Ecosystem quality and trends in nitrogen availability, 1994-2021

Nitrogen deposition in natural areas above critical levels

The critical deposition load (CDL) is the maximum amount of nitrogen that an ecosystem can be exposed to for long periods without significant harmful effects occurring. The difference between actual deposition and the CDL is a measure of the risk of a decline in ecological quality. The higher the exceedance and the longer it lasts, the greater the effect. From the early 1990s to about 2010 nitrogen deposition declined, and so exceedance of the CDL also declined. As a result, the environmental pressure from nitrogen deposition on terrestrial ecosystems has also been reduced. The area of terrestrial ecosystems where exceedance of the CDL is extremely high (more than 20 kg N/ha/y) fell from 51% in 1994 to about 1% in 2021. The total area of terrestrial ecosystems where nitrogen deposition exceeds the CDL has decreased from about 75% in 1994 to about 64% in 2021. Over the past decade there has been no further decline in deposition levels.

Increase in area with better environmental conditions
The decline in nitrogen deposition has led to an increase in the area of natural and semi-natural habitat with better environmental conditions. Environmental conditions, such as nitrogen deposition, acidity (pH) and average spring groundwater level (GVG), are assessed according to the WMBN monitoring and evaluation methodology, which has three categories ('good', 'poor' and 'bad') (van Beek et al., 2018). This indicator concerns only nitrogen deposition. From 1994 the area of terrestrial ecosystems with 'good' conditions has increased from about 4% to 14%, but in 2021 remains inadequate. The area where nitrogen deposition does not exceed the CDL matches the area where environmental conditions are assessed as 'good' and where nitrogen deposition levels do not prevent the sustainable conservation of ecosystems such as heath and forest.

• Stikstofdepositie, 1990-2022

Vulnerable plant species disappearing

Too much available nitrogen in the soil is a major cause of the loss of rare species in ecosystems. About two-thirds of all the nitrogen deposited on soils in the Netherlands is in the form of ammonia. Most of this is from agricultural emissions; the remainder is from nitrogen oxide emissions from transport, industry and other sources. When nitrogen deposition exceeds the CDL, the probability that vulnerable species will disappear increases. Ecosystems that require nutrient-poor conditions are particularly sensitive to nitrogen deposition.

• Ammoniakemissie door de land- en tuinbouw, 1990-2022

Exceedance of CDL has the biggest impact on sandy soils

Approximately three-quarters of the total area of terrestrial ecosystems in the Netherlands are affected by high levels of nitrogen deposition. In ecosystems that are particularly sensitive to nitrogen deposition, such as forest, heath and open dunes on sandy soils, environmental conditions throughout the majority of the area are 'poor' to 'bad'. Critical loads are exceeded in 96% of the area of 'heath' ecosystem, and virtually the entire area of heath falls in the quality categories 'poor' to 'bad'. For open dunes the situation is slightly better as most of the area falls within the category 'poor'. Eutrophication by nitrogen deposition is particularly problematic on the nutrient-poor sandy soils in the south and east of the Netherlands, which support ecosystems that are highly sensitive to nitrogen deposition and where deposition levels from intensive livestock farming are especially high. Many of the natural and semi-natural grasslands and marshes, particularly those in river and marine clay regions in the north and west of the country, are not sensitive to nitrogen deposition.

• Ammoniak in lucht, 2005-2022

Policy focuses on reducing environmental pressure

To prevent the effects of eutrophication and acidification, Dutch environmental policy focuses on reducing emissions of eutrophying and acidifying substances in the Netherlands.
Over the last few decades, both national and international environmental policies have led to cleaner air, resulting in lower acid and nitrogen deposition on ecosystems. However, the achievements of environmental policy are not yet sufficient to create 'good' conditions for the sustainable conservation of all ecosystems and species.

• Grootschalige luchtverontreiniging de "National Emission Ceilings": emissies, 1990 - 2021

Since 2010 the reduction in nitrogen deposition has stagnated, primarily because ammonia emissions have hardly decreased. Between 2013 and 2017 ammonia emissions even increased slightly owing to an increase in the number of dairy cattle as a consequence of the lifting of milk quota. Since 2018 ammonia emissions have fallen slightly again. This trend has also been observed in the ammonia concentrations measured at 35 sampling points in the National Air Quality Monitoring Network (LML) and the Ammonia Monitoring Network in Natural Areas (MAN). It is an indication that the nitrogen load on ecosystems has hardly declined, whereas this is necessary for the sustainable conservation of these ecosystems.

The Integrated Approach to Nitrogen (PAS) was introduced in 2015 with the aim of reducing nitrogen deposition and improving ecological quality in Natura 2000 sites while at the same time permitting economic development. In 2019 the Council of State decided that the PAS cannot guarantee that the conditions for nature conservation and restoration will be good enough to provide a sufficient basis for permitting new development or activities. To resolve the nitrogen crisis, the government will have to take ambitious measures to reduce nitrogen emissions to levels that will allow the nature conservation objectives to be achieved (Adviescollege Stikstofproblematiek, 2020). This is the purpose of the Nitrogen Reduction and Nature Improvement Act, which entered into force on 1 July 2021. Among other things, the Act permits the introduction of binding nitrogen reduction targets. It also requires that a programme of measures be drawn up to achieve those targets and restore ecosystem quality. The Act sets targets for the area of nitrogen-sensitive habitat in Natura 2000 sites where the nitrogen deposition level is lower than the CDL: the target for 2025 is 40%, for 2030 is 50% and for 2035 is 74%.

The indicator on this page shows the exceedance of the CDL in all Dutch terrestrial ecosystems, including those outside Natura 2000 sites. The area of nitrogen-sensitive habitat types in Natura 2000 sites where nitrogen deposition levels are below the CDL increased from 20% in 2005 to 30% in 2021.

• Overschrijding van kritische depositiewaarde in Natura 2000-gebieden, 2005-2023
• Ammoniak in lucht, 2005-2022
• Grootschalige luchtverontreiniging de "National Emission Ceilings": emissies, 1990 - 2021
• Ammoniakemissie door de land- en tuinbouw, 1990-2022

Restoration measures to improve environmental conditions

Nature restoration measures have been taken in natural areas to combat the effects of acidification and eutrophication since 1989, first under the subsidy scheme for effect-oriented measures (EGM), subsequently under the 'quality initiative for nature and landscape' (SKNL) and the Integrated Approach to Nitrogen (PAS), and recently under the 'Nature Programme' (Programma Natuur). The Nature Programme is aimed at restoring and improving the quality of natural and semi-natural habitats in Natura 2000 sites in addition to the agreements made in the Nature Pact. In the Nature Pact (EZ, 2013) the national and provincial governments have agreed to maintain ecological quality within the national ecological network by providing a sufficient level of standard conservation management and to raise ecological quality by intensifying efforts for temporary or permanent restoration measures aimed at improving water quality and environmental conditions.

Many of the restoration measures are not only geared to removing nutrients, but also aim to combat acidification and reduced groundwater levels/desiccation. The availability of nutrients depends not only on the current deposition of nitrogen, but also on reduced water levels and the quality of surface water and groundwater. Nitrogen deposition raises the acidity of soils in natural areas, leading to the decline or disappearance of plant and animal species in those areas. Soil acidity can also be influenced by changes in hydrological conditions, such as a loss of base-rich groundwater seepage or the accumulation of organic matter in the humus layer. Acidification, eutrophication and desiccation are environmental factors that can reinforce each other.

• Geschiktheid zuurgraad bodem verzuringsgevoelige landnatuur, 2018
• Geschiktheid grondwaterstand verdrogingsgevoelige landnatuur, 2018