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
Indigenous groups protest hydropower congress as controversy hits meeting in Malaysia
(05/22/2013) The opening of the International Hydropower Association (IHA) World Congress in the Malaysian state of Sarawak was marred today by indigenous protests and controversy after a local indigenous leader was barred from attending a pre-conference workshop. Over 300 people from local indigenous people protested the ongoing construction of around a dozen mega-dams in the state that threaten to flood traditional lands, force villages to move, and upend lives in the state. The Sarawak hydropower plans are some of the most controversial in the world—making the choice of Kuching, Sarawak for the IHA meeting an arguably ironic one—with critics contending that the dams are have been mired in political corruption, including kickbacks and bribes. IHA brings together dam builders, banks, and various related organizations worldwide every two years.
China approves another mega-dam that will imperil endangered species
(05/21/2013) Chinese environmental authorities have approved construction plans for what could become the world's tallest dam, while acknowledging that the project would affect endangered plants and rare fish species.
Biosphere conservation: monumental action is critical to avert global environmental crisis
(05/20/2013) Human-caused changes to our biosphere—the global total of the world's ecosystems—are now so great and alarmingly rapid that human lives and societies undoubtedly face epic challenges in the near future as our biosphere deteriorates, planetary boundaries are reached, and tipping points exceeded. We may survive, we may painfully adapt, but it is a fair bet that grave hardship, loss, and sacrifice lay ahead. The nature and extent of impacts among human populations hinges on how successfully we respond to the biosphere crisis with extraordinary leadership, balanced solutions applied at global scales, and unprecedented cooperation—or not.
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.
More rainforest news
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