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European critical loads: database, biodiversity and ecosystems at risk

With this Final Report 2017 the Coordination Centre for Effects (CCE) located at the National Institute for Public Health and the Environment (RIVM, Bilthoven, the Netherlands) is concluding its work. In 1990, tasks of the CCE were offered by the Netherlands to the Convention on Long-range Transboundary Air Pollution (LRTAP Convention) of the United Nations Economic Commission for Europe (UNECE). The LRTAP Convention then adopted the CCE as programme centre of the “International Cooperative Programme for the Modelling and Mapping of Critical Loads and Levels and Air Pollution Effects, Risks and Trends” (ICP M&M) under its Working Group on Effects.

The main task of the CCE includes the development of methodologies and databases enabling the assessment of thresholds (“critical loads”) for the protection of ecosystems against adverse effects of atmospheric pollutants, with an emphasis on acid and nitrogen depositions. For this task, the CCE collaborates with a European network of National Focal Centres of the ICP M&M. In this context, the CCE is regularly requested by the Convention to issue calls for data to these centres. The CCE is finally responsible for the compilation of national information on critical loads into a European database. The European critical loads database is then used in the Greenhouse Gas Interactions and Synergy Model (GAINS) held by the Centre for Integrated Assessment Modelling of the LRTAP Convention (located at IIASA, Austria) in support of European air pollution abatement policies.


In this report, latest results of the CCE are described (Part 1) with special attention for the consolidation of information in a manner that is tailored for use by the - at the time of writing this report not yet identified - successor of the CCE. Part 2 contains detailed accounts of the work conducted by National Focal Centres over the past two years.


Chapter 2 focuses on the call for critical loads data 2015-2017. A novel element consisted of requesting National Focal Centres to include methods to compile critical loads for biodiversity, i.e. thresholds of acid and nitrogen deposition below which the loss of specific plant species does not occur according to present knowledge. Consensus on these methods had been achieved under the ICP M&M during a number of preparatory meetings and workshops prior to the 2015-2017 call for data. In addition to these novel critical loads, also data were requested to enable an update of the European critical loads database that had been used in support of LRTAP Convention protocols and the National Emission Ceilings Directive of the European Union.


Fourteen Parties to the Convention, i.e. twelve EU Member States plus Switzerland and Norway, submitted critical loads of nitrogen and of sulphur, including seven Parties that also submitted critical loads for biodiversity. It is noted that that the data required for the assessment of critical loads for biodiversity need to be further completed to include more NFC submissions and more nature types. In view of this, a possible improvement of the modelling of relationships between the probability of occurrence of plant species and abiotic conditions is described in Chapter 4.


For countries that do not submit data, the CCE developed over the years a so-called European background database, described in Chapter 3, in collaboration with Alterra (the Netherlands). The use of this database enables computed critical loads for acidity, nitrogen and biodiversity to cover ecosystems in the whole of Europe. Thus, critical loads are available for European ecosystems categorized according to the European Nature Information System of the EEA, covering an area between two and three million km2.


The updated European database on critical loads, has then been used for the analysis of effects of air pollution abatement alternatives (Chapter 1) to illustrate results of the application of the database in the GAINS model. It turns out that a simulation of abatement policies embedded in the so-called Current Legislation pathway leads to a reduction of the ecosystem areas being at risk of excessive nitrogen deposition from 67 % in 2005 to about 58 % of in 2020. For the EU28 these percentages are 81 % and 71 % respectively. When acidification is used as endpoint a reduction from 11 to 4 percent of areas at risk can be noted between these years.

In addition, the impact of climate change on critical loads and exceedances is included in Chapter 1 to illustrate the potential capability of methodologies to assess interactions with effects of air pollution as expressed in the long-term strategy of the Convention.


Finally, it is recommended that knowledge of effects of interactions between air pollution and climate change be further strengthened by improving critical loads of biodiversity. This could include various interactions that affect the health of ecosystems, such as between temperature, drought, ozone, nitrogen and aerosol exposure. These assessments could help support multi-effect oriented policies that are jointly framed under UN-Conventions and EU strategies for air pollution, climate and biodiversity.


The successor of the Coordination Centre for Effects is encouraged to continue the coordination and programming of this scientific challenge in collaboration with other effect-based programmes under the LRTAP Convention.


Keywords: air pollution, biodiversity, CCE, critical loads, ecosystem, exceedance, impacts.