Biodiversity in European rivers has recovered in many places over the decades thanks to decisive protective measures – but this upswing has long since stagnated. The original richness in species is far from being reached again, report scientists from Frankfurt and Berlin, among others, in the science journal Nature. They followed the development using the example of invertebrates in freshwater.
“Our data show that rivers can certainly recover if we as a society implement the right measures,” explained co-author Sonja Jähnig from the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) in Berlin. “However, since 2010 we have made little progress on the state of biodiversity, so additional efforts are needed today.”
“The biological quality of the rivers is still inadequate in many places.”
For the study, 1816 time series collected between 1968 and 2020 for rivers in 22 European countries were analyzed. The observations concerned 2648 species. The evaluations show that species diversity has increased significantly again for more than 50 years. “However, these increases mainly occurred before 2010 and have unfortunately leveled off at a more or less constant level since then,” Peter Haase of the Senckenberg Research Institute and Natural History Museum in Frankfurt, who was involved in the study.
The increase in biodiversity in the 1990s and 2000s is likely due to “the effectiveness of water quality improvements and restoration projects,” Haase said. The subsequent stagnation “indicates that previous measures have been exhausted”.
Inland waters are exposed to pollution from agriculture and cities, for example from pollutants, sewage or pesticides. Countermeasures were taken in response to the poor state of water bodies in the 1950s and 1960s, such as the EU Water Framework Directive.
“These measures led to a significant decrease in organic pollution and acidification from about 1980,” explains Ellen Welti, a scientist at the Smithsonian’s Conservation Ecology Center in the US. But now 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, the authors write. For example, sewage treatment plants must be improved and fertilizers and pesticides from agricultural land must be prevented from being washed into the rivers during floods.
According to the researchers, invertebrates such as the larvae of stoneflies and caddis flies contribute to important ecosystem processes in freshwater. They break down organic matter, filter water and transport nutrients. Such so-called invertebrates (animals without a spine) have long been “a cornerstone for monitoring water quality”.