Impacts of acid rain

Acid deposition can cause damage to other natural systems and also the manmade environment. For example, widespread forest decline has been reported in many countries. In Europe, forests, particularly in Scandinavia, Germany, Poland and the Czech Republic, have been affected, with damage to as much as 40 per cent of them. Deposition of the incoming acids on the leaves of trees can cause harm both through acidic intakes into the stomata of the leaves but also may damage the waxy cuticle on the surface of leaves and needles. It is thought that such damage makes the leaves more prone to disease. Other factors, such as fungal and bacterial infections and increasing concentrations of aluminium, are believed to have brought about weakening of the quality of the tree growth and damage to roots.

Although there is no doubt that acid deposition is causing forest decline the exact mechanisms leading to it need further understanding.There is much evidence now for the increasing acidification of freshwater bodies such lakes and rivers with the result that the range and numbers of aquatic fauna have decreased. The acidity comes directly from the precipitation and from the acid waters that leach out of the soil. There is now much evidence for declining fish populations in acidified lakes and here the link between acid rain and fish mortality is convincing. The disappearance of brown trout from Scandinavian lakes has been associated with increasing acidification of the lake water. It has been shown that increasing amounts of aluminium, much of it derived from the soil, but now found in many water bodies is also toxic to fish.

During the 1960s 'smog' was a word that entered the English vocabulary. It was used to describe the heavy fogs smelling greatly of sulphur that descended on our cities on a fairly regular basis, reducing visibility to just a few metres. This was real evidence of the presence of large amounts of sulphur in the atmosphere, put there by the factory chimneys. In addition to being a threat to the countryside these smogs were also a threat to human beings, particularly their bronchial tracts. They were also a threat to many of the buildings of the cities which were vulnerable to degradation through the effects of sulphurous compounds. Fortunately the last 20 years has seen a partial cleanup of such unwanted legacies but in some parts of the world acid deposition continues to be a problem. Annual costs associated with acid rain have been estimated to be many billions of £s. It is a problem that affects many parts of our society and the need for preventative measures continues.