Why does Lake Geneva emit large quantities of CO2? A forgotten piece of lakes’ carbon cycle, say researchers

Lake Geneva [credit: discoverwalks.com]

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A co-author/professor in the study says: ““It’s very important to have in-depth knowledge of how CO2 is naturally transported, stored and transformed between continents, water and the atmosphere”. In other words, knowledge of nature’s carbon cycle. But to then assert their findings can help with ‘fighting global warming’ is opinion, not science.
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Unlike oceans, lakes are significant emitters of CO₂, says the University of Lausanne (via EurekAlert).

But why is this the case, and what mechanisms are at play?

For the first time, UNIL scientists have successfully explained the complete carbon cycle in Lake Geneva, creating a model that can be applied to several of the world’s largest lakes.

— Contrary to previous beliefs, it is the natural erosion of rocks that is responsible for the significant CO2 emissions from Lake Geneva and many of the world’s large lakes.
— This study provides the missing piece for understanding the carbon cycle in lakes.
— The LéXPLORE lake platform in Switzerland played a major role in this discovery of international significance.

Like most lakes in the world, Lake Geneva is an emitter of greenhouse gases, particularly carbon dioxide (CO2). Annually, it produces as much CO2 as the automobile transport of the city of Lausanne (≃ 150,000 inhabitants).

This phenomenon – the production of CO2 by lakes – has been known for years. There is, however, widespread debate as to the mechanisms at work.

Traditional scientific theories suggest that lake CO2 emissions are primarily due to the influx of organic matter from surrounding soils. This material, originating from the decomposition of plant and animal residues, is carried into the lake by rainfall, where it is broken down by microorganisms, leading to the release of CO2.

This process is known as respiration. While this theory accounts for the behavior of some lakes, it doesn’t apply to Lake Geneva, which receives very little organic matter from its shores.

In theory, its annual carbon balance should be neutral, with winter CO2 production (from organic matter decomposition and water mixing) balanced by summer CO2 absorption (due to algae photosynthesis). So why does Lake Geneva still emit large amounts of CO2?

A team of UNIL scientists has just deciphered the mechanisms involved. Most of the emissions actually come from the natural erosion of rocks in the lake’s upstream basin.

When rainwater hits the rocks, it releases bicarbonate and calcium ions, which then find their way into the lake. In summer, under the effect of heat and the growth of algae – which change the PH of the water and act as a catalyst – the ions form microparticles of limestone. This is known as calcite precipitation.

This chemical reaction releases CO2, giving the lake its milky blue-green appearance in the warm season. Algae continue to absorbCO2, but this is not enough to compensate for the massive production resulting from rock erosion.

The additional emissions are therefore the result of a geological process, not just a biological one, as previously thought.

Full news release here.
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Image: Lake Geneva [credit: discoverwalks.com]

Source: https://tallbloke.wordpress.com/2024/10/31/why-does-lake-geneva-emit-large-quantities-of-co2-a-forgotten-piece-of-lakes-carbon-cycle-say-researchers/