Measures exhausted: biodiversity in European rivers has stagnated since 2010

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River in Triglav National Park in Slovenia (symbolic image)

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Biodiversity in European rivers has recovered over a long period of time thanks to decisive measures in many places, but this upswing has long since stagnated. However, the original species richness is far from being restored, scientists report in the journal "Nature". They have followed the development using the example of invertebrates in freshwater.

"Our data show that rivers can recover if we as a society implement the right measures," explained co-author Sonja Jähnig from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin. "However, since 2010 we have made little progress in the state of biodiversity, so additional efforts are needed today."

For the study, 1816 time series collected between 1968 and 2020 for rivers in 22 European countries were analyzed, and the researchers observed 2648 species. The evaluations show that biodiversity has increased significantly for more than 50 years. "However, these increases occurred mainly before 2010 and have unfortunately leveled off at a more or less constant level since then," said first author Peter Haase from the Senckenberg Research Institute and Natural History Museum Frankfurt.

»Exhaustion of previous measures«

The increase in biodiversity in the 1990s and 2000s was probably due to "the effectiveness of water quality improvements and restoration projects," Haase said. The subsequent stagnation "indicates an exhaustion of the measures taken so far".

Pollutants, for example in wastewater from cities or fertilizers and pesticides from agriculture, pollute inland waters. In response to the poor state of affairs in the 1950s and 1960s, countermeasures were taken, for example with the EU Water Framework Directive. "These measures led to a significant decline in organic pollution and acidification from about 1980 onwards," said Ellen Welti of the Smithsonian's Conservation Ecology Center in the USA. Now, however, the "stress factors" are increasing again. The biological quality of the rivers is still inadequate in many places."

In order for the positive development to continue, "considerable investments" are required, according to the team of authors. For example, sewage treatment plants must be improved and fertilisers and pesticides from agricultural land must be prevented from being washed into rivers during floods.

Tiny animals are also important for ecosystems. For example, invertebrates such as the larvae of stoneflies and caddisflies contribute to important ecosystem processes in freshwaters, according to the researchers. They decompose organic matter, filter water and transport nutrients. Such so-called invertebrates (animals without spines) have long been "a cornerstone for monitoring water quality".

ani/dpa