The biggest environmental disaster on the Oder last year could happen again in 2023

Scientists have warned that the algal bloom that killed hundreds of thousands of fish in the Oder River between Germany and Poland in 2022 could repeat itself this summer with devastating consequences.

About 360 tons of dead fish were caught from the Oder River, which stretches for 840 kilometers along the German-Polish border, between July and August last year after a strong bloom of poisonous algae. Primnesium parvum.

The European Commission called it “one of the biggest environmental disasters in recent European river history”.

Primnesium parvum commonly found in brackish water estuaries. Scientists aren’t sure how it ended up in the Gliwice Canal in Poland, a spur of the Oder that lies hundreds of kilometers from the coast and where the bloom is thought to have originated.

But now the algae is present in the waters, and fresh color could appear in the Oder or nearby rivers if conditions are right, scientists fear.

“That’s one of the main concerns we have, that it will repeat itself in this river, but also that it can spread to other polluted rivers,” says Gary Free from the European Commission’s Joint Research Center (JRC), who published a study into the death of fish on the Oder in 2022.

The poor quality of the water in the river provided a “perfect soup” for Primnesium parvum to flourish, Free and his colleagues concluded.

Due to agricultural and sewage discharges, the Oder is already suffering from excess levels of nitrogen and phosphorus, nutrients that promote algae blooms.

The problem was exacerbated by successive heat waves and an extended drought in July and August 2022, which lowered the river’s water levels and increased pollution.

The release of saline sewage from industrial sites near the Gliwice Canal then caused a spike in the river’s salt levels, leading to algae blooms. It’s not clear if the discharges were illegal or within permits issued under the permits, Free says. According to Polish data, at least 34 sites in the Oder watershed are licensed to dump saline waste.

The JRC report said the environmental damage was exacerbated by poor communication between German and Polish authorities, with “late and incomplete” exchanges of information hampering response efforts.

A German environment ministry spokesman said in a statement that authorities were only notified of the incident on August 11, after the dead fish had already been washed downstream inside the country’s borders. It says the international pollution alert system is being reviewed, adding: “In the future, it will become even clearer that a transboundary and timely warning should be issued in cases such as fish deaths, for example.” Polish Waters, Poland’s national water authority, has reached out for comment.

According to Dietrich Borchardt of the Center for Environmental Research. Helmholtz in Germany, along with the huge number of fish that died in this event, populations of invertebrates such as mussels and snails were severely affected. These filter feeders usually help control algae blooms, he said, so their decline makes the river more susceptible to new blooms this summer and beyond.

“Due to the loss of invertebrate life – which is not as noticeable compared to fish, but which is definitely there – I think there is a significant possibility that the river is now in a much more vulnerable state compared to last spring.” says Borchardt.

Further blooms could devastate the river’s ecology as studies show fish stocks in the river have already halved since the first incident, according to a study by the Leibniz Institute for Freshwater Ecology and Inland Fisheries in Germany.

Jan Köhler from the Institute has just started research on the effects of Primnesium parvum affects the survival and efficiency of filter feeders such as mussels. He is also concerned about increased algal blooms. “We fear that the reduction in filtration activity will contribute to future mass developments Primnesium,” He says.

According to Free, the Oder needs “intensive care” to prevent further blooms, as well as urgent action to control industrial pollution along the river and reduce nutrient load. For example, authorities should be able to suspend industrial discharges of salt waste when the threat of algal blooms is high, the JRC recommends.

Others believe that to protect the health of rivers in the future, it will be necessary to completely change the rules governing industrial discharges, especially as the European summer is getting hotter and drier in the face of climate change. Emissions licenses need to be rewritten to reflect the effects of climate change, Borchardt said. “We have to ask if permits, for example, to discharge wastewater, are enough in the face of climate change,” he says. — I assume it is not.

Link: JRC Publications Repository, DOI: 10.2760/067386