Why do rivers play a crucial role in the global carbon cycle?

When we talk about the main actors involved in the global carbon cycle, we always think primarily of oceans and land, but rarely of rivers. However, their role is central, explains Tom Battin, head of the River Ecosystems Research Laboratory (RIVER) at EPFL. With the invitation of the scientific journal Naturehe elaborates on their importance in the context of global changes.

A full professor at the Faculty of Natural, Architectural and Built Environments (ENAC) convinced ten scientists in the field to collaborate on the writing of this paper, including Ronny Lauerwald of INRAE ​​and Pierre Regnier of the Faculty of Sciences. Brussels. First time, their The overview demonstrates with modern hard data why river systems were so important to the Carboniferous.

Calculation of carbon flux

Scientists present detailed analysis of ecosystem metabolism of river systems. “Much more complex than human metabolism, rivers both consume and produce oxygen CHO₂ through microbial respiration and photosynthesis. You have to understand it well to be able to calculate the consequences of it,” explains Tom Battin. Pierre Regnier, professor at the Free University of Brussels and co-author of the paper, adds: “Knowing the metabolism of ecosystems is crucial to better calculate the carbon cycle, as it controls the exchange of greenhouse gases and oxygen with the atmosphere.” “The latest global estimates are available for lakes, coastal environments and the open ocean. “Our study of rivers brings the missing piece to the puzzle, opening the door to global and integrated quantification of this fundamental process for the entire blue planet.” For this, scientists compiled all currently available measurements of respiration and photosynthesis of river ecosystems.

The data highlight the link between the river exchange and the terrestrial and marine carbon cycle on a global scale. When rivers flow into the oceans, their metabolism consumes terrestrial organic carbon such as leaves. This process then produces CO₂ released into the atmosphere. Unmetabolized terrestrial organic matter in rivers and CO₂ those not released to the atmosphere are transported to the oceans, where these forms of carbon can affect the biogeochemistry of coastal waters.

In addition, Tom Battin and his colleagues detail how river metabolism is particularly affected by climate change, urbanization, agriculture, or regulation of water flows such as dams. For example, agriculture releases large amounts of nitrogen from fertilizers into rivers. Excess nitrogen can cause eutrophication along with rising temperatures due to global warming. Through this phenomenon, algae reproduce and then die, creating a favorable environment for the production of methane, a more powerful greenhouse gas than CO.₂. Eutrophication can also be enhanced by the construction of dams, resulting in a possible increase in CO emissions₂ and methane.

“The rivers export is important quantities of carbon of biosphere worldly, whose a big part does given in atmosphere under form by CO2 rivers. If he exist of estimates global of export common of carbon worms they are rivers, they are stay uncertain and he it was not said up to here it is impossible to say Yes the proportion of it carbon Between in the network under the river form of carbon organic was evacuated of floors or carbon inorganic from breathing of microorganisms and of the roots in they are floors. we there is can to guess they are losses global of carbon worldly worms they are rivers Between 3.2 and 4.2 billion tons per year and us to guess that the carbon organic no represented about a quarter of this stream, does of carbon inorganic from from his breath soil Source main of carbon worms they are rivers », highlighted Ronny Lauerwald, seeker hour INRAE.

Creation of a river observatory

Following these findings, the researchers propose to create a global river observation system called RIOS (River Observation Systems), specifically designed to analyze carbon fluxes. This RIOS will allow combining data transmitted by sensors in rivers with a satellite observation system to feed mathematical models and obtain predictions on carbon fluxes. “RIOS will also act as a diagnostic tool to measure the pulse of rivers in real-time and intervene when problems arise. Rivers are like our blood system. They have to work so as not to paralyze the whole system,” says Tom Battin. So the call was initiated.