) crops can be used to reduce the use of fertilisers

• GM crops are crop plants in which the DNA has been deliberately altered using genetic engineering

GM crops can reduce fertiliser use as follows:

• Low-phosphate-tolerant rice can continue growing despite phosphate-poor soil, reducing the need for phosphate fertilisers

• Nitrogen-efficient wheat and rice varieties can use nitrates from the soil more efficiently, allowing them to survive when nitrate levels are low and decreasing the need for nitrate fertilisers