Climate change set back for acidified rivers

The research, by Professor Steve Ormerod and Dr Isabelle Durance of the School of Biosciences took place over a 25 year period around Llyn Brianne in mid-Wales. Their findings are published online today in the British Ecological Society's Journal of Applied Ecology.

Carried out in 14 streams, the research involved assessing the number and variety of stream insects present each year, measuring concentrations of acid and other aspects of stream chemistry, and documenting climatic variation such as warmer, wetter winters.

With average acidity in rivers falling due to improvements in the levels of acid rain, the researchers expected that up to 29 insect species should have re-colonised the improving Welsh streams. Typical among them should be sensitive mayflies and other groups often eaten by trout and salmon.

Their findings, however, showed a large short-fall in biological recovery, with just four new species added to the recovering rivers sampled.

Professor Steve Ormerod, who has led the project since it began in the early 1980s, said: “Since the 1970’s, there have been huge efforts to clean-up sources of acid rain, and our research shows that rivers are heading in the right direction. However, our results support the theory that acid conditions during rainstorms kill sensitive animals. During recent wetter winters, upland streams have been acidified enough to cancel out up to 40 percent of the last 25 years’ improvements: climatic effects have clearly worked against our best efforts.”

Dr Isabelle Durance, who co-authored the paper said: “More and more evidence now shows that some of the worst effects of climate change on natural habitats come from interactions with existing stressors – in this case acid rain. A wider suggestion from our research is that by reducing these other environmental problems, we can minimise at least some climate change impacts.”

S J Ormerod and Isabelle Durance (2008). Restoration and recovery from acidification in upland Welsh streams over 25 years. Journal of Applied Ecology, doi: 10.1111/j.1365-2664.2008.01587.x, is published online on 3 December 2008, www3.interscience.wiley.com/journal/119878127/issue