Biodiversity recovery in European rivers has stagnated since 2010
Biodiversity in European rivers increased between 1968 and 2010 due to improved water quality following decades of environmental pollution, according to a new study. However, this trend of biodiversity recovery has stalled since 2010.
Writing in the journal Nature, an international team of researchers attribute this finding to the limited potential of existing measures to continue to drive water quality improvements. This is due to the growing impacts of complex stressors such as climate change, which need to be urgently tackled with ambitious new environmental restoration and policy strategies, the authors argue.
“Our data show that rivers can indeed recover if we as a society take the right measures,” said co-author Professor Sonja Jähnig from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB). “However, we have hardly made any progress in the state of biodiversity since 2010, so additional efforts are needed today.”
The researchers examined invertebrate records to trace the history of freshwater biodiversity in European rivers. Invertebrates such as mayflies, stoneflies and caddisflies are crucial to healthy freshwater ecosystems, and have been extensively studied in water quality monitoring programmes. The research team analysed 1,816 studies of invertebrate communities collected across 22 European countries between 1968 and 2020.
“Invertebrates such as mayflies or caddisflies have long been a pillar for monitoring water quality, so we were able to draw on a very good database,” said lead author Professor Peter Haase from the Senckenberg Research Institute and Natural History Museum in Frankfurt. “These data also show that a stagnation set in after 2010, which indicates that the measures taken so far have been exhausted.”
Rivers across Europe were extensively polluted through industrial, agricultural and urban expansion through the 20th century. In response, governments began to take action to tackle the poor water quality of many rivers by adopting measures to reduce pollution and acidification from the 1970s onwards. These measures – including better wastewater treatment – drove slow but steady improvements in water quality across the continent, which were further supported by legislation such as the EU Urban Waste Water Treatment Directive (1991) and Water Framework Directive (2000).
The new study suggests that biodiversity recovery in European rivers as a result of better water quality has plateaued in the last decade, and ambitious new measures are needed to continue ecological restoration in the face of complex and ever-changing environmental threats.
“The improvement of freshwater biodiversity in Europe is a great achievement, but we cannot afford to be complacent,” said co-author Professor Iwan Jones, Head of the River Communities Group at the School of Biological and Chemical Sciences at Queen Mary University of London. “Our research shows that we need to redouble our efforts to protect these vital ecosystems. We need to act now to further reduce pollution, prevent invasive species from spreading, and help our river systems to cope with climate change.”
Rivers in heavily urban or agricultural catchments – and those downstream of dams – showed the lowest improvements in biodiversity in the study period. Further, rivers already significantly affected by climate change had lower rates of biodiversity improvements – a trend that is likely to accelerate as temperatures increase and climate extremes become more common in the future.
“The fact that biodiversity recovers less in some rivers is due to the fact that downstream of urban areas, micropollutants and nutrients enter the watercourses, and cities are also often gateways for alien invasive species,” said co-author Dr Sami Domisch from IGB. “On the other hand, fine sediments, pesticides and fertilisers are more likely to be washed into the watercourses from farmland. And dams fragment water bodies and change the flow and temperature regimes.”
The study is published at a time of intense political negotiation over the future of Europe’s biodiversity. The European Union is currently preparing to launch its new Biodiversity Strategy for 2030, aiming to halt the loss of biodiversity and restore degraded ecosystems. And following months of debate, the EU Nature Restoration Law is nearing official finalisation.
Crucially, the study suggests that existing environmental legislation has not responded to emerging threats such as climate change, which has caused freshwater biodiversity recovery to stagnate. As a result, there is the pressing need to tailor ambitious new policies to the realities of the contemporary environment, and couple them with extensive restoration projects to help continue the recovery of Europe’s rivers in the future.
“It is no longer enough to improve water quality; we need to restore ecosystems on a large scale and fundamentally improve the connectivity of European watercourses,” said Prof Jähnig. “This would not only boost aquatic biodiversity, but would also support natural flood protection, water retention in the landscape and the self-purification capacity of water bodies.”
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This article is supported by the MERLIN project.
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