The problem was first described in Southern Norway at the beginning of this century when declining salmon populations were associated with increasing acidity in lakes and rivers. Widespread research has been carried out in Europe and North America in recent years into the many mechanisms of acidification with a view to substantially reducing or eliminating the causative agents and restoring the damaged environment. There is a continuous movement of water vapour into the upper atmosphere through evaporation from oceans, lakes, rivers and soil. On cooling, this water vapour condenses and falls as rain or snow. Depending on the amount of CO2 and S present, the pH of the ensuing rainfall can be in the range 4.5-5.6.
Acids fall to the ground in particulate form.
This occurs downwind of the source of the emissions. The water bodies most susceptible to change due to acid precipitation are those whose catchments have shallow soil cover and poorly weathering bedrock, e.g. granite and quartzite. These soil types are characterised by the absence of carbonates that could neutralise acidity. The run-off water from such areas is less buffered than from areas such as limestone catchments, with an adequate level of carbonate. The principal areas with such characteristics in Ireland are shown in Fig. 2 and are mostly associated with granite or quartzite bedrock.