Acid rain and eutrophication

Questions related to the acidification and eutrophication of rivers, water and soil have been a central research area for NILU for several decades. In the 1960s, the relationship between sulphur oxide emissions from Europe and the acidification of waterways in Scandinavia began to be clear. Fish kills in southern Norway were seen in the context of air pollution from the European continent.

Research during the 1970s showed how emissions of SOx (sulphur oxides) and NOx (nitrogen oxides) could be transported over long distances in the atmosphere, and then deposited on the soil or in the water via precipitation or particulate matter. This acidic deposition caused considerable environmental damage. In the same way, releases of ammonia (NH3) from activities such as agriculture can result in overfertilization (eutrophication) of waterways. Eutrophication can result in algal blooms, which then cause oxygen depletion.

In 1979, the United Nations Economic Commission for Europe (UNECE) approved the “Convention on Long-range Transboundary Air Pollution”, which formally came into force in 1983. The convention has resulted in the creation of eight so-called protocols, which set requirements for each country’s emissions of acidifying compounds such as SOx and NOx, and compounds that can cause eutrophication, such as NH3.

NILU has played a central role in the UN’s long-range transport convention right from the beginning through its roles as the “Chemical Coordinating Centre” for EMEP (the European Monitoring and Evaluation Programme). An important aspect of this effort is NILU’s monitoring of compounds in the air and in precipitation that can cause acidification or eutrophication. NILU is also a data centre, and takes responsibility for quality control and data reporting of these compounds under EMEP and the long-rang transport convention.

In the case of sulphur, the convention has been an unqualified success. Using both measurement data and computer modelling, gradually stricter protocols have been developed under the convention, which has resulted in significant drops in sulphur levels in waterways. Nitrogen, however, remains a significant environmental problem in Europe, both as an acidifying compound and as a substance that can cause eutrophication, and nitrogen pollution levels have unfortunately not dropped as much as sulphur levels.