李丹

The Ruki， a tributary of the CongoRiver， is the darkest river in the world，with water so dark that you can't even seeyour hand in front of your face.

In what is considered the firsteverscientific study of the African river， scientistsconcluded that the darkcoloredwateris caused by the high levels of dissolved organicmatter from the surrounding rainforest.Scientists found that the color iscaused by carbonrichcompounds leachedout of rotting plant matter and washed intothe Ruki River by rainwater and floods. DrTravis Drake， lead author of the publishedstudy， said that the Ruki is “essentiallyjungle tea” in which carbonrichplant matteris brewed. The resulting coloration ofthe water makes the Ruki darker than theRio Negro.

“The organic compounds leachedfrom this vegetation absorb light， so thehigher the concentration， the darker thewater will appear，” Dr Drake said. “It?would be like brewing an extra concentratedtea using many tea bags.”

Using a measurement system， theteam of scientists from ETH Zurich， inSwitzerland， found that the Ruki was 1.5times darker than the Amazons Rio Negro，the worlds blackwaterriver. And althoughthe Ruki only makes up a twentiethof the Congo Basin， it provides a fifth of alldissolved carbon in the Congo.

“The Ruki is one of the mostDOCrichriver systems in the world，”Matti Barthel， the studys coauthor，said.Its water contains four times as many organiccarbon compounds as the Congosand 1.5 times as many as the Rio Negrosin the Amazon.

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