The impact of artificial light pollution on natural ecosystems has long been a concern, but new research suggests that even minimal light exposure could have significant consequences for freshwater systems.
Studies have revealed that artificial light, particularly the faint ‘skyglow’ from urban areas, can contribute to the proliferation of toxic algal blooms, such as those caused by cyanobacteria. These algal blooms can disrupt water quality and harm aquatic life.
According to New Scientist, the effects of artificial light on ecosystems are far-reaching, often amplifying issues like nutrient pollution and altering critical microbial populations in freshwater bodies. This growing issue highlights the need for a deeper understanding of light pollution’s role in ecosystem health.
The Unseen Consequences of Skyglow
Skyglow, the diffused artificial light from cities that scatters through the atmosphere, has been found to extend its influence beyond urban areas.
Recent findings highlight that even weak levels of light pollution can reach remote lakes and disrupt the delicate balance of microorganisms that play critical roles in freshwater ecosystems. This subtle yet significant environmental disturbance may alter the way carbon and nutrients circulate in these water bodies.
Researchers at the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) found that even extremely low levels of artificial light can affect freshwater systems, triggering rises in specific types of algae and contributing to the development of harmful algal blooms.
These changes in microbial dynamics also impact the overall health of freshwater ecosystems.
The effects of skyglow on freshwater ecosystems were largely unknown until recently. However, we have now learned that many of the organisms in lakes follow a day-night rhythm – Said IGB researcher Hans-Peter Grossart, who led the research.
In our study, we have shown that artificial light at night promotes the proliferation of cyanobacteria, also known as blue-green algae, which can produce toxins. Skyglow also stimulates carbon cycling in freshwaters, further complicating the dynamics of algal blooms.
Experimental Evidence from the Leibniz Institute of Freshwater Ecology
Researchers from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) conducted a comprehensive study using their LakeLab platform to examine the effects of artificial light on freshwater organisms.
The experiment involved 24 separate enclosures, each containing 1,300 cubic meters of lake water, isolating their contents from the rest of the environment. At the start of the experiment, algae, bacteria, fungi, and small crustaceans were evenly distributed across all the enclosures.
Ten of these sections were illuminated at night for a month using a specially designed system that introduced varying levels of artificial light, ranging from 0.06 lux (resembling typical skyglow in urbanized areas) to 6 lux (the highest documented skyglow level ever measured). Five enclosures were left dark as controls.
The IGB LakeLab offers ideal conditions for such a large-scale experiment where cause-and-effect relationships can be ascertained in realistic field settings by comparing responses of lit and unlit control enclosures – said study co-author Mark Gessner, one of the coordinators of the project.
The study found that even low light exposure, as minimal as 0.06 lux, was sufficient to promote the growth of cyanobacteria (blue-green algae), a type of algae capable of producing harmful toxins. This highlights how artificial light pollution, even at very low intensities, can fuel the growth of potentially toxic algal blooms.
Disrupting Carbon and Nutrient Cycling
cyanobacteria, along with other photosynthetic microorganisms, play an essential role in the cycling of carbon and nutrients in freshwater systems. However, their uncontrolled proliferation, triggered by artificial light, can disrupt these cycles.
During the trial, bacterial populations, particularly cyanobacteria and other light-dependent bacteria, increased by an average factor of 32 in the lit enclosures compared to the dark ones. This substantial increase was observed even with the weakest light levels of 0.06 lux, which is equivalent to the lighting conditions typically found in urban areas due to distant city lights scattering in the atmosphere.
As we observed in our experiments, even very low light intensities of 0.06 lux were sufficient to elicit a response – Explained co-author Stella Berger, a phytoplankton expert at IGB.
As a result of this increased microbial growth, bacterial decomposition of organic substances ramped up considerably. This disruption not only affects water quality but also promotes the formation of harmful toxins, which can be dangerous to fish, wildlife, and even humans, especially if they accumulate in drinking water sources.
The presence of algal blooms exacerbates the issue, posing further risks to water quality and ecosystem health.
An illuminance of 0.06 lux is roughly the illuminance to which organisms can be exposed over large urban areas
Added IGB researcher Franz Hölker, co-author of the study and second coordinator of the project. This subtle glow matches the lighting that rural or distant locations may experience due to the scattering of city lights in the atmosphere.
Implications for Water Quality and Management
The findings from this study have important implications for the management of freshwater resources. While nutrient pollution has long been recognized as a key factor in the development of harmful algal blooms, the role of artificial light pollution must now be considered as well.
Even in the absence of other environmental stressors, light pollution could be tipping the balance in favor of harmful algal blooms. This underscores the need for a broader approach to managing and mitigating water quality issues.
The study also suggests that for cases where algal blooms are not easily explained, light pollution should be considered as a contributing factor. Researchers propose that the global increase in artificial lighting could spark far-reaching changes in ecosystems that were never intended to be illuminated.
As artificial light pollution continues to increase globally, the consequences for ecosystems that were not intended to be illuminated are becoming more apparent.
