What is Eutrophication?

Eutrophication is one of the lesser known environmental issues when compared to deforestation, land pollution, smog and so on. Eutrophication is the process of enrichment of an ecosystem’s water body by the addition of nutrients by artificial or natural means, leading to plentiful plant growth.

It sounds like a good thing but not essentially. It mainly occurs due to the addition of phosphates in the water, whose availability is the limiting factor for plant and algae growth. The excess supply of nutrients may be through detergents, fertilizers, or sewage, to an aquatic system. It can be a natural process in lakes, occurring as they age through geological time. Phosphate easily mixes with soil, so the main form of phosphate transportation is with erosion, like with deforestation leading to soil erosion leading to eutrophication.

Due to the excessive phosphate content in the water leading to excessive plant growth, this makes the plants absorb more oxygen from the water and enable them to grow substantially in the water body. With excessive plant growth, comes excessive plant decay generally of algae, thereby creating the state of hypoxia. Hypoxia refers to the low oxygen conditions in water. Due to the load of the extra plant growth, the oxygen content of water is sucked up by the plants usually by algae, making the oxygen content being lower than what is required for the aquatic life to survive.

There are many human activities which cause Eutrophication, but it can not be blamed solely on human actions. Some natural processes occurring in lakes in temperate grasslands also cause Eutrophication. There are reverse processes also which causes meiotrophication and makes the lake less nutrient rich with time.

However, when compared to a freshwater system, this process is more common in coastal waters. At the coastal areas, the deposition from estuaries is enough to supply the excess nutrients. The amount of nitrogen present in water is the prime limiting nutrient in the case of marine water.


Causes of Eutrophication:

On the basis of how Eutrophication occurs, they can be classified into 2 types :

  1. Anthropogenic Eutrophication:

    It a typical result of human activity where the excessive use of fertilizers tends to happen in places like farms, golf courses, lawns and so on. These fertilizers are the perfect type of nutrients to feed hungry algae and plankton. These fertilizers run off into lakes, streams, rivers, and oceans supplying algae and plankton with nutrients in plenty leading to Eutrophication. Deforestation to meet man’s greed leads to soil erosion. Which in turn leads to Eutrophication.

  2. Natural Eutrophication:

    Eutrophication from natural events. If a stream, river or lake floods, it may wash away any excess nutrients off the land and into the water. Natural Eutrophication takes a lot more time to happen when compared to Anthropogenic Eutrophication.

Ecological Effects of Eutrophication:

  • Phytoplankton grows much faster in such situations.
  • These phytoplankton species are toxic and are inedible.
  • Gelatinous zooplankton blooms fast in these waters.
  • Increased biomass of benthic and epiphytic algae.
  • Changes in macrophyte species composition and biomass.
  • Decreases in water transparency.
  • Colour, smell, and water treatment problems.
  • Dissolved oxygen depletion.
  • Increased incidences of a fish kill.
  • Loss of desirable fish species.
  • Reductions in harvestable fish and shellfish.
  • Decreases in the perceived aesthetic value of the water body.

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