Europe’s rivers and streams: Positive biodiversity trend in European rivers and streams has come to an end

The publication in the renowned journal shows that biodiversity in most streams and rivers in Europe is still far from expected reference condition, a measure of near pristine condition. NIVA researchers Jes Rasmussen and Tor Erik Eriksen emphasize the urgency of strengthening efforts to preserve biodiversity in Europe's streams and rivers.

"We need more comprehensive and effective measures. These measures should target the most important remaining stressors, such as poor habitat quality, barriers that prevent species from migrating, and connecting streams and rivers to their floodplains," says Jes Rasmussen.

According to the NIVA researcher, streams and rivers are among the most threatened ecosystem types on Earth. In addition to the above, pollution from agriculture and urban runoff, alien species and climate change are also identified as threats to biodiversity.

Ecological recovery takes time

Huge inputs of untreated wastewater have been discharged into Europe's rivers and streams over the past century. This has led to what is known as microbial respiration and harmful low oxygen levels, which in turn has led to the loss of most invertebrate species and fish with low tolerance to low oxygen conditions.

However, the introduction of wastewater treatment plants in the 1980s and 1990s significantly reduced pollution levels. The ecological quality improved for many years. But now, according to the NIVA researchers, it is likely that the positive trend is coming to a halt, because the ecosystems are also affected by so many other factors.

“When traditionally dominant pressures, such as sewage, eutrophication and acidification, are improved, other stressors may become more visible," says Tor Erik Eriksen.

"The positive development in biodiversity several decades after these treatment plants were introduced, illustrates the importance of measures; but also that ecological recovery takes a long time," concludes the NIVA researcher.