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20 minutes – Winter brewing not deep enough

The winter mixing of Lake Lman was only partial this winter. The oxygen level in the bottom layers thus remains low, which can promote the release of pig phosphorus in the sediments.

The last complete mixing of the Lman dates back to 2012, said Thursday the International Commission for the Protection of the Waters of the Lman (CIPEL) in a press release. This year, brewing was carried out up to 100 meters, or about a third of the maximum depth of the Lman, which reached 309 meters.

Brewing is linked to winter weather conditions. When the surface waters cool, gaining in density, they plunge to the depths, also pushed by the winds favoring the movements. This phenomenon makes it possible to bring oxygen into the deep layers.

Algae proliferation

Without complete mixing, the oxygen level at the bottom of the Lman remains low, releasing the phosphorus pig in the sediments. However, an increase in phosphorus concentrations in water is undesirable, emphasizes CIPEL.

This excess phosphorus leads to the proliferation of algae. At the end of their life, these algae settle at the bottom of the lake. As they decompose, they consume oxygen, which increases the oxygen deficit in deep waters.

To limit these undesirable effects, it is necessary to reduce the phosphorus intake of human origin. This includes developing an efficient wastewater treatment network.

(ats)

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