Europe’s rivers are heavily obstructed. The Adaptive Management of Barriers in European Rivers (AMBER) project, funded by the EU’s Horizon 2020 scheme, has identified at least 1.2 million instream barriers that are currently obstructing the natural flow of the continent’s rivers.
The team, spearheaded by researchers at Swansea University, assembled river-management databases from 36 European countries into the AMBER Barrier Atlas. Their analysis of the data suggests that European countries have underestimated the true number of barriers along European rivers by 61 per cent.
In the UK, AMBER found that 99 per cent of rivers are fragmented by artificial barriers such as dams, weirs and culverts, with one such barrier punctuating every 1.5-kilometre stretch of river on average. This isn’t always a bad thing. Barriers are often needed to halt or divert the flow of rivers and they can help to produce drinking water, enable irrigation, produce energy and protect land from flooding. However, they often come with negative consequences for wildlife and for the natural flow of nutrients and sediments. It’s already clear that the ecological status of freshwater bodies in the UK needs addressing – more than half have failed to achieve ‘good’ ecological status under the Water Framework Directive.
‘Fragmentation is one of the biggest threats to the conservation of water biodiversity in Europe,’ says Carlos Garcia de Leaniz, principal investigator at AMBER. In 2020, the Living Planet Index – a measure of the state of global biological diversity developed by the Zoological Society of London and WWF –
delivered a damning report on the conservation status of migratory fish. Globally, numbers decreased by more than three quarters between 1970 and 2016 – a three per cent annual decline. During the same period, Europe experienced declines of 93 per cent.
Atlantic salmon, in particular, have grabbed headlines. ‘People understand that salmon need to move upstream to spawn and then come back downstream to grow as juveniles. But the fragmentation issue isn’t limited to salmon,’ says Peter Jones, a postdoctoral researcher at Swansea University. European eels, lamprey and sea trout are also in decline. ‘There’s a perception that non-migratory fish are static, but they need to move up- and downstream to complete their life cycles.’ Fish are also important ecosystem engineers. Many species swallow the seeds of aquatic plants and move them downstream – similar to the seed dispersal function performed by terrestrial herbivores.
Promisingly, the European Commission recently announced a target of freeing 25,000 kilometres of rivers across the continent. ‘We all think this is fantastic news,’ says Garcia de Leaniz. AMBER has received funding to help meet those targets. ‘What we are advocating is a two-pronged approach. To enhance connectivity, we need to halt further fragmentation, and we need to remove or mitigate obsolete barriers.’ To do so, AMBER is adding national-level data to the AMBER Barrier Atlas, which will then be continually supplemented with data provided by the public. Walkers across Europe can download AMBER’s Barrier Tracker app to submit information on barriers encountered along rivers and waterways. It’s hoped that this information will help water managers to identify and remove obsolete barriers while optimising those that need to remain.