Two-thirds of world’s longest rivers choked by mankind
Only a third of longest rivers flow freely, with dams, reservoirs and power projects damaging biodiversity, study says.
Almost two-thirds of Earth’s longest rivers have been degraded by dams, reservoirs or other man-made constructions, severely damaging some of the most important ecosystems on the planet, researchers say.
Using the latest satellite data and computer-modelling software, an international team looked at the connectivity of 12 million kilometres of rivers worldwide, providing the first global assessment of human impact on the planet’s waterways. They found that of the 91 rivers longer than 1,000km in length, just 21 retained a direct connection between source and sea. Just a little over a third (37 percent) of the 242 longest rivers had retained their free flow, something experts said was having a profound effect on Earth’s biodiversity.
Just a little over a third (37 percent) of the 242 longest rivers had retained their free flow, something experts said was having a profound effect on Earth’s biodiversity.
The researchers found that the longer the river is, the greater the likelihood of it being impeded. While 97 percent of the world’s shortest rivers (those no longer than 62 miles) still remain free-flowing, only very few rivers longer than 310 miles remain that way in the United States, China, western Europe, and other parts of the world.
Most of the remaining free-flowing rivers were confined to remote parts of the Arctic, the Amazon and the Congo basins.
The study, published in the journal Nature, laid bare in intricate detail just how drastically man-made activity is impacting our waterways. It estimated a total of 60,000 large dams at least 15 metres tall were blocking rivers, of a total of 2.8 million worldwide.
The blocking or damming of rivers disrupts the flow of nutrients vital to replace those lost through agriculture, and diminishes the numbers of river-born species that can complete their life-cycles. It also lessens the sediment flows river deltas provide coastal regions with, which currently help to protect millions of people against sea level rises. Less than a quarter of free-flowing rivers now connect to oceans, depriving estuary environments from vital nutrients and sediments.
The study also identified more than 3,700 hydropower projects either planned or currently under construction, including some on rivers offering vital life support for the human populations who live along them.
The health of Earth’s rivers will also be impacted as climate change accelerates, affecting flow patterns and water quality, as well as bringing more invasive species, the researchers said.
