Long-term study in Hesse: Drastic decline in water insects
The brook, called Breitenbach, in the East Hessian Highlands is one of the best-studied waters in the world: Since 1969, researchers of the Max Planck Society have been analyzing the insect world of the brook, which is located in a nature reserve and thus far away from direct human influence. For decades, Dr. Rüdiger Wagner carried out these investigations in a leading position, from 2006 to 2010 as Professor of Limnology at Kassel University. In 2010 a flood destroyed the last measuring point at the Breitenbach.
About a decade later, scientists from the LMU Munich and the Senckenberg Society for Nature Research have now analysed the data using new methods and approaches. Previously unpublished information was included in the new analyses. They found drastic changes: According to reports in the journal Conservation Biology, the number of individuals fell by more than 80 percent during the period under study. The researchers attribute this decline to global climate change.
From January 1969 to December 2010, insects were regularly collected in the Breitenbach and environmental factors such as water runoff and temperature were permanently recorded. "As early as the 1990s, we were able to establish and publish that the insect world of the Breitenbach changed over time," Wagner recalls. "Climate change is here. And it is not only reflected in the rise in temperature, but in a body of water like the Breitenbach, for example, in the seasonal dynamics of the water flow. Of course this has an impact on the aquatic fauna." These include typical species like amphipods and insect larvae.
Not all data of the long-term study had been evaluated and published. Now, LMU zoologist Dr. Viktor Baranov and Professor Peter Haase from the Senckenberg Research Institute and Natural History Museum in Frankfurt, together with other colleagues, have been given the opportunity to build on this data and investigate the influence of climate change on the ecosystem of this typical low mountain stream in greater detail.
The results are alarming: Since the start of the investigations, the average water temperature of the Breitenbach has risen by 1.8 degrees, while the number of insect individuals has decreased by 81.6 percent. "In contrast to this 'loss of abundance', we are registering an overall increase in biodiversity in the Breitenbach - we have fewer individuals but more species," says Haase. The researchers explain this development with a shift in the characteristics of the brook: "42 years ago, the sampled section was a classic upper stream section. Due to the rise in temperature, it now rather belongs to a stream middle section in which more species can generally be found," Baranov adds. However, the data also show that this trend is reversing again - the measurements of the last two decades have shown that species diversity is decreasing again in the Breitenbach. Shifts due to climate change play an important role: Since 1990, dry years with corresponding effects on aquatic insects have dominated. "As climate change continues to progress, it can be assumed that this will continue," says Baranov.
For Rüdiger Wagner, the long-term study was a lifetime achievement. Initially he worked as a scientific employee of the Max Planck Society, later he took on a management role. From 2006, research at Breitenbach was incorporated into his work as a professor at Kassel University. Wagner retired in 2016. "I am delighted that our data treasure has now come into the focus of young scientists," he says. "In many ecological studies, the significance of the data is limited due to the limited time frame. There are a few long-term studies like ours that truly deserve the name."
Publication: Baranov, V., Jourdan, J., Pilotto, F., Wagner, R. and Haase, P. (2020), Complex and nonlinear climate-driven changes in freshwater insect communities over 42 years. Conservation Biology. Accepted Author Manuscript. doi:10.1111/cobi.13477
This text uses information from a press release of the Senckenberg Society for Natural Research.
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