The eutrophication it is an excess of nutrients contributed to a body of water, generating a population explosion of algae, cyanobacteria and aquatic plants. This phenomenon in turn causes the decrease of dissolved oxygen in the water and, therefore, affects underwater life.
Dissolved oxygen decreases due to reduced photosynthesis by submerged algae and plants. This occurs both due to the blockage of sunlight due to surface plant proliferation, as well as the higher rate of oxygen consumption by these populations..
Eutrophication can occur due to natural causes when the size or flow of a body of water is reduced or exceptional rains that carry nutritional loads to bodies of water. However, in most cases eutrophication occurs from human-generated (anthropic) causes..
The problem of eutrophication is growing worldwide and more than half of the world's lakes suffer from it at some level. Similarly, dead zones proliferate in the seas due to the occurrence of this phenomenon, identifying more than 700 of them.
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Eutrophication begins with the contribution to the water of unusual amounts of nutrients, especially nitrogen (N) and phosphorus (P). These contributions can come from both natural and human (anthropic) sources, but in any case they are the product and cause of an ecological imbalance.
The exceptional intake of essential nutrients for plant growth favors the development of invasive aquatic plants and algae. It can be both phytoplankton and macroalgae and the proliferation of cyanobacteria also occurs.
These organisms have high reproductive rates and are fast growing, so having enough nutrients, they have competitive advantages. They grow on the surface of the body of water, and cover the entire surface.
Floating algae and aquatic plants that cover the surface prevent sunlight from penetrating to the lower layers of water. Due to this, submerged algae and plants cannot photosynthesize and begin to die..
The blockage of underwater photosynthesis by this superficial proliferation of plant mass also implies the decrease of dissolved oxygen in the water. In addition, other sources of dissolved oxygen are limited, such as exchange with the atmosphere due to the blockage exerted by the superficial plant mass..
Below the surface, the activity of decomposing organisms, especially bacteria and archaea, increases. This implies an increase in the demand for dissolved oxygen, which is reduced.
The increase in decomposing activity is a consequence of the greater supply of organic matter as a result of the outbreak of the surface population. The increase in the death of underwater organisms also influences.
The internal contribution of organic matter and the external one by contaminated effluents requires more oxygen for its biochemical stabilization (Biochemical Oxygen Demand). When oxygen is scarce, semi-decomposed organic matter accumulates, the entire ecosystem goes into crisis and life disappears.
Eutrophication is caused by a nutrient supply greater than the usual balance of the ecosystem. Which can happen by both natural and artificial causes, although the former are rare..
Deep cold water currents can cause phytoplankton population bursts by pulling nutrients from the ocean floor to the surface (upwelling). Similarly, algal blooms or outcrops are natural phenomena caused by different factors that favor the growth of phytoplankton..
In such favorable conditions, unusual population increases of dinoflagellates and diatoms occur. Some species of microalgae are harmless and beneficial, but others are toxic algae, such as dinoflagellates of the genus Alexandrium.
This toxicity is due to the emission by microalgae of toxins such as saxitoxin, ciguatoxin and gonyatoxins..
The rivers in their derivation along the channel generate meanders or marked curves, which sometimes remain isolated. In this way horseshoe lagoons are produced, which are fed by rainwater, runoff or the periodic overflows of the river.
In these water reservoirs there is a concentration of nutrients higher than that of the river, because there is no outflow. Therefore, natural eutrophication phenomena occur with the proliferation of algae and aquatic vegetation..
The most important cause of eutrophication today is the contamination of water bodies by human activities. Especially wastewater without adequate treatment and diffuse pollution from agriculture, which is the most important worldwide..
Chemical fertilizers consist of compounds specially formulated to provide essential nutrients for plant growth. The main fertilizer formula includes nitrogen (N), phosphorus (P) and potassium (K).
In agricultural systems the application of these products is inefficient, so that about 60% is washed by runoff water. These nutrients end up in water bodies such as rivers or finally lakes and oceans, transported by runoff water..
Sewage from homes, offices and factories provides a large amount of organic matter and inorganic substances that promote eutrophication. Domestic sewage carries a high load of organic matter that, if not treated, reaches the water bodies.
Soaps and detergents used in personal hygiene, home and other facilities, also include phosphates and nitrates.
Industries emit gases containing nitrogen oxides among other compounds into the atmosphere. These gases when reacting with water vapor produce acids that precipitate and reach bodies of water.
These compounds are additional sources of nitrates that are one of the main nutrients that promote plant growth..
Rising global temperatures favor eutrophication, as warm waters promote the growth of algae and aquatic plants. On the other hand, the amount of dissolved oxygen decreases in proportion to the increase in water temperature..
Other factors contribute to the development of eutrophication, including lack of water mobility, shallow depth, low flow, and high water temperatures. The less water there is in the aquatic ecosystem or the slower its renewal rate, the faster the nutrient saturation is reached.
Eutrophication is a serious problem that mainly affects freshwater ecosystems, but it also occurs in marine ecosystems. Worldwide, around half of the lakes have some level of eutrophication and many rivers as well as coastal areas have dead areas due to this cause..
The main consequence of eutrophication is the decrease of biodiversity in the ecosystem and finally the disappearance of aquatic life. In the early stages, excess nutrients favor the proliferation of invading organisms that show rapid growth and reproduction under these conditions..
To the extent that these species predominate, they displace the rest of the species in the ecosystem, reducing their biological diversity. As eutrophication proceeds, conditions at the underwater level become unfavorable to life and organisms die.
In this way, submerged fish, algae and plants disappear, as well as other aquatic organisms due to lack of oxygen and light. The final destination, if eutrophication continues, is the almost total disappearance of aquatic life..
The activity of anaerobic bacteria produces toxic gases such as hydrogen sulfide, causing large deaths of aquatic organisms..
The impact extends to terrestrial ecosystems, since those living beings that depend on the body of water also perish or migrate. This is due both to the loss of the food source and to the degradation of the drinking quality of the water..
In eutrophied areas, food production decreases as fishing decreases because the first organisms to be affected are fish. These, in the case of rivers and seas, are forced to leave the area, while in the lakes they end up disappearing.
Drinking water must meet quality conditions, including dissolved oxygen level, pH and absence of organic and inorganic impurities. When eutrophication occurs, the water in the ecosystem reduces its dissolved oxygen content and accumulates large amounts of decomposing organic matter..
This in turn is harmful to health and causes bad odors and color changes, incompatible with its use as drinking water. The pH of the water is altered, becoming more acidic due to the presence of organic acids.
Public health can be affected by the consumption of non-potable water from eutrophic bodies of water. In addition, the proliferation of certain microalgae contribute toxins to the water and to the organisms that consume it.
Similarly, the increase in anaerobic bacteria generates the emission of toxic gases such as hydrogen sulfide and methane..
Aquatic ecosystems are important poles of tourist attraction, generating sources of work and local development. These benefits are threatened by eutrophication, since it affects both the biodiversity and the landscape values of the area..
As a consequence of all the above, eutrophication leads to great economic losses in terms of decreased fishing, tourism income and water use..
Solutions to the problem of eutrophication must be approached from the perspective of prevention of the phenomenon and from its remediation.
The starting point for the prevention of eutrophication is the awareness of the citizen about its existence, causes and consequences. In this way, citizens can lobby for the necessary measures to be adopted.
The basic solution to the problem of eutrophication due to anthropogenic causes is the reduction of water pollution. For this, it is necessary to implement the adequate treatment of domestic and industrial sewage before being discharged into water bodies..
It is also necessary to control other indirect sources of water pollution, such as gas emissions that generate acid rain..
Water pollution caused by agricultural and livestock activities is diffuse, that is, the polluting sources cannot be exactly identified. In such a way that the solution to the problem of the contribution of pollutants by these activities is to change the technological production schemes.
An agriculture that uses fewer inputs is required, especially fertilizers and herbicides, compounds that contribute nitrites and phosphates to water. Thus, agricultural systems with closed circulation of nutrients such as hydroponics are less polluting in terms of contributions to ecosystems.
Attention is also required to the management of organic waste, the collection and treatment of sewage in animal production systems..
Once the eutrophication process of a body of water is underway, there are several alternatives to remedy the problem.
Given the proliferation of floating aquatic plants such as lenna (Lennaceae), bora (Eichhornia crassipes) or others, it is feasible to implement collection programs. This consists of massively removing the plants from the surface of the body of water using dragging mayas..
In severe cases of contamination, the water can be subjected to purification treatments recirculating from the water body to treatment plants.
There are some organisms that consume algae and aquatic plants that proliferate in eutrophication. Heterotrophic grazing protists have been used, that is, they consume microalgae to reduce the populations that proliferate in eutrophication..
The fungus has also been used Cercospora piaropi for the control of Eichhornia crassipes, a floating angiosperm that proliferates under eutrophic conditions.
Causing the flocculation and precipitation of microalgae is an alternative, especially in cases of toxic algal blooms. This is achieved by adding products such as sodium hypochlorite (NaOCl), clays (kaolinite) or combinations such as polyaluminum chloride with bentonite. These products attract and adhere the microalgae, forming flocs or masses that then precipitate to the bottom.
The United Nations Environment Program indicates the existence of more than 700 dead areas in the world's oceans. These dead zones are due to a low concentration of dissolved oxygen due to eutrophication and their estimated area is greater than 240,000 km².
One of the most extensive marine dead zones in the world is the so-called Dead Zone of the Gulf of Mexico. It is more than 20,700 km² of sea that suffer serious problems of eutrophication, with the proliferation of floating macro and microalgae.
The central cause of the eutrophication of this area is the polluted waters of the Mississippi River that has its mouth in the Gulf. The Mississippi runs through much of the agricultural area of North America, being a catchment basin with a high load of agricultural pollutants.
In this inland sea located between Europe and Asia, an increase in algal blooms has been reported since the 1970s. This has resulted in declining populations of shallow-water species.
According to information from the European Environmental Agency, hypoxic and anoxic phenomena occur every summer as a result of the activity of algae. All this due to eutrophication by the nutrients provided by agricultural and industrial activities in the basin of this sea..
Being an inland sea whose only indirect oceanic connection is the Bosphorus channel, the renewal of the waters is very slow. This, together with the high levels of contamination in the basins that feed it, makes it especially susceptible to eutrophication..
In fact, the average concentrations of nitrates and phosphates have increased 18 times from 1960 to 1992. The greatest contributions of pollutants come from the basins of the Danube, Dnieper and Dniester rivers..
This lake, also called Los Tacariguas lake, is located in the north-central part of Venezuela with an area of 344 km². It forms an endorheic basin, that is to say, closed, of 3,140 km². Many of its tributaries pass through cities in the center of the country such as Valencia and Maracay, with high populations and industrial zones..
Most urban and industrial wastewater is discharged into rivers converted into drainage channels without adequate treatment. This has resulted in huge amounts of pollutants accumulating over decades, including organic and inorganic nutrients..
Since 1974 nitrogen concentrations have doubled and phosphorus tripled in the lake. Placing itself above what is admitted in 146% for nitrogen and 250% for phosphorus. All this has caused an extensive phenomenon of eutrophication that today is well advanced.
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