Post a comment on the text below

7.5.3.      Case studies

Trends in European acidification of surface water bodies

Source: Skjelkvåle, B.L., and de Wit, H. A. 2011

From 1990 to 2008 the concentrations of sulphate and nitrate in precipitation have decreased in large areas in Europe and North America due to emission reductions. The reductions were larger from 1990 to 1999 than from 1999 to 2008. The same pattern can also be seen for sulphate in surface water. Nitrate, in contrast to sulphate, does not show uniform decreasing trends despite the decrease in nitrogen deposition.

Biological recovery is under way in Europe, but full recovery is still far ahead.

The acidity of lakes and rivers has decreased due to the decrease in sulphate and many places there are good conditions for recovery of aquatic biological communities that have been damaged due to acidification (see figure 7.13).  Six countries (Czech Republic, Finland, Germany, Norway, Sweden and Switzerland) reported on biological recovery from national monitoring programmes. Most contributions focused on recovery of zoobenthos (small organisms that live on the bottom of rivers and lakes such as aquatic insects, worms and snails), but status of fish populations, algae and macrophytes (water plants) were also given. Zoobenthos have a short life cycle and are therefore able to respond more quickly to improved water chemistry than fish, which makes these organisms suitable as early indicators of biological recovery.

Almost all contributions reported evidence of biological recovery which was attributed to improved water quality, although other factors such as climate also contributed to explaining temporal variations. Higher species diversity was observed while species composition in many places has become more similar to non-acidified communities.

Full biological recovery is not documented anywhere. A return to pre-industrial biodiversity is unlikely in most cases, because original species are extinct, new species have been introduced and biological processes are often non-reversible. Several areas in Europe will never achieve good (non-acidified) water quality with current legislation of emissions of acidifying components. Future reductions of both S and N deposition are necessary to achieve biological recovery.