During this last week of July, the residents of Liège noticed that the Meuse River had taken on a distinctive color. Striking green reflections were visible all along the riverbanks. Water samples were collected and analyzed by the laboratory of Professor Annick Wilmotte, an expert in cyanobacteria at ULiège, and revealed the presence of cyanobacteria, explaining this unusual color.
According to Professor Annick Wilmotte, “this unusual color is due to the presence of a cyanobacterial bloom (or proliferation). Microscopic examination revealed the presence of the genera Microcystisand Planktothrix, which are potential toxin producers. The origin of the bloom is likely to be found in tributaries where the current is weaker, but more in-depth studies of the watershed would be needed to confirm this.”
Jean-Pierre Descy, a professor at UNamur and a research collaborator at ULiège, also notes that “the presence of planktonic cyanobacteria in rivers remains a rare phenomenon. In the 1990s, there was no Microcystisin the Belgian Meuse.”
The exact concentration of cyanobacteria in the samples has not yet been measured; however, Prof. Dail Laughinghouse (University of Florida), a collaborator in Professor Annick Wilmotte’s laboratory, indicates that 20 µg/L of chlorophyll was measured, which is considered indicative of a bloom. It is also their visible presence that signals a dysfunction in aquatic ecosystems. Generally speaking, cyanobacteria are part of normal phytoplankton, but in this case, a problematic proliferation has been observed.
According to scientists, the high temperatures of recent days—and, by extension, global warming—are likely the cause of this phenomenon. The presence of cyanobacteria has also been suspected near Visé. These algae can release toxic substances that may cause health problems in humans—though this is rare, since we do not drink water from the Meuse—and in animals, particularly dogs, which can become poisoned if they drink from an area where a bloom is present. Their presence can also have consequences for aquatic ecosystems, irrigation, and livestock watering.
Note that from August 3 to 7, the InBios-BCCM laboratory at the University of Liège is hosting the23rdSymposium of the International Association for Cyanophyte/Cyanobacteria Research— Symposium of the International Association for Cyanophyte/Cyanobacteria Research). “Bloom Day” on August 6 will be open to the general public and science enthusiasts. In the realm of citizen science, the interuniversity network ” (Sciences.be; ) launched the“Bloomin’ Algae” project at the beginning of the summer—the first participatory survey of cyanobacteria in French-speaking Belgium.
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