What is eutrophication?

Eutrophication, also known as hypertrophy, is a term used in ecology to refer to the phenomenon by which an aquatic ecosystem is excessively enriched in minerals and nutrients, which causes an overgrowth of primary producers: plants, algae and other phytoplanktonic organisms.

The problem with eutrophication is that biomass increases considerably in the ecosystem, but with a great impoverishment of biodiversity, water quality decreases and even the production of toxic substances for animals and plants.

Eutrophic water bodies become cloudy and typically colored green, yellow, brown or red, depending on which phytoplankton microorganisms have grown the most.

eutrophication mechanism

Eutrophication is usually due to a large supply of nutrients mainly composed of nitrogen and phosphorus leading to an overgrowth of plants, algae and phytoplanktonic organisms.

When these organisms die, the decomposition of organic matter by bacteria consumes large amounts of dissolved oxygen in the water and creates hypoxic conditions that negatively affect fish and other aquatic animals, even with their death.

Eutrophication process in an aquatic ecosystem

Phosphates are considered the main limiting factor of eutrophication in fresh water. A high availability of phosphorus generally produces a high rate of growth and death of pisan and favors the growth of algae, bacteria and other simpler organisms that are part of the plankton, causing a severe reduction in the quality of the water.

For its part, nitrogen IS the most limiting nutrient for growth. algae, therefore, is also the most limiting element for eutrophication in marine waters.

Although natural phenomena of eutrophication can occur, it is of great interest as an environmental problem derived from human activity.

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The sources of nutrients that cause eutrophication come mainly from urban runoff, both industrial and domestic, and from agricultural runoff, rich in phosphates, nitrates and other fertilizers.

rivers and lakes

In this satellite image of the Caspian Sea you can see eutrophication in its northern area

After eutrophication, when algae and planktonic organisms die, their organic matter is decomposed by the action of saprotrophic organisms.

The decomposition process consumes large amounts of oxygen which dissolves in the water, reducing its concentration and its availability to other organisms, including fish and aquatic animals, leading to reduced biodiversity.

In addition, the large load of organic matter that accumulates in the bottoms and benthic zones promotes the activity of anaerobic organisms and the release of greenhouse gases such as methane and carbon dioxide.

coastal areas

Eutrophication is a very common phenomenon in coastal areas. In seawater, the most limiting nutrient is usually nitrogen rather than phosphorus, which is more limiting in freshwater bodies.

the estuary where marine and fresh waters converge, can be limited by both elements, and often show signs of eutrophication with hypoxic zones on the bottom, low diversity of fish and marine life, and habitat degradation to a greater or lesser degree.

According to data from the World Resources Institute (WRI, World Resources Institute) there are at least 375 coastal areas that are clearly hypoxic on the planet, mainly in Western Europe, on the east and south coasts of the United States and in East Asia, especially in Japan.

In addition to runoff from the continent, eutrophication of seawater is favored by discharges from fish farms and industrial discharges rich in ammonia and other nitrogenous compounds.

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ecological effects

Eutrophication began to be recognized as a water pollution problem in Europe and North America in the mid-20th century, and has been increasing ever since.

It is estimated that more than half of the lakes in Asia, Europe and North America suffer from eutrophication. In South America these estimates are 40% and 30% in Africa.

The ecological effects derived from eutrophication are diverse and numerous, although these three are generally the most obvious: loss of biodiversity, changes in ecosystem species composition, and toxic effects.

Decline in biodiversity

Faced with a large availability of nutrients, primary producers are the first to accelerate their growth and reproduction, experiencing population explosions.

The primary producers in aquatic ecosystems are essentially photosynthetic organisms, such as algae, cyanobacteria, and dinoflagellates, which produce oxygen during the day and consume oxygen at night. Oxygen is also consumed by animals, both during the day and at night.

Under eutrophic conditions, dissolved oxygen in water increases considerably during the day, but also decreases greatly at night. In addition, as dead organic matter increases, the activity of decomposing microorganisms that also consume oxygen increases.

the decrease in the concentration of oxygen in the water create hypoxic conditions that can become critical for fish and marine animals, many of which die. In extreme conditions, complete anoxic conditions and the appearance of dead zones.

Invasive species and ecosystem composition

Under eutrophication conditions, the availability of limiting nutrients is altered. For example, nitrogen, a generally limiting element, may be available in large quantities.

These changes can cause the invasion of species that were not present in the original ecosystem and competitively displace native species.

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toxic effects

Some organisms that undergo population explosions during eutrophication produce substances that are toxic to animals and plants.

These toxins can reach humans by consuming contaminated animals, something relatively common in many cases of crustacean poisoning.

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