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.

The role of microorganisms in the carbon and nitrogen cycles in sufficient detail to illustrate the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification. (The names of individual species are not required.)

Saprobiotic micro-organisms are ones which get their nutrition from dead matter. They decompose plants and animals, releasing carbon and nitrogen back into the air and soil, helping to make the movement of these molecules a continuous cycle.

Ammonification- creating ammonium from molecules that contain it; done by saprobiotic micro-organisms

Nitrification- turning ammonium into nitrate; this is done by some bacteria to create energy

Nitrogen fixing- turning nitrogen in the air into ammonium; done by free living bacteria to create amino acids for themselves; done by mutualistic bacteria to create amino acids for plants in return for carbohydrates

Denitrification- carried out by bacteria for energy

Nitrifying-bacteria are aerobic and denitrifying-bacteria are anaerobic, so if soil is water logged there will be a decline in nitrification and an increase in denitrification.