It looks like it’s flowing more like black tea or cola than water. But it’s a river. Researchers were stunned by the discovery of a hitherto unexplored region in the interior of Africa. It is even much blacker than the Amazonian Nigger River, so named for obvious reasons. Ruki is the blackest river in the worldSo much so that even if the hand is immersed in water, it cannot be seen. A research team from various countries found the reason for this color.
“Ruki is a pure Karasu tributary in the Congo basin Drying lowland tropical forests.” This is the first sentence of the study titled ‘Hydrology drives carbon export and composition in a pristine tropical river’, recently published in the journal ‘Limnology and Oceanography’.
The main aim of the international research team is to carbon cycle In the Congo River basin. “We were very impressed by the color of the river,” says the study’s lead author, Travis Drake, a researcher at the Federal Institute of Technology Zurich.
The color of a river depends mainly on what it carries, as well as on its depth and the extent to which it covers the sky. Nutrients, suspended matter and sediment particles can reflect incoming sunlight. On the contrary, organic substances give darker hues to water. Herein lies the key to the mystery.
limnology (the science that studies continental aquatic ecosystems) often refers to brownish or black rivers as black water rivers. The water of white water rivers is clay colored. The color of clear water rivers is from yellow to olive green. These three tones dominate river species in the tropics.
Virgin primary forests
In Ruki’s case, The water is black because it contains large amounts of dissolved organic matter, rich in carbon, but little sediment. Because its slope is low. Most carbon-rich substances are washed into the river by rain; When rain falls on the forest’s dead vegetation, it filters out the organic compounds in this decaying matter.
During the rainy season, the river floods much of the forest, and the water, which is often one meter above the ground, can take weeks to recede and flows very slowly. In other words, it filters organic substances during this period. “Ruki is actually forest tea.. And a good candidate one of the most pristine and homogeneous large tropical basins in the world“says Drake.
But the color of the water is only one of the characteristics of the Ruki River, which is very large (one kilometer wide) and is a tributary of the Congo. The drainage basin, which is five times the size of Catalonia, is still covered with virgin primary rainforest. from the plains.
Other features of Ruki: There are large peat bogs along the river that contain huge amounts of dead, undecomposed plant material. (peat). Peatlands are the most important terrestrial carbon sinksQ. Part of this peat complex is located in areas classified as ‘wetlands of international importance’ according to the Ramsar Convention.
To understand why Ruki is so black, researchers took samples and measured water levels and discharge amounts over the course of a year. The river where it is located in the middle of a virgin forestIt has been known for almost a century, but has never been scientifically studied, and until now no data was available on its chemical composition.
A “slow and calm” river
Analysis confirmed the visual impression: “The Ruki is one of the richest river systems in dissolved organic carbon in the world“says Matti Barthel, co-author of the study. Its water contains four times more organic carbon compounds than those in the Congo and one and a half times more than those in the Negro River. Although the Ruki basin accounts for only one twentieth of the world, the entire Congo contains one fifth of the dissolved organic carbon in this river It comes from this branch.
Researchers observed that: Very little organic matter is currently released Since in the Ruki River the steppes are under water almost all year round and therefore have no contact with oxygen.
Dissolved organic carbon usually occurs in the form of organic acids, which increase the acidity of river water. This stimulates the release of carbon dioxide as the acids dissolve the carbonates present in the water.
“CO2 emissions are relatively high in the Ruki drainage basin, but are no different from other tropical rivers,” explains Drake. The reason for this is Ruki is a “slow and calm” riverIt makes it harder for CO2 to escape from the water into the air. “In a turbulent river, we see greater emissions,” he emphasizes.
Analysis of carbon isotopes showed that: Most carbon comes from forest vegetation, not peat. The researchers found evidence that for only a short period of time, peatlands released carbon into the water following heavy runoff at the end of the rainy season (between March and April).
The fact that there is little peat in the river has been described as “very positive” by some researchers, as it means the peat bogs are stable and currently, There is no danger of the organic matter they contain being releasedbecause they are under water almost all year round.
The danger comes from: Companies that want to benefit from the natural resources of the Ruki basin. Changes in land use and deforestation can alter river regimes and cause peatlands to dry out, be decomposed by bacteria and release large amounts of CO2.
This is no trivial matter: “Peatlands in the Congo Basin store approximately 29 billion tonnes of carbon“, Barthel warns. “It would be better for the climate if they stayed wet,” he warns.
Reference work: https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lno.12436
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