Impact Of Hydroelectric Dams On Biodiversity Underestimated

The Belo Monte hydroelectric dam in Brazil will be the third largest in the world when it is completed in 2016. Kirk Winemiller/Texas A&M

As a way to generate energy in remote parts of the world, hydroelectric dams are being proposed and built at a staggering pace. Within just the world’s three largest river basins – the Amazon, Congo, and Mekong – there are 450 dams either under construction or being planned. But far from the renewable and cheap energy source it is often touted as, a new study has detailed how these projects more often than not overestimate the economic benefits, while underestimating the long-term impacts on biodiversity and local communities.

“Even when environmental impact assessments are mandated, millions of dollars may be spent on studies that have no actual influence on design parameters, sometimes because they are completed after construction is underway,” explains Leandro Castello, who coauthored the study published in Science. “A lack of transparency during dam approval raises doubts about whether funders and the public are aware of the risks and impacts on millions of people.”

A map of the three river basins showing the extent of current dams, and ones being planned, along with the number of species living in each region. Winemiller et al. 2015

With the three largest river basins being home to an estimated third of all freshwater fish species, the regions are critically important as fisheries and subsistence for the people who depend on them. Despite the significance of these fish species, many of which migrate, little is done to try and mitigate this problem.

The researchers claim that there is plenty of evidence to suggest that the systems in place to facilitate the migration of fish past dams are at their best ineffective, and at their worst even more damaging to the fish populations. In fact, many reservoirs formed by the dams are not stocked with highly prized fish, but are instead dominated by low-value species.   

Populations of pink river dolphins are already being seperated by the construction of dams along the rivers in which they live. Kevin Schafer/Fundacion Caja Mediterraneo/Flickr CC BY-NC-ND 2.0

Other larger species are also affected by the projects, such as the pink river dolphin population in the Amazon being carved up into separate populations due to dam constructions along the rivers in which they live. But the impacts are not solely limited to those species that live in the rivers. As dams block and trap sediment as it flows down the rivers, the nutrient cycle on which the forests themselves rely on is altered, which then affects marine species that also depend on this flow of nutrients out into the oceans.   

These impacts on the biodiversity and fisheries, both in the rivers themselves and the coastal waters surrounding the estuaries, then trickle down to the millions of people who rely on them for their livelihoods. While the physical movement of communities out of areas that will be flooded is often (though not always) considered, it is these impacts that will only come to light further down the line that are frequently missed.

The river basins provide critical subsistance for many communities which live within it, such as these fish from the Mekong in Cambodia. Kirk Winemiller

“Long-term ripple effects on ecosystem services and biodiversity are rarely weighed appropriately during dam planning in the tropics,” says Peter McIntyre, another of the coauthors of the study. “There is good reason for skepticism that rural communities in the Amazon, Congo, and Mekong basins will experience benefits of energy supply and job creation that exceed costs of lost fisheries, agriculture, and property.”

The researchers argue that there needs to be more transparency in the approval processes of major hydroelectric projects in tropical river basins. Not only that, but the large-scale impacts of dam building, especially the cumulative effect of building more and more in the same river system, also need to be taken into account, along with the true economic and financial costs.   

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