Alarm around recreation area – Lobau is running out of water – Science

Ecologist Thomas Hein warns that the Au has been losing bodies of water for decades, and people are watching it die. There are solutions, why is nothing happening?

“The Lobau is running out of water,” warns ecologist Thomas Hein in an interview with the Austria Press Agency (APA). “It’s been losing bodies of water for decades, and we’re watching it dry out and die as a floodplain.” The floodplain area could be saved with the supply of very small amounts of water, for example from the Danube. However, this step is omitted due to the potential risk of contamination of drinking water. The symposium “Lobau shall live” will take place in Vienna on Wednesday and Thursday.

50 percent fewer bodies of water since the 1930s

According to image comparisons and other studies, the surface area of ​​the Lobau has been halved since the 1930s, explained Thomas Hein, who works at the Institute for Hydrobiology and Water Management (IHG) at the University of Natural Resources and Life Sciences (Boku) in Vienna. Above all, the smaller, heavily structured side arms silt up and are no longer available as a habitat for aquatic organisms.

“The process does not run evenly, but rather increases in speed,” he said: Because the shallower a body of water becomes, the more vegetation grows in and the faster plant biomass and sediments are deposited there, which accelerate silting up. Climate change is also contributing its mite: longer dry phases in the vegetation period bring pronounced low water phases to the Danube and as a result the water level in the floodplain falls.

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Water supply would help

“So the finding is very clear: the Lobau is running out of water,” explained Hein. He and his team used models to investigate what a water supply could bring – with very clear results: Even small amounts would help, and the more water the floodplain gets, the more its health will improve.

It could, for example, be infused from the New Danube by means of “water donations”. “Because this water has very little turbidity and particle load, a lot could be achieved with small amounts,” says the researcher: “You could, for example, connect bodies of water and small floodplain ponds, which are very important for amphibians, for example, would form.” . At least the status quo would be preserved and local improvements would be possible.

Another option would be to allow water to flow directly from the Danube into the Lobau. But then it should be larger amounts that can also flow out again, because otherwise it brings too many particles and nutrients into the floodplain. As with other water systems along the Danube downstream from Vienna, such as the Spittelauer arm, the old arm system Haslau- Regelsbrunn and near Orth, it would even be possible to create an intact water system in the Lobau in this way, says Hein. The Au would then be revived.

Shipping would not lack the water. “As with other water body restorations, for example at low water – when the Danube flows at around 900 cubic meters per second – no more than five cubic meters per second would have to be branched off,” explained Hein: “That is manageable for shipping”. It would also return to the Danube below the Lobau.

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Solutions on the table – why is nothing happening?

The research projects have now been completed for a few years and were carried out in cooperation with the municipality of Vienna, reports Hein. But no action was taken. “It’s frustrating,” he said. He explains why nothing happened, although various possible solutions are on the table, by saying that “there are still problems in other sectors that have not yet been completely solved”.

It has not been clearly clarified whether the water donations into the floodplain would actually have an impact on the groundwater used as drinking water. “But that could be found out in an experiment by feeding water into the floodplain in a targeted manner and with accompanying safety measures and seeing whether this feared risk to the groundwater can be observed”. In this case, protective measures could be taken.

High investments for the Lobau Tunnel, but not for the Au

“The other risk, namely the drying out and thus dying of the floodplain aspect of this area, is a reality, and we look on and do nothing,” says the water ecologist. In the case of the controversial Lobau tunnel, the protection of the floodplain is mentioned by the municipality of Vienna as an advantage in addition to the protection of the population from traffic. “If you want to protect the Lobau with such very high investments, it makes no sense to me if you simultaneously neglect it and let it dry up as an Au area,” explained Hein.

In terms of water ecology, visitor use is not a major problem for the Lobau. “I see the recreational function very positively,” he said: “More than a million people visit the Lobau every year and it is important that the former imperial hunting grounds are kept available for local recreation for the population.”

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