Damming the Amazon

Balbina dam outside Manaus, Brazil The Balbina dam flooded some 2,400 square kilometers (920 square miles) of rainforest when it was completed. Phillip Fearnside, a leading expert on the Amazon, calculated that in the first three years of its existence, the Balbina Reservoir emitted 23,750,000 tons of carbon dioxide and 140,000 tons of methane, both potent greenhouse gases which contribute to global climate change.

Increasing demands for energy are putting the world's rivers at risk. Hydroelectric projects are responsible for flooding vast areas of rainforest. The decay of forest wood adds more greenhouse gases to the atmosphere contributing to global warming. This flooding means that terrestrial species, including humans, must migrate to new areas usually leading to more deforestation. Fish species adapted to the riverine environment must adapt to lake conditions or perish. Dams disrupt the migration of species which move up- or downriver to spawn.

Erosion is a well-known result of deforestation with serious consequences for river commerce and river life. Sediments build up creating sandbars and shallows and interfering with river transportation. Similarly, sediment build-up reduces the effectiveness of existing hydroelectric projects. Erosion and the resulting decline in water clarity causes downstream mayhem for offshore coral reefs. River inhabitants also suffer due to the reduced water clarity. Species that rely primarily on sight decline the most, while the increased amount of suspended particles interferes with fish gills. Erosion inhibits plant growth and hinders the development of fish eggs.

Overfishing is a problem that plagues the world's oceans (35-60 percent are overfished worldwide) and freshwater habitats. Regional declines in catch have been reported throughout the Amazon. The loss of certain species responsible for seed dispersal will have a negative effect on the renewal of the rainforest.

Poisoning from spills and pollution from industrial processes mining, and sewage continue to reduce the diversity of rainforest waters, in addition to affecting human populations. The much publicized spill on the Essequibo river, along with the continued spilling of oil in Peru and Ecuador, has had an impact of river life.

Article on the effects of mercury in aquatic habitats (mercury pollution in the Amazon frequently results from mining activities).


Review questions:

• How are rainforest rivers under threat?
• How do dams contribute to global warming?
• Why are dams usually bad for native fish species?