Ecosystem quality and trends in nitrogen availability, 2020

Nitrogen deposition in natural areas above critical levels

The difference (exceedance) between deposition and critical load is a measure of the risk of a decline in ecological quality. The area of terrestrial ecosystems where nitrogen deposition exceeds the critical loads has decreased from about 75% in 1994 to about 62% in 2020. In the same period, the area of terrestrial ecosystems where the exceedance of critical loads was more than 20 kg N/ha/y decreased from 50% to almost 0%.

The sharp decline in nitrogen deposition since the early 1990s has led to an increase in the area of natural and semi-natural habitat with better conditions, although the area of terrestrial ecosystems with good conditions was still limited in 2020. The area where nitrogen deposition does not exceed the critical load (green) matches the area of ecosystem assessed as being of 'good ecological quality' in relation to the environmental condition 'nitrogen load' and where nitrogen conditions are suitable for the sustainable conservation of ecosystems such as heath and forest.

• Nitrogen deposition, 1990-2018

Vulnerable plant species disappearing

Too much available nitrogen in the soil is a major cause of the loss of rare species in ecosystems. 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 critical load, the probability that vulnerable species will disappear increases. The higher the exceedance and the longer the period of exceedance, the greater the impact. Ecosystems that require nutrient-poor conditions are particularly sensitive to nitrogen deposition.

Exceedance of critical nitrogen deposition load 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, conditions throughout the majority of the area are moderate to bad. Critical loads are exceeded in 90% of the area of heath, and virtually the entire area of heath falls in the quality categories moderate to bad. For open dunes the situation is slightly better as most of the surface area falls within the category moderate. Eutrophication via 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 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.

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 (Buijsman et al., 2010). However, the achievements of environmental policy are not yet sufficient to create good conditions for the sustainable conservation of all ecosystems and species.
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 natural areas 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. In its coalition agreement the Dutch government is committed to bringing forward the targets set for 2035 under the Nitrogen Reduction and Nature Improvement Act and making additional funding available.

• 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.

• Ecosystem quality and trends in soil pH, 2018
• Ecosystem quality and trends in groundwater-dependent ecosystems, 2018