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ILES – Illuminating Lake Ecosystems

Light is key in structuring ecosystems and biological communities. Since the introduction of the electric bulb in the late 19th century and the subsequent dramatic increase of artificial lighting, the natural light regime has been significantly changed. During the last decades light emission increased by 3 to 6 percent per year in the global average, occasionally even up to 20 percent. This is much faster than the rise of the global economy, the world’s population or the emission of the climate relevant greenhouse gas carbon dioxide in the same periode. The "loss of night" affects all industrialised regions in the world and is thus an additional element of the global environmental change caused by humans.


Also lakes can be disturbed by light pollution – the riparian areas through direct lighting, the open water above all by a diffuse illuminated night sky. This phenomenon of skyglow mostly occurs during cloudy weather above areas with artificial lighting (e.g. towns, greenhouses): The light propagated into the atmosphere is scattered back to the ground by molecules and aerosols so that the clouds appear like a glowing dome in the sky. Although the intensity of skyglow compared to direct light is low, it extends over very large areas and can therefore also affect lakes and aquatic organisms. The influence of the loss of the night for the ecosystem and its biodiversity are largely unknown, but could be significant.


With the project "Illuminating lake ecosystems – ILES", we want to study the ecological consequences of such light pollution and the underlying mechanisms. The experiments are performed in the LakeLab, where skyglow is simulated in 10 enclosures using a specially developed light system. We expect that the new lighting conditions will influence the physiology and behavior of key species. Our special focus is on daphnia and other representatives of the zooplankton. They usually show a diel vertical migration pattern: While during the day they hide in the darkness of the deep water avoiding to be an easy prey for the fish, at night times they migrate up to the surface water in order to feed on algae. However, an altered migratory behavior would also change the interactions between organisms in the food web and thus the material flows in the lake. Our results promise both fundamental new insights into the effects of nocturnal lighting on lakes as well as important information on the water management.

  • Direction:
    Prof. Dr. Mark Gessner and Dr. Franz Hölker
  • Project duration:
    07/2015 — 06/2018
  • Funding:
    Leibniz Association


Photograph: Skyglow above Los Llanos on the canary island of La Palma.
© Martina Bauchrowitz, IGB