Mbandaka — In a groundbreaking discovery, scientists have identified the Ruki River, a tributary of the Congo River, as potentially the darkest large blackwater river in the world. This natural marvel is darker even than the Rio Negro of the Amazon.
According to a new release by World Economic Forum, an ETH Zurich researcher, and his colleagues from the Sustainable Agroecosystems Group led by Johan Six, the Ruki River’s unique darkness is attributed to large amounts of dissolved organic material. Contrasting with other major tropical rivers, the Ruki stands out due to its low sedimentation, largely because of its low gradient.
The organic material in the Ruki comes primarily from rain falling on decaying jungle vegetation. During the rainy season, the river floods the forest, leaching out carbon-rich substances over weeks. “The Ruki is essentially jungle tea,” Drake noted.
Untouched Ecosystems and Carbon Sinks
The Ruki River’s drainage basin, which is four times the size of Switzerland, is covered by untouched primary lowland rainforest. Adjacent to the river are extensive peat bogs that serve as significant carbon sinks, containing immense amounts of undecomposed dead plant material.
Historically, the Ruki had been largely ignored by scientific research. Though seasonal water levels have been recorded since the 1930s, its chemical composition remained a mystery. To bridge this knowledge gap, the research team established a measurement station near Mbandaka in 2019, undertaking bi-weekly water discharge and daily water level measurements for an entire year.
Analytical Insights
Water samples were subsequently sent to ETH Zurich labs where they were analyzed for dissolved organic carbon (DOC) content and the age of the organic material. The analysis revealed that Ruki’s water contains four times as much DOC as the Congo’s and 1.5 times as much as Rio Negro’s.
Intriguingly, although Ruki’s drainage basin constitutes only a twentieth of the entire Congo Basin, a fifth of the dissolved organic carbon in the Congo originates from this one tributary.
Environmental Implications
Travis Drake stressed that despite its high carbon content, the CO2 emissions from the Ruki River’s drainage basin are comparable to other tropical rivers due to its sluggish flow. However, land-use changes, such as deforestation, could disrupt this fragile ecosystem and potentially release huge amounts of CO2 stored in the peat bogs.
“It would be better for the climate if they stayed wet,” concluded Matti Barthel, study co-author, emphasizing the importance of the 29 billion tonnes of carbon stored in the Congo Basin’s peat bogs.
This recent discovery is part of a long-standing research project focusing on the carbon cycle of the Congo Basin, led by Johan Six and his group, who have been studying the region since 2008.