1 Background 4 Objectives and coverage 4
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- 11.3. Acidification
- 11.4. Environmental impacts of toxic metals
11.2. EutrophicationEutrophication refers to an excess of nutrients in the soil or water. It threatens biodiversity through the excessive growth of a few species that thrive in the presence of the added nutrients, to the detriment of a larger number of species that have long been part of the ecosystem but are accustomed to a lower-nutrient environment. The two major causes of eutrophication are excess nutrient nitrogen (mainly nitrates and ammonium) and excess phosphates in ecosystems. Air pollution contributes to the excess of nutrient nitrogen, as the nitrogen emitted to the air, namely NOx (mainly from combustion of fuels) and NH3 (mostly from livestock breeding), deposits on soils, vegetation surfaces and waters. Atmospheric nitrogen deposition contributes to eutrophication in freshwater and in the sea. Eutrophication often leads to algae ‘blooms’, that is, the rapid growth of algae which form dense patches near the surface of the water and prevent light from penetrating into deeper layers of the water. Eutrophication effects are estimated using the ‘critical load’ concept, a term that describes the ecosystem’s ability to absorb eutrophying nitrogen pollutants that have been deposited from the atmosphere, without the potential to cause negative effects on the natural environment. Exceedances of these spatially determined critical loads present a risk of damage or change to the existing ecosystems. Such exceedances are estimated using ecosystem classification methods and model calculations. The EEA (2014a) estimated that 63 % of the total EU-28 ecosystem area and 73 % of Natura 2000 area was at risk of eutrophication in 2010, owing to excessive atmospheric nitrogen covering most of continental Europe as well as Ireland and southern areas of the United Kingdom and Sweden. The reduction of ecosystem area at risk of eutrophication has merely been moderate. For 2005, 67 % of EU-28 ecosystem area and 78 % of the Natura 2000 area were estimated at risk of eutrophication. The risks of ecosystem eutrophication and its geographical coverage have thereby diminished only slightly over the past decade, and it is still widespread across Europe. Furthermore, the projections for 2020 and 2030 indicate that ecosystems exposure to eutrophication will still be widespread (EEA, 2016b; Maas and Grennfelt (eds), 2016). This conflicts with the EU’s long-term objective of not exceeding critical loads of airborne acidifying and eutrophying substances in European ecosystem areas (EU, 2001; EU, 2002; European Commission, 2005). 11.3. AcidificationThe emission of nitrogen and sulphur into the atmosphere creates nitric acid and sulphuric acid, respectively. These compounds fall to the earth and its waters as acid deposition, reducing the pH level of the soil and water and leading to acidification. Acidification damages plant and animal life, both on land and in water. Owing to the considerable SOx emission reductions over the past decades, nitrogen compounds emitted as NOx and NH3 have become the principal acidifying components in both terrestrial and aquatic ecosystems, in addition to their role causing eutrophication. However, emissions of SOx, which have a higher acidifying potential than NOx and NH3, still contribute to acidification. As with eutrophication effects, acidification effects are estimated using the concept of ‘critical load’, which describes an ecosystem’s ability to absorb acidifying pollutants that have been deposited from the atmosphere without negative effects on the natural environment. Exceedance of these spatially determined critical loads presents a risk of damage. Such exceedances are also estimated using information on ecosystem classification and model calculations. EEA (2014a) estimated that 7 % of the total EU-28 ecosystem area and 5 % of the Natura 2000 area were at risk of acidification in 2010. This represents a reduction by 30 % and 40 %, respectively, from 2005 levels. Compared with 1990, the area of sensitive ecosystems in the EU-28 in which the acidity critical load was exceeded had declined by 94 % in 2010. This improvement is primarily attributed to sharp reductions in SOx emissions over the past two decades. However, soil and surface water acidification remain an issue in the most sensitive areas of Nordic countries, the UK and central Europe. Recovery of acidified soils and waters will take decades to centuries, because of depleted base cations in soils, which recover through the slow process of mineral weathering. Further reductions in nitrogen and sulphur emissions will improve the situation and shorten the time for recovery (Maas and Grennfelt (eds), 2016). The area at risk may be reduced to about 2% in 2020 under the revised Gothenburg Protocol and including the implementation of current legislation. A further decrease to 1% could be achieved in 2030 under Maximum Feasible Reductions (Hettelingh et al., 2015).
Atmospheric deposition of toxic metals into the environment contributes to the exposure of ecosystems and organisms to these and, therefore, to the risk of bioaccumulation. Some ecosystem areas are at risk owing to the atmospheric deposition of Cd, Pb and Hg. The share of national ecosystem areas in Europe exceeding critical loads for Cd is < 1 % in most countries, except countries that have set lower critical loads than other countries (Slootweg et al., 2010). As regards Pb, the area and extent of the exceedances of critical loads are much higher. Atmospheric deposition of Pb exceeds the critical loads in > 12 % of the EU ecosystem area (Slootweg et al., 2010). The largest exceedances of toxic metal critical loads involve Hg. Almost half of all EEA member and cooperating countries (37) have exceedances of critical loads for Hg across nearly 90 % or more of their ecosystem area. In total, the atmospheric deposition of Hg exceeds the critical loads across 54 % of the EU ecosystem area (Slootweg et al., 2010).
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