Executive summary

Nature of the problem

• Increased public and institutional awareness of both the benefits and threats of nitrogen has the potential to greatly increase the efficacy of nitrogen policy.

• Insufficient recognition of the financial, behavioural and cultural barriers to achieving an optimal nitrogen future risks policy antagonisms and failure.

• Here we examine some of the key societal levers for and barriers to achieving an optimal nitrogen future in Europe, drawing lessons from the more-developed societal and policy challenge of climate change mitigation.

Key findings/state of knowledge

• There is currently a very low level of public and media awareness of nitrogen impacts and policies. However, awareness is high regarding the threats and benefits of ‘carbon’ to society (e.g. energy use and enhanced climate change).

• Many national climate change mitigation policies now overtly recognize the importance of societal choice, and are increasingly utilizing behavioural change strategies to achieve greenhouse gas emission reduction targets.

• In achieving an optimal nitrogen future, lessons can and should be learned from existing climate change-focused communication and behavioural science (e.g. use of a ‘segmented strategy’ to reach disparate groups of stakeholders).

• Key sectors where societal choice has the potential to greatly influence nitrogen use efficiency include food production, consumption and waste.

Executive summary

Nature of the problem

• Anthropogenic releases of reactive nitrogen (Nr) can disturb natural systems and affect human health and welfare in many different ways. Scientific and policy views of the nitrogen cycle have typically addressed these problems from separate perspectives, looking in each case at only part of the overall issue.

• Given the multi-faceted nature of the nitrogen cycle, it is a major challenge to develop a more-integrated understanding of how different areas of nitrogen science and policies fit together.

Approaches

• Observations from the first part of the European Nitrogen Assessment (ENA Part I) are summarized, considering the distinctive character of Nr in Europe, the benefits and threats, and the current policies. Approaches to developing the following parts of the Assessment are discussed with an emphasis on how to draw out the key issues.

Key findings

• Recognizing the multi-pollutant, multi-phase complexity of the nitrogen cycle, it is concluded that it is essential to focus on a limited set of priority issues to allow effective communication between nitrogen scientists and policy makers.

• A pathway is developed for prioritization of the key environmental concerns of excess Nr. Starting with around twenty environmental effects, the list is reduced down, first to nine main concerns, and then to five key societal threats.

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Executive summary

Nature of the problem

• Europe, and especially the European Union (EU), has many governmental policy measures aimed at decreasing unwanted reactive nitrogen (Nr) emissions from combustion, agriculture and urban wastes. Many of these policy measures have an ‘effects-based approach’, and focus on single Nr compounds, single sectors and either on air or waters.

• This chapter addresses the origin, objectives and targets of EU policy measures related to Nr emissions, considers which instruments are being used to implement the policies and briefly discusses the effects of the policy measures.

Approaches

• The chapter starts with a brief description of the basic elements of governmental policy measures.

• A review of the main international conventions and EU policies related to emissions of Nr to air and water is then provided.

• Finally the chapter provides a semi-quantitative assessment of the effectiveness and efficiency of European policy measures.

Key findings/state of knowledge

• International conventions and other treaties have played a key role in raising awareness and establishing policy measures for Nr emissions abatement in EU through so-called Directives and Regulations.

• There are many different EU Directives, often addressing individual Nr compounds from individual sectors (e.g. NOx emissions from combustion; NH3 emissions from agriculture, pollution of groundwater and surface water by nitrates from agriculture, discharge of total nitrogen from urban sewage to surface waters).

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Executive summary

Nature of the problem

• The transfer of nitrogen by either farm management activities or natural processes (through the atmosphere and the hydrological network) can feed into the N cascade and lead to indirect and unexpected reactive nitrogen emissions.

• This transfer can lead to large N deposition rates and impacts to sensitive ecosystems. It can also promote further N2O emission in areas where conditions are more favourable for denitrification.

• In rural landscapes, the relevant scale is the scale where N is managed by farm activities and where environmental measures are applied.

Approaches

• Mitigating nitrogen at landscape scale requires consideration of the interactions between natural and anthropogenic (i.e. farm management) processes.

• Owing to the complex nature and spatial extent of rural landscapes, experimental assessments of reactive N flows at this scale are difficult and often incomplete. It should include measurement of N flows in the different compartments of the environment and comprehensive datasets on the environment (soils, hydrology, land use, etc.) and on farm management.

• Modelling is the preferred tool to investigate the complex relationships between anthropogenic and natural processes at landscape scale although verification by measurements is required. Up to now, no model includes all the components of landscape scale N flows: farm functioning, short range atmospheric transfer, hydrology and ecosystem modelling.

Executive summary

Nature of the problem

• Reactive nitrogen has both positive and negative effects on ecosystems and human health. Reactive nitrogen is formed through the use of fossil fuels releasing large amounts of nitrogen oxides into the atmosphere and through the production of ammonia by the Haber–Bosch process and using it in agriculture to increase our food, feed and fuel production. While the use of nitrogen as a fertilizer and chemical product has brought enormous benefits, losses of fertilizer nitrogen and combustion nitrogen to the environment lead to many side effects on human health, ecosystem health, biodiversity and climate.

Approaches

• The European nitrogen problem is placed in a global perspective, showing the European nitrogen fixation, transport and environmental impacts compared with different regions of the globe.

Key findings/state of knowledge

• Humans, largely through agriculture, but also through burning of fossil fuels, have had a huge impact on the nitrogen budget of the Earth. Europe is one of the leading producers of reactive nitrogen, but it is also the first region in the world where the issue was recognized and in some parts of Europe the reactive nitrogen losses to the environment started to decrease. Europe is a nitrogen hotspot in the world with high nitrogen export through rivers to the coast, NOx and particulate matter concentrations and 10% of the global N2O emissions.

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Executive summary

Nature of the problem

• Biodiversity is the variability among living organisms, from genes to the biosphere. The value of biodiversity is multifold, from preserving the integrity of the biosphere as a whole, to providing food and medicines, to spiritual and aesthetic well-being.

• One of the major drivers of biodiversity loss in Europe is atmospheric deposition of reactive nitrogen (Nr).

Approaches

• This chapter focuses on Nr impacts on European plant species diversity; in particular, the number and abundance of different species in a given area, and the presence of characteristic species of sensitive ecosystems.

• We summarise both the scientific and the policy aspects of Nr impacts on diversity and identify, using a range of evidence, the most vulnerable ecosystems and regions in Europe.

Key findings/state of knowledge

• Reactive nitrogen impacts vegetation diversity through direct foliar damage, eutrophication, acidification, and susceptibility to secondary stress.

• Species and communities most sensitive to chronically elevated Nr deposition are those that are adapted to low nutrient levels, or are poorly buffered against acidification. Grassland, heathland, peatland, forest, and arctic/montane ecosystems are recognised as vulnerable habitats in Europe; other habitats may be vulnerable but are still poorly studied.

• It is not yet clear if different wet-deposited forms of Nr (e.g. nitrate, NO3− versus ammonium, NH4+) have different effects on biodiversity. However, gaseous ammonia (NH3) can be particularly harmful to vegetation, especially lower plants, through direct foliar damage.

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A new challenge from a past solution

Human perturbation of the nitrogen cycle represents a major example of global geo-engineering. Historically, the limited availability of reactive nitrogen compounds has provided a key constraint to human activities. Although the element nitrogen is extremely abundant, making up 78% of the Earth's atmosphere, it exists mainly as unreactive di-nitrogen (N2). By contrast, to be useable by most plants and animals, reactive nitrogen (Nr) forms are needed. These include oxidized and reduced nitrogen compounds, such as nitric acid, ammonia, nitrates, ammonium and organic nitrogen compounds, each of which is normally scarce in the natural environment.

The two main historical needs for reactive nitrogen have been to provide fertilizers to increase food production and as a basis for the manufacture of munitions. Biological nitrogen fixation has always added new reactive nitrogen into the system, but the inputs have been barely sufficient for human needs. As a result, traditional agricultural production was highly dependent on effective recycling of nitrogen in manures.

By the end of the nineteenth century, an increasing human population combined with expanding military needs required that large amounts of extra reactive nitrogen be added into circulation. These demands were met by increased mining of reactive nitrogen deposits, including Chile saltpetre and guano, supplemented by the extraction of reactive nitrogen from coal and peat (Vincent, 1901; Clow and Clow, 1952; Watt, 2003; Sutton et al., 2008).

Main messages

Too much nitrogen harms the environment and the economy

• Over the past century humans have caused unprecedented changes to the global nitrogen cycle, converting atmospheric di-nitrogen (N2) into many reactive nitrogen (Nr) forms, doubling the total fixation of Nr globally and more than tripling it in Europe.

• The increased use of Nr as fertilizer allows a growing world population, but has considerable adverse effects on the environment and human health. Five key societal threats of Nr can be identified: to water quality, air quality, greenhouse balance, ecosystems and biodiversity, and soil quality.

• Cost–benefit analysis highlights how the overall environmental costs of all Nr losses in Europe (estimated at €70–€320 billion per year at current rates) outweigh the direct economic benefits of Nr in agriculture. The highest societal costs are associated with loss of air quality and water quality, linked to impacts on ecosystems and especially on human health.

Nitrogen cascade and budgets

• The different forms of Nr inter-convert through the environment, so that one atom of Nr may take part in many environmental effects, until it is immobilized or eventually denitrified back to N2. The fate of anthropogenic Nr can therefore be seen as a cascade of Nr forms and effects. The cascade highlights how policy responses to different Nr forms and issues are inter-related, and that a holistic approach is needed, maximizing the abatement synergies and minimizing the trade-offs.

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Executive summary

Nature of the problem

• Environmental problems related to nitrogen concern all economic sectors and impact all media: atmosphere, pedosphere, hydrosphere and anthroposphere.

• Therefore, the integration of fluxes allows an overall coverage of problems related to reactive nitrogen (Nr) in the environment, which is not accessible from sectoral approaches or by focusing on specific media.

Approaches

• This chapter presents a set of high resolution maps showing key elements of the N flux budget across Europe, including N2 and Nr fluxes.

• Comparative nitrogen budgets are also presented for a range of European countries, highlighting the most efficient strategies for mitigating Nr problems at a national scale. A new European Nitrogen Budget (EU-27) is presented on the basis of state-of-the-art Europe-wide models and databases focusing on different segments of Europe's society.

Key findings

• From c. 18 Tg Nr yr−1 input to agriculture in the EU-27, only about 7 Tg Nr yr−1 find their way to the consumer or are further processed by industry.

• Some 3.7 Tg Nr yr−1 is released by the burning of fossil fuels in the EU-27, whereby the contribution of the industry and energy sectors is equal to that of the transport sector. More than 8 Tg Nr yr−1 are disposed of to the hydrosphere, while the EU-27 is a net exporter of reactive nitrogen through atmospheric transport of c. 2.3 Tg Nr yr−1.

• The largest single sink for Nr appears to be denitrification to N2 in European coastal shelf regions (potentially as large as the input of mineral fertilizer, about 11 Tg N yr–1 for the EU-27); however, this sink is also the most uncertain, because of the uncertainty of Nr import from the open ocean.