© Volker Crone
This year’s summer experiment at the LakeLab is again focusing on how a changed light regime affects lakes. Already in 2016 a large-scale experiment on light pollution had been carried out. At that time, a special lighting system was developed for the experimental cylinders, with which the diffuse light of artificial skyglow can be simulated. This phenomenon occurs above clouded areas with artificial lighting (e.g., cities, greenhouses). The light emitted into the night sky is scattered back from the clouds to the earth's surface so that the clouds appear like a glowing dome in the sky. Although the intensity of skyglow is low compared to punctual light sources such as street lights, it extends over large distances and can therefore also affect organisms in the middle of lakes.
The opposing light effect, i.e. the darkening due to water constituents, was already investigated by the IGB scientists in a LakeLab experiment in 2015. It involved the addition of small amounts of humic substances to the enclosures. This dissolved organic matter, which occurs during microbial degradation of plant biomass in soils, may be transported throughout extensive rainfalls from the catchments into lakes. It results in a brownification of the water. According to forecasts, extreme rain events and thus also the release of dissolved organic matter into waters are increasingly expected in the course of climate change. Also our region is affected by this phenomenon. For example, the concentration of dissolved organic matter at Lake Gollin quintupled after a period of intense rainfall a few years ago. First results from the LakeLab experiment with the humic substance show that a changed water quality due to browning has a strong effect on the organisms and processes in the lake. The algal population collapsed almost completely by virtue of the changed light climate.
Because ecosystems are often affected by multiple environmental changes at the same time, this year’s LakeLab experiment will therefor include both stress factors. In addition to five untreated control cylinders, five enclosures each will either be exposed only to humic substances or nocturnal lighting, or to both humic substances and nocturnal lighting. By doing so, the scientists hope to find out whether the two stressors have synergistic or antagonistic effects.
