In 2014, a heat wave in Germany led to the almost complete extinction of fish in the Elbe, one of Germany’s largest rivers. According to the daily “Tageszeitung”, there were about 100 tons of dead fish in the river below the port of Hamburg.
At that time, there was no doubt that the heat and low rainfall caused the death of thousands of fish.
“For several days, the oxygen content in the water was only about 1.5 mg per liter, and the minimum necessary for a fish to survive is twice that. The normal value is 6 to 8 mg per liter. One of the factors that caused the lack of oxygen to increase algal blooms in the water” – Books portal taz.de. The process of deepening the Elbe River was mentioned as a second reason.
At that time, the Germans were highly dependent on the change of weather. It was also noted that “periods of hypoxia in the Elbe are increasing”, which is especially evident in the summer.
A significant decrease in the oxygen content in the water causes the so-called dormancy, the result of which is the mass extinction of organisms living in a particular water body.
Hot and dry summers, and therefore – low water levels – favor the bruzocchi phenomenon. Decomposition of organic residues at the bottom or a strong algal bloom may then occur, which leads to darkening and inhibits photosynthesis. Large amounts of oxygen in the water are used to decompose dead algae, so its content gradually decreases.
This year, according to data available on the web, Precipitation in July 2022 in Germany was exceptionally low, less than half the long-term average. A few days ago, the media reported that the water level in European rivers would drop in the record-hot summer of 2022.
“Warmer water can also kill fish. Hundreds of fish died in Austria last month due to heat draining Lake Zixi; the same is happening in Spain, France and Germany.”
– Politico wrote on Friday.
At the beginning of July 2022, German media also reported several fish deaths in the Lower Elbe. The Czechs also face a similar problem. In the second half of July, about 40 tons of dead fish were caught from the Dija River in the south of the country, the cause of their death being a lack of oxygen caused by an overgrowth of cyanobacteria.
Could this also be the cause of the mass extinction of fish in the Odra River, which we have been observing for some time? Initial studies ruled out mercury or heavy metals as the cause of fish death, and mercury itself and other toxic substances were not detected in river water samples.
– Today we took a decision to send some samples to other foreign laboratories for testing. (…]In the coming hours, all samples will be tested in order to look for 300 possible substances. Pesticides are now being tested
Minister Anna Moscow announced today.
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