What causes eutrophication?

The main causes of eutrophication are an increase in the concentration of nutrients to an ecosystem. Increased nutrient enrichment can arise from both point and non-point sources:

• Point source pollution: Pollution that comes from contaminants that enter a waterway from a single identifiable source such as stationary locations or fixed facilities. Examples are discharges from a sewage treatment plant or industrial plants and fish farms.
• Non-point source pollution: Pollution from widespread including human activities with no specific point of discharge or entry into receiving watercourses. Examples are leaching out of nitrogen compounds from fertilized agricultural lands and losses from atmospheric deposition.

File:Industrial_pollution.jpg|300px|right|thumb|Industrial pollution, an example of point source pollution (Photo credit: Monika Thorpe) File:manure_run-off.jpg|300px|left|thumb|Manure run-off, an example of non-point source pollution (Photo credit: Chris Court)

The enrichment of water by nutrients can be of a natural origin (natural eutrophication) but is often dramatically increased by human activities (cultural or anthropogenic eutrophication). Natural eutrophication has been occurring for millennia. It is the process of addition, flow and accumulation of nutrients to water bodies resulting in changes to the primary production and species composition of the community. Cultural eutrophication is the process that speeds up natural eutrophication because of human activity. There are three main sources of anthropogenic nutrient input: erosion and leaching from fertilized agricultural areas, and sewage from cities and industrial waste water. Atmospheric deposition of nitrogen (from animal breeding and combustion gases) can also be important.

The most common nutrients causing eutrophication are nitrogen and phosphorus. The main source of nitrogen pollutants is run-off from agricultural land, whereas most phosphorus pollution comes from households and industry, including phosphorus-based detergents. These nutrients enter aquatic ecosystems via the air, surface water or groundwater. Most of the commercially fixed nitrogen and mined phosphorus goes into production of fertilizer. The rising demand for fertilizer has come from the need to meet the nutritional demands of our rapidly expanding human population. The rise in intensive fertilizer use has serious implications for coastal habitats because greater application results in greater runoff, and the fraction of fertilizer lost from fields will increase with intensity of application. Increased global production of nitrogenous fertilizers have largely been linked to concerns over the relationship between water quality and eutrophication. Nutrient removal in sewage treatment plants and promotion of phosphorus-free detergents are vital to minimize the impact of nitrogen and phosphorus pollution in Europe's waters.

References

1. Causes, historical development, effects and future challenges of a common environmental problem: eutrophication. De Jonge, V.N.; Elliot, M.; Orive, E. (2002). Hydrobiologia 475-476:1-19.
2. Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. European Environment Agency (2005). EEA Report, 7 Office for Official Publications of the European Communities: Luxembourg. ISBN 92-9167-777-9.48 pp.
3. Eutrophication and health. European Commission (2002). Office for Official Publications of the European Communities: Luxembourg. ISBN 92-894-4413-4.28 pp.