Freshwater Umbrella Presentations
Acidification of standing waters in areas of conservation importance in Great Britain
Martin Kernan, Chris J, Curtis and Gavin L. Simpson
Abstract
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 2010 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 2010. 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.
Presentation
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