Hydroelectric dams might cause 70 percent of nearby wildlife to go extinct, according to a study released on Wednesday that raises new concern about what is often touted as a green energy source.
The study in the journal PLOS ONE focused on how animals in a tropical rainforest were coping as a result of the Balbina Dam in the central Amazon basin in Brazil.
The dam has helped create one of the world’s largest hydroelectric reservoirs, known as Balbina Lake, by flooding an area that used to be continuous forest land and making it into 3,546 islands.
On all but the biggest islands, the change in landscape has meant a drastic loss of mammals, birds and tortoises over the past 26 years and is likely to wipe out nearly three-quarters of all wildlife in the region, the study found.
“We predicted an overall local extinction rate of more than 70 percent of the 124,110 wildlife populations of the species we studied occurring in all 3,546 islands across the entire archipelago,” said coauthor Carlos Peres, a researcher at the University of East Anglia’s School of Environmental Sciences.
Just 25 of the islands — the biggest ones — were estimated to retain most of their original species.
“We found that only a few islands larger than 475 hectares still contained a diverse community of animal and bird species, which corresponds to only 0.7 percent of all islands in the reservoir,” said lead author Maira Benchimol, a researcher at Universidade Estadual de Santa Cruz, Bahia, Brazil.
Dams can also lead to flooding in areas beyond their reservoirs.
While it was previously known that flooded areas would lose wildlife, the impact of shrinking animals’ habitats into small islands would impact survival was not well understood.
Not only was it harder for some species to find mates, but wildfires also exacted a deadly toll on some of the islands during a drought driven by El Nino in 1997 and 1998, researchers found.
“Post-burn islands retained even fewer wildlife species than islands of similar size that had not been affected by wildfires,” Benchimol said.
Since Brazil plans to build even more hydroelectric dams, researchers urged the government to incorporate their findings into future studies of environmental impact.
“We are only beginning to realize the staggering extent of extinctions in forest areas that remain above water as habitat islands,” Peres said. “The Brazilian government is currently planning to build hundreds of new dams in some of the world’s most biodiverse tropical forest regions, but the high biodiversity costs of mega dams should be carefully weighed against any benefits of hydropower production.”
Hydroelectric dams were once touted as a major source of clean energy because they do not require the burning of fossil fuels.
However, a series of research papers in recent years has shown they can have devastating effects on fisheries and local communities.
They can also cause spikes in methane and greenhouse gas emissions from rotting vegetation.
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