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What is Eutrophication? Types, Causes and Effects of Eutrophication explained

What is Eutrophication? Types, Causes and Effects of Eutrophication explained


  • GS 3 II Environment II Biodiversity II Marine organisms

Why in the news?

Change in water environment is one of the serious concern, it is often heard in news about the various problem occurring in water bodies


The term ‘Eutrophication’ is derived from the Greek word ‘eutrophos’ which means nourished or enriched. In context with the environment, the Eutrophication can be defined as the addition of artificial or non-artificial substances such as nitrates andphosphate, through fertilizers or sewage, to a fresh water system. It leads to increase in the primary productivity of the water body or ‘bloom’ of phytoplankton

What is Eutrophication?

  • Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use”.
  • This is one of the first definitions given to the eutrophic process by the OECD(Organization for Economic Cooperation and Development) in the 70s.
  • The term Eutrophication is more widely known in relation to human activities where the artificial introduction of plant nutrients has led to community changes and a deterioration of water quality in many freshwater systems.
  • This aspect has become increasingly important with increases in human population and more extensive development of agriculture and eutrophication now ranks with other major anthropogenic effects such as deforestation, global warming depletion of the ozone layer and large scale environmental disturbance in relation to its potentially harmful effect on natural ecosystems.

Types of eutrophication:

  • Natural Eutrophication: In this eutrophication, water body like the lake is characterised by nutrient enrichment. During this process, oligotrophic lake is converted into a eutrophic lake. It permits the production of phytoplankton, algal blooms and aquatic vegetation that in turn provide ample food for herbivorous zooplankton and fish.
  • Cultural Eutrophication: It is caused by human activities because they are responsible for the addition of 80% nitrogen and 75% phosphorous in lake and stream.
  • Anthropogenic Eutrophication: Anthropogenic eutrophication is caused by human activity – Agricultural farms, golf courses, lawns, etc. are supplied with nutrients by humans in the form of fertilizers. These fertilizers are washed away by rains and eventually find their way into water bodies such as lakes and rivers.

According to the Survey of the State of the World’s Lakes, eutrophication affects:

  • 54%of Asian lakes,
  • 53% of those in Europe,
  • 48% of those in North America
  • 41% of those in South America and
  • 28% of those in Africa
  • Dead zones:
    • Dead zones (biological deserts) are increasing in the coastal delta and estuarine regions.
    • Hypoxic zones (zones deprived of oxygen) can occur naturally (due to upwelling of nutrients).
    • They can be created or enhanced by human activity to form dead zones.
    • Dead zones are areas in the ocean with very low oxygen concentration (hypoxic conditions).
    • Dead zones emerge when influx of chemical nutrients spur algae growth.
    • These zones usually occur 200-800 meters (in the saltwater layer) below the surface.
    • Dead zones are detrimental to animal life. Most of the animal life either dies or migrates from the zone.
    • One of the largest dead zones forms in the Gulf of Mexico every spring (farmers fertilize their crops and rain washes fertilizer off the land and into streams and rivers).
    • There’s a dead zone in Gulf of Oman and it’s growing.

Causes of Eutrophication:

  • The availability of nutrients such as nitrogen and phosphorus limits the growth of plant life in an ecosystem. When water bodies are overly enriched with these nutrients, the growth of algae, plankton, and other simple plant life is favoured over the growth of more complex plant life.
  • Excessive use of fertilizers.
  • Concentrated animal feeding operations (CAFOs) are also a major source of polluting nutrients.
  • Industrial and domestic waste.
  • Hypoxic conditions:
    • The excessive growth of algae in eutrophic waters is accompanied by the generation of a large biomass of dead algae. These dead algae sink to the bottom of the water body where they are broken down by bacteria, which consume oxygen in the process.
    • The overconsumption of oxygen leads to hypoxic conditions (conditions in which the availability of oxygen is low) in the water. The hypoxic conditions at the lower levels of the water body lead to the suffocation and eventual death of larger life forms such as fish.

Effects of Eutrophication:

  • Algal blooms cover the water bodies like river, lake, stream or ocean, blocks light from reaching the water which prevents the aquatic plants from photosynthesizing.
  • Lack of photosynthesis causes oxygen deficiency which results in a decline of marine species.
  • Hypoxic condition forms the dead zones which have not only negative ecological impacts but also have economic issues.
  • The water can have a bad taste, colour and odour, which has a negative impact on tourism. Governments have to invest more in waste water treatment.
  • Depletion of dissolved oxygen in the water body.
  • Frequent fish kill incidents occur and many desirable fish species are removed from the water body.
  • The populations of shellfish and harvestable fish are lowered.
  • The aesthetic value of the water body diminishes significantly.

Preventive measures:

  • Industrial and domestic waste water must be treated before its discharge into water bodies.
  • Recycling of nutrients through harvesting, removal of algal blood.
  • Precipitants like alum, lime, iron and sodium aluminate may use.
  • Physicochemical methods can be applied to remove nutrients. For Example- Phosphorous can be removed by precipitation and nitrogen by nitrification or denitrification
  • Conventionally, there have been some methods to control/reduce eutrophication viz. the alteration of excess nutrients, physical mixing of the water, application of powerful herbicides and algaecides among others.
  • These methods have proven to be ineffective, expensive and impractical for large ecosystems.
  • Today, the major control mechanism against eutrophication process is premised on prevention techniques like taking out the nutrients that are introduced into water bodies.
  • The strategy is to limit the concentrations of one of the two main nutrients (nitrogen and phosphorus) in water bodies.
  • It is scientifically proven that in particular phosphorus is the main limiting factor for the growth of algae. Hence, when the offload of nitrogen or phosphorus is controlled then there is a visible reduction in the process of eutrophication in water bodies.
  • Increase in efficiency of nitrogen & phosphorous fertilizers and using them only in an adequate level.
  • Reduction in nitrogen emission from vehicles and power plants.
  • There is an ever-increasing population pressure and hence sustained food security will become a more pressing concern. This will magnify the already increasing demands on farmland productivity.
  • But organic farming is very costly and hence farmers will turn to the continued use of phosphate- and nitrogen-rich fertilizers.
  • These fertilizers will catalyse the growth of eutrophic zones. Hence, there is a need to address this dimension of the eutrophication problem.

Curative procedures:

  • Removal and treatment of deep water in contact with the sediments rich in nutrients since in direct contact with the release source;
  • Drainage of the upper part of sediment subject to biological reactions and with high phosphorus concentrations;
  • Oxygenation of water for restoring the ecological conditions,
  • chemical precipitation of phosphorus by the addition of iron or aluminium salts or calcium carbonate to the water


Water is not a commercial product like any other but rather a heritage which must be defended and protected, especially in the presence of a global decline in the availability of drinking water and increase in its demand. Despite the considerable efforts made to improve the water quality by limiting nutrient enrichment, cultural eutrophication and the resulting algal blooms continue to be the main cause of water pollution. The prevention and protection action that countries must adopt to safeguard the quality of surface water as requested not only by the scientific community and other experts, but to an increasing extent also by citizens and environmental organizations, is therefore increasingly important.

Mains oriented question:

Improper waste management is one of the reason for excess of deposition in water bodies which disturb the water ecosystem and hence ecological balance. Explain. (200 words)