A team of scientists, led by Gunther Grill, has used satellite and computer simulation data to analyze the connectivity of 12 million kilometers of rivers worldwide (40 times the distance that separates us from the Moon) and has achieved the First global assessment of the human impact on the planet’s waterways. The results, published in Nature, indicate that almost two out of every three of the longest rivers on Earth have been cut by dams, reservoirs or other human-made constructions. And these infrastructures seriously damage some of the most important ecosystems on the planet.
The Grill team discovered that of the 91 rivers over 1,000 kilometers, only 21 maintained a direct connection between the source and the sea. Only slightly more than a third (37%) of the 242 longest rivers had retained their free flow, something experts said was having a profound effect on Earth’s biodiversity.
“The rivers of the world,” explains Grill in a statement, “form an intricate network with vital links to the earth, groundwater and the atmosphere. Rivers that flow freely are important for both humans and the environment, but the economic development worldwide is making them increasingly rare.”
The study notes that most of the rivers that do not show obstacles were limited to remote areas of the Arctic, Amazon and Congo basins.
This week, the UN panel on biodiversity published a summary of its devastating assessment of the state of nature. It details that 50% of rivers “manifest serious degradation impacts” of human activity. The blocking of the rivers interrupts the flow of vital nutrients to replace those lost through agriculture, and decreases the amount of species in the river. It also decreases the sediment flows that river deltas provide to coastal regions, which currently help protect millions of people from rising sea levels.
The Grill team warned that the dams had already caused a significant drop in river fish, which provide almost all animal protein consumed by about 160 million people. Finally, the health of the Earth’s rivers will also be affected as climate change accelerates, which will influence flow patterns and water quality, in addition to facilitating the arrival of more invasive species.
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