This year there was an extreme plague of algae on the southern Easter lakes.
This had an impact on many other lake residents.
Iffeldorf -
The washing lake below the Landgasthof Osterseen as well as the Schiffhüttensee and the Sengsee were particularly affected by the extreme algae development, as Uta Raeder from the Limnological Station of the Technical University of Munich explained when asked.
Her institute based in Iffeldorf has been researching the lakes on site since 1986.
Algae plague at the Easter lakes: expert explains enormous growth
The fact that thick green lumps of algae - so-called “algae floods” - float on the surface of the lake, “has happened again and again,” explains Raeder.
In 2020 alone, student assistants fished around six tons of algae biomass from the water surfaces of the affected lakes with the help of special rakes between May and October.
How many tons there were this year, she couldn't say exactly.
In your estimation, however, it was significantly more than in 2020.
The reason for the strong algae growth at the three Easter lakes is that all three are fed by groundwater.
“And that brings plant fertilizers into the lake,” says Raeder.
Above all, additional phosphorus gets into the water - and this stimulates the growth of algae.
Osterseen: flora and fauna in the lake acutely endangered
The algae mud flats that formed grew exponentially on the surface of the lake and consisted of various algae such as blue or diatoms, but also of aquatic mosses and aquatic plants.
“It's not just an ugly sight and an unpleasant smell,” emphasizes Raeder.
The algae mud flats are also harmful to the flora and fauna in the lake.
For example because they cover other aquatic plants such as the pine frond with filamentous spun algae.
This aquatic plant actually provides shelter and breeding space for numerous aquatic animals such as fish and insect larvae - an important function that, however, severely restricts the filamentous algae spider.
In addition, the fir frond has been listed on the red list since 2018.
If the algae floss towards the ground over time, they are broken down by bacteria.
This consumes oxygen, which is bad for the fish, said Raeder.
In addition, the process would release nutrients that would further stimulate the growth of algae in the next year in addition to the entry via the groundwater.
Therefore, the algae floss had to be removed every year.
If this was not done, “the lakes would gradually become richer in algae.
The living space would be impaired ”.
Algae plague at Easter lakes: students and fire brigade fish green stuff out of the water
This year, according to Raeder, student assistants had almost every week cleared the floating greenery from the surface of the water. The Iffeldorf fire brigade has also helped several times, says Raeder, pleased about the good cooperation between the armed forces and their institute. The measure is being financed by the Weilheim-Schongau Landscape Management Association. Raeder can only guess why the algae plague was particularly strong this year: Maybe it's because it's getting warmer.
This could have increased the degradation processes in the soil.
But because the substances that stimulate the growth of algae get into the soil through agriculture, it appeals to farmers to only fertilize as much as the plants absorb.
The algae are to be fished from the lakes again next year.
Raeder has already submitted an application to the Landscape Management Association.
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