People violated the most important functions of rivers

(ORDO NEWS) — Over the past 40 years, humans have caused unprecedented changes in the formation of river sediment.

River sediments – mainly sand, silt and clay – play an important ecological role, providing a habitat for various organisms. They also benefit humans by providing nutrients to agricultural soils and curbing climate change-driven sea level rise by delivering sand to deltas and coastlines. However, now all these features are under threat.

Using images from NASA’s Landsat satellites and digital archives of hydrological data, the Dartmouth researchers studied how sediment supply to the oceans from the world’s 414 major rivers changed from 1984 to 2020.

It turned out that in the two hemispheres of the planet there was a completely opposite picture. In the north, over the past 40 years, the amount of river sediment has significantly decreased, while in the south it has increased significantly.

Developed countries have succeeded in “changing the world’s major rivers at an unprecedented rate” in a geologically short period of time, said study lead author Evan Dethier, a research fellow at Dartmouth University.

The data obtained show that the massive construction of dams in the 20th century in the global hydrological north – in North America and Eurasia – reduced the total flow of river sediment into the world ocean by 49%.

Even a significant increase (by 36%) in the supply of sediments from the global hydrological south South America, Africa, and Oceania did not prevent such a decrease.

The rise in the south was driven mainly by intense land-use change, mainly deforestation, driven by logging in Malaysia, gold mining in South America and sub-Saharan Africa, sand mining in Bangladesh and India, and palm oil plantations in most parts of Oceania.

People violated the most important functions of rivers 2
The Three Gorges Dam, completed in 2003, has drastically reduced the amount of sediment carried by the Yangtze River in China

In the north, dam building has been a major factor in changing rivers in the last few centuries. Only in the USA – more than 90 thousand such structures.

“Thus, our nation has been building an average of one dam a day since the signing of the Declaration of Independence,” said study co-author Francis Magilligan.

At the same time, the States are experiencing a crisis in the reduction of fertile soils, which the authors of the work attribute to the fact that sediments get stuck behind numerous dams.

The results of the construction of dams in the north give a hint of what awaits the southern hemisphere, as more than 300 such structures are planned to be built on the major rivers of South America and Oceania today. Including the Amazon, which carries more sediment than any other river in the world.

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