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

• 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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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

• Reactive nitrogen (Nr) occurs in different forms, arises from a wide range of activities and sources, and leads to environmental impacts over different spatial and temporal scales.

• Integrated approaches to N management are anticipated to provide more effective (larger decreases in unwanted emissions) and /or more efficient (less side effects, less costs) policy measures than policy measures based on single sources and pollutant species.

• There are many notions of integrated approaches, but as yet little consensus about the best integrated approaches. There is also little quantitative empirical evidence of the performance of these approaches in practice.

• The pitfall of integrated approaches is that they may be more complex to agree, leading to a delayed implementation.

Approaches

• Based on recent literature and a discussion among experts, the present chapter provides a conceptual framework for developing integrated approaches to N management.

• Whilst discussing the framework, various examples of existing partially integrated N management approaches have been considered.

• A package of key actions in different sectors is envisaged that, together, should contribute to further developing integrated approaches to N management in the future

Executive summary

Nature of the issue

• Reactive nitrogen (Nr) has well-documented positive effects in agricultural and industrial production systems, human nutrition and food security. Limited Nr supply was a key constraint to European food and industrial production, which has been overcome by Nr from the Haber–Bosch process.

• Given the huge diversity in Nr uses, it becomes a major challenge to summarize an overall inventory of Nr benefits. This full list of benefits needs to be quantified if society is to develop sound approaches to optimize Nr management, balancing the benefits against the environmental threats.

Approaches

• When reviewing trends in European Nr production rates, including those from chemical and biological fixation processes, and the consumption of this Nr in human activities, agriculture is by far the largest sector driving Nr creation.

• Particular attention has been given to relationships between N application rates, productivity and quality of products from major crops and livestock types, including consideration of the mechanisms underlying variations in N response/outputs and the derived impacts on land use and land requirements.

Key findings/state of knowledge

• The economic value of N benefits to the European economy is very substantial. Almost half of the global food can be produced because of Nr from the Haber–Bosch, and cereal yields in Europe without fertilizer would only amount to half to two-thirds of those with fertilizer application at economically optimal rates.

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Executive summary

Nature of the problem

• Anthropogenic increase of nitrogen in water poses direct threats to human and aquatic ecosystems. High nitrate concentrations in drinking water are dangerous for human health. In aquatic ecosystems the nitrogen enrichment produces eutrophication, which is responsible for toxic algal blooms, water anoxia, fish kills and habitat and biodiversity loss.

• The continuous nitrogen export to waters reduces the capacity of aquatic ecosystems to absorb, reorganise and adapt to external stress, increasing their vulnerability to future unexpected natural or climate events.

Key findings/state of knowledge

• Nitrogen concentrations in European rivers, lakes, aquifers and coastal waters are high in many regions. In addition nitrate concentrations are increasing in groundwaters, threatening the long term quality of the resource.

• In Europe, nitrogen pressures occur over large areas, implying elevated costs for meeting the long-term good chemical and ecological water quality requirements. A significant part of the European population could be potentially exposed to high nitrate values in drinking water if adequate treatments were not in place. Furthermore many of European aquatic ecosystems are eutrophic or at risk of eutrophication.

• Nitrogen pressures have reduced biodiversity and damaged the resilience of aquatic ecosystems and continue to pose a threat to the aquatic environment and to the provision of goods and services from the aquatic ecosystems.

• Even under favourable land use scenarios the nitrogen export to European waters and seas is likely to remain significant in the near future. The effects of climate change on nitrogen export to water are still uncertain.

Executive summary

Nature of the problem

• Freshwater ecosystems play a key role in the European nitrogen (N) cycle, both as a reactive agent that transfers, stores and processes N loadings from the atmosphere and terrestrial ecosystems, and as a natural environment severely impacted by the increase of these loadings.

Approaches

• This chapter is a review of major processes and factors controlling N transport and transformations for running waters, standing waters, groundwaters and riparian wetlands.

Key findings/state of knowledge

• The major factor controlling N processes in freshwater ecosystems is the residence time of water, which varies widely both in space and in time, and which is sensitive to changes in climate, land use and management.

• The effects of increased N loadings to European freshwaters include acidification in semi-natural environments, and eutrophication in more disturbed ecosystems, with associated loss of biodiversity in both cases.

• An important part of the nitrogen transferred by surface waters is in the form of organic N, as dissolved organic N (DON) and particulate organic N (PON). This part is dominant in semi-natural catchments throughout Europe and remains a significant component of the total N load even in nitrate enriched rivers.

• In eutrophicated standing freshwaters N can be a factor limiting or co-limiting biological production, and control of both N and phosphorus (P) loading is often needed in impacted areas, if ecological quality is to be restored.

Executive summary

Nature of the problem

• Single issue policies have been an effective means of reducing reactive nitrogen (Nr) emissions in the EU, but to make further reductions more-integrated approaches are required.

Approaches

• This chapter shows how cost–benefit analysis (CBA) can provide guidance for the setting of new policy priorities for the abatement of the European Nr emissions from an integrated perspective.

• Data on costs and benefits of Nr-abatement, including four national and regional case studies, are reviewed and made comparable by expression in euro per kg of added Nr (agriculture) or euro per kg of reduced Nr emission (unit cost approach).

• Social cost estimates are based on Willingness to Pay (WTP) for human life or health, for ecosystem services and greenhouse gas (GHG) emission reduction.

Key findings

• The total annual Nr-related damage in EU27 ranges between 70 and 320 billion Euro, equivalent to 150–750 euro/capita, of which about 75% is related to health damage and air pollution. This damage cost constitutes 1%–4% of the average European income.

• Inferred social costs of health impacts from NOx are highest (10–30 euro per kg of pollutant-Nr emission). Health costs from secondary ammonium particles (2–20 euro/kg N), from GHG balance effects of N2O (5–15 euro/kg N), from ecosystem impacts via N-runoff (5–20 euro/kg N) and by N-deposition (2–10 euro/kg N) are intermediate. Costs of health impacts from NO3 in drinking water (0–4 euro/kg N) and by N2O via stratospheric ozone depletion (1–3 euro/kg N) are estimated to be low.

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