Eutrophication

Eutrophication, strictly speaking, means an increase in chemical nutrients -- typically compounds containing nitrates or phosphates -- in an ecosystem. It may occur on land or in water. The term is however often used to mean the resultant increase in the ecosystem's primary productivity -- in other words excessive plant growth and decay -- and even further impacts, including lack of oxygen and severe reductions in water quality and in fish and other animal populations.

Eutrophication is frequently a result of nutrient pollution such as the release of sewage effluent and run-off from lawn fertilisers into natural waters (rivers or coasts) although it may also occur naturally in situations where nutrients accumulate (e.g. depositional environments) or where they flow into systems. Eutrophication generally promotes excessive plant growth and decay, favours certain weedy species over others, and is likely to cause severe reductions in water quality . In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen in the water, needed for fish and shellfish to survive. The water then becomes cloudy, coloured a shade of green, yellow, brown or red. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation, fishing, hunting, and aesthetic enjoyment are hindered. Health-related problems can occur where eutrophic conditions interfere with drinking water treatment.