AsianScientist (Dec. 5, 2019) –
“Raised sharing the magical peninsula,
Side by side we construct liberty.
River silt nourishing our floras,
The water of Mekong reflects our azure sky.”
These lyrics are learned by heart by the people of the Mekong’s Nine Dragons Delta in my home country of Vietnam, from the song, “Spring has arrived on the river Mekong.” Indeed, the Mekong River—the tenth largest river hosting the second largest biodiversity in the world—is a gorgeous natural treasure that six countries on the Asian continent are blessed with.
Her 4,909-kilometer journey commences on the vast hills of the Tibetan Plateau, spanning the territories of China, Myanmar, Laos PDR, Thailand, Cambodia and Vietnam before immersing in the waters of the South China Sea. Her body, whose living diversity is second only to the Amazon, boasts approximately 1,200 freshwater creatures, including the last specimens of endangered fish species such as the Irrawaddy dolphin, giant freshwater stingray and the notorious Mekong giant catfish. This incredible ecosystem and the river’s wealth of silt make the Mekong’s role unique in the planet’s conservation efforts, and irreplaceable for the livelihood of 70 million people currently relying on her abundant resources.
One such resource is electricity. Such a potent river undoubtedly possesses immense hydropower capacity, promising the provision of power for a population much larger than the 70 million who live within its vicinity. However, part and parcel with this opportunity comes the risk of upsetting the Mekong’s entire ecological function.
The underwater resonance of dams
Part of the reason hydroelectric dams appear reliable and innocent is their simplicity. The theory is straightforward: a dam gets constructed over the banks of a river, creating a reservoir ready for flood release according to electricity demand. However, a river’s fragile ecosystem is not so straightforward, and many intricate needs must be balanced to maintain its vitality. Ostensibly, a dam’s structure is not sufficient to accommodate these needs.
Dams are barriers to the migration route of 30 percent of fish species in the Mekong River, and being unable to cross them means that the entire sequence of their natural life is perturbed. Belated mating, aberrant weather and random hydrology, being stopped from moving to the right place at the right time… all of these can be of critical danger to fish.
In the dry season, fish often migrate upstream to seek shelter in deeper waters and spawn. They only return in the wet season to lower floodplains, which then naturally have an abundance of nutrition. Erecting dams on their routes prevents a number of species from mating, and even those that succeed in reproducing produce juveniles that stand a much slimmer chance of surviving to adulthood. This could be due to countless reasons: an abnormal concentration of fish in one area lending advantage to certain predatory species, inappropriate water temperatures, inadequate nutrition, or even injury sustained from passing through spillways during downstream return. For species like the Mekong giant catfish, which utilizes a wide variety of habitats throughout its lifetime and migrates hundreds of miles every year, this can be a fatal blow.
In 2012, the Xayaburi Dam in Lao PDR was officially put into function. According to the National Geographic, “The Xayaburi Dam (also) poses a serious threat to several of the largest, and rarest, freshwater fish in the world, including the critically endangered Mekong giant catfish, the critically endangered giant Pangasius and the endangered seven-striped barb.”
The Xayaburi Dam was to be followed by 11 other dams on the Lower Mekong Basin, the joint effect of which has been estimated by the Mekong River Commission to threaten migratory fish and reduce catch by 270,000 metric tons, pressurizing the provision of 20 percent of the world’s freshwater catch.
Mega fish were not the only ones whose limited mobility have caused their species’ population to plummet. 2018 was the year when the last 92 specimens of the Cambodian Irrawaddy dolphin were pushed to the brink of extinction because of the construction of the Sambor Hydropower Dam. The National Heritage Institute stated in a report that the Sambor Dam cuts “perhaps the largest annual migration of fish biomass on the planet.” In an ecosystem with such sophisticated interspecies dependence as the Mekong’s, this can wreak havoc.
An unaccounted for expense on humans
The Mekong does not only have underwater residents. There are also people on land who depend on her for a living as much as the fish do. The depletion of fish stock in sync with the rate of dam activation is a conspicuous repercussion of dams, but the most significant impact on human life lies not in the decline of food and trade source, but from the disappearance of livable land.
One granular substance that plays a pivotal role in both the formation and upkeep of the Mekong deltas in the Lower Mekong Basin is silt. The flow of river water hides this nutritious substance much needed for the accretion of land, but it often gets stuck at the dams’ shutter gates. With hundreds of dams present throughout 4,909 kilometers of the Mekong, the accumulated reduction in the amount of silt can have severe consequences for Lower Mekong Basin residents.
Other than being a source of nourishment for freshwater species, silt adds weight to river flow and thus softens the pace of flow. Without this weight, the river would flow so vigorously that the river bed could be torn apart and banks would subside. Moreover, this weight creates a water shield for the mainland when the river finally pours out into the South China Sea. When sea waves retreat, an area of heavy, brown mud stretching kilometers to the shore is left behind. This layer of muddy water functions as a defense for the mangroves and mainland soil against the kinetic energy from potent sea waves. Once this weight is gone, energy from the waves stays almost perfectly preserved when it strikes mangroves, thus sweeping them out to the sea and causing deforestation.
Vietnamese shores are subsiding at a rate of 10 to 20 milimeters per year, and coastal residential areas at 25 milimeters per year. Specifically, the Nine Dragons Delta has 526 areas of shores and river banks in depression, 57 areas with particularly serious depression, spreading a total length of 800 kilometers. In recent years, this delta has been losing around 500 hectares of land every year, which has forced households to retreat further and further from the shore. Research on the global water crisis released in July 2019 by Australia’s Future Direct International stated that almost 40 percent of the Nine Dragons Delta stands a risk of being submerged by the end of this century. If that happens, millions of people will be pushed out of their homes, and millions more who depend on this delta’s agricultural products will be severely affected.
Despite this, a total of 327 dams on the Mekong have been completed, 43 more are under construction, 77 are in planning, and 15 have just been proposed. In 2014, the Mekong River Commission estimated that the total amount of silt available for the Lower Mekong Basin had halved, and if all of these dams are activated, the remainder is expected to halve again. At that point, the strain hydroelectric dams exert will make their existence uncomfortably pronounced not only for underwater inhabitants, but for human dependents as well.
What have engineers done about this?
One technology imported from North America, called fish passages, has been applied at the Mekong. The three main methods of upstream passage technology are fish ladders; fish elevators and locks; and trapping and trucking. Unlike elevators and trucks where fish are delivered passively, with ladders they have to actively swim up or down. Therefore, deciding on which type of fish passage to build can involve the consideration of many factors, especially the characteristics of the river and the fish.
However, North American fish are significantly different from tropical ones in biological and behavioral terms, and these fishways have not been adjusted for the characteristics of more than 1,200 fish species in the Mekong. As a result, the majority of Mekong fish are still unable to overcome dam hurdles during their life cycles.
The Mekong River Commission has called for a ten-year moratorium on the approval of dams to reevaluate the environmental costs involved. Given the critical global context we have put ourselves into today, such a wait is well worth it. The most biodiverse river, the Amazon, is already in jeopardy. Will the Mekong be next?
This article won third place in the Science Centre Singapore Youth Writing Prize at the 2019 Asian Scientist Writing Prize.
Click here to see photos of the the prize presentation ceremony held on December 4, 2019.
Copyright: Asian Scientist Magazine; Photo: Shutterstock.
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