In many lakes in Europe, the reeds have been declining for decades – including in Berlin. Researchers have now found out why. According to this, the reeds of the Berlin lakes are not only dying due to shipping, bank construction and animal damage, but also due to the increasing sulphate concentration as a result of mining in Lusatia. According to the researchers, if the sulfate concentration had not increased, there would be around 20 percent more reeds on Berlin’s lakes today. They strongly recommend various protective measures.
Reeds play an important role in the lake ecosystem. Among other things, it offers breeding grounds and shelter for waterfowl, fish and insects. But it also cushions the waves and strengthens the shore, preventing severe erosion. At the same time, reed plants filter excess nutrients from the water and thus clean the lake. But since the 1950s, the reeds have been dying in many European lakes.
Wave action, feeding damage and sulphate damage reeds
Lydia Roesel from the Humboldt University in Berlin and Dominik Zak from the Leibniz Institute for Freshwater Ecology and Inland Fisheries have now researched what is causing the reeds to decline in Berlin’s lakes. To do this, they examined 14 lakes in the Berlin catchment area and evaluated various factors that could have influenced the amount of reed between the years 2000 and 2020. These included the nature and use of the riparian zone as well as the concentration of various nutrients, including phosphorus, nitrate and sulfate.
The result: The strongest mechanical stress caused by the waves from shipping, bank construction, feeding damage by water rats and coypu and too little sunlight from shady trees near the shore caused the reed population to decline, as Roesel and Zak report. But the sulphate concentrations, which have been increasing for ten years, have also had an unexpectedly clear effect on the reeds. “If the sulphate concentrations hadn’t increased, there would be around 20 percent more reeds on the lakes today,” explains Zak.
Mysterious sulphate effect
Most of the sulphate measured in the lake water comes from the Lusatian lignite mining area in the upper Spree catchment area. It is formed from iron sulfides released from deeper layers of the ground during mining. But the researchers were surprised that the sulfate had such devastating effects on Berlin’s waters. Because normally, sulfate does not harm reed plants, even in very high concentrations, as they explain. Even if it develops into toxic sulfide under oxygen-free conditions in the bottom of the water, this is usually bound by iron particles in the water, which subsequently render it harmless.
“It would now have to be investigated why this detoxification process is disturbed in some of the sulphate-loaded lakes such as the Müggelsee,” says Zak. Also in order to continue to ensure the supply of clean drinking water from those same lakes. Roesel and Zak recommend various measures that could prove useful against reed dieback. In addition to reducing the sulfate input, this also includes the use of so-called fascines. They consist of bundles of brushwood and rods several meters long, anchored in the water, which protect the reeds from the waves of shipping and are intended to reduce erosion on the shore. In addition, further research should help to find out the exact causes of the reed dieback and ultimately to combat it in a targeted manner.
Source: Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB); Specialist article: Water Research, doi: 10.1016/j.watres.2023.119785