Hydroelectric dams spell disaster for birds, tortoises: study

MIAMI - Hydroelectric dams may cause 70 per cent of wildlife in the nearby area to go extinct, according to a study 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 the tropical rainforest were coping as a result of the Balbina Dam in the central Amazon, in Brazil.

The dam has helped create one of the world's largest hydroelectric reservoirs, known as the 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 per cent of the 124,110 wildlife populations of the species we studied occurring in all 3,546 islands across the entire archipelago," said co-author 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 still have most of their original species.

"We found that only a few islands larger than 475 hectares (1,200 acres) still contained a diverse community of animal and bird species, which corresponds to only 0.7 per cent of all islands in the reservoir," said lead author Maira Benchimol, a researcher at Universidade Estadual de Santa Cruz, Bahia, Brazil.

Dams for power 

Hydroelectric power uses dams to increase the pressure of natural water sources so that more energy can be produced.

Dams can lead to widespread flooding in areas that used to be dry land.

While it was previously known that flooded areas would lose wildlife, it was not well understood how the impact of shrinking animals' habitats into small islands would impact survival.

Not only was it harder for some species to find mates, but wildfires also exacted a deadly toll on some of the islands during an El Nino-driven drought 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," said Benchimol.

Since Brazil plans to build even more hydroelectric dams in the coming years, researchers urged the government to incorporate their findings into future studies of environmental impact.

"We're only beginning to realise the staggering extent of extinctions in forest areas that remain above water as habitat islands," said Peres.

"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.