Diminished Biodiversity after Hydroelectric Dam Construction

Hydroelectric dams have many advantages — the main one being a clean source of energy. The Three Gorges Dam in China is estimated to replace around 50 million tons of coal being burned for energy production. China produces a total of 352.26 GW from hydropower – making it the biggest producer of hydropower in the world. China has planned 23 hydropower dams, on the Lancang River alone, with six already built and operating by November of 2018. All of this has made China one of the best places to study how hydroelectric dams affect the local flora and fauna.

The Three Gorges Dam

Following the Chinese Government’s Thirteenth Five-Year Plan on Hydroelectric Development plan, the Three Gorges Dam was built in 2012. It was the world’s highest capacity hydroelectric dam – until the Itaipu Dam on the Brazil-Paraguay border surpassed it in 2016.

The Yangtze River, where the dam is located, has the most diverse fish population on earth. A study published in March of 2019 found that following the construction of the Three Gorges Dam the local fish population was significantly diminished. On average, 45.3 native species and 19.3 endemic species were eliminated from the region and 113 species were classified as either critically endangered, endangered, vulnerable, or near threatened.
The study also found that the alpha and gamma diversity had significantly decreased – meaning there is less species diversity overall and less species diversity in each ecosystem. The study showed a significant trend toward homogenization when comparing the different ecosystems.

A review of the Lancang River – the river with 23 planned or built hydroelectric dams – published in 2018 came to similar conclusions as the Three Gorges Dam study.

How do Dams Impact Biodiversity?

Dams create a physical barrier that many species cannot pass through. This reduction of mobility will mainly affect spawning fish species. Most spawning fish travel upstream to a specific location. The study of the Lancang river found migratory species to be severely impacted and found that mitigation efforts do little to lessen the impact.

Most aquatic species are very sensitive to changes in the water chemistry — even small changes can spell disaster for some species. Hydroelectric dams lower the temperature and dissolved oxygen content. The Lancang River study found that 20% of species in the river will be negatively impacted by thermal water pollution.

Areas upstream of a hydroelectric dam will be flooded. The flooding changes the environmental conditions of the upstream areas, which will impact species dependent on specific conditions for survival.

Lessons Learned

Mentioned above, the Chinese Government’s Thirteenth Five-Year Plan on Hydroelectric Development Plan includes measures for mitigating the impact the many hydroelectric dams will have on the local ecosystem. The five measures include “promote basic environmental flows; alleviate effects of water temperature; mitigate the damage of high water velocity to downstream; protect aquatic ecological connectivity; and enhance the development of tributary fish reserves”.

Both the study done on the Three Gorges Dam and the Lancang River dams found that the ecosystems are not being adequately protected from the impacts of the hydroelectric dams. In fact, the study of the Lancang River found that none of the 20 planned or built dams studied – three dams had no information available to researchers – met all five of the mitigation measures. Researchers suggested that the findings inform future designers of hydroelectric dams – in China and other nations – to better protect ecosystems while pursuing this clean and abundant source of power.