Acidification of lakes and watercourses in a global perspective

In the approximately 10,000 years since the last ice age, human activities have caused far more extensive acidification in Europe and North America than natural processes. Only 5–10% of the present acidifying load in Europe comes from natural sources. The majority of the anthropogenic load consists of sulphur emissions from electricity and heat generation. In several areas, airborne nitrogen emissions and forestry also play a significant role; nitrogen acidification is on the increase, while the role of sulphur is declining.Acidification is one of the foremost environmental problems in Europe and North America and has caused damage to forested land, surface waters, historical buildings, monuments and technical structures. In Europe, 50,000–100,000 lakes have been affected by acidification. Over 85% of all acidified lakes and watercourses are to be found in six countries: Sweden, Norway, Canada, the USA, Scotland and Finland.During the 1980s, emissions of acidifying substances in Europe and North America declined by 20–30%. It is estimated that a similar reduction will be possible during the 1990s if international agreements are adhered to. In order to prevent further acidification in Europe during coming decades, however, emissions of both sulphur and nitrogen must be cut by 70–75% between 1990 and 2010. The cost of achieving such a reduction is estimated at approximately 0.3–0.4% of the total annual European Gross Domestic Product (GDP), i.e. about three times as much as today.Even if long-term reductions in emissions were to be achieved, it would take several decades for many of the lakes and watercourses to recover. Supplementary action is therefore being taken in the form of liming, which is being performed extensively in Sweden and on a smaller scale in Norway, the USA, Canada, Scotland, Finland, Wales and Germany.