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.
James Hutton Institute
The James Hutton Institute is a world-leading scientific organisation encompassing a distinctive range of integrated strengths in land, crop, waters, environmental and socio-economic science. It undertakes research for customers including the Scottish and UK Governments, the EU and other organisations worldwide. The institute has a staff of around 600 and 150 PhD students.
