Satellite image of the Turucui dam and associated deforestation in Brazil. (Photo courtesy of DigitalEarth)
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THREATS TO TROPICAL RIVERS AND LAKES
By Rhett Butler | Last updated July 31, 2012
Tropical rainforest waters are highly threatened today by hydroelectric projects, erosion from deforestation, overfishing,
and pollution from industrial activities, including oil spills and mining waste. The effects from the degradation of these waters are widespread, inflicting damage on the global economy, the environment, and local peoples.
Dams
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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 23.75 million tons of carbon dioxide and 140,000 tons of methane, both potent greenhouse gases which contribute to global climate change.
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Increasing demands for energy are putting the world's rivers at risk, with hundreds of dams planned in the Amazon Basin, Borneo, the Mekong watershed, Central America, and Central Africa. Hydroelectric projects have been responsible for flooding vast areas of rainforest, with significant detrimental impacts for climate, wildlife, and river-dependent people.
Dams in the tropics have two principle greenhouse gas emissions sources: carbon released from soil carbon stocks and dying vegetation when the reservoir is flooded and methane formed where organic matter decays under low oxygen conditions at the bottom of the reservoir. Methane emissions are facilitated by a dam's turbines, which usually draw from the bottom of the reservoir and spray methane-dense water into the air upon release. Emissions from rotting vegetation occur on an ongoing basis when the levels of the reservoir fluctuate: during the dry season weeds, emerge from the muddy drop-down zone, only to rot again when waters return. The effect turns a typical tropical dam into what Philip Fearnside, an expert on the Amazon, calls a "methane factory".
Planned dams in Brazil. Courtesy of Dams in the Amazon.
Dams can also be enablers of deforestation, spawning roads that facilitate new clearing and generating electricity for industrial farms, mines, and aluminum manufacturing. For example, the controversial Belo Monte dam on the Xingu River in the state of Pará, Brazil, illustrates many of the concerns with dam-building in the Amazon, where 146 dams are planned in coming decades. The dam will flood a quarter of the city of Altamira and divert 80 percent of the Xingu's flow from the main stem of the river, leaving 60 miles (100 km) of one of the Amazon's largest tributaries nearly dry. Communities of that stretch of the river will lose their primary source of livelihoods — fishing. The dam will also impede migration of some of the river's largest fish species, potentially affecting fish populations elsewhere in the river basin. (A number of Amazon fish species move upriver or downriver to spawn). Other communities will suffer from inundation. In these areas, people are being removed by force, according to Fearnside.
But the dam has bigger problems. As currently designed, Belo Monte will suffer from the Xingu's seasonal variation in water flows. The most expensive parts of the dam to operate — turbines and transmission lines — would need to be idled for four months each year due to low water. That issue makes it likely that Brazil will push forth with a plan to build additional dams upstream from Belo Monte (up to six dams were planned on the Xingu until 2008). These dams would capture water, ensuring more consistent flow for Belo Monte. However greater water level fluctuation upstream means these dams will have even higher methane emissions relative to their generating capacity.
Damming the Amazon
Erosion
Erosion is a conspicuous impact 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 can cause
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 can hinder the development of fish eggs.
Overfishing
Overfishing is a problem that plagues the world's oceans (35-60 percent are overfished worldwide [overfishing news]) 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.
Pollution
Poisoning from spills and pollution from industrial processes mining, and sewage impact the diversity of rainforest waters, in addition to affecting human populations. Chemical spills are usually associated with oil development and mining.
Review questions:
- How are rainforest rivers under threat?
- How do dams contribute to global warming?
- Why are dams usually bad for native fish species?
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Continued: People of the rainforest
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WEEKLY NEWSLETTER
INTERACT
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Recent news
Amazon's flood/drought cycle becoming more extreme, less predictable
(05/14/2013) The Amazon River's hydrological cycle has become more extreme over the past two decades with increasing seasonal precipitation across much of the basin despite drier conditions in the southern parts of Earth's largest rainforest, finds a new study published in Geophysical Research Letters. The research analyzed monthly Amazon River discharge at Óbidos, a point that drains 77 percent of the Amazon Basin, and compared it with regional precipitation patterns.
Rainforest tribe urges Norwegian king to recall energy executive
(05/13/2013) In an unusual bid to stop a series of dams that will flood their rainforest home, a group of tribesmen in Borneo are urging King Harald V of Norway to call one of his subjects home. The subject is Torstein Dale Sjøtveit, a Norwegian citizen who is the CEO of Sarawak Energy, a Malaysian firm that is building several dams in the state of Sarawak. The hydroelectric projects are controversial because they require the forced displacement of indigenous communities and will flood large tracts of rainforest.
Deforestation will undercut effectiveness of rainforest dams
(05/13/2013) Deforestation may significantly decrease the hydroelectric potential of tropical rainforest regions, warns a new study published in Proceedings of the National Academy of Science. The study, used climate, hydrological, and land use models to forecast the impact of potential forest loss on hydropower generation on the Xingu River, a major tributary of the Amazon where the world's third largest dam — Belo Monte — is currently under construction.
Tribesmen launch 'occupy' protest at dam site in the Amazon rainforest
(05/03/2013) On Thursday roughly 200 indigenous people launched an occupation of a key construction site for the controversial Belo Monte dam in the Brazilian Amazon. The protestors, who represent communities that will be affected by the massive dam, are demanding immediate suspension of all work on hydroelectric projects on the Xingu, Tapajós and Teles Pires rivers until they are properly consulted, according to a coalition of environmental groups opposing the projects.
Mekong region has lost a third of its forests in 30 years, may lose another third by 2030
(05/03/2013) The Greater Mekong region of Cambodia, Laos, Myanmar (Burma), Thailand and Vietnam will lose a third of its remaining forest cover by 2030 unless regional governments improve management of natural resources and transition toward a greener growth model, warns a new report issued by WWF.
More rainforest news
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