Freshwater Umbrella Presentations

Acidification of standing waters in areas of conservation importance in Great Britain

Martin Kernan, Chris J, Curtis and Gavin L. Simpson


A national assessment of the current acidification status of all standing in acidified regions of the UK has been undertaken in relation to (i) pre-acidification reference conditions and (ii) 1970 deposition worst state conditions. Part of this study included an examination of standing waters of conservation importance. Using a GIS in tandem with the UK Lakes inventory all standing waters within the boundaries of Special Areas of Conservation (SACs) with specific freshwater designations and also in regions that have been identified as acidified or sensitive to acidification were identified. Twenty nine lakes were sampled for water chemistry, one in each freshwater designated SAC in acid sensitive areas. To assess whether these may have been affected by acidification, critical loads and critical load exceedances were calculated for all sites with baseline, 1970 and 1995-97 deposition using FAB with 0, 20, 40 and variable ANC. Palaeolimnological analysis of biological assemblages was undertaken using bottom and top analysis of sediment cores. State-change over baseline, (pristine) conditions was determined using established statistical techniques providing an insight into the status of sites of conservation importance located in acidified regions.

Of the 29 conservation sites, a maximum of 10 exceeded their critical loads in 1970. This figure declined to 8 by 1995–1997 and 6 at present (based on 1999–2001 deposition data). No further sites are protected by emissions reductions up to 2024 when the 6 currently exceeded remain so. If it is assumed that the 29 sites sampled representative of the standing waters within each SAC, then over 20% (6 out of 29) of lakes in freshwater SACs in sensitive areas are still exceeding critical loads by 2024. Emission reductions required under the National Emission Ceilings Directive (NECD) are insufficient to protect freshwater SACs in the UK. Further emissions reductions beyond those required under the NECD will be required if all UK waters of conservation interest are to be protected. Critical loads exceedance indicates that good ecological status is unlikely to be maintained or achieved in the long-term at 20% of conservation sites under the NECD.

Sediment tops and bottoms were analysed from a sub-set of 10 sites from the 29 were analysed in tandem with top and bottom samples from 30 sites in freshwater SACs sampled in previous studies. The results of the core top-bottom analyses show that many acids sensitive sites in freshwater designated SACs have experienced substantial change in their diatom communities since pre-industrial period. These results indicate that 64% (26 out of 42 sites) sites have undergone substantial change with a further 28% having undergone moderate change. Only 10% of the studies sites show only minor changes in diatom communities compared with those found under reference conditions. If reference conditions are taken as a guideline target of good ecological status then most conservation sites fail to meet this target. Acid deposition may have been a major driver of observed changes in the past but other forcing factors may also have been important. A greater understanding of the interactions between these forcing factors is required to inform policy decisions on measures to achieve good ecological status or some other measure of recovery.


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