Air pollution still harms ecosystems

© Lars-Erik Håkansson

While acidification has been greatly reduced since its peak in 1980, emissions of nitrogen-containing air pollutants continue to damage more than half of sensitive ecosystems.

According to the EU’s Environment Action Programme, the long-term objective and core of the EU’s air quality policy is to attain air quality levels that do not give rise to significant negative impacts on, or risks for, human health and the environment. Specifically for ecosystems, the long-term objective is to achieve “no exceedance of the critical loads and levels”, i.e. scientifically determined limits of ecosystem tolerance to air pollution exposure. This objective was recently echoed in the Commission’s Clean Air Package proposal from December 2013.

A new study by the European Environment Agency (EEA) evaluates how European ecosystems were affected by acidifying and eutrophying air pollutants in the past decades, and projects the levels of impacts in the near future under a scenario where the 2012 amended Gothenburg Protocol under the Convention on Long-range Transboundary Air Pollution (LRTAP) is assumed to be fully implemented by 2020.

The deposition of acidifying air pollutants causes acidification of surface waters (lakes, rivers and streams) and forest soils, leading to loss of nutrients such as potassium and magnesium from soils and the release of toxic aluminium into soils and waters, resulting in adverse effects on animals and plants.

Looking at the historical development of the acidification problem shows that peaks in exceedances of the critical loads for acidification of fresh water and forest soils occurred in 1980, with 43 per cent of the EU’s ecosystem area suffering from excess deposition of acidifying air pollutants.

The high political profile of the “acid rain” and “forest dieback” problems in the late 1970s and early 1980s generated both national and international action to cut emissions, initially focussing on sulphur dioxide (SO₂). International co-operation under the LRTAP Convention, and later also within the EU, contributed significantly to reducing emissions.

Twenty years later, in the year 2000, the area suffering from excess acid inputs had shrunk to 18 per cent, and by 2010 it was further reduced to seven per cent. Findings suggest that by 2020 the ecosystem area where acidification critical loads are exceeded, as well as the magnitude of the exceedances, will be as low as they were in 1880, i.e. only four per cent of the EU area will still be in exceedance.

It should be noted, however, that even though most EU ecosystems in the future will receive deposition levels not exceeding the critical loads, some countries will still have a significant percentage of their ecosystem area exceeded in 2020. This is the case, for example, in the Netherlands (63%), Czech Republic (50%), Lithuania (30%) and Poland (24%).

And despite some countries showing seemingly low percentage figures of exceedance, the actual area at risk can still be very significant in those countries that have a large total area of ecosystems. For example, the projected exceedance figure for 2020 for Sweden is down to six per cent. However, in practice this means that sensitive ecosystems will still be exposed to excess acid inputs over more than 17,000 square kilometres, equivalent to over half the area of Belgium.

Moreover, research has shown that both chemical and biological recovery from acidification damage can be very slow, and in many areas it may take several decades before a full recovery from past acidification damage occurs.

Excess input of nitrogen compounds – emitted as nitrogen oxides or ammonia – into terrestrial ecosystems causes eutrophication (nutrient enrichment) resulting among other things in increased plant growth and changes in biodiversity, such as a lowering in species richness.

Exceedances of critical loads for eutrophication peaked in 1990, with 84 per cent of the EU’s ecosystem area under threat. Reductions in the emissions of nitrogen oxides (NOx) and ammonia (NH₃) started later and have been much slower, as compared to those for SO₂. Consequently, improvements in the eutrophication status have also been slower.

By 2000 and 2010, the area exceeded had come down to 78 and 63 per cent, respectively, and it is projected to decrease to 54 per cent by 2020 under the amended Gothenburg Protocol. As the total amount of nutrient nitrogen that is deposited annually on each hectare decreases, the absolute magnitude of the exceedance will be reduced considerably in most areas, with the exception of a few “hot spot” areas in western France and the border areas between the Netherlands, Belgium and Germany, as well as in northern Italy.

Specifically for Natura 2000 areas, the extent of eutrophication critical load exceedance is still projected to be 65 per cent in 2020. Natura 2000 is an EU-wide network of nature protection areas, set up with the aim to ensure the long-term survival of the most valuable and threatened species and habitats.

A first assessment of possible impacts of nutrient nitrogen deposition on species richness in nutrient-poor grasslands is presented in the report. The results show that the computed species richness in these grasslands is projected to improve from below 70 per cent in 1980 to 82 per cent by 2020. This relative (percentage) increase in species richness indicates that emission reductions have a positive effect on biodiversity.

Hans Bruyninckx, EEA Executive Director said: “Although air pollution does not cause as much harm as it once did, we are still struggling to protect sensitive ecosystems from harmful effects such as eutrophication. This changes habitats, endangering a wide range of species from fish to flowering plants. It is particularly striking that the problem appears to be just as bad in Europe’s protected natural areas.”

Christer Ågren

The report: Effects of air pollution on European ecosystems: Past and future exposure of European freshwater and terrestrial habitats to acidifying and eutrophying air pollutants (June 2014). EEA Technical report No 11/2014. 

Figure: Development since 1880 of the area at risk in Europe (in per cent, top graph) and magnitude (in equivalents per hectare and year, lower graph) of exceedance of acidification (red) and eutrophication (green), with projections for 2020 and 2030.

Table: Ecosystem area in EU28 exposed to excess nitrogen deposition (eutrophication) and acid deposition (acidification).