The study identified 141 SSSIs throughout Britain in which freshwater habitats have probably suffered acidification damage. Although these represent only 2.5% of Britain's 5,749 SSSIs, the proportion of the SSSI area affected is much larger at 24.1%. This is because the largest SSSIs are in upland areas which are the worst hit by acid deposition.
The areas affected by freshwater acidification are concentrated in the uplands of Wales, Dartmoor, northern England and parts of Scotland, with some damage in high ground in the south of England (see table ).
Wales is suffering the most severe damage, with 55% of the SSSI area in north Wales affected. According to the report, this reflects the "relative proximity of sulphur emission sources in the Midlands combined with a large percentage of high altitude upland habitat with poor geology and soils." The uplands of central Wales are also seriously affected. No sites in south Wales were considered due to lack of data.
The scale of the acidification problem in Wales helps to explain why HMIP is apparently intent on refusing National Power permission to burn the high-sulphur fuel Orimulsion at its Pembroke power station without acid gas abatement equipment (ENDS Report 208, pp 6-7 ).
The report also has some important pointers for HMIP for the slightly longer term. HMIP is under a statutory duty to ensure that the best affordable techniques are used to prevent releases which may cause harm. According to English Nature, many SSSIs are still likely to be suffering harm when the official national plan to reduce emissions of sulphur and nitrogen oxides is achieved.
Under a 1988 EC Directive which the national plan is intended to implement, emissions of SO2 from existing large combustion plants are to be cut by 60% from 1980 levels by 2003. These sources presently account for over 80% of the UK's total SO2 emissions.
English Nature is adamant that "further reductions in emissions are necessary beyond the 60% level in order to safeguard aquatic and riparian species...over a large area of upland Britain." This echoes the results of Department of the Environment projections based on the "critical loads" approach (ENDS Report 208, pp 7-8 ), and will have to be taken into account by HMIP when it determines the applications for authorisation submitted by National Power and PowerGen for their power stations.
A further key recommendation of the report is that afforestation should not be carried out in areas suffering from acidification. And liming, promoted by the electricity industry as an ameliorative measure to counteract acidification of watercourses, should also be strongly discouraged within SSSIs because the ecological consequences can be severe.