Mega dams and their environmental impacts

Mega dams and their environmental impacts

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By Clar Alejandra, Sosa Rosana

Hydropower is often considered a "clean" or "green" energy, but is this really the case? Anyone who stands before the immensity of concrete that is the Itaipu dam cannot help but realize that such a human footprint must, necessarily, have an impact on the environment. The fact that this energy does not depend on the use of fossil fuels should not make us fall into the error of thinking that it has no adverse effects on the environment; The so-called "clean" energies are never clean when they are produced on such a large scale or when they produce such a drastic change in the environment, on the contrary, they have serious impacts on human lives and natural ecosystems, many times irreversible.

The area of ​​influence of a dam includes not only its surroundings and the reservoir, but also the river basin, downstream of the dam. There are direct environmental impacts associated with the construction of the dam, but the most important impacts are the result of the water reservoir, the flooding of the land to form the reservoir, and the alteration of the water flow downstream of the dam. These effects have direct impacts on the soils, vegetation, fauna, climate and human population of the area. There are also indirect effects that include those associated with the construction, maintenance and operation of the dam and the development of agricultural, industrial or municipal activities made possible by the water source that the dam reservoir represents.

Despite this, increasing energy shortages due to the impending depletion of oil and other fossil fuels, coupled with the propaganda that hydroelectric power is "green", is causing more and more dams to be planned and built. It is worth mentioning that these same arguments are used to promote another type of energy: nuclear.

Despite the fact that modern hydropower is now over a century old (the first hydropower station was built in 1880 in England), awareness of its negative impacts is only a few decades old (from roughly the 1960s to 1970s). According to Mauricio Schoijet, this late awareness is due to two reasons: on the one hand, due to a general order consisting in that ecological concerns only began to have force at that time (or even later depending on the country), and, on the other hand On the other hand, for the specific reason related to how hydropower has developed over time in the world. This refers to the fact that the first countries in which this energy was developed were countries with a cold or temperate climate, with low population density on riverbanks and with adequate services and sanitary conditions (such as Western Europe, Canada and the United States ), and that in these cases the dams built did not have the monumental size of mega-dams, such as Itaipú, since, being developed, urbanized and industrialized countries, with their population settled in a stable manner, the best sites for hydroelectric exploitation were already dedicated for other purposes.

The negative effects of hydroelectric energy began to be perceived as it was developed in tropical and sub-tropical countries since in these regions the dams were built with the opposite conditions to those mentioned before: hot climate, poor sanitary conditions and high density of riverine population. This situation, added to the fact that the dams built in Third World countries tend to have monumental dimensions, previously unknown, revealed the true impacts of the dams.

Another aspect of great relevance is that many of these mega-dams are built in wetland areas (for example, in our country this happens in the Delta region and the Paraná Islands). These ecosystems are very important, since, among other things, they have enormous biodiversity and productivity, they act as "sponges" that retain excess water, preventing floods, recharge aquifers and purify water. Wetlands are “pulse” ecosystems, that is, their proper functioning requires the pulsations of regular floods to survive, which is why dams are especially harmful. In addition to the alteration of its natural regime, another of the most harmful impacts is the favoring of a process called “clogging” that occurs when the water in the area of ​​the dam stops flowing and, upstream, the original river and its tributaries continue to flow, but in an altered state, with a very slow flow. This causes sediments that would normally move downstream to settle, gradually reducing the porosity of the soil. This alters the absorption capacity of the wetland, causing flooding and preventing the recharge of aquifers and the purification of water.

In our country, the environmental problem of dams greatly affects the Delta and Paraná Islands ecoregion, not only due to the presence of the Yacyretá dam, but also because Brazil is a country with a great “bet” on energy hydroelectric, so that in the upper course of the Paraná River there are a high number of dams, which alter the middle and lower reaches of it. This is compounded by the fact that, although the impacts of the dams are known, there are currently plans for many new hydroelectric projects in the area, both in Brazil and in our country.

Faced with this panorama, it becomes especially relevant to re-evaluate the impacts of these complexes and promote awareness of the environmental cost they imply for society.

Global Impacts: Contributions of Dams to the Global Ecological Crisis

No one can, at present, deny the fact that we are facing an ecological crisis on a global level: the effects of global warming are already being felt and will only increase, there is a growing crisis, both energy, water and food, the Soil is degrading, oceans acidifying, etcetera.

Although these phenomena are known and evident, so is the scarcity of instruments that humanity has (although many are being developed) to measure most of these processes, and thus be able to define which limits should not be crossed (for example , what concentration of CO2 in the atmosphere should not be exceeded).

A model that has been proposed for this is the one postulated by an international group of scientists led by Johan Rockström (Center for Resilience, Stockholm University, Sweden), in the article: “Planetary boundaries: a safe operating space for humanity. " In this nine processes are identified that they consider key in the terrestrial systems and the limits within each one that should not be transgressed by humanity to avoid causing irreversible changes on our planet.

The proposed limits are for: climate change, biological diversity, nitrogen and phosphorus inputs into the biosphere and oceans, stratospheric ozone, land use change, freshwater use, ocean acidification, aerosol loads, and chemical pollution . The essay also postulates that it is very possible that the first three of these limits have already been crossed and remarks that they are all highly interconnected, so crossing one can greatly affect some of the others.

We found it interesting, then, to evaluate the global impacts of dams, analyzing to which of the global processes described by Rockström they contribute.

Biodiversity loss:

Although in nature there is the process of extinction of species without human intervention, this process has been accelerated gradually by anthropic processes since the Industrial Revolution. The situation has reached a point where the speed of this process is between 100 and 1000 times faster than what would happen naturally.

This enormous loss is a very serious process since biodiversity not only provides numerous environmental services to man, but also, as species become extinct and the functions they fulfill are destroyed, ecosystems become more vulnerable to disturbances and , therefore, its fragility increases.

Dams contribute significantly to this process by:

The water discharges from the dam, which in many cases is colder than the surface water over the falls, may lack oxygen and have hydrogen sulfide, or have a lower pH, all of which have a great impact on fauna. aquatic.

· The alteration of the hydrological regime of rivers.

· The change from a habitat of flowing water, well oxygenated and with a lot of light, to one of still water, with little oxygen and dark.

· The permanent flooding of large areas of terrestrial ecosystems, which are often tropical or subtropical areas, with forests and jungles, where some of the world's richest ecosystems in biodiversity develop. Furthermore, these complexes are generally built in regions far from cities and industries, which are the last refuge for displaced species.

· The possible depletion of oxygen in the dammed water.

· The interruption of migratory routes due to the blockade of the river.

· Deforestation, which occurs due to the need for roads to pass machinery and other infrastructures, and is aggravated because it opens the door to timber traffickers.

· The invasion of exotic species that compete with the native ones. Hydroelectric dams are built on waterfalls. These previously acted as ecological barriers for fauna and flora, but when building one of these complexes, the water is stored in the dam (in which species of flora and fauna infiltrate) and then released in such a way that these organisms they survive and may move to downstream habitat that they did not previously inhabit.

· The proliferation of floating aquatic plants, which reproduce very quickly and are very easy to adapt, so they quickly supplant the rest of the flora.

Climate change:

This anthropic process is already indisputable and its effects are appreciable. It is one of the most critical current environmental problems, as its consequences are highly unpredictable and greatly affect biodiversity and most of the other processes discussed in Rockström's article. It is also very relevant because the measures that should be taken to mitigate it would imply a decrease in consumption, and, for the moment, there does not seem to be a trend towards this attitude.

Dams contribute to this process because:

· They cause great deforestation, which has a great influence on climate change, since forests and jungles are sinks of carbon dioxide.

· If you don't deforest to build the dam, the trees go under water and die, generating methane, a greenhouse gas even greater than carbon dioxide.

· Most of the dams, after their useful life, are abandoned under water without treatment, with some of their materials in decomposition processes, which also generates greenhouse gas emissions.

Nitrogen and Phosphorus Cycles:

These global natural cycles have been greatly altered anthropically by the enormous influx of different chemical forms of these materials for human activities, especially agriculture.

The reservoirs of the dams provide a great source of water for irrigation, which is why nearby areas are often used for agriculture, causing contamination with fertilizers that contain species of both elements.

These can also reach the water due to contamination by tributaries, either by nearby urban centers or by industries installed in the vicinity of the reservoir.

These processes are especially critical in dam reservoirs because, by stopping the river, its self-purifying capacity is lost due to the silting process.

Global freshwater use:

It is a process of enormous importance since it affects biodiversity, the functioning of ecosystems and food and health security. The human being has exponentially increased this use (to which is added the loss of water due to its contamination), so that today this resource is already in many areas in crisis.

Projections estimate that, even with technological improvements for greater water efficiency, by 2030 there will be a gap between supply and demand of at least 60%. However, many countries, like ours and Brazil, continue to act as if fresh water were an inexhaustible resource. It is critical to promote a change in attitude and begin to adopt strategies for their future conservation.

The effect on the use of water from dams is given by:

· Deforestation, which causes the alteration of the region's rainfall regime.

· The accumulation of stored water, which reduces the loss of water through evaporation and perchlorination.

· The installation of industries and the development of agriculture in the vicinity of the reservoir for the use of said water source, which are the activities responsible for most of the world's water consumption.

· The loss of water due to its contamination by hydrogen sulfide, accumulation of organic matter, pesticides, fertilizers, discharge of effluents, etc., aggravated by the loss of the river's self-purification capacity. Also, if the dam is in an area with an aquifer, the contamination could reach the groundwater.

· The decrease in the flow of the rivers downstream of the dam, which alters the availability of water in this area and the replacement of water from aquifers.

Land use change

It is mainly due to the expansion of agriculture and associated deforestation, and affects biodiversity, soil quality and climate, among others.

Dams cause a big change in land use by deforestation and by flooding large areas that were not under water before. In addition, as we said before, the nearby lands are often used for agriculture and the installation of industries to take advantage of the source of fresh water from the reservoir.

Acidification of the oceans:

This problem is a great threat to marine biodiversity and to the role of the oceans as carbon sinks. The main cause of this phenomenon is the increasing concentration of atmospheric carbon dioxide. This is because between the atmosphere and the oceans there is a chemical equilibrium in which atmospheric carbon dioxide dissolves in water and is transformed into carbonic acid and bicarbonate, lowering the pH of the water.

So dams influence this process because, as we mentioned previously, they release carbon dioxide into the atmosphere.

Chemical contamination:

The dam itself does not contribute much to this process, since, although it releases species such as hydrogen sulfide, which is harmful to fauna, this type of pollutant is neither persistent nor of anthropic origin.

What it does contribute is agriculture, with its use of pesticides, and the industries that develop near the hydroelectric complex.

Release of aerosols into the atmosphere:

Although there is still no way to measure them globally and their effects are not well known, it is known that they affect climate and human health.

The greatest contribution of dams to the release of aerosols occurs during their construction and, subsequently, by the exposure of the soil due to deforestation.

Other impacts of dams

Direct impact on human health:

Stagnant waters caused by dams can cause a wide variety of diseases as disease-carrying agents, such as insects and snails, proliferate in still water.

One of the typical diseases of tropical and subtropical areas with dams is schistosomiasis, which is transmitted to humans when larval forms of the parasite, released by freshwater snails, penetrate the skin during contact with infested waters.

This chronic disease is characterized by disorders of the liver, urinary tract, lungs, or nervous system.

For the life cycle of this parasite to occur, stagnant or slow-moving waters are needed, so the disease is directly related to dams, and has spread geographically in recent times. This is the case, for example, of southern Brazil, a tropical region with a high number of dams.

Other diseases associated with the construction of the dams are dengue, malaria and yellow fever due to the ideal environment for the proliferation of mosquitoes that generates stagnant water. Cases of these have been found in the surroundings of the Itaipú and Yacyretá dams.

It can also increase the chances of illnesses such as dysentery, diarrhea, skin rashes, and others.

Sociocultural Impacts

Among numerous social impacts are:

• Disintegration of communities and displacement and separation of their members.

• Inadequate mitigation, resettlement and development programs for displaced people.

• Greater impoverishment.

• Loss of economic activities such as fishing and, on many occasions, tourism.

• Social and environmental costs to be borne by future generations.

• Corruption: hydroelectric dams are always a source of great corruption. To begin with, there is always an attempt to "deceive the public", of "false propaganda": dams are presented as a source of employment and energy (also "clean") for everyone and as something that will enrich the region, when in the majority of the cases generate more costs than benefits. Environmental impact assessments (EIA) are manipulated and used as tools by some industries and countries, benefiting from dams at the expense of local people, to generate this positive image. On the other hand, dams require a huge initial investment, which can be used as a bribe for approval, as government officials and politicians can easily appropriate part of it.

Conclusions: environmental debt, environmental liabilities and dams

Dams and their impacts are one more example of the current functioning of the economic system, which benefits a few and harms many, and which is considered superior to all other aspects of life and, therefore, entitled to govern them. The effects of hydroelectric ventures are another example that the consequences of economic activities (“externalities”) affect third parties and are not collateral damage, but rather central impacts of the system (“environmental liabilities”), and that they are the environment and society those who must pay its cost.

The fact that mega-dams are mostly built in Third World countries is another example of the usual asymmetry between how environmental risks are managed in developed and undeveloped countries. On the other hand, most of the energy produced by these hydroelectric dams is not destined for the population, but for the industries in the area (generally subsidized by the State), which also abuse water consumption and pollute. It should be noted that most of these industries are not national, but transnational from developed countries. In other words, the dams of the third world countries are, in general, one more part of the ecological debt that the “Northern” countries have with the “South”.

By ecological debt we understand "the debt contracted by the industrialized countries with the others for the dispossession of natural resources, the environmental impacts exported and the free use of space to deposit their waste."

Dams contribute to:

· The Carbon Debt due to its emission of greenhouse gases.

· Environmental Liabilities for all the impacts studied.

· The Export of Toxic Waste due to contamination by imported fertilizers and biocides used for agriculture, and due to contamination by foreign industries.

Part of this debt could be quantified monetarily: reversible environmental impacts, with a calculable economic cost. However, one wonders who would bear these costs: those responsible for the dams? the industries? the farmers? In a situation like this, where it is not possible to clearly distinguish where the responsibility of one actor ends and that of another begins, it is most likely that no one will take care of the remediation of these effects.

However, in many cases the impacts are irreversible (such as the loss of biodiversity and the change in the lives of displaced people). Calculating a monetary value for these would involve an arbitrary evaluation and, in our opinion, it would be unethical.

While it is not possible to calculate an exact value of the ecological debt of the dams (and, in any case, it is not clear who the claim would be or if it would be ethical), it seems to us that it is a useful argument to promote a mitigation of their impacts and a cessation of the construction of hydroelectric projects.



SCHOIJET, Mauritius. "An introduction to the problem of" impacts "." Chapter 7 of the book "Dams and their effects on health" of the Pan American Health Organization. 1984.

PIELOU, E. C. "Fresh water." TheUniversity of Chicago Press, 1998.

Collective for the Diffusion of Ecological Debt (CDEs). "Ecological Debt: The North is in Debt with the Countries of the South". Observatory of Debt in Globalization, 2002.

Magazine Articles:

CASTRO SOTO, G. "Impacts and consequences of dams", Ecoportal, 06/08/05.

WRM (World Forest Movement). "Large hydroelectric dams", Ecoportal, 04/05/11.

"Three of the nine planetary limits have already been exceeded to control the health of the terrestrial ecosystem", Ecoportal, 03/05/12.

ROCKSTRÖM, J. 2009. "Planetary boundaries: Exploring the Safe Operating Space for Humanity", Ecology and Society, Vol. 14, No. 2.

Internet pages:

International releases:

COMMUNICATION: "Planetary limits: a safe operating space for humanity." STOCKHOLM, 9/16/11, PRNewswire. Communiqué from the Stockholm Resilience Center of Stockholm University, Potsdam Institute for Climate Impact Research, The Australian National University, University of Copenhagen and the University of Minnesota.



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