How it works riversThe health of these ecosystems depends largely on the amount of sediment they carry. and deposit. Such sediments play a critical ecological role by providing a habitat for organisms in downstream and estuaries. It is also important for human life to feed agricultural soils in floodplains with nutrients and to buffer the sea level rise due to climate change by carrying sand to deltas and coasts.
However, these functions are seriously threatened. Over the last 40 years, humans have caused unprecedented changes in river sediment transport.According to a study published by Dartmouth scientists, Science.
Using satellite imagery and runoff data, the researchers studied changes in the amount of sediment carried into the oceans. 414 of the world’s largest rivers from 1984 to 2020.
The results were alarming: According to lead author Evan Dethier, “Humans have succeeded in changing the world’s greatest rivers at an unprecedented rate in the recent geological record.”
“The amount of sediment carried by rivers is often determined by natural processes in watersheds, such as how much rain is falling or whether there is landslides or vegetation. We have found that human activities have outstripped these natural processes and outstripped the effects of climate change.”
It was reduced by 49% after the construction of the dams.
The findings show that dams were widely built in the northern regions of the Earth (North America, Europe and Asia) in the 20th century. reduced the global distribution of sediment transported by water from rivers to the oceans by 49% with regard to conditions prior to those dams.
However, andIn the southern regions of the world (South America, Africa and Oceania), sediment transport increased in 36% of rivers due to large changes in land use, much of which is associated with deforestation.
In the north, the construction of dams has been the main driver of change in rivers in recent centuries. “One of the motivations for this research has been the global expansion of large dam construction,” says co-author Francis Magilligan, a Dartmouth geographer who studies dams and dam removal.
Rivers are responsible for creating floodplains, levees, estuaries and deltas due to the sediments they carry. Again, When a dam is built, this sediment source, including nutrients, is usually shut off.
The results in the north are surprising and could herald future changes for the south. The study claims There are more than 300 dams planned for major rivers in South America and Oceania, including the Amazon RiverCarrying more sediment than any river in the world.
“Rivers are pretty accurate indicators of what we’re doing on the Earth’s surface — they’re like a thermometer for land use change,” says co-author Carl Renshaw, an earth scientist at Dartmouth. “It’s very well known that there is a land loss crisis in the US, but we don’t see it in the sediment export record because everything gets stuck behind these dams, whereas we can see the signal from the rivers. South.
Reference work: https://www.science.org/doi/10.1126/science.abn7980
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