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As part of the 11th grade ecology unit, pupils and teacher Silke Däumling-Horray from Alexander-von-Humboldt-Gymnasium undertook a special final event. Under the expert guidance of biology teaching students Janina Utz and Franka Welsch, the young researchers went on an exciting excursion to Lake Constance, where they studied the microbial ecosystem in the lake's open water.

Thanks to the preparation in class, the pupils were well equipped for the diverse topics that were discussed during this excursion. The investigations focused on plankton filtration and microscopy, with the diatom Asterionella in particular being observed in large numbers.

In the weeks before the excursion, sunny and warm days caused the water temperature in the uppermost layer of Lake Constance to rise to 22.5°C and this change had a strong impact on the ecosystem. The phytoplankton in the upper 20 meters of the water had increased almost explosively compared to the previous week. An impressive representation of this process resulted in a so-called depth profile, which was created on the trip and discussed with the students. The blue curve represents the temperature profile of the water column down to a depth of 40 meters, while the green curve shows the chlorophyll fluorescence as an indicator of the density of phytoplankton. The results illustrate the drastic changes in such a short time.

With the increased photosynthetic activity and the associated rise in the pH value in the water, calcite precipitation began in the lake at the same time. These microscopic calcite crystals led to a striking discoloration of the water, which increasingly shimmered a Caribbean turquoise green - a natural spectacle that is likely to be observed even more intensively in the coming days and weeks.
A particular highlight of the excursion was undoubtedly the return journey, during which several pupils were able to disembark directly at the jetty in their home town of Dingelsdorf.

Overall, the excursion was a complete success and a valuable addition to the lessons. The direct experience and practical work on Lake Constance gave the pupils a deep insight into the complex interrelationships of ecological systems - knowledge that can hardly be taught so vividly in the classroom.