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Photosynthesis by aquatic organisms ‘counters’ impact of global warming

Stream at Hengill, Iceland (c) Benoit Demars
"This is the most robust study of the fundamental thermal response of aquatic photosynthesis at ecosystem scale to date.

Changes in temperature can greatly affect the rate at which aquatic organisms such as algae process inorganic carbon present in streams and waterways, an international team of researchers has found.

The study, which saw researchers explore streams in geothermal areas of Iceland and Russia, showed that photosynthesis by aquatic ecosystems increases faster with warming than previously thought within a temperature range of 4°C to 45°C. This has far-reaching implications for global carbon cycling.

The current increase of global carbon dioxide (CO2) in the atmosphere, mostly from fossil fuel and cement production emissions, is dampened in two ways: diffusion into oceans and fixation by terrestrial plants. Some of the carbon processed by plants finds its way into streams and rivers, where much of it is processed and returned to the atmosphere as CO2.

One of the major mechanisms of control of these CO2 emissions in waterways is the biological cycle between photosynthesis, the fixation of CO2, and respiration, the production of CO2. The study demonstrates that the sensitivity of photosynthesis to changes in temperature is not lower, as previously thought, but the same as respiration in streams with temperatures between 4°C and 45°C.

Hence aquatic photosynthesis has the ability to counter respiration, and thus CO2 emissions with warming. Findings suggest that rising supply of organic matter from terrestrial ecosystems in waterways will likely shift the metabolic balance and result in further increase of CO2 emissions from streams and rivers with warming.

Dr Benoît Demars, honorary research associate at the James Hutton Institute and co-author of the study, said: “This is the most robust study of the fundamental thermal response of aquatic photosynthesis at ecosystem scale to date. We have determined, for the first time, the thermal response of photosynthesis in aquatic ecosystems with temperatures between 4°C and 70°C. The optimum temperature was 45°C, beyond which photosynthesis declined.”

The study is published in the latest issue of Nature Geoscience; it is hoped the research could help redefine the way carbon emissions are modelled in future.

Notes to editors:

Paper: Benoît O. L. Demars, Gísli M. Gíslason, Jón S. Ólafsson, J. Russell Manson, Nikolai Friberg, James M. Hood, Joshua J. D. Thompson and Thomas E. Freitag (2016) Impact of warming on CO2 emissions from streams countered by aquatic photosynthesis. Nature Geoscience, doi: 10.1038/ngeo2807

Partner institutions: The James Hutton Institute, UK; University of Iceland, Iceland; Marine and Freshwater Research Institute, Iceland; Stockton University, USA; Norwegian Institute for Water Research, Norway; University of Leeds, UK; Montana State University, USA; Bangor University, UK; Ohio State University, USA; Smithsonian Environmental Research Center, USA.

Funders of the research include the Scottish Government Rural and Environmental Science and Analytical Services (RESAS); Icelandic National Power Company's Energy and Environmental Fund; Stockton University; AU IDEAS; Icelandic Research Fund and NERC. 

More information from: Bernardo Rodriguez Salcedo, Media and External Relations Coordinator, James Hutton Institute, Tel: +44 (0)1224 395089 (direct line), +44 (0)344 928 5428 (switchboard) or 07791 193918 (mobile).

Press and media enquiries: 

Bernardo Rodriguez-Salcedo, Media Manager, Tel: +44 (0)1224 395089 (direct line), +44 (0)344 928 5428 (switchboard) or +44 (0)7791 193918 (mobile).

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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.