Freshwater ecosystems are among the most vulnerable to biodiversity loss due to human pressures exerted on them throughout history. The measures that have been taken to improve this situation –installation of sewage treatment plants, removal of obstacles, etc.– have improved environmental quality and boosted the recovery of freshwater biodiversity.

Ecologists from 22 European countries collaborating in various initiatives, including the UPV/EHU’s Group of Stream Ecology, sought to investigate, over time, the trend relating to the diversity and organisation of invertebrates in rivers and how they have responded to environmental pressures and changes. To do this, they used 1,816 time-series data on invertebrates subjected to sampling in the river systems of these countries between 1968 and 2020. “Samples were taken from 1,816 points across Europe over many years, and from them we deduced the evolution of these rivers and streams during 40 years” said Aitor Larrañaga, a UPV/EHU researcher and lecturer.

The study concludes that, “in general, the biodiversity of rivers and streams improved up until the 2000s with increases in both species and populations. And that is a good sign. But since then the improvement in biodiversity has stagnated: we no longer see the increases that used to take place,” he said. “This improvement observed in the 1990s and 2000s reveals the effectiveness of measures implemented to improve water quality, as well as work for recovery purposes, but the fact that in the 2010s this improvement trend slowed down suggests that the effectiveness of the measures currently in place diminished,” Larrañaga pointed out.

Importance of monitoring river ecosystems

The researcher pointed out that signs of complacency must be put to one side. “To some extent, it is clear that highly polluted areas have improved and that as the number of highly polluted streams is reduced, it is more difficult to substantially improve their ecological status, as even the most simple solutions in highly polluted areas generate significant improvements. However, black holes remain on Europe's water quality map. There are places that are quite polluted, not everything has been done.”

Researchers stress that there are new and enduring pressures damaging freshwater ecosystems, such as new pollutants, climate change and invasive species, which require a redoubling of efforts to go on restoring the biodiversity of these ecosystems. “New pollutants are continually being produced. It is very difficult to deduce causality, i.e. what might account for the stagnation over the last decade. But it is likely to be a consequence of the emergence of new pollutants. The study of the impact of each of these new pollutants must be approached with caution, a subject on which numerous studies have emerged in recent years. In any case, this is a particularly significant issue from the point of view of the status of ecosystems, as new pollutants appear at a very fast rate and the interactions between them can be very complex. We are calling for more research and, at the same time, caution,” said Dr Larrañaga.

Larrañaga attaches great importance to the work to monitor rivers in the Basque Autonomous Community. “Thanks to the huge amount of sampling work carried out in the Basque Autonomous Community, a large amount of information of great interest is obtained, which is unparalleled in many places, even worldwide. Based on the information provided by the data gathered over decades, we can reliably inform about what is happening and thus make decisions to manage our waters.”

Additional information

Aitor Larrañaga-Arrizabalaga is a lecturer in the Department of Plant Biology and Ecology at the UPV/EHU and lectures on the Bachelor's Degree course in Biology and the Master's Degree course in Biodiversity, Functioning and Management of Ecosystems.