It's the age-old conundrum for potential Prius owners - emit CO2 and cause global warming using combustion engines or pollute the ground and water with acid rain due to batteries.   Climate scientists at Cardiff have found a way to stop having the environmental money maker for the 2000s fighting against the environmental moneymaker of the 1980s - climate change is hampering acid rain recovery, they say.

Yes, wet weather in Wales is keeping rivers from getting better.

The research by Professor Steve Ormerod and Dr Isabelle Durance of the School of Biosciences is based on observations 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. 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-colonized 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.

Professor 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 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."