Studies show acid rain still harms seas and upland streams

Industrial emissions are still causing periods of acidification in the upland streams of Scotland and Wales, despite stricter controls. Researchers have discovered that brief bursts of acidification during periods of heavy rainfall and snow melt are hindering the streams’ biological recovery.1

The study explains why the ecological status of upland streams and rivers remains patchy despite sulphur deposition having fallen by as much as 50% since the 1970s.

Professor Steve Ormerod and staff from the Centre for Ecology and Hydrology assessed around 90 sites in Scotland and Wales. Ninety per cent of the Welsh streams and 50% of the Scottish ones suffered from chronic or episodic acidification. Chemical analysis showed anthropogenic sulphate and nitrate were to blame at around 30% of all sites and more than 40% of the episodic ones. Natural causes such as the deposition of sea salt were to blame elsewhere.

The locations affected by episodic acidification had fewer invertebrate species and were lacking the more acid-sensitive ones.

The results may have implications for the EU water framework Directive, which demands that all water bodies are of ‘good ecological’ quality by 2015. However, the UK’s current definition of a water body would leave many of the small headwaters sampled by Professor Ormerod outside the Directive and the acidification problems unaddressed. (ENDS Report 379, pp 19-20 ).

The Environment Agency and Natural England put forward proposals for an expansion of the definitions to include smaller streams in autumn 2006, but the Environment Department (DEFRA) has yet to make a decision.

Another recent study by US researchers suggests emissions of sulphur dioxide and nitrogen oxides may also be contributing to ocean acidification, exacerbating the acidification caused by rising atmospheric carbon dioxide concentrations (ENDS Report 366, p 7 ).2 The effect is relatively small at the global scale but could be increasing the acidification of coastal waters by 10-50% with “severe implications” for coastal communities reliant on coral reefs and acid-sensitive fisheries, the researchers said.

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