Acid Deposition

Status and Trends
for eastern Canada, improving; for some parts of western Canada, getting worse
Concern, some improvements, some worsening
trends are clear
High confidence in finding

KEY FINDING 13. Thresholds related to ecological impact of acid deposition, including acid rain, are exceeded in some areas, acidifying emissions are increasing in some areas, and biological recovery has not kept pace with emission reductions in other areas.

This key finding is divided into four sections:

Acid deposition, sometimes referred to as acid rain, is produced when sulphur and nitrogen-based pollutants react with water in the atmosphere and are deposited on the Earth’s surface.1 More than just acid rain, it includes acidifying gases and dry particles. The pollutants originate from industrial processes and can travel thousands of kilometres. It is the combination of acid deposition and the sensitivity of the land, water, flora, and fauna to acid that determines the severity of the impact on biodiversity. Acid deposition is important because algae, invertebrates, fish, amphibians, and birds are affected by increased acidity through reduced survival, growth and reproductive success, and loss or alteration of prey species.1-6 The acidification of aquatic systems can lead to increases in methylmercury, which bioaccumulates, affecting embryos and young animals.7-10 Acidification may also negatively affect the growth rate and health of trees, for example, sugar maple and red spruce in northeastern North America.11, 12


Global Trends

Once recognized as a problem only in Europe and parts of North America, acid deposition is now also an environmental issue in Asia and Pacific regions.31 Significant reductions in sulphur emissions have been achieved in parts of Europe.32






Key finding overview