3. Natural Acidification Only

3. Natural Acidification Only. Photo: Hans Bjurling/Johnér Bildbyrå."The acidifying effects of deposition and land use must not exceed the limits that can be tolerated by soil and water. In addition, deposition of acidifying substances must not increase the rate of corrosion of technical materials located in the ground, water main systems, archaeological objects and rock carvings."

Forest soils, lakes and streams are often naturally acidic, but atmospheric deposition of acidifying pollutants has accelerated acidification. This process affects plants and animals and increases corrosion, i.e. chemical attack on materials. Corrosion causes damage, for example, to archaeological remains and water mains. There can also be adverse impacts on human health, for instance from drinking water obtained from acidified wells.

The substances giving rise to acidification are sulphur dioxide, nitrogen oxides and ammonia. These originate mainly from road traffic and shipping, power stations, district heating plants and factories, and agriculture.

Forestry also contributes to acidification, both as trees grow and when they are harvested. With increasing demand for biofuels, whole-tree harvesting has become more common. If not carried out correctly, this practice can result in increased acidification of the soil and depletion of nutrients.

What are the challenges?

Recovery of the natural environment is a slow process. Despite a sharp fall in total emissions of sulphur dioxide and nitrogen oxides in Europe over the last decades, Sweden’s lakes and watercourses have seen only a gradual improvement. One in ten lakes is still judged to be acidified as a result of human activities. Forest soils and groundwaters are taking even longer to recover.

Most acidifying pollutants deposited in Sweden are brought here by winds from other countries or from international shipping. Curbing Swedish emissions is thus not enough to reduce acidification in the country. However, international agreements to cut emissions are in place, both at EU level and under the UN Convention on Long-Range Transboundary Air Pollution.

The biggest challenge is to further reduce acid emissions from the transport sector, in Sweden and internationally. This also applies to international shipping, which emits large quantities of nitrogen oxides. The relative importance of acidifying effects of forestry is increasing since the deposition is decreasing. National measures concerning a sustainable forestry is therefor of importance.