Ecosystem quality and trends in nitrogen availability, 2018

Nitrogen deposition in natural areas above critical levels

The area of terrestrial ecosystems where nitrogen deposition exceeds the critical loads has decreased from about 80% in 1995 to about 70% in 2018. The difference (exceedance) between nitrogen deposition and critical load is a measure of the risk of a decline in ecological quality.

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 (moderate) conditions, although the area of terrestrial ecosystems with good conditions was still limited in 2018. The increase in area with good conditions is particularly noticeable in the dunes. In all ecosystems there has on average been no net improvement in conditions since 2010. 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 conditions are suitable for ecosystem conservation.

Vulnerable plant species disappearing

Too much available nitrogen in the soil is a major reason for the loss of rare species in ecosystems. The increase in nitrogen concentrations in the soil is caused, among other things, by the atmospheric deposition of nitrogen. Two-thirds of the nitrogen deposited on the soil is in the form of ammonia from agricultural emissions; the remainder is from nitrogen oxide emissions from transport, industry and other sources. When nitrogen deposition exceeds the critical load, vulnerable species will disappear. The higher the exceedance and the longer the period of exceedance, the greater the impacts. Nutrient-poor ecosystems are especially 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 subject to high levels of nitrogen deposition. In ecosystems that are particularly sensitive to nitrogen deposition, such as forest, heath and open dunes, conditions throughout almost the entire area are moderate to bad. Critical loads are exceeded in almost the entire area of heath, and virtually the entire area falls in the quality categories moderate to bad. For open dunes the situation is slightly better; here most of the surface area falls within the category moderate. Eutrophication via nitrogen deposition is particularly problematic on the nutrient-poor sandy soils, which are highly sensitive to nitrogen deposition and where deposition levels from intensive livestock farming are especially high. Many of the ecosystems in the north and west of the country are less sensitive to nitrogen deposition. Most of these are naturally nutrient-rich grasslands and marshes in areas of marine clay or river clay.

• Ammoniak in lucht, 2005-2022

Policy focuses on improving environmental conditions

To prevent the effects of eutrophication and acidification, Dutch environmental policy focuses on reducing emissions of eutrophying and acidifying substances in the Netherlands and surrounding countries. 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 ecosystems and species.

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

The concentrations of atmospheric ammonia have not declined since 2000, and have even increased slightly in the period 2005-2014 (Stolk et al. 2017). This trend has also been observed in the Ammonia Monitoring Network in Natural Areas (MAN), which has been operational since 2005. It is an indication that the ammonia load in ecosystems (Natura 2000 sites) is no longer declining, whereas this is necessary for the sustainable conservation of these ecosystems.

In 2015 the government introduced the Integrated Approach to Nitrogen (PAS) with the aim of reducing nitrogen deposition, improving ecological quality in natural areas and 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).

Restoration measures to combat acidification and eutrophication

Nature restoration measures have been taken in natural areas since 1989, first under the subsidy scheme for effect-oriented measures (EGM) and in recent years under the 'quality initiative for nature and landscape' (SKNL) and the Integrated Approach to Nitrogen (PAS). 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