What is eutrophication?

Eutrophication is a negative impact of the use of fertilisers on aquatic lifeforms. When nutrients from fertilisers (eg nitrate and phosphates) leach from farm fields into the water, this allows fast-growing water plants such as algae to 'bloom'. The large amount of algae in the water will outcompete other plants in the ecosystem, which will then die. The death of these plants, as well as the large amount of algae death, will lead to increased activity from decomposing aerobic microbes. These microbes use up oxygen at a faster rate than can be replaced by photosynthesising water plants, leading to oxygen depletion. Due to the lack of oxygen in the water, aerobic animals (such as fish and invertabrates) will die due to an inability to respire, and the lack of oxygen will also encourage the growth of anaerobic bacteria. These bacteria release toxic waste products such as ammonium and hydrogen sulphide.