Lake Geneva also renews itself through its own structure
Published: Monday, Jul 15th 2024, 13:10
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Vertical mixing is not the only driver for the winter renewal of the deep water in Lake Geneva. Strong currents from the basin of the Little Lake and from the shore of the Great Lake can also cause complete mixing. This is shown by a study conducted by the EPF Lausanne.
The winter mixing of water is of crucial importance for the preservation of Lake Geneva's ecosystems, as the Swiss Federal Institute of Technology in Lausanne (EPFL) announced on Monday. In exceptionally cold winters, large-scale vertical mixing - known as full mixing - takes place, which is characterized by a uniform temperature from the surface to the bottom.
Deep vertical mixing in so-called temperate lakes takes place in winter when the surface water cools down due to falling temperatures. This water then becomes dense and cold and moves vertically downwards to mix with the deeper water, transporting oxygen and nutrients.
This process was traditionally regarded as the only way to renew the deep water. According to the authors of the EPFL study published in the journal "Water Resources Research", strong currents generated by the structure in two basins can also cause renewal in the deeper layers. In the case of Lake Geneva, this means through the so-called Great Lake (Grand Lac) in the middle and east near Lausanne and the Small Lake (Petit Lac) in the west near Geneva.
However, due to global warming, complete vertical mixing is becoming increasingly rare: "Temperatures have risen steadily since 2012, and oxygen levels at the bottom of Lake Geneva have fallen by ninety percent in ten years," explains Naifu Peng, researcher at EPFL's Ecological Technology Laboratory (Ecol) and lead author of the study.
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