Hydroelectricity has been promoted as a ‘clean’ energy source, capable of providing huge amounts of electricity without adding to global warming. Brazil already obtains 80 percent of its electricity from this source.
But the reality is that large dams cause immense disruption to the local environment and produce huge amounts of powerful greenhouse gases. These include methane, which is 21 times more powerful in terms of global warming than carbon dioxide, and nitrous oxide, which is 310 times more potent.
Dams in tropical areas are especially polluting. In the early years, they produce many times more global warming than the equivalent amount of electricity obtained from burning fossil fuels. Even decades after they were constructed, dams in the Amazon continue to generate more global warming than equivalent natural gas power stations.
Dams begin to contribute to global warming before the ground is broken. Manufacture of steel and cement, the core materials used to build the dams, are both significant sources of greenhouse gases.
Once the dam begins to fill with water, greenhouse gas production reaches astronomical proportions because of the decaying vegetation from the trees and plants which are drowned as the water rises. These produce a surge of global warming in the early years, which reduces over time as the drowned organic matter decays, eventually reaching a more or less stable state.
But this stable state still produces high levels of greenhouse gases. Even taking into account natural processes of decay which occur in undisturbed tropical forests, these levels are high. They are several times higher than in a similar-sized natural lake. And they continue for the life of the dam.
Were the dam eventually to be decommissioned and drained, there would be yet another pulse of greenhouse gases, as organic matter trapped in sediment is exposed to oxygen and is attacked by
bacteria and other organic processes, releasing yet another raft of carbon dioxide, methane and nitrous oxide.
On a local level, dams interfere with the life cycles of tropical plants, insects, fish and land animals, destroying the ecological balance of the river basin. Fish can no longer reach their spawning grounds, mammal migration routes are blocked, the annual inundation of riverside land (which brings with it nutrients to feed crops and natural plants growing beside the river) is stopped, and insect populations are affected unpredictably. Aquatic life is damaged by changes in the chemistry of the water trapped in the reservoir, causing many fish species to decline dramatically. The dams create ideal conditions for malaria mosquitoes, and malaria becomes endemic in the areas surrounding dams.
This is but one of the social repercussions. People already living in the area will be displaced; the worst affected will, as ever, be the poorest. Few of the self-sufficient settlers who live along the banks of the Xingu have proper legal title to the land they occupy – and may have occupied for generations.
The experience of people in a similar situation who were affected by construction of the Tucurui dam, only 250 km to the southeast, is not encouraging; over twenty years after the dam was completed many people have not seen any compensation, and are forced to live a marginal existence in shanty towns.
Large construction projects inevitably attract thousands of migrant workers. They bring with them increased deforestation, increased demands on already inadequate local infrastructure, and increased social stress between the immigrant population and the people already living in the area. The problems worsen on completion of the construction, which leaves the new population largely unemployed. Neither the companies involved in the construction and operation of the dam nor the government are prepared to take responsibility for these problems.
Belo Monte, the latest scheme for the Xingu being promoted by the Brazilian government-owned electricity company Eletrobrás , promises to bring all of these problems to the Xingu, with very little benefit.
Further hydroelectric dams are proposed for all of the tributaries of the Xingu. These so-called ‘Small Hydroelectric Plants’ will have a far from small impact on the river and its people, affecting water quality and flow throughout the Xingu basin. The entire ecology of the river will be damaged, disrupting food sources and transportation.
For the indigenous people the dams will destroy their lifestlyes and their very cultures. We must support them in their fight to prevent this unwanted and unjustifiable destruction.
Further reading:
Philip Fearnside on Greenhouse Gas emmissions
International Rivers: Fizzy Science
© Patrick Cunningham
