It has been decades since science began to understand the key role of ecosystems in regulating the concentration of carbon dioxide in the atmosphere. The pieces of this gigantic puzzle still don’t quite fit together, and from time to time new pieces are still found to fit. An international research project led by scientists from the Catalan Water Research Institute (ICRA) , the University of Barcelona (UB) , and the Helmholtz Center for Environmental Research in Germany (UFZ) has just announced a surprising discovery which adds a piece to the puzzle: rivers, lakes and reservoirs release large amounts of carbon dioxide into the atmosphere when they dry up. The finding was published today in the journal Nature Communications .

“It all started in 2012, during a campaign of measurements in the Fluvià river,” says Biel Obrador, from the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB. Together with Rafa Marcé (ICRA) and Daniel von Schiller (UB), they studied the release of greenhouse gases in small dams of this river . “It was summer and parts of the river bed were dry. Out of curiosity, we decided to take some measurements in these areas as well,” explains Rafa Marcé. “The results surprised us; we expected limited biological activity due to the lack of water in these areas, but they released huge amounts of carbon dioxide. We wondered if this could also be the case in other ecosystems around the world and if we were experiencing high an important piece for understanding the regulation of atmospheric carbon dioxide by ecosystems,” says Matthias Koschorreck of the UFZ.

To answer this question, they decided to communicate the finding to researchers around the world to organize a program to measure emissions in dry leeches on a global scale. “Researchers are often reluctant to share ideas about future projects, because the competition in the world of research is very high and that pushes you to secrecy”, explains Rafa Marcé, “but in this case we saw it clearly: nobody had data on carbon dioxide emissions in dry sediments, so if we wanted to know if they had a global scope we had to share the idea with everyone who wanted to collaborate”. This is how the DryFlux network was born. “We used our international contacts to convince research teams to measure carbon dioxide emissions in dry riverbeds, lakes, and reservoirs using a common protocol with just the right amount of complexity so that everyone could replicate it” , adds Núria Catalán, now at the United States Geological Survey and who led the drafting of the protocol. The response exceeded expectations. A total of twenty-four research teams from around the world decided to participate , providing ecosystem measurements on every continent except Antarctica. Daniel von Schiller explains that “we were surprised by such a positive response, because although the methodology and equipment were relatively affordable for a research team, participating in field work has substantial costs, and each team had to take care of theirs, we didn’t have the resources to cover all these expenses”.

The data obtained were analyzed by Philipp Keller, doctoral researcher at the Department of Lakes Research at the UFZ and first author of the study. “We found significant emissions of carbon dioxide from dry areas of freshwater ecosystems in all climate zones,” says Keller. “So it really is a global phenomenon. If you factor these emissions into the current global freshwater estimates, your emissions increase by six percent.” But, what mechanisms are responsible for the release of carbon dioxide in dry sediments? “Respiration processes of microorganisms”, says Phillip Keller. “We still don’t fully understand the biological mechanisms behind it, but it’s clear that the more moisture, temperature and organic matter, the more carbon dioxide is released.” Based on the results of the study, the researchers concluded that the factors responsible for the release of carbon dioxide are essentially the same around the world. “It is surprising that the sediments of a dry mountain river or a salty lagoon in the middle of a desert plain respond in the same way to environmental factors such as humidity or temperature, this suggests the presence of microorganisms capable of adapting to extraordinarily diverse conditions and in some cases very hard”, explains Núria Catalán.

So what do the study’s results mean for future assessment of the role of ecosystems in regulating atmospheric carbon dioxide? “Our study shows that we are still missing many pieces to fully understand the carbon dioxide cycle on a planetary scale, because there are many small cogs that need to be understood if we are to predict how ecosystems will respond to the current increase of carbon dioxide in the atmosphere,” says Biel Obrador, “we hope that our work will help ensure that dry areas of freshwater ecosystems are included in future calculations. With the progression of climate change and human impacts , freshwater will dry up more and more often in large regions of the planet, and some forever, such as the Aral Sea in Central Asia. So emissions from dry lakes will only increase.” . For Rafa Marcé “this study includes another message: competing is not the only, or the best, way to do research. Collaborating openly allows you to answer more ambitious questions. In the times we are living in, it is a lesson that should be taken into account”.

Publication :

S. Keller, N. Catalán, D. von Schiller, H.-P. Grossart, M. Koschorreck, B. Obrador, MA Frassl, N. Karakaya, N. Barros, JA Howitt, C. Mendoza-Lera, A. Pastor, G. Flaim, R. Aben, T. Riis, MI Arce, G Onandia, JR Paranaíba, A. Linkhorst, R. del Campo, AM Amado, S. Cauvy-Fraunié, S. Brothers, J. Condon, RF Mendonça, F. Reverey, E.-I. Rõõm, T. Datry, F. Roland, A. Laas, U. Obertegger, J.-H. Park, H. Wang, S. Kosten, R. Goméz, C. Feijoó, A. Elosegi, MM Sánchez-Montoya, CM Finlayson, M. Melita, ES Oliveira Junior, CC Muniz, L. Gómez-Gener, C. Leigh , Q. Zhang & R. Marcé (2020): Global CO2 emissions from dry inland waters share common drivers across ecosystems. Nature Communications https://www.nature.com/articles/s41467-020-15929-y

Additional information : Dryflux project: https://www.ufz.de/dryflux/

Additional scientific publication : Marcé, R., Obrador, B., Gómez-Gener, L., Catalán, N., Koschorreck, M., Arce, MI, Singer, G., von Schiller, D. (2019): Emissions from dry inland waters are a blind spot in the global carbon cycle. Earth-Sci. rev. 188, 240 – 248