18 August 2020

Methane fluxes from lakes are considerably higher during the day than the night, according to a study conducted by LiU researchers. Consequently, the research group assesses that the contribution of northern lakes to global methane emissions is 15 per cent lower than previously estimated.

Northern lake
Northern lake Monica Westman
The study is published in PNAS, Proceedings of the National Academy of Sciences.

Freshwater lakes, rivers and reservoirs are the second greatest source of emissions of methane, the second most important greenhouse gas for global warming. Methane is also the greenhouse gas that has increased most in the atmosphere over the past 250 years.
“The methane flux has increased irregularly, and we don’t actually know why” says Anna Sieczko, postdoctoral researcher at Environmental Change in the Department of Thematic Studies who, together with colleagues at Linköping University and Umeå University, has published the PNAS paper.

Methane fluxes differ over time and space, and many researchers are trying to find and quantify all sources and sinks, and to understand the flux regulation. The LiU research group, led by Professor David Bastviken from Environmental Change, has measured methane fluxes from lakes – recently discovered to be the second largest natural methane source on Earth.

Day and night measurements

Anna Sieczko and her colleagues made 4,580 measurements to compare day and night methane fluxes on four lakes of different types during the ice-free period, from early summer to autumn.
“Previously methane fluxes from lakes were often measured primarily during daytime, but now we have a representative set of measurements covering both daytime and nightime”, says Anna Sieczko.

A clear pattern emerged: fluxes of methane were considerably higher from 10:00 to 16:00 in 80 per cent of the cases. There are indications that the wind, which is usually stronger during the day, creates turbulence in the water and thereby increases the methane emissions. The wind can explain most, but not all of the variability, which indicates that other environmental factors can influence the day-night differences.

Overestimated emissions

“Current calculations of methane emissions from freshwater lakes don’t include variation between day and night, which means the contribution from northern lakes has been overestimated by about 15 per cent”, says Anna Sieczko.

“It’s essential that we, as in this study, identify and consider variations in time and space when estimating all large-scale fluxes of greenhouse gases. If we don’t, there’s a risk that climate models will be inaccurate and that our priorities of flux mitigation measures become suboptimal. Estimates of all methane sources and sinks are connected via the global methane budget and inaccurate estimates of some fluxes affect our understanding of the whole budget”, says David Bastviken.

The research is part of the METLAKE research, which focusses on methane fluxes from lakes. The study was funded by the European Research Council, the Swedish Research Council, FORMAS (the Swedish Research Council for Sustainable Development) and the Knut and Alice Wallenberg Foundation.

Diel variability of methane emissions from lakes, Anna K. Sieczko, Duc T. Nguyen, Jonathan Schenk, Gustav Pajala, David Rudberg, Henrique O. Sawakuchi, David Bastviken, PNAS 2020, doi 10.1073/pnas.2006024117



More news

Decomposed leaf.

The reaction explaining large carbon sinks

A mystery has finally been solved. Researchers from LiU and Helmholtz Munich have discovered that a certain type of chemical reaction can explain why organic matter found in rivers and lakes is so resistant to degradation.

Two women in the laboratory.

New lab, but still the same

Following a fire, the lab at TEMAM has been under restoration since 2020. Now that it is finished, most of it looks the same as before, as nobody could think of any changes they would like to make to the premises.

David Bastviken.

Climate change affects greenhouse gas emissions from stream networks

Natural greenhouse gas emissions from streams and lakes are strongly linked to water discharge and temperature. This knowledge is necessary to assess how man-made climate change is altering greenhouse emissions from natural landscapes.

Latest news from LiU

Woman with arms crossed.

She wants to make robots behave better

Researcher Hannah Pelikan believes that we will see increased conflicts between humans and robots in the future.  In her research, she films everyday encounters between humans and machines to see what happens.

Two men in a computer server hall.

International collaboration lays the foundation for AI for materials

AI is accelerating the development of new materials. Large-scale use and exchange of data on materials is facilitated by a broad international standard. A major international collaboration now presents an extended version of the OPTIMADE standard.

Female PhD student lectures to master's students in the lab.

From sketches to a robot with artificial intelligence

How do you develop a product with as little human involvement as possible? LiU students built a robot using generative artificial intelligence.