Lake Constance is warming, and that could be a problem – Climate

The Baden-Württemberg Environmental Research Institute (LUBW) has been measuring the water temperature in the lake since 1962. The average water temperature back then was 10.5 degrees. The assessment shows that in 2022, the average annual temperature of the inland water surface reached a maximum of 14.1 degrees. Last year the average was 13.6 degrees.

An expert from LUBW explains that the impacts of a warming climate on water bodies are manifold. Temperature is a central parameter of water conditions. “It influences the mixing or stratification conditions of lakes, water chemistry or species composition and impacts pathways in the food web.”

At Lake Constance, warming is accompanied by a weak exchange of deep water with surface water. This reduces the transport of oxygen from the top layer to the depths, thereby increasing the risk of hypoxia for organisms living there. “Conversely, fewer nutrients are transported from the depths to the top layer, which affects the lake’s ecosystem via the food web,” the expert stressed.

The “Lake Climate Change” project is currently investigating in more detail how climate change is affecting fish populations and aquatic plants in Lake Constance. The project will run for three years, until 2026. However, there are already initial signs of its effects.

“We don’t know much yet, but there are initial indications,” says Alexander Brinker, head of the Langen Argen Research Center. For example, higher temperatures can have a negative impact on the bushfish. “For them, the water in the deep sea areas has to be below five degrees, otherwise the eggs cannot develop properly.” However, the air temperatures in the region are already higher, resulting in lower catches.

According to the Institute of Oceanography, the average temperature in the deep sea in 2023 was 5.4 degrees. This is a new peak. Ten years ago it was 4.3 degrees. The temperature is rising year by year.

Whitefish eggs and larvae will also be affected by rising temperatures. The researchers speculate that if it gets too hot, the mortality rate of eggs and larvae will be higher. And for adult whitefish, there is a concern that in the summer, when they normally feed on water fleas in the sunlit areas of the lake, they will no longer swim into these areas because the water temperature is too high. “They are no longer coming to their hunting grounds.”

According to a new study by the Langenargen Fisheries Research Centre, rising temperatures outside Lake Constance are affecting domestic trout farms, which get their water from nearby rivers or springs. Higher temperatures mean stress for trout, which rely on cold, oxygen-rich water. They lead to a reduction or cessation of food intake and increase the likelihood of illness. In extreme cases, the animals die. “On balance, between 37 and 77 percent of current trout farms will find themselves under unfavourable climate conditions by the end of the century,” the research team said.