Acid rain is still responsible for poor water quality in lakes and rivers in the southern half of Norway, and especially in the southernmost counties. Many fish stocks have been depleted or wiped out as a result, and other aquatic animals and plants are also affected.

Sulphur causes most acidification in Norway

Deposition of sulphur is still the most important cause of acidification in Norway. In addition, sulphur deposition is highest in the most sensitive areas of Norway. But because sulphur emissions are being reduced more rapidly than nitrogen emissions, the relative importance of nitrogen as a source of pollution is increasing.

Nitrogen also has other effects

Nitrogen has more complex ecological effects than sulphur, because it can also act as a fertiliser and cause eutrophication. Most nitrogen is absorbed by plants or the soil, but the remainder ends up in fjords and coastal waters, where it can fuel eutrophication and excessive algal growth.

Critical loads low in the southern half of Norway

Critical loads are used to define the amount of pollution different ecosystems can absorb without damage to the natural environment. In Norway, freshwater ecosystems are particularly sensitive to acidification. Critical loads for freshwater are based on the effects on trout. They are particularly low in the southern half of the country, mainly because soils are thin and the bedrock consists of acidic rocks such as gneiss and granite.

Salmon stocks lost in the southernmost counties

Acid rain is still a serious threat to biodiversity in rivers and lakes in Norway. In all, more than 15 000 fish stocks have been lost or depleted. Twenty-five salmon stocks have been lost and at least 20 others have been affected.

Less damage to Norwegian forests

In the 1980s, acid rain resulted in widespread damage to forests in the border areas between Poland and the former East Germany and Czechoslovakia. There was serious concern about similar damage in Norway, and in 1984 the Norwegian Monitoring Programme for Forest Damage was started.

On the whole, Norwegian forests appear to have tolerated sulphur and nitrogen deposition without serious effects. They showed a decrease in vitality (measured as crown density) during the 1990s, but since then conditions have improved. In the last few years, the health of Norwegian forests has remained stable.

Major economic consequences

Damage to fish stocks and forests results in heavy economic losses. In addition to its effects on ecosystems, acid rain damages buildings, sculptures, rock art and other parts of our cultural heritage. Acidification therefore has serious consequences for society as a whole.

Acid rain is mainly caused by combustion of fossil fuels. About 90 per cent of the sulphur and 80 per cent of the nitrogen deposited in Norway originates in other European countries. The UK, Germany and Poland are among the most important sources. This means that the amount of acid rain falling on Norway is to a large extent determined by developments elsewhere in Europe.

Power plants, industrial processes (especially metal production) and transport are the main sources of acidifying emissions.

Sulphur and nitrogen deposition in Norway declining

Inputs of sulphur and nitrogen to Norway have declined as emissions in Europe have been reduced. However, there has been a much smaller overall reduction for nitrogen (sum of oxidised and reduced nitrogen) than for sulphur. There are several reasons for this:

• it took much longer before people began to focus on the harmful effects of nitrogen 
• it took longer before international agreements on the reduction of nitrogen emissions were concluded
• the mix of sources is different for nitrogen, and this has made it more difficult to find effective ways of reducing emissions.

Total deposition of sulphur in Norway was reduced from about 197 000 tonnes in 1980 to 33 000 tonnes in 2008, a reduction of more than 80 per cent.

Total deposition of nitrogen in Norway was about 100 000 tonnes in 1980 and 61 000 tonnes in 2008, a reduction of about 40 per cent. Nitrogen emissions from Europe as a whole did not start to decline until after 1990, and nitrogen inputs to Norway were actually higher in 1990 than in 1980.

From 1990 to 2008, deposition was more than halved, from 130 000 tonnes to 61 000 tonnes.

Norwegian sulphur and nitrogen emissions declining

In Norway, the main sources of sulphur dioxide emissions are metal production, stationary combustion and other industrial processes. Norwegian emissions have been greatly reduced, from about 150 000 tonnes a year in the 1970s to about 16 000 tonnes in 2009.

The main sources of nitrogen emissions in Norway are coastal shipping, fishing vessels, road traffic and the oil and gas industry. In 2009, emissions were about 190 000 tonnes, 15 per cent lower than in 1990.

Acid rain does not respect national borders, and is a problem for most European countries. The answer has been to join forces to reduce overall European emissions of sulphur and nitrogen.

Binding international agreements

Most European countries have undertaken to reduce their emissions of acidifying substances through the Convention on Long-range Transboundary Air Pollution. Several binding protocols have been adopted under the convention, including the Gothenburg Protocol, which entered into force in 2005. It is being used to control emissions of sulphur and nitrogen in Europe up to 2010.

Norway has undertaken to reduce its emissions of sulphur dioxide to a maximum of 22 000 tonnes. The targets for nitrogen are maximum emissions of 156 000 tonnes nitrogen oxides (NOx) and 23 000 tonnes of ammonia (NH3).

Liming reduces damage

Liming of rivers and lakes is an important means of remedying the worst of the damage caused by acid rain. The aim is to give animals and plants a chance to re-establish themselves. Each year more than 50 000 tonnes are applied in Norwegian rivers and lakes. The liming programme is most extensive in Telemark, Aust-Agder, Vest-Agder and Rogaland counties.