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Published: 2019-06-09

Biological processes influence how Arctic rivers emit carbon dioxide

NEWS Arctic waters contributes significantly to global carbon dioxide emissions. Gerard Rocher-Ros states that in order to accurately predict climate change we need to better understand how carbon dioxide is being emitted from rivers and lakes. Gerard defends his thesis on Friday June 14 at Umeå University.

Text: Ingrid Söderbergh

Emissions of carbon dioxide to the atmosphere are causing a major challenge for humanity, i.e. climate change. When we think about carbon dioxide emissions, we often picture cars, planes or factories burning fossil fuels, but for the past decade, scientists are discovering that rivers and lakes emit a substantial amount of carbon dioxide.

 “The current estimate is that rivers and lakes emit as much carbon dioxide as China and Europe combined, but we didn’t know about it until 2007!”, says Gerard Rocher-Ros, PhD student at the Department of Ecology and Environmental Science at Umeå University.

However, there is a lot of uncertainty on carbon dioxide emissions from running waters: we need better tools to calculate carbon dioxide emissions from rivers and to understand how it is produced. For the past decade, the global estimate of carbon dioxide emissions from rivers and lakes has increased fivefold. This change is not due to changes in emissions, but rather due to the increased effort of scientists measuring carbon dioxide emissions around the globe, but huge uncertainties remain.

The research by Gerard Rocher-Ros focused on how carbon dioxide is emitted from arctic streams and where it is produced with the aim to improve our capability to better understand the role of running waters in the global carbon cycle.

“We currently use data at large spatial scales to quantify carbon dioxide emissions, but rivers are very dynamic – with waterfalls, ripples and still waters– and this profoundly affects our ability to quantify carbon dioxide emissions from rivers” says Gerard Rocher-Ros.

Instead, Gerard used measurements at high spatial and temporal resolution to understand landscape patterns of carbon dioxide emissions and its sources.

His results shows that current estimates of carbon dioxide emissions may be too high due to how we predict carbon dioxide emissions in the landscape.

Gerard Rocher-Ros’ research project was performed in the Arctic regions in Sweden and Alaska. The Arctic is much more sensitive to climate change than other regions, and Arctic soils store large amounts of carbon in the frozen ground.

“This means that thawing induced by climate warming can cause a large release of carbon dioxide to the atmosphere in the Arctic, which will in turn make climate change worse. It is a very dangerous feedback we need to understand better”, says Gerard Rocher-Ros.

Previously it was thought that carbon dioxide emissions in Arctic rivers was mostly due to soil inputs of carbon dioxide or abiotic processes such as photo-oxidation, where organic matter is broken into carbon dioxide by light.

“I show in my work that biological processes in Arctic rivers play an important role in producing carbon dioxide emissions from rivers (streams). Aquatic respiration, when organic matter is consumed and produces carbon dioxide and energy, is an important source of carbon dioxide in rivers”.

Gerard Rocher-Ros also shows that another biological process, photosynthesis, strongly can affect carbon dioxide emission in Arctic rivers. When photosynthesis occurs at daylight, it can significantly decrease carbon dioxide concentrations, causing carbon dioxide emission rates to be higher at night than at daytime.

Read the whole thesis digitally


About the dissertation:

On Friday June 14, Gerard Rocher-Ros, Department of Ecology and Environmental Science at Umeå University, defends his thesis entitled: Biophysical controls on CO2 evasion from Arctic inland waters. 

The defence takes place at 9:30 in Stora hörsalen, KBC building

Faculty Opponent is Professor Paul del Giorgio, from Université du Québec à Montréal, Montréal, Canada

Main supervisor has been Professor Reiner Giesler