About five times more carbon dioxide (CO2) escapes from the world’s rivers and streams per year than from all its lakes.
The finding comes from a study reported in Nature, titled “Global carbon dioxide emissions from inland waters”, carried out by an international team of scientists.
The connection between inland water and the sea is not only important for the water cycle, but also for the global movement of nutrients, metals and not least, greenhouse gases, which affects the carbon cycle, a dynamic component of the global carbon budget.
However, as the scientists (from Belgium, Canada, Finland, France, Germany and the US) note in their study report, we don’t know enough about how these diverse sources and sinks of carbon interact.
Hans Dürr, a research professor from the Faculty of Science at the University of Waterloo in Canada, whose model – Coastal Segmentation and related Catchments (COSCAT) – was key to the research, says:
“Identifying the sources and amounts of carbon dioxide released from continental water sources has been a gap in understanding the carbon cycle. Our findings show just how much carbon dioxide inland waters release and identified that rivers and streams are the main source not lakes and reservoirs, as previously thought.”
The COSCAT model is a global database of water catchments like streams, rivers, lakes and reservoirs, that link to oceans.
The model helped the researchers estimate that the rate of escape of CO2 – known as “CO2 evasion” – from lakes and reservoirs was lower than previous estimates.
They suggest the global CO2 evasion rate from rivers and streams is around 1.8 billion tons of carbon per year, compared with 0.32 billion tons from lakes and reservoirs.
The rate of CO2 evasion is even greater in faster-moving, smaller streams, they note.
Prof. Hans Dürr, who is also a member of the Ecohydrology Research Group and Water Institute at Waterloo, says this type of research is a good example of the new knowledge that results from “bringing together different tools, techniques and ideas from hundreds of scientists to tackle a global issue.”
However, while the findings add valuable new insights into how rivers and streams affect the global carbon cycle, CO2 evasion rates for inland waters in the northern hemisphere remain a mystery.
It is important to have reliable estimates for the northern hemisphere because current climate models suggest temperature increases in regions whose latitude is above 60 degrees north will be higher than the global average.
The current models use data from satellite products that don’t yet exist for these latitudes, says a press statement from the University of Waterloo, in which Prof. Dürr notes:
“More integrated, international collaborations like this are needed.”
In November 2013, Market Business News reported a study led by Princeton University in the US that found even if CO2 emission stopped, global warming would continue for centuries.