River recovery 'dampened by rain'

Mayflies and other insects eaten by fish have been affected

Climate change is affecting the recovery of rivers from acid rain, according to a new university study.

Scientists from Cardiff University took measurements over a 25-year period around Llyn Brianne, Carmarthenshire.

Their findings are published online in the British Ecological Society's Journal of Applied Ecology.

Professor Steve Ormerod said: "Upland streams have been acidified enough to cancel out up to 40% of the last 25 years improvements."

Prof Ormerod and Dr Isabelle Durance of the school of biosciences carried out research in 14 streams, assessing the number and variety of stream insects present each year.

The scientists measured concentrations of acid and other aspects of stream chemistry, and documented 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 would have re-colonised the less acidic Welsh streams.

Climatic effects have clearly worked against our best efforts Prof Steve Ormerod of Cardiff University

These included sensitive mayflies and other groups often eaten by trout and salmon.

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

Prof Steve Ormerod, who has led the project since it began in the early 1980s, said: "Since the 1970s, 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% of the last 25 years improvements: climatic effects have clearly worked against our best efforts."

Dr 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."