Lake Constance Experiences Continuous Rise in Temperature
The impact of global warming is evident at Lake Constance, with its average temperature steadily climbing. The potential impact on the aquatic life isn't crystal clear yet, but there are some hints emerging.
Based on an assessment by the Lake Constance Research Institute (Seeforschungsinstitut Langenargen) of the Baden-Württemberg State Environment Agency (LUBW), the lake water temperature hit a record high of 14.1 degrees Celsius at the surface in annual average in 2022, surpassing the previous average of 13.6 degrees. The lake's temperature was just 10.5 degrees back in 1962 when the measurements began.
Climate heating brings about diverse effects on water bodies as per an expert from the State Environment Agency. Temperature is a crucial factor for the overall water quality. "It impacts the mixing or stratification relationships of lakes, water chemistry, or the species composition and the influence paths of food webs."
In Lake Constance, warming coincides with a weak exchange between deep and surface water. This lessens the oxygen transport from the upper layers to the depths and escalates the risk of oxygen deficiency for the organisms residing in those areas. "On the flip side, fewer nutrients are transported from the depths to the surface layer, which affects the food web of the lake ecosystem."
The project "Seewandel-Klima" is presently scrutinizing in depth how climate change impacts the fish population and water plants in Lake Constance. This project will last for three years until 2026, and some preliminary findings are already available.
Warming temperatures in the depths are a concern
"We're still clueless about it, but there are some preliminary signs," said Alexander Brinker, head of the research station in Langenargen. The increasing temperature poses a negative impact on species like roach, for instance. "For them, the water in the deep layer must remain below 5 degrees Celsius for their eggs to develop properly. The temperature in that area is already above that, resulting in lower catch numbers."
According to the evaluation by the Lake Constance Research Institute, the temperature in the deep layer averaged 5.4 degrees Celsius in annual average in 2023, marking a new record high. A decade ago, it was still 4.3 degrees. The temperature keeps climbing year after year.
Perch eggs and larvae also suffer from the rising temperatures. Researchers anticipate a higher mortality rate of eggs and larvae if it gets too warm. Adult perch may also cease to swim to their feeding grounds in the surface layer during the summer, where they typically feed on water fleas in the well-lit areas of the lake surface, due to the overly heated water. "They no longer visit their feeding grounds."
A recent study by the Fisheries Research Station Langenargen reveals that higher temperatures outside the Bodensee affect native trout farming that collects water from adjoining rivers or springs. For trout reliant on cold and oxygen-rich water, higher temperatures cause stress. They lead to a decrease or halt in food intake and an increased susceptibility to diseases. In severe cases, the animals could perish. "Considering the long-term perspective, between 37 and 77 percent of current trout farming will be exposed to unfavorable climate conditions by the end of the century," asserts the research team.
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The project "Seewandel-Klima" is investigating how global warming affects the fish population and water plants in Lake Constance. The rising temperatures are negatively impacting fish species like roach and perch, with the water in the deep layer already exceeding the optimal temperature for their egg development.
The increased temperature in Lake Constance is not only affecting the fish population but also impacting native trout farms that rely on cold and oxygen-rich water. Higher temperatures are leading to stress, decreased food intake, increased susceptibility to diseases, and in severe cases, the animals' demise.
