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An EPFL study has prompted scientists to rethink a standard approach used to calculate the velocity of gas exchange between mountain streams and the atmosphere. Research conducted in streams in Vaud and Valais indicate that equations used to predict gas exchange based on data from lowland streams undershoots the actual gas exchange velocity in mountain streams on average by a factor of 100.
This discovery, published in Nature Geoscience, will enable scientists to develop more accurate models of the role that mountain streams play in global biogeochemical fluxes. Considering that more than 30% of the Earth's surface is covered by mountains, the ramifications of this discovery are considerable.
Study - EPFL - Stream - Biofilm - Ecosystem
The study was conducted at EPFL's Stream Biofilm and Ecosystem Research Laboratory (SBER), within the School of Architecture, Civil and Environmental Engineering (ENAC).
In aquatic ecosystems, such as the world's oceans, streams and lakes, numerous aquatic organisms ranging from bacteria to fish respire oxygen and exhale CO2. These gases must therefore be continually "exchanged" from the atmosphere to the water and vice-versa. Because mountain streams often flow over steep drops and rugged terrain, this creates a lot of turbulence and traps air bubbles in the water, which appear white (aka "white water").
Bubbles - Gas - Exchange - Mechanism - Work
These bubbles accelerate the gas exchange. Strikingly, the same mechanism is at work when white-capped waves appear on the surface of rough seas. Until now, scientists have ignored the contribution from air bubbles and have used the same approach to calculate gas exchange velocities in mountain streams than in calm lowland streams.
It is intuitive...
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