CO2 emissions from dry inland waters globally underestimated
Inland waters such as rivers, lakes and reservoirs play an important role in the global carbon cycle. Calculations that scale up the carbon dioxide emissions from land and water surface areas do not take account of inland waters that dry out intermittently. This means that the actual emissions from inland waters have been significantly underestimated – as shown by the results of a recent international research project involving 46 scientists from all over the world, measuring carbon dioxide emissions from 196 different sites on every continent except Antarctica. The study was published in Nature Communications.
Each of the 24 teams, including researchers from Limnology at Uppsala University who are estimating greenhouse gas emission from Brazilian reservoirs, carried out three closed-chamber measurements in dry areas of at least three freshwater systems in their region – a river, lake, reservoir or pond. This involves placing a special measuring container with its open end downwards on the ground, separating the air inside the container from the ambient air. An analytical device is then used to measure the change in the amount of carbon dioxide inside the container. At the same location, the project partners also took samples of the dry sediment and measured its moisture, organic matter and salt content, temperature, and pH.
The study showed that carbon dioxide emissions from inland waters worldwide have been significantly underestimated up until now. It showed significant carbon dioxide emissions from dry areas of inland waters across all climate zones. The study also discovered that these emissions are in fact often higher than typical emissions from water surfaces of the same size. If dried-out inland waters were taken account for global calculations for inland waters, the carbon dioxide emissions could increase by six percent.
But what mechanisms are responsible for the release of carbon dioxide from dry inland water sediments? Respiration processes of microorganisms is dependent on factors such as available substrate, temperature and sediment moisture. The more substrate available – the more organic matter in the soil – and the more favourable the conditions like temperature and sediment moisture, the more active they are and the more carbon dioxide is released. From the results of the study, it was concluded that the factors responsible for carbon dioxide release are essentially the same all over the globe. The interaction of local conditions like temperature, moisture and the organic matter content of the sediments is crucial, and it has a bigger influence than regional climate conditions.
With the progression of climate change, more surface waters are probably drying out and thus, CO2 emissions will likely increase.
P. S. Keller, N. Catalán, D. von Schiller, H.-P. Grossart, M. Koschorreck, B. Obrador, M. A. Frassl, N. Karakaya, N. Barros, J. A. Howitt, C. Mendoza-Lera, A. Pastor, G. Flaim, R. Aben, T. Riis, M. I. Arce, G. Onandia, J. R. Paranaíba, A. Linkhorst, R. del Campo, A. M. Amado, S. Cauvy-Fraunié, S. Brothers, J. Condon, R. F. 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, M. M. Sánchez-Montoya, C. M. Finlayson, M. Melita, E. S. Oliveira Junior, C. C. 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://doi.org/10.1038/s41467-020-15929-y
Dryflux project: https://www.ufz.de/dryflux/
This text is based on a press release by the Helmholtz Centre for Environmental Research (UFZ) in Magdeburg, Germany.