2023-09-21 06:00:29
Global change is changing the composition of microbial layers in water – more cyanobacteria, whose toxins can be harmful to humans and animals.
The effects that toxic cyanobacteria can have was demonstrated this summer in the Ottenstein reservoir in the Waldviertel (Lower Austria), where swimming was discouraged due to exposure to toxins from these bacteria. A research team with Austrian participation has now shown that the thin microbial layer (biofilm) covering stones, aquatic plants and soil in mountain lakes is becoming increasingly toxic due to global change. The study appeared in the journal “Water Research”.
It is now well established that biodiversity, particularly in freshwater, is declining dramatically due to human activities. This has been documented primarily in animals and plants, but little attention has been paid to microbial communities. Microorganisms are of great importance for the functioning of ecosystems.
The slimy layer on various surfaces in water, such as stones, consists of billions of microorganisms. These microbes not only form the basis of the food web in water, they also purify and detoxify it by breaking down organic pollutants. This means they have a major influence on water quality.
26 lakes in France were studied for years
A research team led by Dirk Schmeller and Hugo Sentenac from the Institut National Polytechnique de Toulouse (France), which also includes Luca Zoccarato from the Institute for Computational Biology at the University of Natural Resources and Life Sciences (Boku) Vienna and scientists from the German Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) examined biofilms in 26 lakes in the French Pyrenees over five years. They showed that the composition of biofilm communities has changed significantly and the considerable biodiversity in the microbial layers has decreased over time: certain algae such as cyanobacteria have increased, while other microbial species that indicate good water quality, such as diatoms, have lost weight. The problem is that some cyanobacteria produce cyanotoxins that are harmful to animals and humans.
Problems with cyanobacteria have previously been known to occur in lowland lakes. There are repeated cases of poisoning of dogs and wild animals by cyanotoxins. In mountain lakes, the changes in biofilm composition “might cause cascading effects in food webs and threaten the resilience of the entire lake ecosystem. The increase in potentially toxigenic cyanobacteria also increases the risk of poisoning for humans, domestic animals, wild animals and livestock using mountain lakes,” the scientists write in their paper.
They attribute the changes in the composition of the biofilm to several factors acting at the same time. They specifically examined fluctuations in pH and water hardness as important drivers. “They will continue to increase under the influence of climate change due to leaching of the rock,” explained Schmeller in a press release. The researchers therefore recommend developing management strategies to relieve mountain lakes of controllable stress factors such as fish populations and invasive species.
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