The environmental impacts
associated with large scale dams often have significant negative impacts
on the environment. The Three Gorges Dam is no different. The creation
of the dam and associated reservoir has impacts both upstream from the
dam and downstream. It affects species in the area, some endangered, water
quality, and may increase the likelihood of earthquakes and mudslides in
the area.
A number of species
will be adversely affected by the construction of the dam. There are
300 species of fish in the Yangtze River. The dam
will create a barrier in the river that these species will not be able
to cross. Fish will not be able to travel upstream to spawn, so the populations
of the species will decrease. Other affected species include the Chinese
River Dolphin, Chinese Sturgeon, Chinese Tiger, Chinese Alligator, Siberian
Crane, and the Giant Panda. There are a total of forty-seven rare or
endangered species in the Three Gorges Dam area that are protected by
Chinese national law. The only natural habitat of the Chinese River Dolphin
is the Yangtze River, and there are less than one-hundred of these endangered
dolphins in the river. The reservoir created from the construction of
the dam covers a significant amount of the dolphins’ natural habitat.
The government plans to sustain the River Dolphin and other endangered
species by creating natural reserves and artificial spawning programs.
It should be noted that past attempts to relocate the Yangtze River Dolphin
have failed.dolphins in the river. The reservoir created from the construction
of the dam covers a significant amount of the dolphins’ natural
habitat. The government plans to sustain the River Dolphin and other
endangered
species by creating natural reserves and artificial spawning programs.
It should be noted that past attempts to relocate the Yangtze River Dolphin
have failed.
Photo
of the Baiji Dolphin. Its only natural habitat is the Yangtze River.
Towns and forests located in areas that will be inundated
will have to be demolished and removed in order to increase navigability
on the river. The loss of forests and agricultural lands will lead to
erosion and the build up of sediment at the base of the river and reservoir.
This could lead to increased flooding upstream. Sediments and silt contain
valuable nutrients necessary to agricultural production. The blocking
of sediments behind the dam means that these nutrients may not reach
fertile farmland downstream of the dam. This could reduce the fertility
of the land.
The destruction of the villages also leads to problems
of pollution. The Yangtze River is already polluted from the shipping
of coal, acid rain, and its central location in Chinese industrial activity.
Pollutants from towns and waste dumps that will be inundated will add
to this pollution. Some funds were set up to aid in cleaning the area
for the reservoir, but only the future will show whether a sufficient
job was done. Water moves slower in the reservoir and some are concerned
that the pollution will sit and worsen water quality of the river.
Overhead
view of Three Gorges Dam. Note flooding of land on left side of the
photo. Courtesy
of European Space Agency.
Other consequences of the Three Gorges Dam are lower
temperature and dissolved oxygen content in water down-gradient from
the dam. Dissolved oxygen is necessary for healthy aerobic activity in
aquatic ecosystems. Fish and plants depend on oxygen to survive. The
presence of the dam will disrupt the natural processes of aeration (the
movement of water) and diffusion, ways oxygen dissolves into water. Water
will move more slowly downstream, thus making it more difficult for available
oxygen to be present in the water. This could have a negative impact
on the aquatic ecosystem downstream.
Some
positive results of the Three Gorges Dam include the use of water,
a natural and renewable resource, as an energy supply.
Hydroelectricity is clean since no greenhouse gases are emitted from
producing this type of energy. The Three Gorges Dam will replace up to
50 million tons of raw coal in China’s energy use, prevent more
acid rain, and improve health standards, since the air will be cleaner.
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