The environmental issues arising from the use of fertilisers. Leaching and eutrophication. Candidates should be able to analyse, interpret and evaluate data relating to eutrophication.

Nitrogen is circulated between existence in the atmosphere, in the soil, and in living things. The diagram shows how nitrogen is passed from one form to another.

In plants, animals and decomposers nitrogen exists as ammonium containing molecules like proteins and nucleic acids.

In farming this natural cycle is disrupted because dead matter is removed from the area (as is waste). This means that nitrogen in the soil is not replaced and so fertilizers must be used to replenish levels so that plants can grow there.

Natural fertilisers consist of waste and or dead matter. Artificial fertilisers are made from nitrogen extracted from rocks or made in the harbour process.

Eutrophication happens when water leeches nitrogen from soil and takes it into a water system: here the nitrogen helps algae to grow causing a bloom (large layer of algae); this blocks light for other organisms, like fish, and uses up their oxygen, causing them to die; decomposers increase as they feed on the dead, using up even more oxygen; oxygen is so low that no other organisms can survive.

Nitrogen can leech into supplies of drinking water too.