Fish deaths in the Oder: The ecosystems are so vulnerable due to the climate crisis

  Masses of fish have died in the Oder. Forces from the Federal Agency for Technical Relief salvage several tons of dead fish from the river. Masses of fish have died in the Oder. Forces from the Federal Agency for Technical Relief salvage several tons of dead fish from the river. picture: IMAGO / Winfried Mausolf Analyse

It is an environmental catastrophe of as yet unknown dimensions that is currently taking place in the 866-kilometer-long Oder - which rises in the Czech Republic and flows into the Baltic Sea: a massive fish kill. The environmental organization 'BUND' estimates the amount of dead fish at up to 100 tons.

The exact causes are still unclear, the investigations are ongoing. The carcasses are to be examined for more than 300 harmful substances, including pesticides. In addition, the fish corpses should be dissected and the behavior of the Animals to be examined shortly before her death. So far, only mercury can be ruled out as the cause of death.

  Experts estimate the number of dead fish at up to 100 tons. Experts estimate the number of dead fish at up to 100 tons. picture: imago / winfried mausolf

What is the cause of the massive fish kill?

The Polish government suspects that a huge amount of chemical waste may have been dumped into the Oder. Data from water measuring stations along the Oder provided by the Brandenburg State Office for environment be published, but also show: The river water showed abnormalities a few days before the fish died.

  The low water level reveals the seriousness of the fish kill. The low water level reveals the seriousness of the fish kill. Image: imago images / winfried mausolf

Does that speak for the algae theory, which the Brandenburg Ministry of Agriculture, Environment and climate protection suspected behind the fish kill?

This would at least explain the high oxygen content despite the high temperatures.



But the salt content in the water continues to give the researchers puzzle and speaks against the algae theory. Rather, everything points to a supply of toxins.

What role do the consequences of Climate crisis with a massive fish kill like in the Oder? And how well are our ecosystems prepared to collapse? Watson spoke to experts about this.

Whether the fish kill in the Oder is related to intoxication, as Karsten Rinke suspects, or not: 'The climate situation exacerbates the problem immensely.' Rinke is head of the lake research department at the Helmholtz Center for Environmental Research (UFZ) in Magdeburg. He emphasizes to watson how stressed water bodies are when it's hot: 'The higher the temperature, the less oxygen can dissolve in the water. At the same time, the Degradation processes are getting faster because bacterial activity is increasing.'

'And that's why global warming alone - even without the additional poisoning of the water body - leads to a deterioration in the ecosystem.' Karsten Rinke, Head of the Lake Research Department at the UFZ

In addition, the bacteria become more active at higher water temperatures. Rinke says: 'And that's why global warming alone - even without the additional poisoning of the water body - leads to a deterioration in the ecosystem.'

Climate crisis throws ecosystems off balance

Massive fish die-offs are already occurring due to overheating in numerous bodies of water. The reason: the water temperature is too high, the oxygen levels drop and the fish suffocate. Ammonia, a breakdown product of bacterial activity, can also form, as Rinke explains. This is a potent poison - which can also induce fish kills.

To Watson he adds:

'Due to the climate crisis, we can definitely prepare for the fact that there will be mass fish kills more often, as we were already able to observe in the years from 2018 to 2020. This will increase in the future, because heat waves will become more frequent and the Bodies of water are simply much more vulnerable at these high temperatures.'

Christian Wolter from the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) in Berlin confirms that our ecosystems are becoming more vulnerable as a result of the consequences of the climate crisis. To Watson he says: 'It is therefore important to finally start adapting to the consequences of climate change instead of hoping that climate change can be stopped.'

He insists on the urgently needed move away from technical flood protection towards natural flood protection through functioning floodplains. These would not only protect against flooding, but would also give fish the opportunity to leave the main stream during toxic waves such as are currently in the Oder.

'Here too, water retention in the landscape and shading help to reduce evaporation losses.' Christian Wolter, fish ecologist at the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB)

Another problem: Small bodies of water in particular, but also large rivers such as the Rhine, are in danger of drying out. 'Here, too, water retention in the landscape and shading help to reduce evaporation losses,' says fish ecologist Wolter. A widening of the water bodies, as is currently being carried out on the Oder-Havel Canal, is counterproductive - it only promotes evaporation.

Climate change promotes low water levels in rivers

René Orth from the Max Planck Institute for Biogeochemistry in Jena has also observed that the water level in many rivers and lakes drops in summer.

There are four reasons for this:

  1. 'The first and most obvious cause, which is also always discussed, is the lack of precipitation,' the expert tells watson. This summer in particular, there is 'a fairly large precipitation deficit, so much less precipitation than in other summers'.
  2. More water evaporates: 'When it's warm, the air can absorb more water – so more water evaporates from both the soil and the rivers,' says Orth.
  3. Declining glaciers: Many larger rivers, such as the Rhine, are fed in part by glacial melt. 'But if the glaciers get smaller and smaller, less ice can melt and help keep the river level up,' explains Orth.
  4. Snowmelt: Both snowmelt and glacial melt help bring additional water into the rivers, 'even in the summer,' Orth points out.
  The Rhine level falls to a new low. The Rhine level falls to a new low. Bild: imago images / panama pictures

What causes contribute to a low water level?

However, the extent to which a falling water level is linked to the climate crisis cannot be answered very clearly – one has to look at each of the four causes separately.

Although it has rained less than usual this summer, according to Orth, no long-term trends can be observed in terms of precipitation decreasing.

'One can say that climate change will ensure that there will be more low water levels in summer.' René Orth vom Max-Planck-Institut

'It's different with evaporation, which is closely related to temperature,' says Orth. 'Temperatures have risen significantly in recent years, so you can clearly see that climate change is playing a role.' It's the same with glaciers.

Orth adds to watson:

'If you look at how the glaciers have developed over the past 30 years, you can see that they have been constantly shrinking, which of course has to do with rising temperatures - and thus also with climate change.'

When it comes to snowmelt, Orth estimates the role of the climate crisis to be less. According to him, more rain falls rather than less, which falls as snow at higher elevations. 'Of course, if it gets too warm, it won't snow anymore, but rain,' he puts it into perspective. However, this is not to be expected in the coming years.

'The low water levels mean that any pollutants that get into the rivers are less likely to dilute and cause more damage.' René Orth vom Max-Planck-Institut

And yet - the consequences of the climate crisis on the stability of the river ecosystem cannot be overlooked: 'One can certainly say that climate change will ensure that there will be more low water levels in summer, but not necessarily to the same extent and consistency , as is the case this year,' says Orth.

However: 'The low water levels mean that any pollutants that get into the rivers are less able to dilute and thus cause greater damage.'

The negative cycle closes.

Source: watson.de