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Ruki: As dark as tea
Photograph:
Matti Barthel / ETH Zurich
According to a study from Zurich, a jungle stream in Africa that has hardly been studied so far is one of the darkest blackwater rivers in the world – if not the darkest. A research team led by the Swiss University of ETH Zurich has analysed the Ruki in the Democratic Republic of Congo and compared it with other dark rivers. Despite its size, the river has never been scientifically studied, the Swiss explained.
Certain organic substances such as humic acids in the water are responsible for the colour of black water rivers. The ruki contains significantly more of it than the famous Rio Negro (black river) in the Brazilian Amazon, the university said. They couldn't find a stronger concentration anywhere. "The ruki is actually jungle tea," co-author Travis Drake was quoted as saying. The team was deeply impressed by the colour: the water was so dark that you could no longer see your hand in front of your eyes.
The dissolved organic matter in the wide river came from dead jungle vegetation in the surrounding area and was washed into the stream by rainwater, the research team explained. The forest floor in the area is often waist-deep under water for weeks at a time, which drains only slowly.
The Ruki is a tributary of the Congo River. It has hardly any gradient and, bordered by peat bogs, leads mostly through rainforest – "almost completely original", as the study puts it. Only five percent of the catchment area is used for agriculture. The estuary is located near the town of Mbandaka, about 645 kilometers upstream of the capital Kinshasa. The Congo Basin is the second largest supplier of fresh water and organic carbon to the oceans after the Amazon.
The team had spent a year taking measurements, taking samples and analysing them. The results have been published in the journal Limnology and Oceanography. Limnology is the science of inland waters.
ahh/dpa