5 February 2024

Analysis of a river in Congo reveals carbon dynamics

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As a tributary of the Congo River, the Ruki provides one-fifth of the dissolved carbon in the region’s main waterway. A figure that suggests a lower sequestration capacity by the local forest, says a research

by Matteo Cavallito

 

Among its tributaries, Ruki river is the largest contributor of dissolved carbon to the Congo River, one of the largest waterways on the Planet. The finding emerges from an analysis published in the journal Limnology and Oceaonography that carries relevant implications.

The study, led by a team of researchers from several centers (including ETH Zurich, the Congolese Institute for Nature Conservation, and the Universities of Ghent, Belgium, and Tallahassee, Florida) questioned the methods commonly used to calculate the amount of carbon stored in tropical forests. Suggesting, in particular, that this would be overestimated.

The River

Located in the center of the Congo Basin within the DRC, the Ruki River, say scientists quoted by the Australian network The Conversation, “supplies 20% of the dissolved carbon in the Congo River though it makes up only 5% of the Congo’s watershed by area.” Indeed, its waters are characterized by high concentrations of organic matter, a result of soil leaching.

Measurements were conducted for about a year, from the end of 2019 and the following 12 months, and covered different aggregations of the element.

“We measured fortnightly concentrations of all major species of C borne by the river, including DOC, dissolved inorganic carbon (DIC), dissolved carbon dioxide (pCO2), dissolved methane (pCH4), and particulate organic carbon (POC),” the study explains. “Using these concentrations and their relationships with discharge, we modeled instantaneous daily fluxes and estimated the cumulative annual fluxes into the Congo mainstem.”

Congo’s peatlands are still safe

The presence of carbon in the waters, the study explains, is not linked, as feared, to peatland erosion. Which, in that case, would cause a high CO2 leakage into the atmosphere also because of the high presence of the element (according to some estimates, 28 percent of the carbon stored in the Planet’s tropical peatlands would be found precisely in the Democratic Republic of Congo).

In fact, element dating carried out through isotope analysis shows that at the origin of the accumulation is mainly the collection of recently formed forest vegetation and soil. “This is good news for now, but it’s something to keep an eye on if periods of drought or human activity disturb these carbon-rich peat soils,” The Conversation says.

Is forest carbon overestimated?

By quantifying the amount of carbon transported by the Ruki River, the authors have made an additional contribution to knowledge about the region’s climate dynamics. In fact, the data on the presence of the element in the watercourse makes it possible to more accurately determine the net balance between the amount absorbed and released by forests.

Element loss due to water action, moreover, is often ignored by most assessments.

This means that forested areas in the Congo Basin that lie along the Ruki River may retain less carbon to date than expected. Finally, the study results “can serve as a benchmark against which to assess the effects of future anticipated impacts such as deforestation or the drainage of peatlands.”