Communities around the world trying to manage blooms of toxic algae and cyanobacteria already know they have to control nutrient pollution. But now it seems they may have another factor to worry about: too much artificial light.
鈥淵ou have light pollution in urbanised areas where you may also have a nutrient pollution problem,鈥� says at the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Germany. 鈥淚t could be that the combination of both favours cyanobacteria blooms.鈥�
Photosynthetic microbes like cyanobacteria are critical components of aquatic ecosystems, but they can cause problems if they grow out of control and form a bloom 鈥� particularly as some species produce toxins. Pollution in the water from fertiliser runoff or sewage, as well as warming temperatures due to climate change, are the main drivers of the growing frequency of such harmful algal and cyanobacterial blooms. But they aren鈥檛 the only factor.
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Grossart and his colleagues tested how the 鈥�skyglow鈥� produced by artificial lights bouncing off clouds could affect aquatic ecosystems, even far from the bright cities that produce most of the light pollution.
The researchers worked at a lake 80 kilometres north of Berlin, selected for its uncommonly dark skies. 鈥淲e needed an area where you have low light pollution, so you can mimic light pollution,鈥� says Grossart.
They used a floating platform called to divide the water into a number of different 鈥渂asins鈥�. Then, over a four-week period, they used diffuse LED lights to expose each of these basins to varying levels of skyglow, regularly sampling the microbial communities in the water to assess their response.
In basins exposed to skyglow, they found populations of cyanobacteria and other light-sensitive microbes were between 10 and 54 times more abundant than in basins not exposed to any artificial light. The effect on microbial abundance was greatest in basins exposed to the most intense skyglow, comparable to what might occur on the outskirts of a large city such as Shanghai.
鈥淚t鈥檚 definitely a significant change, and it may have some ecological consequences, because you shift the community composition,鈥� says Grossart. That change at the base of the food chain could ripple up the food web to other species. The added light could also favour the growth of species that produce toxins.
The cyanobacteria appear to take advantage of the additional light at night to grow, which gives them an advantage compared with other phytoplankton, says Grossart. 鈥淚t could worsen the problem of having harmful cyanobacterial blooms.鈥�
Water Research
