Dams on the Mekong are causing mayhem

28 Mei 2020

The Mighty Mekong is one of the world’s most iconic rivers, but it is at grave risk of turning into a shadow of its former self.

“Everywhere you look there are indications that this river, which has provided for so many, for so long, is at a breaking point,” Zeb Hogan, a fish biologist at the University of Nevada, stressed in an interview with National Geographic.

That is no mere hyperbole. The Mekong, which originates in China and empties into the South China Sea in Vietnam, is losing much of its rich biodiversity throughout its length of 4,350km. The river is home to more than 1,000 species of fish, many of which depend on seasonal floods and sediments for breeding. A variety of birds, amphibians and other animals, too, rely on seasonal changes in the river .

Yet a series of hydroelectric dams built in China and Laos have caused the natural flow of the river to be severely disrupted and its water levels to plunge precipitously for months on end. Sand mining and overfishing have dealt further blows to riverine ecosystems.

In a newly published study the U.S.-based research company Eyes on Earth Inc. points the finger for the river’s troubles at China’s hydroelectric dams upriver, which it says restrict the flow of water in the Mekong and cause severe water shortages downstream.

Such hoarding of river water by China is of especial concern during the dry season. “When drought sets in, China effectively controls the flow of the river,” said Brian Eyler, the Southeast Asia director of the Stimson Center think tank in Washington D.C.

Yet even during the monsoon season last year water levels in the Mekong plunged to record lows. The river’s water level reached only up to 2.5 meters, a third of the usual rate of 7.5 meters. In the dry season, meanwhile, much of the riverbed was exposed with scarcely any water in it.

The dams have also impacted nutrient-rich silt and sediments that permeate the river’s water. Silt-absorbing nutrients like phosphorus and nitrogen are carried by the water flow from upstream to downstream all the way to the open sea in the Mekong Delta in Vietnam.

Along the way the waterborne nutrients nourish aquatic species in the river as well as in its floodplains. This natural sediment system helps support an abundance of agriculture and fisheries in the region. Last year, however, the water has turned blue, which experts said was the result of a lack of sediments in the river, leading to a phenomenon known as “hungry river effect.”

And it isn’t just aquatic animals that have been feeling the pinch. The Mekong provides millions of people with their livelihoods in China, Myanmar, Laos, Thailand, Cambodia and Vietnam, and water scarcity has badly impacted fish stocks and agricultural output in the river basin.

And worse is likely yet to come. China and Laos are planning further dams to exploit the Mekong for electricity generation. The effects, which are bad enough as they are already, could become catastrophic.

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