The excess of salt in the water changes the biological structure of the river. The species characteristic of rivers are replaced by species seen in seas – hydrologist prof. Maciej Zalewski explains where new, poisonous species of algae, i.e. algae, may have appeared in the Oder. However, the strong growth of algae causes their interspecies competition and the production of dangerous toxins.
Although the ecological disaster in the Odra River has not yet been clarified, more and more talk about its indirect nature the reason may be the increased salinity of the river. – Excess salt in the water changes the biological structure of the river – explains prof. Maciej Zalewski, director of the European Regional Center for Ecohydrology of the Polish Academy of Sciences under the auspices of UNESCO.
Species succession
What does this change look like? – Species characteristic of the river, both fish, algae and other organisms, die or migrate, and in their place species usually seen in the seas appear – says Prof. Zalewski.
This is the so-called “species succession” phenomenon, one of the stages of which is to increase the amount of algae present in the river. This, in turn, leads to interspecific competition between these algae and the increased secretion of harmful toxins by them. – Algae fight each other chemically, for example with proteins that are neurotoxic in nature. Cyanobacteria in particular are characterized by such an effect – notes Prof. Roman Żurek, hydrobiologist from the Department of Ecological Research.
Cyanobacteria and dinoflagellates in the Oder river
Prof. In the context of the Odra disaster, Maciej Zalewski points to such toxic sea algae as, among others, dinoflagellates and cyanobacteria, which are a frequent cause of closing Baltic baths. In his opinion, it is more likely that the first of these species contributed to the Oder catastrophe.
– Cyanobacteria secrete mainly hepatotoxins, substances that are harmful to the liver. Symptoms of poisoning with them most often concern the digestive system: we are talking about abdominal pain, diarrhea or vomiting – he explains. – In turn, dinoflagellates attack the nervous system. Therefore, it seems that their operation is more in line with what we observe in the Odra River, says Prof. Zalewski.
Regardless of the species of algae responsible for it, the appearance of large amounts of toxins in the river becomes deadly to the entire river ecosystem. – Very strong growth of algae, especially if these algae release toxins, can lead to the death of aquatic animals, including fish – explains Prof. Roman Żurek. As he explains, the bodies of fish, after their death, secrete minerals that become additional food for the growing population of algae. – This way the circle closes – sums up prof. Sour soup.
“Golden alga” – what is this algae?
Scientists from the Berlin Leibniz Institute for Freshwater Ecology and Inland Fisheries believe that the fish extinction in the Oder could also have contributed to as yet unidentified toxic species of algae. They suspect that he may be walking for “golden algae”which detection in water samples from the Odra River on Thursday was confirmed by the Minister of Climate and Environment Anna Moscow.
Dr. Alicja Pawelec, WWF water protection specialist, emphasized on TVN24 that it is “highly toxic algae, deadly to aquatic organisms, but not to humans”. – This algae may have entered the river, or may have been transported by waterfowl or migrating fish. In a sweet river, with which everything would be fine, it would certainly not develop – explained Dr. Pawelec.
Golden algae are single-celled algae from the haptophyte cluster and bear the Latin name Prymnesium parvum (“parvum” means “fine”). They can live in different types of water, both fresh and saline, but the most suitable for them are brackish transitional waters – found in estuaries or near river mouths. Their presence in Europe has been recorded since Iceland to Russia, including the Baltic Sea and the Black Sea (but not in Polish rivers), and in the world, inter alia, in USA and Brazil, ChinaAustralia and New Zealand.
Deadly bloom
Golden algae can live in a water reservoir or river for months without causing problems: only their bloom, i.e. sudden population growth, is deadly. The bloom mechanism is still being investigated – it is known that the right temperature, salinity, high electrical conductivity of water and high pH are needed. There would be no bloom in a clean river that is not flooded with saline water and other sewage.
During the bloom of these algae, the water turns golden, coppery or brown in color. There is also white foam. The blooms caused by “golden algae” are also associated with the release of toxins. These are so-called ichthyotoxins – especially toxic to fish and other aquatic animals with gills, such as clams or tadpoles. There is no evidence that ichthyotoxins are toxic to mammals and birds that eat fish, but experts advise against eating fish killed by the toxin.
Some of these toxins are easily broken down by light and inactivated in an acidic environment. In practice, however, there is no way to speed up this process in the river. Interestingly, Prymnesium parvum are natural competitors of Microcystis, Cytophaga and Synechococcus cyanobacteria, whose blooms become less likely in the presence of golden algae.
The blooms of Prymnesium parvum occurred in many places around the world, causing – as in the case of the Odra River – a sudden plague of fish. They could last for days, weeks or even months, sometimes affecting only part of one lake, for example, and the location of the problem could vary from day to day. The blooms were favored by a rather low temperature and they subsided with its growth and increased activity of other algae – but that was also not a rule. Blooming could have had a long-lasting effect on fish farming and caused economic problems.
Main photo source: PAP / Marcin Bielecki