Recovery of Biodiversity of European Freshwater Comes to a Halt

Smithsonian’s National Zoo and Conservation Biology Institute scientist Ellen Welti, Ph.D., and her colleagues from the Senckenberg Research Institute and Natural History Museum Frankfurt, Germany, examined biodiversity data from river systems spanning 22 European countries over 52 years. The findings of this study were published Aug. 9, 2023, in the journal Nature. Ellen shared some of the key findings from the study, and explained why there’s reason to be hopeful, despite the underlying concerns.

In this publication, you and your colleagues identify a number of causes for the loss of biodiversity in these European waterways, including agriculture, industry and infrastructure. What impact does the lack of biodiversity have on the health of these ecosystems and for the people around them? 

The invertebrates that live in these waterways perform key ecosystem services that we depend on. Some examples include filtering the water we all need to survive or decomposing dead plants and animals in the water. They also eat pests, such as mosquitos. They may be small, but they do a lot for us.

Your research spanned more than 20 countries and over 50 years of data. How large was your data pool?

We included more than 1,800 stream or river sites in this paper, and each site’s data set included at least eight years of aquatic macroinvertebrate sampling. One of our criteria for including a site in our study was that the data had to include all the macroinvertebrates the researchers caught—it couldn’t just be data on mayflies or stoneflies for example.

There were more than 2,500 taxa of macroinvertebrates included in this study. Macroinvertebrates are animals without a spine large enough to be seen without using a microscope. It’s quite a broad swath, including things like dragonflies, caddisflies, crayfish and snails.  

With a data set so large, you could have seen varying results. What did your team find?

If you average across all the sites and time periods that we covered, you see a positive trend—an increase in abundance and richness of taxa over time. Which is good!  

But if you zoom in to how that trend is changing over the trajectory of the time periods we're covering, another picture emerges. Those increases are happening earlier on, they're happening in the 90s and the early 2000s. This lines up with legislation passed from the 1970s to about 2000 to clean up European waterways.  

Right around 2010, we start to see a deceleration of that trend. Many of the sites today have trends that have flatlined; not necessarily declining, but they're not increasing either.  

Lots of other data on freshwater systems in Europe show those waterways are still in a fairly degraded state. This led us to believe the biodiversity recovery process has come to a halt.