Human Acceleration of the Nitrogen Cycle Managing Risks and Uncertainty

POLICY HIGHLIGHTS NITROGEN POLICY HIGHLIGHTSPOLICY

Three ways to tackle nitrogen pollution

Despite immense benefits in terms of food and energy security, the use of fertilisers and the burning of fossil fuels Did you know? release excess reactive nitrogen that poses serious threats Until one century ago, to health and the environment. Chilean saltpetre (and The use of chemically-reactive nitrogen in fertilisers has before it Peruvian brought immense benefits in terms of agriculture productivity guano) was the main and food security. Nitrogen also has many industrial uses and source of nitrogen for the combustion of fossil fuels releases reactive nitrogen to the world agriculture and atmosphere as a by-product. Since the start of the 20th century, industry. humans have doubled the inputs of reactive nitrogen to the environment (Fowler et al., 2013) and this now poses serious threats to health and the environment.

Excess nitrogen pollutes air, soil and water; increases greenhouse gas emissions; and impacts biodiversity and ecosystem functioning. Reactive nitrogen stimulates the formation of ground- level ozone and particles in the atmosphere; increases soil acidification; and, the transfer of nitrogen from terrestrial to coastal systems is leading to algal blooms and a decline in the quality of aquatic ecosystems. Not only is nitrogen a greenhouse gas (GHG) itself (in the form of nitrous oxide), but it also contributes to depletion of the stratospheric ozone.

Countering nitrogen pollution in a cost-effective way requires a threefold approach: l Implement impact-pathway analysis (IPA) to better managing the risks of air, soil, water and ecosystem pollution. l Manage nitrous oxide as part of GHG mitigation policies. l Monitor and manage any residual nitrogen excess by measuring the effect of the above measures on the national nitrogen budget.

Measures to counter nitrogen pollution should be based on their impact and applied as close as possible to the point of emission to maximise effectiveness and cost-efficiency. Often, the best environmental outcome and greater political acceptability will require a combination of measures: “polluter pays” and “beneficiary pays” policies, alongside direct environmental regulation.

THREE WAYS TO TACKLE NITROGEN POLUTION . 1 How excess nitrogen threatens 1health and the environment

AIR

Human activity – especially the burning of fossil fuels Air motions play a key role in the distribution of

– is a major source of nitrogen oxides (NOx) in the reactive nitrogen in the atmosphere and in its troposphere, the lowest region of Earth’s atmosphere. transport distance before “deposition” on the ground. In such combustion processes, under high temperature In the United States, the National Atmospheric

and pressure conditions, atmospheric nitrogen (N2) Deposition Program (NADP) has mapped the risk

combines with oxygen atoms to create NOx. Human of nitrogen aerosol deposition. As evidenced by the activity – especially agricultural practices – is also a risk assessment, it can be expected that ammonium + major source of ammonia (NH3). (NH4 ) wet deposition occurs near or downwind of – major agricultural centres, and that nitrate (NO3 )

In the atmosphere, nitrogen dioxide (NO2) and, to a levels in wet deposition are consistent with NOx

lesser extent, NH3, are directly harmful to human emissions (USEPA-SAB, 2011). health, increasing likelihood of respiratory problems.

NH3 and NOx can react with each other or with The health impact of air pollution by nitrogen incurs atmospheric components, contributing to the most social costs that are already in the hundreds of serious air pollution problems for human health billions of USD. This is because nitrogen compounds – airborne particulate matter (PM). The effects of represent a significant part of urban pollution with

PM can range from eye and respiratory irritation to fine particles (PM2.5) whose health cost in terms of cardiovascular disease, lung cancer and consequent premature deaths is estimated at USD 1.8 trillion in premature death. Exposure to high levels of ground-level OECD countries and USD 3.0 trillion in the BRIICS

ozone, caused by NOx and volatile organic compounds countries (Brazil, Russia, India, Indonesia, China that react under the influence of heat and the sun, and South Africa) (Roy and Braathen, 2017). For increases the risk of premature death from lung disease example, nitrogen-containing aerosols accounted

and also affects vegetation by damaging leaves and for an estimated 30% of PM2.5 emissions measured

reducing growth. NH3 can also be harmful to vegetation, in Beijing from June 2014 to April 2015 (Huang et al., especially lower plants, through direct damage to leaves. 2017).

Did you know? The atmosphere we breathe is 78%

dinitrogen (N2). However, if we had to rely on dinitrogen only, it would be like floating on the sea, dying of thirst.

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When adding ground-level ozone pollution, of which N2O contributes not only to climate change but also nitrogen is also a precursor, health costs amount to to the depletion of the stratospheric ozone layer, USD 1.9 trillion in OECD countries and USD 3.2 trillion which protects life on Earth by absorbing some of in BRIICS countries (Roy and Braathen, 2017). the ultraviolet rays from the sun. With the phasing-

out of chlorofluorocarbons (CFCs), 2N O has become a

Despite a steady decline in NOx emissions since major depleting threat for ozone in the stratosphere 2000, most EU countries have at least one city where (Ravishankara et al., 2009) and is currently unregulated the annual average concentration of NO2 exceeds by the Montreal Protocol on Substances that Deplete (sometimes considerably) the EU’s legal limit values, the Ozone Layer. which are set equal to the World Health Organisation (WHO) Air Quality Guideline (OECD, 2017). SOIL

GREENHOUSE BALANCE AND THE STRATOSPHERIC Many of the natural transformations involved in OZONE LAYER the biogeochemical nitrogen cycle are carried out

by microorganisms in soil. Conversion of N2 to Microbial “denitrification” is a key pathway in the biologically available (“reactive”) nitrogen, a process nitrogen cycle of soils and oceans, but a pathway called “fixation”, involves several processes, as part of that is still poorly understood. Denitrification returns the nitrogen cycle. nitrogen from the biosphere to the atmosphere as N2, thereby closing the nitrogen cycle; this may Nitrogen-fixing bacteria convert N2 to NH3, which + involve the production of nitrous oxide (N2O) as an tends to converts into NH4 in non-alkaline soils. intermediate product. Human activity – especially Under aerobic conditions (in the presence of oxygen), + - agriculture – is a major source of N2O production. nitrifying bacteria can oxidise NH4 to NO3 as an

N2O emissions of crops depend on the type of energy-yielding process. Because it releases hydrogen, fertiliser (with emissions typically being higher for nitrification contributes to the acidification of soils. urea than for ammonium nitrate) and soil type, with emissions generally high for clay soils with poor Under anaerobic conditions (in the absence of - drainage. oxygen), denitrifying bacteria can use NO3 in

place of oxygen, reducing it to N2. In the process,

N2O is the third most common long-lived GHG denitrification may generate 2N O. after carbon dioxide (CO2) and methane. The N2O greenhouse effect is partially offset by increased CO2 Microbial activity in soils is also driven by by ecosystems uptake due to nitrogen deposition. “rhizodeposition” – the release of organic carbon and

Did you know? Microbial denitrification is a key pathway in the nitrogen cycle of soils and oceans, but a pathway that is still poorly understood.

HOW EXCESS NITROGEN THREATENS HEALTH AND THE ENVIRONMENT . 3 THE MODELLING PHILOSOPHY . 4 organic nitrogen (e.g. amino acids) by plant roots Nitrogen finds its way into fresh water via pathways into their surrounding environment – and microbial that are mainly fed by agriculture, such as mineralisation of soil organic matter. While the groundwater, drainage water and runoff, as well available organic carbon and oxygen have a major as direct discharges of wastewater from firms and impact on total denitrification, the soil pH mainly sewage treatment plants, and atmospheric deposition. influences the 2N O/N2 ratio (the ratio tends to increase Nitrogen pathways in marine water include nitrogen with decreasing pH). imports by river discharge and precipitation; microbial

fixation of 2N ; and bacterial remineralisation of dead The major nitrogen threats to soil quality, for both particulate biomass in sediments. agricultural soils and natural soils, are related to acidification and loss of soil biodiversity. Soil Oceanic currents may shift the impact of excess acidification may lead to a decrease in crop and nitrogen over long distances. For example, nitrogen forest growth and leaching of components negatively from the Amazonian Basin, where soils are washed affecting water quality, including heavy metals. away by the rains as a result of deforestation and - Nitrogen may also be lost from soils as NO3 , via intensive agriculture, has largely contributed to the leaching, or in gaseous forms such as NH3, by proliferation of algae in coastal areas of the Caribbean. volatilisation, or else N2O and N2, via denitrification. Climate change could aggravate fresh water pollution The effect of nitrogen on diversity of soil micro by nitrogen. For example, climate change-induced organisms and the effects of changes of soil biodiversity precipitation changes alone are projected by one on soil fertility, crop production and nitrogen emissions recent study to increase runoff nitrogen in U.S. towards the environment are not fully understood. waterways by 19% on average over the remainder Very few studies have examined the links between the of the century under a business-as-usual climate nitrogen cycle, plant activity, and associated changes scenario (Sinha et al., 2017). Ocean dead zones are in microbial diversity. Despite the significance of soil particularly vulnerable to climate change, which organic matter in agricultural ecosystems, current exacerbates hypoxic conditions by increasing knowledge of the soil organic matter dynamics is still sea temperature, ocean acidification, sea level, limited. New nitrogen source discovered in Earth’s precipitation, and, in some regions, wind and storms bedrock challenges estimates of carbon sequestration (Altieri and Gedan, 2015). by natural ecosystems (Houlton et al., 2018).

WATER

Water pollution by nitrogen has high costs for human health as well as for ecosystems. High - concentrations of NO3 in drinking water can cause blood disorder in infants and may also increase risk of colorectal cancer (Schullehner et al., 2018). - NO3 contributes to eutrophication of coastal waters, which is responsible for algal blooms (including toxic algal blooms) on the surface and can lead to the reduction or even the disappearance of oxygen (“hypoxia”) and thus of fish in the deep waters that become “dead zones”. There is compelling evidence of a rapid increase in the number of ocean dead zones for about 50 years, since the term was first applied to the hypoxic area of the northern Gulf of Mexico, which receives large amounts of nutrients from the Mississippi and Atchafalaya river basins. Robert Diaz, of the Virginia Institute of Marine Sciences, has so far identifiedSource: W no less than 884 ocean dead zones in the world.

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Did you know? 70% of protected ecosystems across Europe exceed critical loads for eutrophication due to nitrogen deposition. (Posch et al., 2018)

ECOSYSTEMS AND BIODIVERSITY Act were affected by the direct toxicity of nitrogen, by eutrophication of their habitat or by the Nitrogen reduces the diversity of vegetation primarily spread of non-native plant species due to nitrogen through eutrophication and acidification. The pollution. accumulation of extra nutrients (eutrophication) is harming habitats whose biodiversity developed in Little recognition has been given to the direct response to low nutrient levels. Acidification environmental consequences of nutrients that fall is a cumulative problem for non-alkaline soils; as from the air as wet and dry deposition onto aquatic the acid-neutralising capacity of soils gets depleted, ecosystems. Even if nitrogen deposition rates were the ecosystems become increasingly sensitive to to be significantly reduced in the future, habitat additional acid inputs. More generally, ecosystem recovery can be very slow (Stevens, 2016). – + responses to the form of nitrogen (e.g. NO3 , NH3, NH4 , nitrogen-containing aerosols, ground-level ozone) Excess nitrogen (and phosphorus) in water can cause are complex and habitat dependent, with conversion overstimulation of growth of aquatic plants and between nitrogen forms resulting from the activities algae. Excessive growth of these organisms, in turn, of soil microbes. can use up dissolved oxygen as they decompose, and block the passage of light to deeper waters. Habitat changes caused by nitrogen excess may affect Eutrophication of lakes and coastal areas can occur, all taxonomic groups. Hernández et al., 2016 showed which produces unsightly scums of algae on the that 78 of the 1 400 species of invertebrates, vertebrates water surface, can occasionally result in fish kills, and plants listed under the US Endangered Species and can even “kill” a lake by depriving it of oxygen.

Table 1. KEY THREATS OF EXCESSIVE RELEASE OF NITROGEN INTO THE ENVIRONMENT

Environmental issue Adverse impact on health Main form of nitrogen Main activity and the environment involved

– Water Freshwater and marine water Nitrate (NO3 ) Agriculture, atmospheric deposition, pollution sewage discharge

Air Effects on human health Nitrogen oxides (NOx) Burning fossil fuels to a large extent

and vegetation Ammonia (NH3) Manure storage and spreading

Particulate matter Formed from NOx and NH3 precursors

Ground-level ozone Formed from NOx precursor

Greenhouse balance Climate change and ozone Nitrous oxide (N2O) Agriculture to a large extent and ozone layer layer depletion

+ Ecosystems and Eutrophication and acidification Nitrate, ammonium (NH4 ) Agriculture, atmospheric deposition, biodiversity of terrestrial ecosystems and organic nitrogen sewage discharge and freshwater and marine ecosystems Soil Soil acidification Chemical fertilisers and Agriculture organic nitrogen

HOW EXCESS NITROGEN THREATENS HEALTH AND THE ENVIRONMENT . 5 Understanding the “Nitrogen Cascade”

2In contrast with many other pollutants, nitrogen can change form and go a long way once released into the environment. As it moves through the biogeochemical pathways, the same nitrogen atom can cause a sequence of negative effects – in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on the climate.

For example, the biogeochemical path of a nitrogen Many transformations of nitrogen in various forms atom from its point of formation could be the contribute to its movement within and between

following. NOx emissions from cars and power plants terrestrial, atmospheric, and aquatic ecosystems. As

can form NO2, a vector of asthma, then create ground- a result, the intended beneficial effects of a policy for

level ozone (O3), a component of smog, and then be one ecosystem may become unintended detrimental

converted to nitric acid (HNO3), a major component effects for adjacent ecosystems, or even within the

of acid deposition; or, NOx can combine with NH3 to ecosystem in which nitrogen is released.

form fine particles of ammonium nitrate (NH4NO3), the inhalation of which can cause serious health Agricultural practices, in particular, can have problems. Once removed from the atmosphere, nitric unintended consequences if the nitrogen cascade is acid and ammonium nitrate particles can cause both not taken into account. Increased use of commercial fertilisation and acidification of soils, which in turn nitrogen fertiliser in the United States, by 72% - (via NO3 runoff and leaching) can lead to acidification between 1970 and 2010, for example, has fuelled - and eutrophication of freshwater. NO3 can then be an increase in yields but has also posed increased transported to coastal areas, where it contributes to risks to environmental quality. The Natural Resource the formation of dead zones: when fishermen trawl Conservation Service (NRCS) of the U.S. Department in these areas, little to nothing is caught. Finally, of Agriculture evaluated the use of conservation bacteria can convert reactive nitrogen in soil and practices on U.S. cropland in major river basins using

water into N2O, contributing to the greenhouse survey data collected over 2003-06. The NRCS found effect in the troposphere and the destruction of the that, on the whole, a great deal of improvement ozone layer in the stratosphere. This complex web was needed. For example, injecting or incorporating of transformations has been called the “nitrogen inorganic and organic nitrogen fertiliser into the soil cascade” (Figure 1). reduces atmospheric losses, but can increase nitrate leaching. Fertilising only during the growing season can reduce nitrate loss to water but may increase Did you know? nitrous oxide emissions to the atmosphere.

Nitrogen dioxide The “cascading nature” of nitrogen flows in the environment suggests there are benefits to (NO2) and ammonia coordination of practices, and of policies to incentivise them, rather than piecemeal control. Focusing on (NH3) are not only one particular environmental medium, such as air, air pollutants, but can create incentives for management that result in they can also form degradation in a different medium, such as water.

ammonium nitrate In general, not creating pollution in the first place (NH NO ) particles avoids the problems posed by trying to control 4 3 different nitrogen pathways. In the case of cropland, that are particularly application of the 4R concept (the right type of harmful to health. fertiliser at the right rate applied at the right time in the right place) to achieve better nitrogen use efficiency reduces nitrogen loss along all pathways, avoiding the trade-offs characteristic of most other conservation practices.

6 . OECD POLICY HIGHLIGHTS | Human Acceleration of the Nitrogen Cycle: Managing Risks and Uncertainty POLICY HIGHLIGHTS O 2 N 7

. O 2

N x 3 H org O N N N tion gases e tion tion Oceans Landscape Grasslands hica ne depl i ca p o z d org org o ci greenhouse Soils Soils a N N eutro x x Populated Vegetated O H N N y y O O People Forests Coastal bays and estuaries N N troposphere stratosphere UNDERSTANDING “NITROGEN THE UNDERSTANDING CASCADE” n tio matter and wetlands Surface water

i ca Animals e t oductivity cid r a p

Soils rticula a tems p Agriculture system sys co co Groundwater e e ne Crops o z o Terrestrial Aquatic Atmospheric y x H org O N N N x x O H N N denitriﬁcation potential Food production fertilisers and creation of synthetic “NEW”NITROGEN Energy production fuels and combustion of fossil The Nitrogen Cascade The Nitrogen .pdf. Science Advisory nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_008785 (undated), Board US EPA Source: THE NITROGEN CASCADE AND ITS IMPACTS ITS CASCADE AND NITROGEN 1. THE Figure Nitrogen pathways analysis and risk 3management

Three approaches exist to counter nitrogen pollution: that contribute to this impact. Better knowledge of these pathways can improve risk management l The spatially targeted risk approach seeks to better by identifying the points of cost-effective policy manage well-documented risks of air, soil and water intervention. For example, for a given risk of water

pollution and associated ecosystems through a pollution, reducing the NOx emissions that contribute detailed analysis of the biogeochemical pathways to the risk (by atmospheric deposition) may prove between nitrogen sources and impacts (“impact- more beneficial than reducing nitrogen from land-

pathway analysis”). based sources when NOx also causes health problems prior to deposition. l The global risk approach addresses the steady increase in nitrous oxide concentrations in the Impact-pathway analysis (IPA) evaluates the atmosphere. Nitrous oxide, which affects climate pathways that generate an impact (including through change and the stratospheric ozone layer, is the modelling) to estimate the expected benefits of only form of nitrogen that has a global impact. It is possible emissions changes. IPA recognises that a long-lived and well-mixed gas in the atmosphere, nitrogen can move between environmental media so the challenges it poses can only be tackled (air, water, soil and biota) as it travels along pathways globally. from one or more sources to a receptor.

l The precautionary approach takes into account IPA can be carried out in four steps: the uncertainty of cascading effects and anticipates potentially significant long-term impacts, such as l First, identify and delineate the different “nitrogen the risk of undermining the resilience (of exceeding emission zones” of relevance to the impact (i.e. the the coping capacity) of ecosystems to nitrogen “risk area”). overload. It aims to monitor and manage trends in the excess of nitrogen entering the environment l Second, estimate the potential for new or additional by measuring the overall effect of the two previous emission reductions in each emission zone. approaches on the national nitrogen balance. l Third, compare the cost-effectiveness of emission THE SPATIALLY TARGETED RISK APPROACH: USING reductions in the different emission zones. IMPACT-PATHWAY ANALYSIS l Fourth, estimate the co-benefits of reducing Policies aimed at managing the risks posed by nitrogen emissions in the different emission zones nitrogen often focus on a specific impact without – that is, the damage avoided in all of the regions fully considering the biogeochemical pathways through which that nitrogen would cascade.

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NITROGEN PATHWAYS ANALYSIS AND RISK MANAGEMENT RISK AND ANALYSIS PATHWAYS NITROGEN takes – the “nitrogen cascade” and consequently the and consequently cascade” “nitrogen – the takes and ecosystems. to human health damages extent of that this suggests principle” “precautionary But the acting to limit not stop us from uncertainty should entering the environment. the amount of nitrogen when an principle, precautionary to the According human health or the of harm to threats raises activity be taken, should measures precautionary environment, not fully are relationships if some cause and effect even established scientifically. require does not necessarily uncertainty Managing the Rather, in all emission sources. a reduction associated should be closely approach precautionary part of a dual method of as with the risk approach A cycle. human impacts on the nitrogen managing the total aim to limit would approach precautionary where entering the system and, load nitrogen reactive to and in in addition measures propose appropriate, measures. with risk management line the thorny raises approach precautionary The of the question of the limit to be set in terms planet. of the or even balance of a country, nitrogen limit but in the such to discuss any It is too early countries could establish an economy- meantime, balance and begin to monitor and, wide nitrogen involve would This trends. manage as appropriate, introduced assessing the total amount of nitrogen and monitoring all sources from into the environment and source – both by to report in order these sources year, each released – the amount of nitrogen overall should This also taking into account denitrification. to with risk-based efforts parallel in be undertaken impacts. specific nitrogen manage

O as possible 2 O, because risk exposure – be because risk exposure O, 2 O is part of a basket of GHGs of a basket part O is 2 O emissions. The climate change mitigation goal set mitigation climate change The O emissions. 2 out in the Paris Agreement does not set an individual Agreement out in the Paris global a but rather GHG, for each target reduction N target. temperature under the United Nations Framework Convention Convention under the United Nations Framework will on Climate Change (UNFCCC) and countries prioritise GHG emission reductions to decide how gases in their nationally sectors and different across the five-yearly informed by determined contributions, Agreement. under the Paris envisaged global stocktakes it the risk of climate change or the risk of depleting or the risk of it the risk of climate change Delineating emission zones, global. – is the ozone layer the more Indeed, be of no use. would possible, if even to find the one it is likely the more compare, to sources is the most cost-effective. emission reduction which for of N sources as many words, In other Applying a global approach does not necessarily mean does not necessarily global approach a Applying in aim for a reduction must government that each N should be identified, wherever they are in a given given in a are they wherever should be identified, possible the costs – and if so as to compare country, reducing their emissions. the ancillary – of benefits The increased amount of reactive nitrogen produced nitrogen of reactive amount increased The andproduction) (for food intentionally humans, by of fossil fuel combustion and (result unintentionally has enhanced the speed ofprocesses) industrial is being nitrogen which at – the rates cycling nitrogen remains There the environment. to and lost from added of thewhat this acceleration uncertainty about exactly that nitrogen pathways means for the cycle nitrogen THE PRECAUTIONARY APPROACH: ANTICIPATING ANTICIPATING APPROACH: PRECAUTIONARY THE IMPACTS LONG-TERM IPA does not apply to N does not apply IPA THE GLOBAL RISK APPROACH: MANAGING NITROUS NITROUS MANAGING APPROACH: RISK GLOBAL THE OXIDE To implement the spatially targeted risk approach, approach, risk targeted the spatially implement To but efficient, economically not only policies need to be vital, is Public acceptability feasible. practically also to delineate of stakeholders including the agreement Administrative zones. and emission risk areas pathways nitrogen also arise: feasibility issues may boundaries. administrative seldom follow The feasibility of IPA raises the issue of cost. As a issue of cost. the raises feasibility of IPA The sophistication of IPA the level principle, general pollution of nitrogen the expected level should match and precise a at stake, impacts are When major risk. On the other 2). 1 and (Boxes is required detailed IPA be used. can a basic IPA low, are when risk levels hand, Targeted policies to halt nitrogen pollution

4Nitrogen emissions have been reduced in the OECD area over the past three decades, but there are hotspots of nitrogen pollution in air, soil and water.

OECD countries have adopted measures to reduce long- cumulative concentration of N2O in the atmosphere range transported air emissions as well as targeted continues to increase (by 6% between 1990 and 2016 measures to reduce local emissions (e.g. in cities and to according to the National Oceanic and Atmospheric protect sensitive ecosystems). Similarly, measures have Administration of the US Department of Commerce). been taken to reduce nitrogen discharges into water. Many groundwater bodies are still highly affected - by NO3 contamination. Overall, there is little

Emissions of NOx – from stationary combustion indication of any fundamental improvement in the installations in the energy sector and from the eutrophication situation in coastal waters as Florida’s transport sector – felt by 46% between 1990 and 2016; red tide blooms reminded us in the summer of 2018.

during this period, N2O emissions decreased by 12% Florida had to declare the state of emergency, the (OECD.stat, accessed 3 October 2018). Agricultural spread of toxic algae killing many fish, threatening to nitrogen surplus, as measured by the OECD nitrogen upturn Florida’s vital summer tourist season. balance indicator, was reduced on average from 85 kg/ ha in 1992 to 67 kg/ha in 2014 (OECD, 2018a). Two case studies show how impact-pathway analysis (IPA) can help manage impacts more cost-

However, air quality standards with regard to NO2, effectively by fostering evidence-informed policy ground-level ozone and PM are still being exceeded making: deposition analysis in urban smog control regularly, particularly in large urban centres. in Paris, and combined management of atmospheric, Terrestrial ecosystems are still being affected by ocean and land-based nitrogen inputs to avoid eutrophication and, to a lower extent, by acidification. eutrophication of the Chesapeake Bay coastal zone in

Although N2O emissions have decreased, the the United States (see Boxes 1 and 2).

Box 1. MONITORING URBAN SMOG IN PARIS

In March 2014, Paris suffered a major peak of particle studies have since revealed that agricultural emissions pollution that lasted for ten days (Figure 2). IPA revealed that have a significant impact on air quality in many cities. For example, agriculture contributes to 23% of the background half of the coarse particles (PM10) were NH4NO3, secondary concentration levels of PM in the 150 urban areas surveyed particles formed by a combination of NOx emitted mainly 2.5 in the EU-28, Norway and Switzerland (Thunis et al., 2017). by urban transport and NH3 originating from farming activity in distant geographical areas. The other half of the

PM10 originated mainly from primary particles formed by Figure 2. PARTICLE ALERT THRESHOLD EXCEEDED combustion of biomass (wood heating) and fuel combustion IN PARIS IN MARCH 2014 (including transport).

This IPA finding had a direct implication for policy. It led the French authorities to argue that it was just as justified to restrict fertiliser application as it was to restrict traffic in order to curb urban air pollution. Measures taken included setting speed limits on roads, making residential parking free of charge, calling on farmers to temporarily limit fertiliser use and firms to limit industrial activity, and promoting the use of public transport.

This example shows how IPA led policymakers to address pollution emanating not only from the household heating Note: On the left, the Eiffel Tower before the particle pollution episode. and transport sectors, but also – and this is more unusual – On the right, a photo taken at the same place on 14 March 2014. from agriculture, which had historically not been considered Source: http://www.natura-sciences.com/environnement/particules-fines-pics- when thinking about reducing urban air pollution. Other pollution810.html.

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Did you know? Did you undeclared areas areas undeclared The first reported first The have been added have to the list of dead to (e.g. in the tropics). (e.g. eutrophication and eutrophication zones, not counting not counting zones, the 1960s; today the the 1960s; today the Gulf of Mexico in gulf is still affected by gulf is still affected ocean dead zone was was dead zone ocean 883 other coastal areas areas 883 other coastal

TARGETED POLICIES TO HALT NITROGEN POLLUTION NITROGEN HALT TO POLICIES TARGETED IPA analysis involves a step-by-step approach. First, data data First, approach. a step-by-step involves analysis IPA change model and an land use a watershed-scale from metrics as other (meteorology, airshed model as well transmitted are nitrogen) of sources point soils, topography, model then predicts watershed The model. a watershed to that and sediment phosphorus, the loads of nitrogen, Quality Water estuarine The inputs. the given from result Model(WQSTM) Transport (also knownand Sediment as Model) water predictsthe Chesapeake Bay in bay changes by quality the changes in input loads provided due to oxygen, dissolved a final step, As model. the watershed assess to clarity measured are and water chlorophyll attained. were quality standards water whether Bay land-based of atmospheric, management combined The inputs in Chesapeake Bay nitrogen and ocean-based 3). Such reality (Figure reflects of the nitrogen the cycle loss in the of oxygen makes the risk management an IPA The Chesapeake Bay cost-effective. more waters bay’s TMDLs the as a whole since has been effective Programme be made to to remains progress although introduced, were nitrogen of 2025. Estimated load target meet the nitrogen 2009 between 9% by decreased watershed loads in the bay and 2016. airshed) x Bay exchange Net ocean Net to model to Chesapeake 3 (e.g. NO (e.g. Air-based sources Air-based and NH x sources (watershed) Land-based REGULATED NITROGEN SOURCES IN THE CHESAPEAKE BAY CHESAPEAKE THE IN SOURCES NITROGEN 3. REGULATED Figure The Chesapeake Bay Watershed covers 90 000 square miles 90 000 square covers Watershed Bay Chesapeake The Maryland, (Delaware, states six U.S. (23 million hectares) across Virginia) and Washington West Virginia, York, Pennsylvania, New (24%), urban (8%) and (64%), agriculture Land use is forest D.C. the from wash other (4%). Nitrogen, phosphorus and sediment in little or resulting of the Bay, the tidal waters into watershed every and tidal rivers in the bay summer. oxygen no dissolved the mainly from results content oxygen dissolved low The such as nitrogen nutrients by of algae caused growth excessive of dead algae consumes decomposition The and phosphorus. forms life. of aquatic depriving fish and other oxygen, In maximum daily load (TMDL) 2010, a total December of tidal Bay the enter to and phosphorus allowed nitrogen in the sources nutrient land-based TMDL applies to set. was a first and, sewage) urban runoff, (agriculture, watershed deposition nitrogen atmospheric to States, in the United where — the area “airshed” relevant The in the watershed. deposition in the Bay’s most to contribute emission sources NO for delineated — was watershed nitrogen deposition. Another TMDL has been established TMDL deposition. Another nitrogen in tidal direct deposition of nitrogen atmospheric for nitrogen also considers pollution management Bay waters. and the ocean. the Bay between exchanges CONTROLLING FOR EUTROPHICATION IN CHESAPEAKE BAY CHESAPEAKE IN EUTROPHICATION FOR 2. CONTROLLING Box Figure 4. CRITERIA TO GUIDE NITROGEN POLICY MAKING

Policy coherence Policy effectiveness Cost-efficiency l Food supply l Policy outcomes l Static cost-efficiency l Energy supply l Policy impacts l Dynamic cost-efficiency l Environment

POLICY ASSESSMENT CRITERIA

Policy feasibility Unintended effects related to the nitrogen cascade l Administrative and legal feasibility l Positive side effects (synergies) l Side effects l Negative side effects (pollution swapping) l Political and public acceptability l Flexibility to deal with risks and uncertainties

A FRAMEWORK FOR ANALYSING THE MERITS OF support can distort energy production and use, such NITROGEN MANAGEMENT POLICY INSTRUMENTS as fossil fuel subsidies. Before designing targeted policies on nitrogen pollution, it is therefore essential Evaluation criteria are needed to select the right to monitor and evaluate policies with other aims and risk management or uncertainty management tools their unwanted effects on nitrogen emissions. (Figure 4). First, it is necessary to evaluate and address the coherence of sectoral policies (e.g. agricultural For example, China has taken steps to phase out policy, energy policy) and environmental policies fertiliser subsidies and aims to cap fertiliser use by (climate policy and others) with the management of 2020. The 2020 Zero-Growth Action Plan for Chemical nitrogen pollution. Fertilisers and Pesticides aims to reduce the annual growth of chemical fertiliser use to below 1% for This first step is crucial to avoid having to introduce the 2015-19 period and achieve zero-growth by 2020 additional policy measures to counter the undesired for major agricultural crops. However, these policy effects of other existing policies (e.g. the imposition developments need to be weighed against a backdrop of of a fertiliser tax to counter support to farm inputs), growing support for Chinese farmers, including forms which would obviously not be economically and of support that distort agricultural production and can perhaps not even environmentally effective. Second, encourage increased fertiliser use (OECD (2018b). nitrogen policy instruments that are cost-effective and whose feasibility of implementation is not problematic Policy coherence must also be sought with may then be selected. Third, due to the nitrogen environmental policies that are not primarily aimed cascade, the effects of an instrument targeting one at reducing nitrogen pollution. For example, in New impact or one form of nitrogen on other impacts or Zealand, a policy to reduce CO2 emissions has helped - forms of nitrogen should be estimated, in order to reduce the leaching of NO3 into water. An Emissions promote synergies and avoid “pollution swapping”. Trading Scheme (ETS) allows GHG emitters who do not want to reduce their emissions to enter into POLICY COHERENCE agreements with farmers who agree to sequester carbon. With financial compensation, farmers Just as some forms of agricultural support can distort undertake to convert pastoral lands into forests, - input use and agricultural production and thus have thereby helping to reduce the leaching of NO3 into negative environmental impacts (such as increased water. GHG emitters receive ETS credits in exchange nitrogen pollutant emissions), some forms of energy for pastoral land converted to forestry.

12 . OECD POLICY HIGHLIGHTS | Human Acceleration of the Nitrogen Cycle: Managing Risks and Uncertainty POLICY HIGHLIGHTS 13

regulation direct environmental TARGETED POLICIES TO HALT NITROGEN POLLUTION NITROGEN HALT TO POLICIES TARGETED instruments with reasons (e.g. various beneficial for be mutually may distortions (such to market vulnerability it reduces harmful and environmentally as split-incentives pollution potential to create as the well subsidies) as hotspots). (and capacity administrative the lowest require use of The costs). the least transaction produce the to increase information instruments is likely or feasibility (or a cost-efficiency effectiveness, when combination of these assessment criteria) with all other instrument categories. combined applied as close as possible to the point of emission point the possible to as close as applied cost-efficiency. and to maximise effectiveness when pollution, in reducing often most effective and enforcement. monitoring subject to credible and informational voluntary with along support), feasible politically often more are instruments, pricing instruments (e.g. pays” “polluter than to be less likely are although they ), mechanisms effective. feasible to politically be more instruments may effectiveness of environmental level given a achieve individually. than either employed Combining pricing or public financial support instruments may and information Voluntary Instruments should be based on their impact and Instruments should are regulation Pricing and direct environmental public financial instruments (e.g. pays” “Beneficiary Combining “polluter with “beneficiary pays” pays” and their combinations. The evaluation leads to six evaluation The combinations. and their conclusions. l l l l l l Broader policy assessment criteria are required required criteria are assessment policy Broader for a more and allow these nuances to capture of desirability of the relative evaluation rounded The applications. instruments for different policy in detail the effectiveness, evaluates full report categories of and feasibility of seven cost-efficiency 3 and 4), instruments (see for example Boxes policy of instrument implementation is essential of instrument implementation is essential Feasibility and function if an instrument is to be introduced into down be broken may concept The effectively. feasibility; side administrative aspects: general five health and competitiveness, on equity, effects (e.g, public acceptability; political and the environment); and feasibility, legal compatibility and institutional respond ability to the flexibility of an instrument (its and uncertainty). to changes gauges whether a policy intervention whether intervention a policy gauges Effectiveness the use (e.g. measures practical has led to successful benefits or overall vehicles) in converters of catalytic Cost- cycle). of the nitrogen disturbance reduced (e.g. is objective whether the intervention’s efficiency asks at the least cost to society. being achieved EFFECTIVENESS, COST-EFFICIENCY AND FEASIBILITY AND COST-EFFICIENCY EFFECTIVENESS, of different a typology provides full report The instruments (e.g. policy management nitrogen regulation, environmental direct pricing instruments, information measures, instruments, financial support analysis policy Existing schemes). voluntary and performance methodologies to assess the tend of the criteria instrument against policy of a efficiency. and economic effectiveness environmental complications world” “real neglects view a But such the effectiveness, policy that often act to limit criterion. “feasibility” CONCLUSION

Box 3. USING A TRADEABLE PERMIT SYSTEM IN THE GREAT MIAMI RIVER WATERSHED

Around 40% of surface waters in the Great Miami River Effectiveness. By mid-2014, 397 agricultural projects were watershed of around 10 000 km2 in Southwest Ohio, contracted, generating over 1.14 million credits worth over United States, were consistently failing to meet regulatory USD 1.6 million, and producing an estimated 572 metric ton water quality standards. In response, the regional water reduction in nutrient discharges to surface waters in the management agency, the Miami Conservancy District (MCD), watershed. in 2004 introduced the Great Miami Watershed Trading Programme (GMWTP) as a pilot scheme for a cost-effective Cost-efficiency. Trades completed have thus far produced approach to improving water quality, in anticipation of a cost of USD 1.48/lb of nutrient abated. This is significantly regulatory measures to set nutrient release limits on point- less than the estimated USD 4.72/lb abated estimated for source wastewater treatment plants (WWTPs). measures implemented directly by WWTPs, suggesting significantly higher cost-efficiency than a regulatory approach Agricultural activities cover around 70% of land in the applied to point sources only. watershed, are the primary contributor to the excess nutrient release and are able to achieve nutrient reductions at a lower Feasibility. The cost-effective nature of the GMWTP makes it cost than WWTPs. The GMWTP encourages farmers to adopt popular amongst WWTPs. During formulation of the GMWTP, voluntary “best practice” measures to generate Emission over a hundred meetings took place with a wide range of Reduction Credits (ERCs), which may be traded to WWTPs to stakeholders, leading to wide acceptance and support for the allow for future regulatory compliance. instrument.

Box 4. DIRECT ENVIRONMENTAL REGULATION: JAPAN’S AUTOMOBILE NOX AND PM LAW

In Japan, levels of NOx pollution continued to rise the registration of high-polluting vehicles and enforcing the throughout the 1980s as a result of increasing vehicle replacement of those already in circulation – was the key traffic. In response, the 1992 Law Concerning Special factor behind this result. Measures for Total Emission Reduction of Nitrogen Oxides

from Automobiles in Specified Areas (NOx Law) was Cost-efficiency. The NOx Law cost up to JPY 521 billion enacted. (around USD 5 billion). The total social benefits of the regulation – including reduced health impacts and spillover The law required the prefectures of the large urban areas effects in neighbouring, non-obligated regions – are likely to of Tokyo and Osaka to establish and implement local plans have exceeded this cost by at least double.

to reduce NOx emissions from vehicles. In 2001 PM was added as a target substance, and Nagoya was added as an Feasibility. Public pressure, along with an increasing additional obligated prefecture. number of successful lawsuits filed by organisations representing victims of pollution-related health damage,

Effectiveness. NOx emissions decreased around 20% had already led to a succession of anti-pollution laws from between 2000 and 2009 in the areas subject to the revised the 1960s onwards. The resulting awareness of pollution- law, twice the rate experienced outside the obligated related health issues in the population is likely to have

prefectures. Regulating vehicle types – including banning provided support for the NOx and PM law.

NITROGEN AS A “CASCADING TARGET” It is therefore necessary to assess risk-risk trade-offs of various policies or best management practices, Whatever the policy approach – risk or precautionary whether in agriculture, fossil fuel combustion, – nitrogen policy instruments also need to be refined industrial processes or treatment of wastewater. by evaluating their unintended effects on other forms of nitrogen due to the nitrogen cascade – the fact For example, using selective catalytic reduction (SCR) that once fixed, nitrogen tends to change form. In systems to reduce NOx emissions from vehicles raises particular, efforts to lessen the impacts caused by new concerns about emissions of the by-products NH3 nitrogen in one area of the environment should (i) not and N2O. In contrast, tertiary treatment of sewage to - result in unintended nitrogen impacts in other areas remove NO3 also reduces N2O emissions from sewage. (“pollution swapping”), and (ii) seize opportunities to However, the incineration of sewage sludge (as is the reduce other nitrogen impacts (“synergy” effects). norm in Switzerland, for example) releases NOx.

14 . OECD POLICY HIGHLIGHTS | Human Acceleration of the Nitrogen Cycle: Managing Risks and Uncertainty POLICY HIGHLIGHTS 15

. CONCLUSION CONCLUSION Responding to nitrogen pollution in a cost- nitrogen Responding to approach: a threefold requires way effective water soil, the risks of air, managing better halting the steady pollution; and ecosystem in concentrations oxide in nitrous increase excess preventing and, the atmosphere; the environment. entering from nitrogen CONCLUSION REFERENCES

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16 . OECD POLICY HIGHLIGHTS | Human Acceleration of the Nitrogen Cycle: Managing Risks and Uncertainty POLICY HIGHLIGHTS Industry Power plant Power . In doing so, however, they often generate they often generate however, . In doing so, 2 Car traffic Car Algal blooms Algal Human sewage Waste and sewage Waste NITROGEN’S DARK SIDE DARK NITROGEN’S ... before it deposits on soils ... 2 ... before The nitrogen produced during fossil-fuel during fossil-fuel produced nitrogen The Adapted from Townsend and Howarth (2010). Townsend from Adapted Source: 1 combustion can cause severe air pollution ... severe can cause combustion Dead zone nitrous oxide, a potent greenhouse gas that also depletes the stratospheric ozone layer. ozone the stratospheric also depletes gas that greenhouse a potent oxide, nitrous ... joins with excess nitrogen from fertilised fields, waste and sewage, and factories ... and sewage, fertilised waste from fields, nitrogen 3 ... joins with excess Fertilised field Fertilised Residential heating Residential productions, and from waste and sewage create risks and generate uncertainty human health and the environment. risks and generate for create and sewage waste and from productions, ... can harm terrestrial biodiversity ... biodiversity 4 ... can harm terrestrial and groundwater rivers entering before drinking it can contaminate where the oceans ... then reaching water algal it can lead to where blooms and the creation dead of coastal zones. gas, the most abundant component of the earth’s atmosphere, is harmless. But, reactive forms emanating from the burning of from emanating forms reactive But, harmless. is atmosphere, of the earth’s component the most abundant gas, 2 fossil fuels in power plants, cars and residential heating, from overuse as inputs for agricultural production certain and agricultural for as inputs industrial overuse from heating, and residential cars plants, in power fuels fossil N In soils and water, denitrifying bacteria reconvert the reactive forms of nitrogen to inert to of nitrogen N forms the reactive denitrifying bacteria reconvert In soils and water, The OECD publication Human Acceleration of the Nitrogen Cycle: Managing Risks and Uncertainty examines the risks associated with the release of excessive nitrogen into the environment (climate change, depletion of the ozone layer, air pollution, water pollution, loss of biodiversity, deterioration of soil quality). The report also examines the uncertainty associated with the ability of nitrogen to move from one ecosystem to another and cause “cascading effects”. In addition to better management of nitrogen risks at the local level, there is a need to consider the global risks associated with the continued increase in nitrous oxide concentrations and to prevent excess nitrogen in all its forms by developing cost-effective strategies for all its sources. Other than the reduction of nitrogen pollution, this report provides guidance on the use of nitrogen policy instruments and how to ensure coherence with objectives such as food security, energy security and environmental objectives.

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