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2019-05-08. Two-thirds of the world’s longest rivers no longer run free.

posted May 12, 2019, 7:50 AM by Alan Gould   [ updated May 12, 2019, 7:51 AM ]
By Elizabeth Pennisi, Science Magazine. [https://www.sciencemag.org/news/2019/05/two-thirds-world-s-longest-rivers-no-longer-run-free] For GSS Ecosystem Change chapter 1 and Population Growth chapter 5. Excerpt: About two-thirds of the world’s longest rivers are no longer free flowing, compromising their ability to move sediment, facilitate fish migration, and perform other vital ecosystem services, according to a new study. And with more than 3700 large dams in the works, the future of free-flowing waterways looks even bleaker, researchers say. ...In particular, the researchers focused on the 246 longest rivers encompassing more than 1000 kilometers of flowing water—think the Nile and Mississippi rivers—because of their huge ecological impact. Just 90 of those big rivers are still unencumbered, they report today in Nature. Most of the remaining unblocked rivers are in the Amazon, the Arctic, and Africa’s Congo basin. “In the U.S., Europe, and more developed areas, these longer, free-flowing rivers don’t really exist,” Poff says. And those free rivers that remain “are some of the most important places for freshwater species,” says Michele Thieme, a WWF freshwater ecologist. Freshwater plants and animals are declining twice as fast as terrestrial and marine populations, WWF has found. And rivers in general have a lot of hidden value not fully appreciated by policymakers, Thieme notes....