In a new study, EPFL professor Tom Battin reviews our current understanding of carbon fluxes in the world’s river networks. He explains their central role in the global carbon cycle and warrants for the creation of a global River Observation System.
In their article, the authors explain the role of the global river ecosystem metabolism. “River ecosystems have a much more complex metabolism than the human body,” said Battin. “They produce both oxygen and CO2 through the combined effect of microbial respiration and plant photosynthesis. It’s important to fully appreciate the underlying mechanisms, so that we can evaluate and quantify the impact of the ecosystem metabolism on carbon fluxes.”
Their results point to a clear link between river ecosystem metabolism and the global carbon cycle. While moving water toward the oceans, river ecosystem metabolism consumes organic carbon derived from terrestrial ecosystems, which produces CO2 emitted into the atmosphere. Residual organic carbon that is not metabolized travels into the oceans, together with CO2 that is not emitted into the atmosphere.
Battin and his team also discuss how global change, especially climate change, urbanization, land use change and flow regulation, including dams, affect river ecosystem metabolism and related greenhouse gas fluxes. For example, rivers that drain agricultural lands receive massive amounts of nitrogen from fertilizers. Increased nitrogen concentrations, combined with rising temperatures due to global warming, can cause eutrophication-a process that leads to the formation of algal blooms. As the algae die, they stimulate the production of methane and nitrous oxide, greenhouse gases that are even more harmful than CO2.
The authors conclude their article by stating the importance of a global River Observing System (RIOS) to better measure and predict the role of rivers for the global carbon cycle. RIOS will integrate data from networks of sensors in the rivers and satellite imagery with mathematical models to create near-real time carbon fluxes related to river ecosystem metabolism.