14 DAY TRIAL // Dr. Tom Battin, a scientist at the University of Vienna, announced recently that the world's rivers also emitted carbon dioxide in the atmosphere, and not only played the role of pipelines, carrying carbon trapped by rain, soil and plants to the oceans. The discovery was inconceivable a few years ago, but lately more and more scientists came to see that the role of rivers in carbon cycles was largely underrated.
Not even the Intergovernmental Panel on Climate Change (IPCC) accounts for the nearly 2 gigatonnes (2x109 tonnes) of carbon dioxide that are emitted into the atmosphere by the largest rivers in the world annually. And Battin says that the smaller rivers and streams also account to the total amount of CO2 put in the air. But, until now, rivers were regarded as inert pipelines, whose only role was to transport carbon to the ocean floors, where it would be consumed by microorganisms, or become trapped in thick layers.
"Surface water drainage networks perfuse and integrate the landscape, across the whole planet," says Battin, "but they are missing from all global carbon cycling, even from the IPCC reports. Rivers are just considered as inert pipelines, receiving organic carbon from Earth and transporting it to the ocean. The actual outgassing of carbon dioxide is probably closer to 2 Gt of carbon per year. Our surface area estimates only consider larger streams and rivers, because it is very hard to estimate accurately the surface area of small streams. So small streams are excluded, although in terms of microbial activity, they are the most reactive in the network."
Worldwide, some 27 GT of CO2 are pumped into the atmosphere each year, mostly from the burn of fossil fuels, such as coal, natural gas and oil, as well as by volcanic eruptions. All models trying to foresee the way the climate will change over the next 100 to 200 years are accounting for all the factors, except this one. A simple calculus shows that rivers most likely account for 7.5 percent of the total amount, which is a lot.
Another disturbing conclusion that Battin made public was the fact that human-made nanoparticles seem to interfere with the way microorganisms in the water perform their carbon "cleansing." "This finding is a real challenge to science. Engineered nanoparticles such as titanium dioxide are expected to increase in the environment, but it remains completely unknown how they might affect the functioning of ecosystems," he concludes.