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Five Ways Mega-Dams Harm the Environment

Energy
The Blue Nile river passes through the Grand Ethiopian Renaissance Dam in Ethiopia on December 26, 2019. EDUARDO SOTERAS / AFP / Getty Images

By Sonya Angelica Diehn

Dams are often touted as environmentally friendly. Although they do represent a renewable source of energy, a closer look reveals that they are far from green. DW lays out the biggest environmental problems of mega-dams.


1. Dams Alter Ecosystems 

Water is life — and since dams block water, that impacts life downstream, both for ecosystems and people. In the case of the Grand Ethiopian Renaissance Dam (GERD), which is being built in Ethiopia and is set to be Africa's largest source of hydroelectric power, Egypt is concerned it will receive less water for things like agriculture.

Downstream ecosystems rely not only on water, but also on sediment, both of which are held back by big dams. As solid materials build up in a manmade reservoir, downstream land becomes less fertile and riverbeds can become deeper or even erode away. Emilio Moran, a professor of geography and environment at Michigan State University in the US, described sediment loss of 30 to 40% as a result of large dams.

"Rivers carry sediment that feeds the fish, it feeds the entire vegetation along the river. So, when you stop sediment flowing freely down the streams, you have a dead river."

And ecosystems may have adapted to natural flooding, which dams take away.

Mega-dams also often have a large footprint on land upstream. Aside from displacing human communities, flooding to create a reservoir also kills plants, and leaves animals to drown or find new homes. Reservoirs can also further fragment valuable habitat and cut off migratory corridors.

2. Dams Reduce Biodiversity and Cause Extinction 

Aquatic species, particularly fish, are vulnerable to the impacts of dams. Moran says the Itaipu Dam, which was constructed on the border between Paraguay and Brazil in the 1970s and 1980s, resulted in a 70 percent loss of biodiversity.

"On the Tucuruí Dam that was built in the 80s in the Amazon," he added, "there was a 60% drop in productivity of fish."

Many fish species rely on the ability to move about freely in a river, be it to seek food or return to where they were born. Migratory species are badly affected by the presence of dams. In 2016, the International Union for the Conservation of Nature (IUCN) reported a 99% drop in catches of sturgeon and paddlefish — both of which are migratory — over a period of three decades. Overfishing and river alteration were cited as major threats to the species' survival.

A 2018 study predicted that fish stocks on Asia's Mekong River could drop by 40% as a result of dam projects – with consequences not only for biodiversity, but for the people whose lives and livelihoods depend on those fish.

The stakes for biodiversity are particularly high for animals threatened with extinction. And not only for aquatic species. The Tapanuli orangutan — the Earth's rarest ape, with only 500 individuals left — could finally be pushed to the brink if a planned hydroelectric project in Sumatra, Indonesia, is completed. Dams can literally snuff out species.

3. Dams Contribute to Climate Change (and Are Affected by It)

As reservoirs fill, upstream forests are flooded, eliminating their function as carbon sinks. As the drowned vegetation decomposes, decaying plants in manmade reservoirs release methane, a powerful greenhouse gas. That makes reservoirs sources of emissions — particularly those in tropical forests, where there is dense growth. It's estimated that greenhouse gas emissions from dams amount to about a billion tons annually, making it a significant global source.

And as the climate changes, more frequent and prolonged drought means dams will capture less water, resulting in lower electricity production. Countries dependent on hydropower will be especially vulnerable as temperatures keep rising.

Moran described a vicious circle, for example in Brazil, which gets 60 to 70% of its energy from hydropower: "If you wipe out half the rainforest, there will a loss of half the rainfall. And then there won't be enough water to provide the amount of power from those dams," he explained.

4. Dams Reduce Water Quality 

Manmade reservoirs trap fertilizers that run into the water from surrounding land. In addition, in some developing countries, sewage flows directly into the reservoirs. This kind of pollution can result in algae blooms that suck the oxygen out of the water, making it acidic and potentially harmful to people and animals.

Still water in large manmade lakes is warm at the top and cold at the bottom, which can also affect water quality. While warm water promotes the growth of harmful algae, the cold water that is often released through turbines from the bottom of a reservoir may contain damagingly high mineral concentrations.

In some cases, water in manmade reservoirs is of such bad quality that it is not even fit to drink.

5. Dams Waste Water 

Since more surface area of the water gets exposed to the sun, reservoirs result in much more evaporation than the natural flow of the river before that dam existed. It's estimated at least 7% of the total amount of freshwater needed for human activities evaporates from the world's reservoirs every year.

This effect is made worse in hot regions, Moran pointed out. "Certainly if you had a reservoir in a tropical area with high temperatures, there is going to be a lot of evaporation," he said. And big reservoirs "are, of course, evaporating constantly."

Reservoirs are also a haven for invasive plant species, and weed-covered reservoir banks can lead to evapotranspiration — or the transfer of water from the land to the atmosphere through evaporation from soil and transpiration from plants. Such evapotranspiration amounts to six times more than the evaporation from the water's surface. And there is even evidence that dams increase water use and promote water waste by creating a false sense of water security.

In the face of dwindling global freshwater resources, some question whether dams should be reconsidered.

So What Are the Alternatives?

The evidence is damning. But if mega-dams have so many harmful environmental effects, what are the alternatives? Although some green groups point to small hydropower as being more ecologically sound, Moran is skeptical. "A dam is a dam - it's blocking the fish, it's blocking the sediment."

He pointed to the need to consider not just how to maximize energy production, but also maintain ecological productivity. One option he cited is the use of in-stream turbines.

And many environment advocates agree that other renewable energies such as solar and wind can provide clean electricity at a far lower environmental cost.

Reposted with permission from Deutsche Welle.

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Cottongrass blows in the wind at the edge of Etivlik Lake, Alaska. Western Arctic National Parklands / Wikimedia Commons / CC by 2.0

By Tara Lohan

Warming temperatures on land and in the water are already forcing many species to seek out more hospitable environments. Atlantic mackerel are swimming farther north; mountain-dwelling pikas are moving upslope; some migratory birds are altering the timing of their flights.

Numerous studies have tracked these shifting ranges, looked at the importance of wildlife corridors to protect these migrations, and identified climate refugia where some species may find a safer climatic haven.

"There's a huge amount of scientific literature about where species will have to move as the climate warms," says U.C. Berkeley biogeographer Matthew Kling. "But there hasn't been much work in terms of actually thinking about how they're going to get there — at least not when it comes to wind-dispersed plants."

Kling and David Ackerly, professor and dean of the College of Natural Resources at U.C. Berkeley, have taken a stab at filling this knowledge gap. Their recent study, published in Nature Climate Change, looks at the vulnerability of wind-dispersed species to climate change.

It's an important field of research, because while a fish can more easily swim toward colder waters, a tree may find its wind-blown seeds landing in places and conditions where they're not adapted to grow.

Kling is careful to point out that the researchers weren't asking how climate change was going to change wind; other research suggests there likely won't be big shifts in global wind patterns.

Instead the study involved exploring those wind patterns — including direction, speed and variability — across the globe. The wind data was then integrated with data on climate variation to build models trying to predict vulnerability patterns showing where wind may either help or hinder biodiversity from responding to climate change.

One of the study's findings was that wind-dispersed or wind-pollinated trees in the tropics and on the windward sides of mountain ranges are more likely to be vulnerable, since the wind isn't likely to move those dispersers in the right direction for a climate-friendly environment.

The researchers also looked specifically at lodgepole pines, a species that's both wind-dispersed and wind-pollinated.

They found that populations of lodgepole pines that already grow along the warmer and drier edges of the species' current range could very well be under threat due to rising temperatures and related climate alterations.

"As temperature increases, we need to think about how the genes that are evolved to tolerate drought and heat are going to get to the portions of the species' range that are going to be getting drier and hotter," says Kling. "So that's what we were able to take a stab at predicting and estimating with these wind models — which populations are mostly likely to receive those beneficial genes in the future."

That's important, he says, because wind-dispersed species like pines, willows and poplars are often keystone species whole ecosystems depend upon — especially in temperate and boreal forests.

And there are even more plants that rely on pollen dispersal by wind.

"That's going to be important for moving genes from the warmer parts of a species' range to the cooler parts of the species' range," he says. "This is not just about species' ranges shifting, but also genetic changes within species."

Kling says this line of research is just beginning, and much more needs to be done to test these models in the field. But there could be important conservation-related benefits to that work.

"All these species and genes need to migrate long distances and we can be thinking more about habitat connectivity and the vulnerability of these systems," he says.

The more we learn, the more we may be able to do to help species adapt.

"The idea is that there will be some landscapes where the wind is likely to help these systems naturally adapt to climate change without much intervention, and other places where land managers might really need to intervene," he says. "That could involve using assisted migration or assisted gene flow to actually get in there, moving seeds or planting trees to help them keep up with rapid climate change."


Tara Lohan is deputy editor of The Revelator and has worked for more than a decade as a digital editor and environmental journalist focused on the intersections of energy, water and climate. Her work has been published by The Nation, American Prospect, High Country News, Grist, Pacific Standard and others. She is the editor of two books on the global water crisis. http://twitter.com/TaraLohan

Reposted with permission from The Revelator.

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An illustration depicts the extinct woolly rhino. Heinrich Harder / Wikimedia Commons

The last Ice Age eliminated some giant mammals, like the woolly rhino. Conventional thinking initially attributed their extinction to hunting. While overhunting may have contributed, a new study pinpointed a different reason for the woolly rhinos' extinction: climate change.

The last of the woolly rhinos went extinct in Siberia nearly 14,000 years ago, just when the Earth's climate began changing from its frozen conditions to something warmer, wetter and less favorable to the large land mammal. DNA tests conducted by scientists on 14 well-preserved rhinos point to rapid warming as the culprit, CNN reported.

"Humans are well known to alter their environment and so the assumption is that if it was a large animal it would have been useful to people as food and that must have caused its demise," says Edana Lord, a graduate student at the Center for Paleogenetics in Stockholm, Sweden, and co-first author of the paper, Smithsonian Magazine reported. "But our findings highlight the role of rapid climate change in the woolly rhino's extinction."

The study, published in Current Biology, notes that the rhino population stayed fairly consistent for tens of thousands of years until 18,500 years ago. That means that people and rhinos lived together in Northern Siberia for roughly 13,000 years before rhinos went extinct, Science News reported.

The findings are an ominous harbinger for large species during the current climate crisis. As EcoWatch reported, nearly 1,000 species are expected to go extinct within the next 100 years due to their inability to adapt to a rapidly changing climate. Tigers, eagles and rhinos are especially vulnerable.

The difference between now and the phenomenon 14,000 years ago is that human activity is directly responsible for the current climate crisis.

To figure out the cause of the woolly rhinos' extinction, scientists examined DNA from different rhinos across Siberia. The tissue, bone and hair samples allowed them to deduce the population size and diversity for tens of thousands of years prior to extinction, CNN reported.

Researchers spent years exploring the Siberian permafrost to find enough samples. Then they had to look for pristine genetic material, Smithsonian Magazine reported.

It turns out the wooly rhinos actually thrived as they lived alongside humans.

"It was initially thought that humans appeared in northeastern Siberia fourteen or fifteen thousand years ago, around when the woolly rhinoceros went extinct. But recently, there have been several discoveries of much older human occupation sites, the most famous of which is around thirty thousand years old," senior author Love Dalén, a professor of evolutionary genetics at the Center for Paleogenetics, said in a press release.

"This paper shows that woolly rhino coexisted with people for millennia without any significant impact on their population," Grant Zazula, a paleontologist for Canada's Yukon territory and Simon Fraser University who was not involved in the research, told Smithsonian Magazine. "Then all of a sudden the climate changed and they went extinct."