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 us

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.

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

Other Effects:

  • These phytoplankton species are toxic and are inedible.
  • Gelatinous zooplankton blooms fast in these waters.
  • 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.
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