Environmental Engineering Reference
In-Depth Information
The ecosystem now cannot support the same amount of life and biodiversity it once could. Much of the wet-
lands have been lost, which in turn decreased the habitats for birds and small mammals, as well as native fish
in the lake. In fact, all fish species once found in the Aral Sea have gone extinct or have been extirpated due to
the extreme salinity levels, and plants and animals living on the surrounding land have vanished from the area
or become extinct as well. The economic impact also has been extreme. The fishing industry that once depen-
ded on the sea is now nonexistent.
The extensive size of the Aral Sea once regulated the region's climate, helping to keep summer heat and winter
cold to moderate temperatures. With the loss of such a high portion of the water from the lake, though, the re-
gional climate is not moderated, leading to hotter and drier summers and colder winters. This has shortened the
growing season and reduced crop yields.
One surprising consequence of the dropping water level in the Aral Sea is increased pace of snow melt in the
Himalayas, in part because of the salty dust that blows from the dried-up Aral Sea and gets deposited on the
mountains. The salty dust affects crops, vegetation, and wildlife. There is also an increased use of chemicals
such as fertilizers and pesticides to help the growth of crops on the deteriorating soils. These chemicals, as well
as contamination from the increasing population in the area, percolate down to the groundwater, the sum of
which impacts human health.
Efforts are being made to improve the health of the ecosystems and of people through increasing flow back in-
to the Aral Sea, implementing more efficient ways to irrigate the lands, purifying groundwater for consump-
tion, using crops that are less water-dependent, and creating wetlands to reinvigorate life at the water's edge.
Promises of a renewed Aral Sea are starting to be seen, including a return of fish to the lake. Although some
parts of the past Aral Sea are forever damaged, there is hope that most of it will eventually return to a product-
ive and thriving ecosystem.
Three Gorges Dam
The building of the Three Gorges Dam, the world's largest, was controversial and problematic. Completed in
2009 on the Yangtze River in China, the dam is being used to provide hydroelectric power throughout the
country. Unfortunately, its construction displaced at least 1.2 million people, as their towns and cities were
flooded when the reservoir was filled, and it flooded priceless archeological sites. The potential for water pol-
lution in the reservoir also exists, since many industrial and agricultural areas, mines, and waste sites were also
flooded. These pollutants can affect not only water, but also bottom sediment and surrounding lands. Because
of the dam, there is less downstream flow of water, which reduces the natural recycling and cleaning processes
that remove chemicals and contaminants. Also, from the slowed water flow of a reservoir, more sediment is de-
posited on the bottom, which can build up over time and slow shipping and block flood control gates.
Ecologically, the Three Gorges Dam presents another set of issues and threats. Upstream, in the flooded areas,
cropland and forests have been lost. Downstream of the dam, there is less nutrient-rich sediment being depos-
ited in the benthic environment, altering the nutrient availability for organisms. The dam also has disrupted the
spawning and migration patterns of some fish below the dam. At the mouth of the Yangtze River, where it runs
into the East China Sea, there has been increased saltwater intrusion into the drinking water due to the de-
creased water flow of the river pushing outward. With less freshwater being held in the groundwater, the salt-
water from the ocean seeps in, taking its place. When the reservoir started filling, there were numerous land-
slides on its banks, with the slippage of large amounts of earth into the water creating huge waves.
However, the ecological impact of the Three Gorges Dam project is not all bad. For example, it has the ability
to generate cleaner energy for at least 10 percent of China's population, from the largest hydrostation in the
