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Recovery from acid rain ‘much slower than expected’

28 September 2007

Acid rain was one of the world’s worst pollution problems of the 1970s and 1980s, affecting large areas of upland Britain, as well as Europe and North America.

In Wales, more than 12,000 km of streams and rivers have been acidified, harming fish, stream insects and river birds such as the dipper.

Over the last 20 years, action has been taken across Europe to clean up acid pollutants from power generation and industry, which was widely expected to bring recovery. However, new research led by Cardiff University’s School of Biosciences shows that the expected improvements in rivers are far short of expectations.

Recent studies in Galloway, the Scottish Highlands and Wales reveal that many streams are still highly acidified. Biological recovery has been particularly poor.

Key findings from the projects, carried out by combined teams from Cardiff University, the Centre for Ecology & Hydrology and National Museum Wales, include:

• Acidity in Welsh headwaters is declining, but only slowly

• More than two thirds of all streams sampled were acid enough during high flow to cause biological damage, with metals at toxic concentrations

• Sulphur pollution from man-made sources is still an important cause of acid episodes, particularly in Wales

• Sensitive insects survive conditions in the most acid streams for only a few days

• Headwater acidification is still a significant problem for important salmon fisheries, and Special Areas of Conservation such as the Welsh River Wye.

Professor Steve Ormerod of the School of Biosciences, a leading researcher into the biological effects of acid rain for more than 20 years, said: "Organisms and ecosystems are the best indicators of recovery from pollution, so these results will alarm anyone interested in the well-being of our rivers. We need to understand the factors responsible for such delayed recovery, particularly since climate change is likely to make the acidification problem even worse."

Dr Chris Evans, an acid-rain specialist from the Centre for Ecology & Hydrology in Bangor, added "Pollution reductions are slowly improving in upland waters, but there is a long way to go. The large biological effects of acid episodes shown by this work mean that it is vital to continue monitoring these ecosystems if we are to protect them in future."

The research contrasts with other recent studies which showed some encouraging early signs and will come as disappointing news to those who thought the acid rain problem was solved.


Notes to Editors:

1. The results of the work can be found in: R. A. Kowalik, D.M. Cooper, C. M. Evans & S. J. Ormerod (2007) Acid episodes retard the biological recovery of upland British streams from acidification. Global Change Biology, doi: 10.1111/j.1365-2486.2007.01437.x . B. R. Lewis, I. Jüttner, B. Reynolds & S. J. Ormerod (2007) Comparative assessment of stream acidity using diatoms and macroinvertebrates: implications for river management and conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 17, 502-519

2. Cardiff University is recognised in independent government assessments as one of Britain’s leading teaching and research universities. Founded by Royal Charter in 1883, the University today combines impressive modern facilities and a dynamic approach to teaching and research. The University’s breadth of expertise in research and research-led teaching encompasses: the humanities; the natural, physical, health, life and social sciences; engineering and technology; preparation for a wide range of professions; and a longstanding commitment to lifelong learning. Cardiff is a member of the Russell Group of the UK’s leading research universities. Visit the University website at:

3. The Centre for Ecology & Hydrology is the UK's leading research organisation for land and freshwater science. Its scientists carry out research to improve our understanding of both the environment and the processes that underlie the Earth's support systems. It is one of the Natural Environment Research Council's research centres.

4. The Natural Environment Research Council funds world-class science, in universities and its own research centres, that increases knowledge and understanding of the natural world. It is tackling major environmental issues such as climate change, biodiversity and natural hazards. NERC receives around £370m a year from the Government's science budget and leads in providing independent research and training in the environmental sciences.

5. Entry to all National Museum Wales - Amgueddfa Cymru sites is free, thanks to the support of the Welsh Assembly Government. For more details, please visit Amgueddfa Cymru - National Museum Wales operates seven national museums across Wales. These are National Museum Cardiff, St Fagans: National History Museum, National Roman Legion Museum, Caerleon, Big Pit: National Coal Museum, Blaenafon, National Wool Museum, Dre-fach Felindre, National Slate Museum, Llanberis and the National Waterfront Museum, Swansea.

Further Information:

For more information, please contact:

Professor Steve Ormerod
School of Biosciences
Cardiff University
+44 (0)2920 875871

Stephen Rouse
Public Relations Office
Cardiff University
+44 (0)2920 875596

Dr Chris Evans
CEH Bangor
+44 (0)1248 374500