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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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By Joe Roman and Taylor Ricketts
The COVID-19 pandemic in the United States is the deepest and longest period of malaise in a dozen years. Our colleagues at the University of Vermont have concluded this by analyzing posts on Twitter. The Vermont Complex Systems Center studies 50 million tweets a day, scoring the "happiness" of people's words to monitor the national mood. That mood today is at its lowest point since 2008 when they started this project.
The Hedonometer measures happiness through analysis of key words on Twitter, which is now used by one in five Americans. This chart covers 18 months from early 2019 to July 2020, showing major dips in 2020. hedonometer.org<p>These same tweets also indicate a potential salve. Before pandemic lockdowns began, doctoral student <a href="https://scholar.google.com/citations?user=0P0ZYbIAAAAJ&hl=en" target="_blank">Aaron Schwartz</a> <a href="https://doi.org/10.1002/pan3.10045" target="_blank">compared tweets before, during, and after visits to 150 parks, playgrounds and plazas</a> in San Francisco. He found that park visits corresponded with a spike in happiness, followed by an afterglow lasting up to four hours.</p><p>Tweets from parks contained fewer negative words such as "no," "not" and "can't," and fewer first-person pronouns like "I" and "me." It seems that nature makes people more positive and less self-obsessed.</p><p>Parks keep people happy in times of global crisis, economic shutdown and public anger. Research has also shown that transmission rates for COVID-19 are <a href="https://www.sfchronicle.com/news/article/Is-risk-of-coronavirus-transmission-lower-15287602.php" target="_blank">much lower outdoors than inside</a>. As scholars who study <a href="https://scholar.google.com/citations?user=yFzb2EUAAAAJ&hl=en" target="_blank">conservation</a> and how nature <a href="https://scholar.google.com/citations?user=CCnUeN8AAAAJ&hl=en" target="_blank">contributes to human well-being</a>, we see opening up parks and creating new ones as a straightforward remedy for Americans' current blues.</p>
Park Visits Are Up During the Pandemic<p>According to the Hedonometer, sentiments expressed online started trending lower in mid-March as the impacts of the pandemic became clear. As lockdowns continued, they registered the lowest sentiment scores on record. Then in late May, effects from George Floyd's death in police custody and the following protests and police response once again could be seen on Twitter. May 31, 2020 was the saddest day of the project.</p><p>Recent surveys of park visitors around the University of Vermont have shown people <a href="https://osf.io/preprints/socarxiv/sd3h6" target="_blank">using green spaces more</a> since COVID-19 lockdowns began. Many people reported that parks were highly important to their well-being during the pandemic.</p>
<div id="4c7e4" class="rm-shortcode" data-rm-shortcode-id="bc0ac146ab2a94228f32d973fc2ab272"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1289428912879964160" data-partner="rebelmouse"><div style="margin:1em 0">#Goldengatepark #sf #quarantinemood https://t.co/9l3ufnbkt6</div> — Suvd (@Suvd)<a href="https://twitter.com/Suvd19486406/statuses/1289428912879964160">1596258783.0</a></blockquote></div><p>The powerful effects of nature are strongest in large parks with more trees, but smaller neighborhood parks also provide a significant boost. Their impact on happiness is real, measurable and lasting.</p><p>Twitter records show that parks increase happiness to a level similar to the bounce at Christmas, which typically is the happiest day of the year. Schwartz has since expanded his <a href="https://arxiv.org/pdf/2006.10658.pdf" target="_blank">Twitter study</a> to the 25 largest cities in the U.S. and found this bounce everywhere.</p><p>Parks and public spaces won't cure COVID-19 or stop police brutality, but they are far more than playgrounds. There is growing evidence that parks contribute to mental and physical health in a range of communities.</p><p>In a 2015 study, for example, Stanford researchers sent people out for one of two walks: through a local park or on a busy street. Those who walked in nature showed <a href="https://doi.org/10.1016/j.landurbplan.2015.02.005" target="_blank">improved moods and better memory performance</a> compared to the urban group. And a team led by <a href="https://penniur.upenn.edu/people/eugenia-gina-south" target="_blank">Gina South</a> of the University of Pennsylvania showed in a 2018 study that greening and cleaning up blighted vacant lots in Philadelphia <a href="http://dx.doi.org/10.1001/jamanetworkopen.2018.0298" target="_blank">reduced local residents' feelings of depression, worthlessness and poor mental health</a>.</p>
Creative Strategies<p>It isn't easy to create new parks on the scale of San Francisco's Golden Gate Park or the Washington Mall, but smaller projects can expand outdoor space. Options include greening vacant lots, closing streets and investing in existing parks to make them safer, greener and shadier and support wildlife.</p><p>These initiatives don't have to be capital-intensive. In the University of Pennsylvania study, for example, renovating a vacant lot by removing trash, planting grass and trees and installing a low fence cost only about US$1,600.</p><p>Urban green space is most needed in neighborhoods that have lacked funding for parks, especially given <a href="https://www.nytimes.com/2020/04/08/nyregion/coronavirus-race-deaths.html" target="_blank">COVID-19's disproportionate impact on Black and Latinx people</a>.</p><p>Cities can also create parklike spaces by <a href="https://theconversation.com/with-fewer-cars-on-us-streets-now-is-the-time-to-reinvent-roadways-and-how-we-use-them-140408" target="_blank">closing streets to cars</a>. Many cities worldwide are currently retooling their transportation systems for the post-COVID-19 world in order to <a href="https://thecityfix.com/blog/bicycles-slower-speeds-livable-city-paris-mayor-anne-hidalgo-plans-ambitious-second-term-dario-hidalgo/" target="_blank">reallocate public space</a>, widen sidewalks and make more space for nature.</p><p>Urban designers, artists, ecologists and other citizens can play a direct role, too, creating pop-up parks and green spaces. Some advocates <a href="https://www.bloomberg.com/news/articles/2017-09-15/a-brief-history-of-park-ing-day" target="_blank">transform parking spaces into mini-parks</a> with grass, potted trees and seating for just the time on the meter, to make a larger point about turning so much public space over to cars.</p><p>Or cities can invest a little more. Minneapolis, Cincinnati and Arlington, Virginia, have won <a href="https://www.tpl.org/parkscore" target="_blank">national recognition</a> for their ambitious investments in public park systems. These areas could serve as models for neighborhoods that lack access to parks.</p>
<div id="25fd0" class="rm-shortcode" data-rm-shortcode-id="383f0d2df0237e9359c30dcce6cd6c42"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1276558744835379201" data-partner="rebelmouse"><div style="margin:1em 0">Looking to safely get outside? Check out the best parks for social distancing in this year's top ten ParkScore citi… https://t.co/HJjEtDsrTD</div> — The Trust for Public Land (@The Trust for Public Land)<a href="https://twitter.com/tpl_org/statuses/1276558744835379201">1593190296.0</a></blockquote></div>
A New Park Deal?<p>The United States has historically driven economic recovery with major infrastructure investments, like the New Deal in the 1930s and the 2009 <a href="https://www.investopedia.com/terms/a/american-recovery-and-reinvestment-act.asp" target="_blank">American Reinvestment and Recovery Act</a>. Such investments could easily include nature-positive spaces.</p><p>Parks are not panaceas, as evidenced by the widely publicized <a href="https://www.nytimes.com/2020/07/06/nyregion/amy-cooper-false-report-charge.html" target="_blank">racist confrontation between a white woman and a Black birder</a> in New York's Central Park in early July. But Hedonometer data add to a <a href="https://advances.sciencemag.org/content/5/7/eaax0903?utm_source=miragenews&utm_medium=miragenews&utm_campaign=news" target="_blank">growing body of evidence</a> that they provide <a href="https://doi.org/10.1073/pnas.1807504116" target="_blank">clear mental health benefits</a>. Creating and expanding parks also <a href="https://www.nrpa.org/contentassets/f568e0ca499743a08148e3593c860fc5/economic-impact-study-summary.pdf" target="_blank">generates jobs and economic activity</a>, with much of the money spent locally.</p><p>We believe investments in nature are well worth it, offering both short-term solace in difficult times and long-term benefits to health, economies and communities.</p>
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