Washington, Dec 13 : A new study by researchers at Cardiff University in the UK has determined that climate change is hampering the long-term recovery of rivers from the effects of acid rain, as wet weather counteracts improvements.

The research, by Professor Steve Ormerod and Dr Isabelle Durance of the School of Biosciences, Cardiff University, took place over a 25 year period around Llyn Brianne in mid-Wales.

Carried out in 14 streams, the research involved 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 to have re-colonised the less acidic Welsh streams.

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

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

According to Professor Steve Ormerod, who has led the project since it began in the early 1980s, "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," he added.

During recent wetter winters, upland streams have been acidified enough to cancel out up to 40 percent of the last 25 years' improvements.

"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," said Dr Isabelle Durance, who co-authored the paper.

"A wider suggestion from our research is that by reducing these other environmental problems, we can minimise at least some climate-change impacts," he added. (ANI)