Eutrophication caused by atmospheric nitrogen deposition in Europe

Air pollution threatens biodiversity. Excess amounts of nitrogen can cause eutrophication, disrupting terrestrial and aquatic ecosystems and leading to changes in species diversity, for example in nutrient-poor grasslands. The main sources of atmospheric nitrogen deposition are combustion processes, which result in nitrogen oxides (NO_x) being emitted to the air, and ammonia (NH₃) emissions from agriculture. Nitrogen deposited in terrestrial ecosystems causes harmful eutrophication when so-called critical loads are exceeded.

The European Commission’s zero pollution action plan aims to reduce pollution in the EU to levels not harmful to human health or ecosystems . Target 3 focuses specifically on protecting ecosystem biodiversity from air pollution, by reducing by 25% the area of ecosystems where nitrogen deposition is above the critical loads for eutrophication by 2030, compared with 2005. This indicator monitors progress towards meeting this target and is also relevant for the ongoing review (2019-2022) and planned revision of the Gothenburg Protocol .

One of the main EU policy instruments for achieving this 25% reduction is the National Emission Reduction Commitments Directive . Under this directive, each Member State must submit a national air pollution control programme (NAPCP), setting out how binding national emission reduction commitments, including for NO_x and NH₃, for 2020-2029 and 2030 onwards will be met. The implementation of NAPCP measures is expected to decrease the ecosystem area affected by eutrophication in the EU (see the second clean air outlook and underpinning study ).

Moreover, the implementation of measures intended to achieve the 50% reduction in nutrient losses set out in the farm to fork strategy and the nature restoration targets of the biodiversity strategy will also contribute to reducing atmospheric nitrogen deposition.

Under the baseline scenario of the European Commissions’ Third Clean Air Outlook, in 2020, critical loads for nitrogen deposition were exceeded in 75% of the total ecosystem area of the 27 Member States, constituting 1,082,200km². This represents a fall of 12% since 2005. For 2030, it is estimated that 984,000km² of ecosystems will be affected by nitrogen deposition above critical loads, a reduction of 20% compared to 2005 .

In both 2005 and 2020, the critical loads for eutrophication were exceeded in almost all EEA member and cooperating countries. Exceedances result from the deposition of both oxidised and reduced nitrogen compounds.

Oxidised nitrogen is emitted by combustion processes. In 2020, of the 32 EEA member and six cooperating countries, the deposition of oxidised nitrogen (NO₂, nitric acid and nitrate-containing particles) was highest in Belgium, northern Germany, northern Italy, the Netherlands and Poland.

Reduced nitrogen in the 32 EEA member countries is emitted mainly from the agriculture sector, which accounted for 94% of all reduced nitrogen (about 73% from livestock) deposited in 2020. Reduced nitrogen is deposited in ecosystems as NH₃ and ammonium (NH₄⁺). Deposition was highest in Belgium, parts of France, northern Germany, northern Italy, the Netherlands and Poland.

On a regional scale, the magnitude of critical load exceedances was highest in the Po Valley in Italy, along the Dutch-German and German-Danish borders, and in north-eastern Spain.