Eutrophication is also known as hypertrophication and is observed when a body of water in an ecosystem displays an excessive growth of algae and plants in it. One such example is the bloom of phytoplankton in water bodies.

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.


An image emphasizing the excessive growth of plant-life in a water body due to eutrophication is provided above. Some important points about this process are listed below.

  • It may sound to be a beneficial process, but eutrophication is essentially harmful to an ecosystem.
  • It mainly occurs due to the addition of phosphates in the water, whose availability is the limiting factor for plant and algae growth.
  • The excessive availability of phosphorus favors the growth of more simple plant life such as plankton and algae over more complex plant life.
  • Apart from phosphates, many other nutrients such as nitrates can also lead to the eutrophication of water bodies.
  • The excess supply of nutrients to these aquatic systems may be through detergents, fertilizers, or sewage.
  • The eutrophication of water bodies can be a natural process in lakes, occurring as they age through geological time. Since Phosphate easily mixes with soil, the main form of phosphate transportation is via soil erosion.
  • Due to the excessive phosphate content in the water which leads to excessive plant growth, the consumption of oxygen present in the aquatic system increases substantially as well.
  • With excessive plant growth, comes excessive plant decay (generally the decay of algae), thereby creating the state of aquatic hypoxia. Hypoxia refers to the low oxygen conditions in water.
  • Due to the sheer amount of extra plant growth, the oxygen content of water is sucked up by the plants (usually by algae). This leads to the oxygen content of the water body being lower than the required for the aquatic life to survive.
  • There are many human activities which cause Eutrophication, but the entirety of it cannot be blamed solely on human actions. Some natural processes occurring in lakes in temperate grasslands also cause Eutrophication.
  • There exist reverse processes which cause meiotrophication and make the aquatic body less nutrient-rich with time.
  • When compared to a freshwater system, this process is more common in coastal waters. At the coastal areas, the deposits from estuaries are enough to supply the nutrients in excess to the aquatic body.

The amount of nitrogen present in water is the prime limiting nutrient in the case of marine water. An illustration detailing the different causes and effects of eutrophication can be found below.

Causes and Effects of Eutrophication

In the case of coastal waters, industrial discharges of ammonia and the nitrogen fixation process in the atmosphere promote the eutrophication of the water bodies.

Causes of Eutrophication

The process of eutrophication can be categorized into two types based on its root cause. Both these types are explained in this subsection.

Anthropogenic Eutrophication

Anthropogenic eutrophication is a typical result of human activity where the excessive use of fertilizers tends to occur in places such as farms, golf courses, lawns, and so on. These fertilizers provide the necessary nutrients to the algae and plankton residing in the water body.

When these fertilizers run off into lakes, streams, rivers, and oceans, they supply the algae and plankton with nutrients in plenty leading to Eutrophication of the aquatic body they were introduced to.

Problems such as overpopulation lead to excessive Deforestation to meet the requirements for agricultural and industrial expansion. The increase in deforestation leads to soil erosion, which in turn leads to Eutrophication.

Natural Eutrophication

Natural eutrophication refers to the excessive enrichment of water bodies via natural events. An example of natural enrichment of aquatic bodies can be observed in the flooding of streams, rivers, or lakes which causes them to wash away the nutrients from the land and enrich themselves with it.

The process of natural eutrophication is much slower when compared to the process of anthropogenic eutrophication.

This process is also somewhat dependant on the temperature of the environment. It may even be complemented by the temperature changes brought on by global warming.

Ecological Effects of Eutrophication

The primary adverse effects of eutrophication on aquatic bodies include a decrease in biodiversity, increase in toxicity of the water body, and change in species dominance. Some more important effects of this process are listed below.

  • 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 epiphytic and benthic algae can be observed.
  • Significant changes arise in the species composition of macrophytes and the biomass.
  • The water loses its transparency due to the eutrophication process.
  • The water body develops a bad smell and color, and its treatment becomes difficult.
  • Depletion of dissolved oxygen in the water body.
  • Frequent fish kill incidents occur.
  • Many desirable fish species are removed from the water body.
  • Lowering of the populations of shellfish and harvestable fish.
  • The aesthetic value of the water body diminishes significantly.

Decrease in Biodiversity

When an aquatic ecosystem is enriched with nutrients by either natural or artificial means, the conditions become extremely beneficial to primary producers. Commonly, algae and other similar species utilize these nutrients and a huge increase in their population (algal bloom) is observed.

These algal blooms hinder the flow of sunlight to the bottom of the aquatic body and also cause wide swings in the dissolved oxygen levels in the water.

When the dissolved oxygen in the water reduces to an amount below the hypoxic level, many marine animals suffocate and die. This reduces the effective biodiversity of the water body.

Increase in Water Toxicity

A few algae are toxic to many plants and animals. When these algae bloom in eutrophic waters, they release neurotoxins and hepatotoxins. These toxins can also move up the food chain via shellfish or other marine animal and lead to the death of many animals.

Toxic algal blooms can also be harmful to humans and are the root cause of many cases of neurotoxic, paralytic, and diarrhoetic shellfish poisoning.

Invasion of New Species

A limiting nutrient corresponding to a water body can be made abundant by the eutrophication process, leading to a shift in the species composition of the aquatic body and the ecosystem surrounding it.

If a nitrogen deficient water body is suddenly enriched with it, many other competitive species might relocate to the water body and out-compete the original inhabitants of the ecosystem. One such example of a new species invading eutrophic conditions is the common carp, which has adapted to these conditions.

Frequently Asked Questions

What are the adverse effects of eutrophication?

The algal blooms in the water body can inhibit the supply of sunlight at the lower depths. This can pose a threat to the survival of many plants and animals. The depletion of the oxygen levels in the water body due to this phenomenon also has an adverse effect on the local biosphere.

What are the signs that indicate eutrophication?

Some of the signs that indicate this include a huge increase in the population of algae in the water body and the presence of a foul odor that emanates from the aqueous body.

What is anthropogenic eutrophication?

It is a type of eutrophication that is a result of human activity and is generally caused by the influx of potassium-rich fertilizers into the aqueous body. Another root cause of this is deforestation, which causes the erosion and transportation of nutrient-rich soil into the water body.

How can eutrophication occur naturally?

Many natural phenomena such as the flooding of lakes or rivers can wash away the nutrient-rich soil from the land surrounding the water bodies. This nutrient-rich soil can promote the growth of algae in the aqueous body. However, this is a rather slow process.

What are the measures that can be taken to prevent eutrophication?

This process can be controlled by preventing the inflow of phosphorus-rich substances into the water bodies. Avoiding the overuse of fertilizers and the proper channeling of agricultural wastes also help in the prevention of eutrophication.

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