Tropical sensations of the Caribbean waft over Lake Constance due to natural occurrences
Lake Constance, nestled in the heart of Germany, has been captivating visitors with its striking turquoise-blue waters for years. This mesmerising spectacle, often causing a stir on international travel blogs, is not the result of a Photoshop filter but a natural phenomenon that scientists have been observing for years.
The primary cause of Lake Constance's turquoise colour is the scattering and absorption of sunlight by water molecules and fine suspended calcium carbonate (CaCO₃) particulates. Unlike some alpine lakes, where finely ground rock flour (glacial flour) creates a milky turquoise hue, Lake Constance's colour is generally attributed to 'whitings'—episodes where calcium carbonate precipitates out of the water, forming microscopic crystals that scatter light and give the lake its characteristic glow.
Diatoms, a group of algae with silica cell walls, play a significant role in the lake's ecology but are not directly responsible for the turquoise colour. Instead, diatom blooms can influence water clarity and the availability of nutrients, which indirectly affect the conditions under which calcium carbonate precipitation occurs.
During spring and summer, diatom populations may increase during mixing events, utilizing nutrients and affecting the pH and carbonate chemistry of the water. In some lakes, high photosynthetic activity (including by diatoms) can raise the pH, indirectly promoting calcium carbonate precipitation when calcium and carbonate concentrations are sufficient. However, diatoms themselves do not produce the visual effect; this is the domain of suspended CaCO₃ particles.
Calcium carbonate precipitation (whitings) is a geochemical process that happens when calcium and bicarbonate ions in the water reach supersaturation, often triggered by increased photosynthesis and pH changes. Photosynthetic activity (by diatoms, cyanobacteria, and other algae) removes carbon dioxide, raising pH and shifting the carbonate equilibrium towards precipitation of CaCO₃.
In calm weather, the calcium slowly disappears from the upper water layers, leaving the lake to return to its more typical blue hue. This natural phenomenon, which delights many visitors, is not a rare occurrence but is not documented separately.
Dr. Thorsten Rennebarth of the Institute for Lake Research in Langenargen explained that they regularly observe a strong increase in these diatoms in the summer. The composition of the plankton also changes over the course of the summer, which affects the water colour. These diatoms become more prevalent in Lake Constance from May onwards each year, transforming the lake into aquamarine to emerald green tones every summer.
The Institute for Lake Research in Langenargen is part of the State Agency for the Environment Baden-Württemberg (LUBW). The calcium crystals reflect sunlight in a unique way, making the water appear turquoise, and the duration of the turquoise colouration depends on factors such as water temperature, wind strength, diatom growth, and the rate at which calcium settles to the bottom. To witness the colourful spectacle, one should be vigilant and have their camera ready.
- Visitors applying for their annual home-and-garden calendar could consider featuring Lake Constance, with its turquoise-blue waters, in the outdoor-living section.
- During summer months, when diatom populations increase and the lake transforms into aquamarine to emerald green tones, makes it an ideal location for photography enthusiasts to apply their skills in capturing the unique turquoise-colored outdoor-living scene of Lake Constance.
