Eutrophication is a type of chemical contamination of water. It occurs when there is an excessive contribution of nutrients to an aquatic ecosystem, which is severely affected by it. It can occur naturally (red tides) but it is the anthropogenic that should most concern us. Phosphorus and nitrogen are the main causes of eutrophication, but also any other substance that may be limiting for the development of different species such as potassium, magnesium and different organic products are relevant.
Eutrophication alters the environmental characteristics of aquatic ecosystems by altering the trophic chain and increasing the entropy (disorder) of the ecosystem. The result is ecosystems with reduced biodiversity, with opportunistic species occupying niches previously occupied by other species. The ecological consequences are obvious but as usual they go hand in hand with economic losses for different reasons. Eutrophication occurs in several stages, which will be described below in grids
.It can also be considered more generally that it also affects soils which have undergone an abnormal nitrogen enrichment and in which there is a tendency for the growth of plants related to the abundance of inorganic nutrients, mainly nitrogen. In this article, however, we will focus on the anthropogenic eutrophication of water. Explaining how and where it occurs and the problems that it causes, as well as what can be done to combat or mitigate it, although it is convenient to keep in mind that both can be quite related to affect the effluents of a land with excess nutrients to the water channels to those who pour their waters that land.
Contribution of nutrients, can be an episode or accident or continuous in time. It can be carried out in a punctual way (a discharge in a point of a river) or of diffuse form, with scattered origin (typical of the agricultural fertilizers).Oligotrophic stage.This is the normal and healthy state of the ecosystem in it opportunistic and cosmopolitan species have a marginal space and there is a dynamic equilibrium with seasonal fluctuations. The water has a considerable transparency and there is an abundance of animals that breathe by filtering the oxygen of the water (fish, molluscs, aquatic arthropods).
The contribution of nutrients causes an explosive growth of plants and algae. There are unicellular algae that grow in the water, in the photic zone of the same. Being photosynthetic algae give the water a greenish color that prevents the passage of light to depths previously reached.
The vegetation below the new fhotic threshold dies, many of the floating algae also die and sink to the bottom due to nutrient depletion caused by exponential growth.
The dead organic substance of the bottom is decomposed by bacteria that consume the oxygen and also can generate toxins lethal for plants and animals.
The absence of oxygen causes bottom mollusks to die and fish and crustaceans die or escape to unaffected areas. Invasive species accustomed to oxygen shortage may appear (for example, barbs and perches may displace salmon and trout).
In certain circumstances an anoxic zone (without oxygen) can be created in the bottom of difficult removal. It is more dense, dark and cold water in which algae and animals can not grow.
Eutrophication is related to the concepts of chemical oxygen demand and biological oxygen demand (DOQ and DOB), which express the amount of oxygen that needs to be consumed in order for the ecosystem to consume a determined quantity of an inorganic pollutant (DOQ) or organic (DOB). Both are used as indicators in water quality control processes and are expressed in units of milligrams of oxygen consumed per liter of sample over a period of 5 days at a temperature of 20 °, although measurements can be made for other conditions. The greater DOB and DOQ in a larger water will be the amount of oxygen necessary for the aerobic organisms of the water to process that nutrient. If they take too high values ??the presence in excess of nutrients will cause eutrophication of these waters and the consumption of all oxygen ending with the underwater life dependent on it (fish, molluscs, arthropods …) and altering the trophic chain of that ecosystem. DOB values ??can range from 1 mg / L of the purest water to 600 mg / L or more of untreated wastewater, a moderately contaminated river can have values ??of 2 to 8 mg / L and wastewater treated in the treatment plants has values ??around 20mg / L.
Eutrophication can not only be detected by biochemical analysis. Using them can be measured, monitored and evaluated. By observing the presence, absence or abundance of certain species (bioindicators) one can check whether a given area is eutrophic or not roughly estimate its level of impact. Another clear indicator of eutrophication is the measure of the transparency of the waters and their color. If the water is green and the light is unable to cross more than a few meters from the water column, there will be eutrophication.
Causes of eutrophication
There are several causes of eutrophication derived from human activity.
The most important at the global level is agriculture due to the use of fertilizers, mainly nitrates, which are often used without proper care and curing and end up in surface or groundwater by leaching and hauling from fertilizers from the land in the ones that were used. Agriculture produces an eminently diffuse eutrophication, increasing the concentration of nutrients in large areas of lakes, rivers, marshes, estuaries and coastal zones.
Another rural activity with a high incidence of eutrophication is cattle ranching . Animal droppings are rich in nutrients, especially those of nitrogen character (ammonia). If they are not managed properly they can end up producing discharges to the nearby waters that when they occur are usually punctual.
Similar to livestock, urban waste can produce eutrophication, although in this case it is necessary to add the possible use of detergents with phosphates which are one of the nutrients that can lead to eutrophication and especially harmful consequences in the waters.
The industrial activity can also be a source of nutrients that may cause eutrophication point source. In the case of industry can be discharged from both nitrogenous and phosphate products among many other toxic. Like the eutrophication caused by urban waste, they are eminently punctual, affecting, when they occur, specific areas with a lot of intensity.
The air pollution , in particular the production of nitrogen oxides and sulfur (NOx and SOx) which react in the atmosphere and produces acid rain, one effect of which is that of increasing the leaching and washing soil nutrients which are washed away by surface and groundwater until they are incorporated into the rivers and aquifers by contaminating them. 30% of the nitrogen that reaches the seas does it by the atmospheric means.
Eutrophication can also trigger forest activity , if forest residues are left in the water.
Effects of eutrophication
The effects of eutrophication occur normally locally and regionally. From a systemic point of view, it increases the primary production (photosynthesis), increases the biomass but diminishes the diversity and the composition, structure and dynamics of the affected ecosystems are altered drastically.
More specific effects are for example the drying of ponds by the deposit during long seasons of sediments and organic remains on which the vegetation grows, transforming the lagoon into marsh and then into forest or meadow. This process is carried out for long periods of time often in a natural way and is called clogging.
Eutrophication has effects on the aquatic and riparian species but also on the quality of the waters since with increasing rotting and depletion of oxygen, the waters acquire a nauseating odor requiring a greater treatment to be consumed or making it directly impossible or undesirable consumption.
The smell of these waters can cause economic losses (tourism, areas that lose their value as residential areas), respiratory problems and their consumption can cause health problems to the people of the area. The taste of water can be altered as well.
Eutrophication can affect the fish production of an area, either this extraction or through cultivation. It is possible that aquaculture can produce a greater contribution of nutrients to the waters surrounding the farm so it is advisable that farms for fish, algae, shellfish … be supervised and managed with the necessary delicacy.
Due to the clogging and the greater presence of algae, a channel previously navigable may cease to be causing communication problems in certain areas.
There are cases where the anoxic conditions of the bottom give rise to the growth of bacteria like Clostridium botulinum that produce lethal toxins for birds and mammals that are not directly affected by the lack of oxygen of the waters. The areas where this happens are called dead zones.
Emergence of invasive species that take advantage of the empty ecological niches by the disappearance of their previous occupants. It is also common for invasive species to be favored by new conditions and to displace local organisms, now at a disadvantage.
Some of the algae outbreaks other than blocking the light, produce toxic to other plants and animals. These substances can cause the death of animals when consumed. Affected animals can act as vectors for toxins, neurotoxins and hepatotoxins affecting other species and reaching humans. Examples are contaminations by mussels, oysters and ciguatera.
Nitrogen itself is also toxic, especially for babies. In fact the limit for oxidized nitrogen products in drinking water is 50mg / l = 50ppm.
Why should we care?
Eutrophication is worrying because today it affects a large part of the world’s surface waters (rivers, lakes, coastal waters) and their effects are detrimental to biodiversity, the quality of water for human consumption … At sea it must be borne in mind that the waters most susceptible to eutrophication are often the richest in biodiversity and those that have a greater economic value for fish production. It is well known that much of the ocean has a very limited production, placing the world’s fisheries in areas of the continental shelf. In terms of biodiversity, marshes, mangroves and estuaries are very sensitive because of their situation and structure to any type of alteration such as construction of reservoirs, rising water levels, construction, pollution, etc.
Chesapeake Bay, USA. One of the areas affected by eutrophication. You can appreciate the large number of rivers that flow into it and its narrow mouth. In the area there are 16.6 million people whose activities cause eutrophication of its waters. All these circumstances facilitate the appearance of such problems.
Examples of eutrophic seas are any whose coast is densely populated and in which the rate of renewal of water is reduced, if the continental shelf is extensive, there are estuaries of nearby rivers and the solar irradiation is high (it is also a limiting factor to the growth ) the chances of eutrophication are increasing. Inland seas such as the Baltic, the Adriatic and other Mediterranean seas, the Black Sea (especially the Azov Sea), the Gulf of California, etc.
Much of the lakes, rivers and reservoirs of Europe, Asia and North America have eutrophication to varying degrees.
Eutrophication is a sign that something good and necessary, when present in too much abundance (nutrients) can be dangerous and harmful (they become pollutants). Although it is not in principle the most dangerous contamination of groundwater and aquifers (compared to radioactive contamination or heavy metals), it should not be forgotten that aquifers form a whole with river and lake systems. If an aquifer is contaminated it may take centuries to clean itself and during all that time its waters will continue to flow slowly towards the rivers that form part of that surface-underground system influencing it and the quality of its waters for human consumption will be seen which may require treatment for long periods after the emission of pollutants has ceased.
What you can do to avoid eutrophication
It is important to take measures to control the discharge of urban and industrial waste into the water. In that sense, it is observed that there are rivers and lakes of developed countries that have recovered part of their old wealth in species thanks to a more sensible management of the waters and to the process of urban black waters, industrial waters and other spills that cause contamination, whether this causes eutrophication or other types.
The control of the discharges must be implemented by the legislative route so that the companies or entities can not obtain a benefit, a saving or a competitive advantage by the fact of not purifying its waters. Education in this type of situation is also important. A conscientious population is able to help in the management by denouncing undesirable activities and less likely to participate in them. NGO’s dedicated to environmental protection can also play an important role in conveying concern for these population issues, cooperating with companies and institutions that follow guidelines and denouncing those that do not.
At European level, the European Commission establishes a directive by which countries must regulate and properly manage wastewater discharges. Spain, Portugal, Belgium, Ireland, the United Kingdom, Germany and France have failed to comply with some of these measures and received warnings.
It is also useful to implement innovative technologies capable of avoiding the dumping of dangerous substances. As an example of success, that of detergents without phosphates. As has been seen, phosphates are among the substances with the greatest capacity to produce eutrophic episodes. The detergents used to use phosphates as emulsifiers and in recent years thanks to the development of new detergents and the legislative momentum has been reduced its use thus avoiding the discharge of thousands of tons of phosphates to rivers and seas in millions of homes. Since the 1960s and 1970s, the phosphate content of detergents has been reduced from about 65% by weight to less than 0.5%
The limiting factor for growth in rivers is usually phosphorus and nitrogen at sea, so the use of appropriate detergents is more positive for rivers, lakes and other freshwater courses.
The process that takes place in the purifiers is the consumption of waste and oxygenation of the water before it is discharged already inert and free of contaminants. The purification is carried out in six stages, one of pre-treatment, three of treatment, one of disinfected to kill the dangerous microorganisms and one last of control of the odor. Each of the first four stages is formed by different steps with the aim of eliminating mechanics (decanting, filtration …), chemically and biologically the different types of contaminants. Phosphorus and nitrogen, so important in eutrophication, are eliminated in the fourth stage (third treatment). With the current technology it is possible to obtain potable water from the waste water,
The introduction of modifications in cropping techniques so that less fertilizer and less irrigation can be used (with the added benefit of saving water and fertilizers) to obtain the same production or to avoid the uncontrolled dumping of the same fields in which it would be interesting to carry out developments and research.Waste water treatment is relatively simple for large populations with good pipelines. For dispersed and rural populations it is more difficult, not technically, of course, but economically: sewage plants have a size below which their price shoots in relation to the amount of water they are able to treat and the creation of water pipes waste is also too expensive. Something similar happens with agriculture, the largest contributor to eutrophication at a global level and of a dispersed origin.