Three Gorges DamColin Orians
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As the longest river in Asia, China's Yangtze River and basin support 400 billion human inhabitants, as well as sustain a diverse population of endemic species. Thanks to the Yangtze's frequent flooding, nutrient rich sediment supports the 6,000 plant species, 500 terrestrial vertebrates and 160 species of fish, leading the Yangtze to be ranked as one of the 25 biodiversity hotspots on the planet.
But such frequent flooding does not come without its cost to the inhabitants. Records show the river floods two or three times a decade with varying intensities. In the 20th century alone, flooding of the Yangtze claimed 325,000 lives. Seeking a way to mitigate the unpredictability of floods, to prevent human tragedy, as well as harness the river for a source of electricity,
China has constructed the Three Gorges Dam. Located in the heart of China's biodiversity hotspot, it was completed in 2008 after a 17 year construction process. The largest in the world, the dam spans 1.3 miles, measures 610 feet high, and will produce as much electricity as 15 nuclear power plants.
Additionally, the dam will create a reservoir roughly 1,087 square kilometers, half the length of California. However, by creating this barrier that both disrupts natural flood patterns and essentially creates a massive lake in place of the river, the effect on biodiversity will be devastating and widespread.
Due to the rising water of the reservoir, two cities, 140 towns, countless peasant villages, and several dozen mountain tops are all submerged. Aside from washing away fertile land used by these communities, this largely stagnant water of the reservoir has begun to accumulate pollution from agricultural runoff and chemical and sanitary discharge.
This pollution has increased the number of toxic algae blooms with blooms occurring in 32 of the Yangtze's tributaries as well. The reservoir has also changed the sediment composition and distribution throughout the Yangtze. Whereas natural flooding delivers nutrients throughout the riverine ecosystem to support plant life, the dam traps sediment,
over 170 million tons yearly, where it settles on the bottom of the river. The lack of sediment downstream has led scientists to notice severe channel erosion, the degradation of the estuary delta, and the decline in plant life from a lack of nutrients. To make matters worse, the dam essentially reverses natural flow and flood patterns of the river.
The typical flood season in central China is during the summer months and endemic plants are used to this time because the flood’s nutrient-rich sediment supports growing patterns. However, the dam now floods in the winter, inundating vegetation when less physiologically active. This irregular flooding has led to greater plant die-offs,
opening up potential colonization space for invasive species and causing downstream bank collapse from fewer plants retaining soil. The loss of these riverine plants in combination with rising waters has made the banks more susceptible to land slides and mud slides.
In fact, more than 2,000 large-scale land slides were discovered along the reservoir banks. To add to this, the changes in water pressure within the reservoir can lead to stresses which potentially cause cracks, more landslides, and local earthquakes. Between sediment loss, greater pollution, and decline in plant abundance the consequences of building the dam and reservoir
put the habitats of many endemic riparian and coastal species in dire circumstances. The Yangtze River has witnessed a decline in the numbers of Chinese carp, the Chinese paddlefish, the finless porpoise, and the Chinese river dolphin. In fact, the Chinese river dolphin has not been spotted since 2009, raising concerns of its extinction.
Additionally, the reservoir's rising waters submerged two rare evergreen shrubs, found only along the Yangtze’s banks. As a result, one went completely extinct with the other nearly wiped out. While it may be too late to stop and reverse much of the environmental and biodiversity devastation caused by the Three Gorges Dam,
it is not too late to use the dam as an indicator of the harmful effects these hydroelectric and flood mitigation projects can cause. With talk of more dams on the nearby Jinsha and Jialing rivers, as well as proposals to dam parts of the Amazon, it is up to us to advocate for more environmentally conscious projects.
Dams offer an appealing way to take advantage of flooding and the sheer power of water, but its time we develop projects that do not trade biodiversity preservation for human gain.