One of the most remarkable labs TU Berlin researchers can use is the LakeLab at Lake Stechlin. Just getting there is an experience in itself: The directions provided by Professor Dr. Mark Gessner, head of the Chair of Applied Aquatic Ecology at Technische Universität Berlin and the Department of Experimental Limnology at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) go something like this: “Whatever you do, don’t turn on your GPS, otherwise you’ll never find us.” As it turns out, you must wind your way down a narrow forest road a few kilometers behind Neuglobsow, and right before driving straight into the lake, you arrive at the IGB buildings on the shore. However, you will still have not made it to the LakeLab. To do so, you must don a life jacket, hop on a boat, and motor 200 meters out into the lake and dock at an aluminum and plastic platform in the middle of the lake.
From the air, the LakeLab is remotely reminiscent of the famed crop circles that supposedly represent UFO landing sites. 24 aluminum basins each measuring nine meters in diameter surround a larger ring 30 meters in diameter. Once you have climbed onto the floating LakeLab from the boat, you see that plastic sheets are fastened to each ring, extending roughly 20 meters down to the bottom of the lake and thus creating 24 columns of water separate from the rest of the lake.
“In effect, you can picture these water columns or experimental units, as we call them, as oversized tubes open at the top and bottom. Within these enclosures, we are able to modify different environmental factors and under realistic field conditions track how organisms and processes in the lake react,” explains Gessner. The LakeLab is a valuable addition to the easy to replicate, but simplified experiments in the lab and the realistic, but often irreplicable trials on a whole-lake scale, such as those in Canada, the USA, and northern Sweden.
The LakeLab’s 24 enclosures make it possible to simultaneously pursue a significant number of experimental approaches including controls. This produces statistically sound results allowing researchers to identify the influence of environmental factors. Additionally, the researchers at Lake Stechlin can draw on long data records, as a research station was already established at this deep clear water lake as early as the 1960s. “These data are extremely valuable to us. They provide us with important information to place recent changes in a long-term context and interpret them,” says Gessner.
Parameters such as water temperature, pH value, oxygen saturation, or nutrient concentration but also the number and makeup of plankton are recorded over the entire year. This is partly performed by autonomous probes installed in each of the LakeLab’s enclosures. They travel through the water columns at hourly intervals and take vertical profiles. The results are saved digitally and transmitted to IGB’s central location in Berlin.
When the coronavirus pandemic is not preventing scientists around the world from traveling, a major weeks-long experiment is conducted, typically in the summer, where up to 70 researchers and students participate. The LakeLab receives numerous cooperation requests each year from across Germany and around the world for collaboration on these experiments. The lab also offers TU Berlin students unique opportunities to work, whether as student assistants during the summer experiments or within the framework of labs, internships or bachelor’s, master’s, or doctoral theses.
Since the LakeLab took up operation in 2012, several major experiments have been conducted. In 2016 and 2018, for example, scientists investigated the impact of light pollution on the lake’s ecosystem. Specifically, they looked at the skyglow, the illumination of the sky that occurs when light emissions from conurbations are scattered back to earth at night from a closed cloud cover. “We wanted to know whether this diffuse and not very bright light has an effect on the lake’s organisms. Our focus was on water fleas and other types of zooplankton, as they demonstrate a special migratory behavior: During the day they burrow deep in the lake away from their predators, fish. At night, they travel to the surface water under the protection of the dark to graze on algae. If their migratory behavior shifts because of the skyglow, this could change the relationships between the organisms in the food web and thus the material flow in lakes,” explains Gessner, describing the experiment’s hypothesis.
In their current project “CONNECT – Connectivity and synchronization of lake ecosystems in space and time” the scientists are examining in a series of trials whether river-connected lakes develop similarly. The overall aim is to understand whether the bloom of potentially toxic blue algae (cyanobacteria) propagates from one lake to another or whether there is a relationship between such algal blooms and the increased emission of climate-relevant gases such as methane or carbon dioxide from lakes.