Swiss researchers fear climate impact in Lake Constance

Commission warns of consequences of climate change for Lake Constance Keystone-SDA

Climate change is having an adverse impact on the mixture of oxygen in Lake Constance, according to Swiss researchers.

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The lake is sufficiently oxygenated at present, but the International Commission for the Protection of Lake Constance (IGKB) believes that this may change with climate change.

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Because the air temperatures and therefore the water are getting warmer and warmer, it no longer circulates sufficiently in winter. In turn, strong mixing is important to ensure that the oxygen also reaches the deep regions of the lake and the lake bed.

“Even this winter, the entire lake was unable to circulate sufficiently to the deepest point,” said Harald Hetzenauer, head of the Institute for Lake Research at the Baden-Württemberg State Institute for the Environment. The institute monitors the condition of the lake on behalf of the IGKB together with the specialised agencies of the other neighbouring countries.

In order for the water to be able to circulate to great depths, the lake must cool down significantly in winter and the temperature must be roughly the same everywhere.

The time window with the right water temperature is getting smaller and smaller, the press release adds. This is because the lake warms up earlier in spring and cools down later in autumn.

Oxygen scarcity threat

“Nevertheless, the deep water is still well supplied with oxygen,” the IGKB stated. In the middle of the lake at a depth of 251 metres, around six milligrams of oxygen per litre above ground were measured in mid-January.

At the beginning of March, it then rose to around seven milligrams per litre. At the same time, it was shown that really good mixing of the water – apart from shallower parts such as the Bregenz Bay – only took place in the late winter of 2017/2018 after 2006.

An imminent lack of oxygen at the bottom of the lake, which is necessary for both fish and many microorganisms, was already an issue in the 1970s. At that time, the excessive enrichment of the lake with nutrients reached its peak, according to the IGKB.

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Because a lot of dead organic matter accumulated at the bottom, oxygen was in danger of becoming scarce. Significantly fewer nutrients are now entering the lake.

Baden-Württemberg, Bavaria, Vorarlberg and the cantons of Thurgau, St Gallen and Graubünden have been working together in the International Commission for the Protection of Lake Constance since 1959.

The two cantons of Appenzell support the water protection measures. The most important goal is to keep the lake clean, as well as the ongoing monitoring and sustainable development of the diverse flora and fauna.

Adapted from German by AI/mga

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