Water Quality and Biodiversity in Europe's Rivers: A Tale of Progress and Challenges

In a recent European study published in the prestigious journal Nature Ecology and Evolution, LIST and its partners presented a nuanced perspective on the state of European rivers. While the findings reveal improvements in ecological quality  in recent decades, they also underscore the persistent challenges in achieving good ecological status and understanding multifaceted biodiversity responses.

Habitat degradation, water pollution, flow alterations  and invasive alien species are just a few examples of anthropogenic pressures impacting freshwater ecosystems. Although the EU Water Framework Directive came into force at the beginning of the 2000s with the aim of better protecting rivers from these pressures, there has been a lack of reliable data to monitor changes in the ecological quality of European rivers over time. This study, published at the end of January, is the first of its kind and highlights the sobering reality that the improvements observed have not consistently translated into the obtention of the required "good" ecological status.

Water Quality of European Rivers: Redoubling Efforts

After examining data on macroinvertebrate communities from no fewer than 1,365 sites across 23 European countries, the international team was indeed  able to highlight positive trends from the 1990s to the 2010s, after which the ecological quality of rivers plateaued. "While there are signs of progress, including reductions in pollution and habitat restoration efforts, 60 to 80% of European rivers still fall short of meeting the stringent criteria for good ecological conditions", declared Alain Dohet, researcher at LIST and part of the scientific consortium. The directives put in place are working, but have not achieved good status everywhere. Furthermore, other problems are emerging, such as climate change or pesticides and pollutants that need regulation.

In Luxembourg, the situation of rivers is no exception to the observed trend; although there is a global improvement, a high proportion of water bodies have still not achieved good ecological status. Since the 2000s, LIST has been developing monitoring programmes that encompass an extensive network of sites, thus providing a robust assessment of river quality and its temporal evolution.

Biodiversity Responses to Water Quality Changes: A complex reality

However, the research does not limit itself to assessing water quality; it also provides valuable insights into biodiversity responses to water quality changes over time. Indeed, many studies show mixed responses and major contradictions; for example, decreased water quality may coincide with increased biodiversity over time. This highlights the frequent mismatch between the metrics used to assess water quality and those used to assess a river's biodiversity.

By examining several biodiversity metrics, such as species abundance and diversity, the researchers observed that these variations mainly depend on the spatial scale considered. "On a local level, we may well see a decrease in species linked to the impact of a particular pesticide, for example. On the other hand, on a more regional scale, we may also see an increase in other, more tolerant species," explained Lionel L'Hoste, researcher at LIST and part of the study.

As the LIST team outlines, these findings underscore the importance of sufficient baseline data and careful metric selection for evaluating and capturing the full range of biodiversity responses to a water quality change. "Just because the quality of rivers has improved in recent decades, it doesn't mean that biodiversity improved as well everywhere ,"  clarified Sarah Vray, a LIST researcher who also worked on the study.

While political and scientific debates regularly focus on the use of a single apex target to measure overall progress towards the achievement of global biodiversity conservation goals, the researchers' findings highlight that one can hardly capture all the complexity of life and its benefits to the human population in one single indicator.

More information:

Sinclair, J.S., Welti, E.A.R., Altermatt, F. et al. Multi-decadal improvements in the ecological quality of European rivers are not consistently reflected in biodiversity metrics. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-023-02305-4

Haase, P., Bowler, D.E., Baker, N.J. et al. The recovery of European freshwater biodiversity has come to a halt. Nature 620, 582–588 (2023). https://doi.org/10.1038/s41586-023-06400-1

Photo: (C) LIST - Ningserbaach, a tributary of the Sûre near Lutzhausen