Assessment of the relation between climate and nitrogen related policy for the Dutch situation

The overall objective of this assessment performed within the framework of the the Netherlands Research Programme on Scientific Assessment and Policy Analysis for Climate Change (WAB) was to investigate the relation between climate policies and nitrogen related policies and to determine the effect of reactive nitrogen abatement on greenhouse gas emissions and sinks in the Netherlands.

In general the major producers of reactive nitrogen, i.e industry (including energy), traffic and agriculture, are also major greenhouse gas emitters. The energy, industry and traffic sector are responsible for more than 90% of the emission of CO₂ equivalents in the Netherlands, while the nitrogen emission from industry, traffic and agriculture mainly consists of the emission of NO_x (90% of total Dutch NO_x emission). Agricultural activities contribute relatively more to the emission of nitrogen than to greenhouse gases. However, due to the interactions between the nitrogen and carbon cycle, agriculture is important both as source and sink of greenhouse gases. On the receptor side terrestrial and aquatic (eco)systems (including coastal waters) are important sinks for nitrogen and greenhouse gas emissions. At the same time these systems can also act as sources and thereby complicating relations between nitrogen and greenhouse gases considerably.

Five comprehensive smaller subsystems were identified for which the interactions between nitrogen and greenhouse gas emission could me more easily assessed and which are also relevant domains for (future) policies. These subsystems are:

• Emission of NH₃, N₂O, CO₂ and fine particles from energy production
• Impact of nitrogen fertilization on net greenhouse gas emissions in agricultural systems
• Impact of biofuel use, and associated land use change, on N and greenhouse gas emissions in the energy sector and agriculture
• Impact of nitrogen deposition and climate policies on net greenhouse gas emissions in terrestrial ecosystems
• Impact of nitrogen inputs on net greenhouse gas emissions in aquatic ecosystems

Besides the different conclusions for the different subsystems, the following policy relevant observations are made:

• Use of bio-fuels or bio-energy requires more knowledge before it is applied on a large-scale because of (1) the uncertainty about their net CO₂ effect, (2) the negative side-effects on the nitrogen cycle and (3) the competition with the need of land for nature and/or food production.
• Stimulating carbon storage in organic matter of natural and semi-natural ecosystems by nitrogen fertilization is a potentially a relevant but temporary option to compensate for the emission of GHG.
• Considering the adverse effects of over fertilization, it is crucial to optimize the production and use of chemical nitrogen fertilizer.
• Integrated nitrogen policy requires more insight in costs and benefits to find a common ground for comparison of different measures and to quantify damage effects per unit of nitrogen for the various nitrogen compounds.