Eutrophication and fertilizer abuse in the ecosystem

The ecosystem was highly stable until industrialization and technological advancement arrived. In this way, the environment became sensitive to the brutal changes that man has been subjecting to the environment over the years. If we focus on water, the continuous supply of nutrients produces alterations in the ecosystem and causes a phenomenon known as eutrophication .

And when this change occurs, the balance is altered and some species start to proliferate over others, so that the entire ecosystem is slowly modified until it collapses, as happened a few years ago with the Mar Menor, in the Region of Murcia.

However, this example is one of many scattered around the world, where not only agriculture and the abuse of fertilizers is the main problem, since the poor management of human waste in cities causes serious alterations in the aquatic environment.

We want to dedicate this article to know with interest the phenomenon of water eutrophication , causes, alterations and possible solutions (which never hurt to know).


The aquatic ecosystem is very complex . Hundreds or thousands of species coexist in both freshwater and saltwater environments, both animals, plants and algae. When residues are added in the form of nutrients, the proliferation of one species over another completely alters the balance , damaging the proper development of the marine environment.

One of the main consequences of eutrophication is the proliferation of different species of algae , multicellular and unicellular, affecting the nutrient content of the water, oxygen and the amount of light that penetrates it.

The cause of all this, as a preliminary text before entering fully into the problem, is nitrogen and phosphorus, but in excess . And we say excess because the sea is one of the main atmospheric nitrogen fixers, due to the activity of different cyanobacteria that live in the water. However, when the cyanobacterial population is controlled by the ecosystem itself, everything is in perfect balance.

As we say in the headline, the continuous contribution of these nutrients does not usually affect the ecosystem, until it says enough and the limits of balance are exceeded.


The concept of eutrophication refers to the contamination of an aquatic environment (salt or fresh water) due to an excessive supply of nutrients, especially nitrogen and phosphorus. In fact, the term eutrophication derives from eutrophos , the literal translation of which is “generously fed.”

This is precisely what happens in the marine ecosystem affected by eutrophication.

The increased concentration of both nitrogen and phosphorus favors the proliferation of different groups of microorganisms, among them, different species of microalgae and phytoplankton that literally go crazy with these nutrients and use them as a food source.

This causes the population to evolve in a dizzying way and to such an extent that it creates an imbalance, altering the oxygen concentration , light penetration, pH and other essential chemical parameters.


Eutrophication is a natural (but not beneficial) activity that involves the contribution of nitrogen and phosphorus to the water. This contribution comes basically from human activity , either through water pollution through unsustainable agriculture or through poor treatment of fecal waste, where the concentration of nitrogen is considerable.

And it is that the nitrogen most used in agriculture and the form that plants absorb the easiest is the form of nitric nitrogen, coincidentally the one that, due to its anion structure (negative charge), is not retained in the soil and infiltrates in layers deep, polluting aquifers that end up drifting into the sea.


The eutrophication process is very slow, taking decades and decades of emissions to the aquatic environment. However, when the limits are reached that exceed the balance, the visual effects are seen in a very short time. Change in water color, death of animals, high presence of algae, etc.


The first symptom of a water contaminated by excess nutrients is the change in the color of the water . The evolution of different species of microalgae and phytoplankton creates a greenish color, because all these species are mixotrophic, that is, they photosynthesize just like plants.

The change in coloration inherently leads to more radical changes in the chemical composition of the water . These changes may not sit well with native species, many of them sensitive. However, the opposite can happen, and these changes stimulate the presence of non-native organisms that now find a favorable environment to develop.

In any case, there are already clear signs of a breakdown in the ecosystem.


As the problem evolves and nitrogen and phosphorus residues continue to accumulate in the water, eutrophication advances and physical alterations appear in the environment. One of them is the blocking of the penetration of light towards the bottom of the ecosystem, caused by a greater evolution of phytoplankton, located on the surface of the water.

The increase in living organisms of unicellular algae increases the concentration of organic matter and, therefore, the amount of decomposing elements, created by organisms that preferably live in environments with low oxygen availability.

Here the fight takes place between the phytoplankton, producer and consumer of oxygen, and organisms that decompose organic matter, which only absorb oxygen, altering the chemical oxygen demand (COD) and the biochemical oxygen demand (BOD).

The accumulation of organic remains of decomposing organic matter increases the problem of eutrophication, especially in stagnant water as is usual in lakes and seas. At this point, the ecosystem looks more and more like a pond or swamp, with low oxygen levels and the presence of animals.


Unfortunately, eutrophication is a very common problem that affects thousands of aquatic areas in Spain and the rest of the world. There are some very visible examples, and others that will take little time to appear, since the alteration of the ecosystem begins slowly until creating the final imbalance.


One of the most extreme cases in Spain, affecting the lagoon located in the Region of Murcia due to nitrogen and phosphorous pollution (agriculture, poor waste management and the rush of water due to torrential rains).

Until recently, it was considered that more than 80% of marine biodiversity had been lost due to the high presence of phytoplankton, with peaks of lack of oxygen (anoxia) and the appearance of rare organisms in the area.


Currently, a considerable increase has been detected in the levels of nitrogen, phosphorus and species of unicellular algae that cause future eutrophication, probably due to an abuse of fertilizers in agriculture.


The Caspian Sea is currently undergoing such severe eutrophication that it can be observed through satellite maps such as Google Maps . In the north you can see an intense green color due to the proliferation of different species of unicellular algae and phytoplankton.


The Gulf of Mexico is another case of great importance, where there are sections with very low oxygen content and a high presence of decomposing organic matter. Poor waste management and practically zero water renewal has exacerbated the problem.


The greatest solution to the problem is to reduce the contribution of nitrogen, phosphorus and organic matter residues to the water. This makes the species that cause the problem decrease, increasing the entry of light, oxygen and favoring the development of native species.

Following this, there are alternatives to reduce the presence of these algae, such as the formation of marine compost, although there are currently few means to be considered as an effective alternative.

At the agricultural level, the use of fertilizers must be managed very well and their abuse prohibited, especially in the case of nitrogen and phosphorus, creating safety cords in environments near water and avoiding the infiltration of nutrients into aquifers.

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