Amazon biodiversity threatened by hundreds of Dams
Along the Amazon there are 140 hydraulic dams that are under construction or already operating. There are plans for the construction of another 428.
AMAZÔNIA — Although only a portion of them will eventually be constructed, scientists believe that their impact on the Amazonian rivers will be “disastrous.”
A global study on the consequences of water dams indicates that they will alter the flow of the river, retaining most of the sediments and river nutrients that will not vivify the Amazonian plain, drowning the life that depends on the river and the ocean where it ultimately ends.
In the Amazon, everything is large. Its main section is about 2,000 kilometers to the mouth of the Atlantic, in an estuary more than 300 kilometers wide.
But there are still another 5,000 kilometers until reaching the opposite end, at its head in the Peruvian Andes.
Some of Amazon’s most important water sources, such as Madeira, Negro or Japura, are among the 10 largest rivers on the planet.
The Amazon basin occupies an area of 6.1 million km2 and the water that flows through the Amazon rivers is equivalent to 20% of the fresh water of Earth’s supply.
Despite such enormity, there is no river that survives 568 dams. That is the main conclusion of a large study involving ecologists and engineers, economists and geologists from a dozen American, German, British and Brazilian universities.
Although each dam is accompanied by its environmental impact study, the regional impact of all existing dams in the Amazon basin had never been studied.
The research, published in Nature, analyzes the cost they will have on the life of the river, from the seasonal floods that give life to the Amazon, to the sediments that will stop dragging nutrients all along the region.
Rivers are not just water. They also carry large amounts of sediment that starts from one side and deposits in the other.
These sediments are the mineral substratum of life in a vast region of more than one million km2, between wetlands and alluvial plains.
In its last stretch, the Amazon transports between 800 and 1.2 million tons of silt, sand and clay and at least half end up in the ocean every year.
With each dam that stands between the river and the sea, a percentage of these sediments will be trapped in the concrete.
“Remember ancient Egypt, which depended on the silt of the river that fertilized the lands of the floodplain,” says University of Texas researcher in Austin (USA) and lead author of the study, Edgardo Latrubesse.
“The Nile is today a river artificially regulated by mega dams. It is a typical case that exemplifies the tremendous impacts produced by infrastructures constructed several decades ago, which produced great social, environmental and economic impacts”, adds this expert in geomorphology of the rivers.
It is not the first time that the situation of modern Egypt is related to the alteration of the course of its great river.
In the case that Latrubesse cites, the Amazonian, the combined impact of the dams could cause more than 60% of the sediments that the river drags to get now stuck along the way.
“In the Yangtze, where the Three Gorges dam was built, the retention now stands at more than 75% and in other rivers like the upper Paraná River in Brazil, the retention is more than 100%.
Values of more than 70-90% are typical in the world. We expect something similar in the Amazon if everything that is supposed to be built is actually built,” he says.
Such interference in the dynamics of the river will have “disastrous consequences,” in the words of Latrubesse.
The sediments not only transport nutrients to the alluvial plain, they are an integral part of the river: “islands and pieces of the alluvial plains are eroded while new areas are generated by sedimentation,” recalls this researcher.
This dynamic helps to maintain a great diversity of environments in the tropics and, for biologists, “this regeneration process is a very important mechanism that contributes to the creation of biodiversity,” he concludes.
The problem will not be less at the mouth. The column of water and sediment that ends in the Atlantic extends for more than 1.3 million km2 of the ocean, half of what occupies the Mediterranean.
In addition to being the base of an extensive coral line on the American coast and the mangroves of the Guayanas and northern Brazil, this enormous Amazon contribution is involved in the regional climate, conditioning the generation and movement of tropical storms in the Caribbean.
The lack of sediments in the coastal zone will also favor marine erosion and salt-water intrusion in aquifers.
The authors of the study have created an index of vulnerability of rivers to the impact of dams. About a maximum of 100, some rivers of the Andean strip, like the Marañón, could reach an index 72.
At its head, 104 dams with more than 1 megawatt (MW) of generating capacity have been built or planned.
Further down, the most vulnerable river is Madeira, one of the 10 largest rivers in the world that alone provides half of the sediments that the Amazon takes to the sea.
With an index of vulnerability higher than 80, the Madeira river hosts about 1,000 species of fish, triple the amount of all the rivers of Europe.
But perhaps the most striking case is that of the Tapajós, the main contributor of the right bank of the Amazon.
Although there are no dams in its main section, it is and will be one of the most affected by the construction of dozens of dams in its affluents, which will create an interconnected system of dams and artificial marshes along 1,000 km.
For Latrubesse, “it would be impossible to construct such dams in developed countries” because of the gigantic environmental impact they have.
The justification for all this was the need to generate energy on which Brazil, Ecuador, Peru or Bolivia could base their development. However, hydroelectric dams do not seem to be the solution.
Oxford University researcher and co-author of the study, Atif Ansar, recalls: “Our previous research has shown that, because of the systematic problem of extra costs and the lengthening of deadlines, the real cost of large dams is too high to recover it”.
Previous studies only included economic impact but did not include environmental impact. Now, he says, “large dams are not only economically unviable but also environmentally damaging.”