What we found
Europe’s rivers have at least 1.2 million instream barriers. The results published today in Nature show that Europe has probably some of the most fragmented rivers in the world. The study detected thousands of large dams, but also a myriad of low-head structures such as weirs, culverts, fords, sluices and ramps which had been overlooked and are the main culprits of fragmentation.
Why it is important
Rivers are important ecosystems that also provide socio-economic services for society. However, human activities have altered their flow with artificial barriers such as dams, weirs, and fords. Some barriers are needed to provide drinking water, irrigation, energy production, flood protection and to cross rivers.
But fragmentation can affect the ecosystems of the rivers - barriers block rivers, fragment waterways, isolate habitats and weaken wildlife populations.
To assess the effects of these barriers and manage their impacts has been impeded by a lack of information.
How we did it
We collated regional, national and global datasets to assess the number of individual barriers on rivers.
We also walked 2,700 km of rivers to record barrier numbers and characteristics, revealing that the original datasets tended to undercount small barriers.
Using field-corrected and upscaled estimates, we found that that the number of barriers in European rivers has been underestimated by 61 per cent. Of the1.2 million in-stream barriers across 36 European countries 68 per cent were small structures (under two metres in height), which are often overlooked by traditional surveys. The highest barrier density is in Central Europe, while the lowest barrier densities are in Scandinavia, Iceland and Scotland.
What it means
No river catchment in Europe is free of artificial barriers, but these findings can help re-connect rivers in Europe. Many barriers are obsolete and removing them provides unprecedented opportunities for restoration. These results feed directly into the new EU Biodiversity Strategy and will help to reconnect at least 25,000 km of Europe’s rivers by 2030
FishBites is a science communication series by the FishBEE research group.
The FishBEE team integrates the Centre for Sustainable Aquatic Research (CSAR), based at Swansea University, UK.
This post is based on the research paper authored by Dr Barbara Belletti and co-authors, entitled More than one million barriers fragment Europe’s rivers.
Belletti, B., Garcia de Leaniz, C., Jones, J. et al. More than one million barriers fragment Europe’s rivers. Nature 588, 436–441 (2020). https://doi.org/10.1038/s41586-020-3005-2