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. He talks in detail about their importance in the context of global changes at the invitation of the scientific journal “Nature”.

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. For the first time, their combined data show with updated figures why river networks are so important in the carbon cycle.

Calculation of carbon flux

Scientists present detailed analysis of ecosystem metabolism of river systems. ” More complex than human metabolism, rivers consume and produce both oxygen and CO2 through microbial respiration and photosynthesis. It must be understood in order to determine its consequences. “, Tom Batin explains. ” 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.Pierre Regnier, a professor at the Free University of Brussels and co-author of the paper, adds. ” Recent global estimates are available for lakes, coastal environments and open ocean. Our study of rivers brings the missing piece to the puzzle, opening the door to global and integrated quantitative calculations 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 produces CO2, which is then released into the atmosphere. In rivers, unmetabolized dry organic matter and non-atmospheric CO2 are transported to the oceans, where these forms of carbon can influence 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 possible increases in CO2 emissions.2 and methane.

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 take the ‘pulse’ of rivers in real-time and intervene when problems arise. Rivers are like our blood system. They must work so as not to paralyze the entire system “says Tom Battin. And so the call began.

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