Why metrics matter: evaluating policy choices for reactive nitrogen in the Chesapeake Bay watershed

Atmospheric Nitrogen Pollution Control Benefits the Coastal Environment

Nitrogen is an essential nutrient and a major limiting element for the ocean ecosystem. Since the preindustrial era, substantial amounts of nitrogen from terrestrial sources have entered the ocean via rivers, groundwater, and atmospheric deposition. China serves as a key hub in the global nitrogen cycle, but the pathways, sources, and potential mitigation strategies for land-ocean nitrogen transport are unclear. By combining the CHANS, WRF-Chem, and WNF models, we estimated that 8 million tonnes (Tg) of nitrogen was transferred into the ocean in 2017 in China, with atmospheric deposition contributing 1/3. About half variation of the offshore chlorophyll concentration was explained by atmospheric deposition. The Bohai Sea was the hot spot of nitrogen input, estimated at 214 kg N ha-1, while other areas were around 25-51 kg N ha-1. The largest contributors are agricultural systems (4 Tg, 55%), followed by domestic sewage (2 Tg, 21%). Abatement measures could reduce nitrogen export to the ocean by 43%, and mitigating ammonia and nitrogen oxide emissions accounts for 33% of this reduction, highlighting the importance of addressing air pollution in resolving ocean pollution. The cost-benefit analysis suggests the priority of nitrogen reduction in cropland and transport systems for the ocean environment.

Footprints in Action: How UVA Is Managing Its Sustainability Stewardship

Evaluating sustainability stewardship at higher educational institutions is essential to working towards improving our environment. Many institutions have used environmental footprint indicators as a way to evaluate, track, and improve their impact on the environment. In this article, we present the web-based Integrated Environmental Footprint Tool (IEFT), which allows users to test how changes in certain activities impact nitrogen (N), greenhouse gases (GHG), phosphorus (P), and water (W) footprints for a university campus. This study uses the University of Virginia (UVA) as a model to show the impacts of their existing sustainability plans on multiple footprint indicators. Strategies from the University of Virginia's (UVA) two exisiting action plans, the GHG Action Plan and the N Action Plan, are evaluated to determine their impact on each of the footprints (GHG, N, P, and W). Based on the 2025 goal year, the strategies in these action plans are estimated to reduce the GHG, N, P, and W footprints by -38%, 32%, 25%, and 2.7% respectively. The damage costs associated with GHG and N footprints are assessed and reveal a 38 percent reduction in damage costs for GHG and a 42 percent reduction in costs for N. Using the IEFT to evaluate the impact of these action plan strategies, UVA optimized environmental outcomes. The model shown here can be used at other institutions to evaluate the environmental impact of planned changes to an institutions' operations.

Integrated Modeling of U.S. Agricultural Soil Emissions of Reactive Nitrogen and Associated Impacts on Air Pollution, Health, and Climate

Agricultural soils are leading sources of reactive nitrogen (Nr) species including nitrogen oxides (NO_x), ammonia (NH₃), and nitrous oxide (N₂O). The propensity of NO_x and NH₃ to generate ozone and fine particulate matter and associated impacts on health are highly variable, whereas the climate impacts of long-lived N₂O are independent of emission timing and location. However, these impacts have rarely been compared on a spatially resolved monetized basis. In this study, we update the nitrogen scheme in an agroecosystem model to simulate the Nr emissions from fertilized soils across the contiguous United States. We then apply a reduced-form air pollution health effect model to assess air quality impacts from NO_x and NH₃ and a social cost of N₂O to assess the climate impacts. Assuming an $8.2 million value of a statistical life and a $13,100/ton social cost of N₂O, the air quality impacts are a factor of ∼7 to 15 times as large as the climate impacts in heavily populated coastal regions, whereas the ratios are closer to 2.5 in sparsely populated regions. Our results show that air pollution, health, and climate should be considered jointly in future assessments of how farming practices affect Nr emissions.

Reactive nitrogen releases and nitrogen footprint during intensive vegetable production affected by partial human manure substitution

Evaluating the sustainability of vegetable production is crucial to secure future food supply. A 2-year field study of four different vegetable crops was performed to investigate the effects of inorganic fertilizer and human manure at different ratios on vegetable yields, reactive gaseous nitrogen emissions (GNrEs), reactive nitrogen (Nr) footprint, and net ecosystem economic income (NEEI) by using life cycle analysis. Four fertilization strategies were studied, including CK (no fertilization); CF (inorganic fertilization); CHF1 (human manure /inorganic fertilizer, N ratio = 1:7); and CHF2 (human manure /inorganic fertilizer, N ratio = 1:3). Results showed that compared with CF treatment, both CHF1 and CHF2 treatments increased the N₂O + NO emissions by 11.8% and 32.4% on average, while decreased the vegetable yields by 6.7% and 7.4%, respectively. Moreover, the addition of human manure increased the proportions of Nr footprint by 6.6% (CHF1) and 2.9% (CHF2) in comparison with CF treatment. However, although CHF2 treatment significantly increased the values of GNrEs and reactive gaseous nitrogen intensity (GNrI) by 8.4% and 12.5%, respectively, in relation to those in CF treatment, it still increased farmers' income by 16,404 CNY ha^-1. These findings suggest that although human manure incorporation could not mitigate Nr releases, the appropriate ratio of inorganic fertilizer and human manure (CHF2) is able to improve net economic income (NEI) and NEEI during intensive vegetable production. Nevertheless, it should be further explored about the relationship between combinatorial treatment of inorganic fertilizer and human manure on Nr release mitigation in intensive vegetable production.

Identifying ecological production functions for use in ecosystem services-based environmental risk assessment of chemicals

There is increasing research interest in the application of the ecosystem services (ES) concept in the environmental risk assessment of chemicals to support formulating and operationalising regulatory environmental protection goals and making environmental risk assessment more policy- and value-relevant. This requires connecting ecosystem structure and processes to ecosystem function and henceforth to provision of ecosystem goods and services and their economic valuation. Ecological production functions (EPFs) may help to quantify these connections in a transparent manner and to predict ES provision based on function-related descriptors for service providing species, communities, ecosystems or habitats. We review scientific literature for EPFs to evaluate availability across provisioning and regulation and maintenance services (CICES v5.1 classification). We found quantitative production functions for nearly all ES, often complemented with economic valuation of physical or monetary flows. We studied the service providing units in these EPFs to evaluate the potential for extrapolation of toxicity data for test species obtained from standardised testing to ES provision. A broad taxonomic representation of service providers was established, but quantitative models directly linking standard test species to ES provision were extremely scarce. A pragmatic way to deal with this data gap would be the use of proxies for related taxa and stepwise functional extrapolation to ES provision and valuation, which we conclude possible for most ES. We suggest that EPFs may be used in defining specific protection goals (SPGs), and illustrate, using pollination as an example, the availability of information for the ecological entity and attribute dimensions of SPGs. Twenty-five pollination EPFs were compiled from the literature for biological entities ranging from 'colony' to 'habitat', with 75% referring to 'functional group'. With about equal representation of the attributes 'function', 'abundance' and 'diversity', SPGs for pollination therefore would seem best substantiated by EPFs at the level of functional group.

Atmospheric nitrogen deposition in the Chesapeake Bay watershed: A history of change

The Chesapeake Bay watershed has been the focus of pioneering studies of the role of atmospheric nitrogen (N) deposition as a nutrient source and driver of estuarine trophic status. Here, we review the history and evolution of scientific investigations of the role of atmospheric N deposition, examine trends from wet and dry deposition networks, and present century-long (1950-2050) atmospheric N deposition estimates. Early investigations demonstrated the importance of atmospheric deposition as an N source to the Bay, providing 25%-40% among all major N sources. These early studies led to the unprecedented inclusion of targeted decreases in atmospheric N deposition as part of the multi-stakeholder effort to reduce N loads to the Bay. Emissions of nitrogen oxides (NO_x) and deposition of wet nitrate, oxidized dry N, and dry ammonium ( NH 4 + ) sharply and synchronously declined by 60%-73% during 1995-2019. These decreases largely resulted from implementation of Title IV of the 1990 Clean Air Act Amendments, which began in 1995. Wet NH 4 + deposition shows no significant trend during this period. The century-long atmospheric N deposition estimates indicate an increase in total atmospheric N deposition in the Chesapeake watershed from 1950 to a peak of ~15 kg N/ha/yr in 1979, trailed by a slight decline of <10% through the mid-1990s, and followed by a sharp decline of about 40% thereafter through 2019. An additional 21% decline in atmospheric N deposition is projected from 2015 to 2050. A comparison of the Potomac River and James River watersheds indicates higher atmospheric N deposition in the Potomac, likely resulting from greater emissions from higher proportions of agricultural and urban land in this basin. Atmospheric N deposition rose from 30% among all N sources to the Chesapeake Bay watershed in 1950 to a peak of 40% in 1973, and a decline to 28% by 2015. These data highlight the important role of atmospheric N deposition in the Chesapeake Bay watershed and present a potential opportunity for decreases in deposition to contribute to further reducing N loads and improving the trophic status of tidal waters.

From hogs to HABs: impacts of industrial farming in the US on nitrogen and phosphorus and greenhouse gas pollution

Nutrient pollution and greenhouse gas emissions related to crop agriculture and confined animal feeding operations (CAFOs) in the US have changed substantially in recent years, in amounts and forms. This review is intended to provide a broad view of how nutrient inputs-from fertilizer and CAFOs-as well as atmospheric NH3 and greenhouse gas emissions, are changing regionally within the US and how these changes compare with nutrient inputs from human wastewater. Use of commercial nitrogen (N) fertilizer in the US, which now exceeds 12,000,000 metric tonnes (MT) continues to increase, at a rate of 60,000 MT per year, while that of phosphorus (P) has remained nearly constant over the past decade at around 1,800,000 MT. The number of CAFOs in the US has increased nearly 10% since 2012, driven largely by a near 13% increase in hog production. The annualized inventory of cattle, dairy cows, hogs, broiler chickens and turkeys is approximately 8.7 billion, but CAFOs are highly regionally concentrated by animal sector. Country-wide, N applied by fertilizer is about threefold greater than manure N inputs, but for P these inputs are more comparable. Total manure inputs now exceed 4,000,000 MT as N and 1,400,000 MT as P. For both N and P, inputs and proportions vary widely by US region. The waste from hog and dairy operations is mainly held in open lagoons that contribute to NH3 and greenhouse gas (as CH4 and N2O) emissions. Emissions of NH3 from animal waste in 2019 were estimated at > 4,500,000 MT. Emissions of CH4 from manure management increased 66% from 1990 to 2017 (that from dairy increased 134%, cattle 9.6%, hogs 29% and poultry 3%), while those of N2O increased 34% over the same time period (dairy 15%, cattle 46%, hogs 58%, and poultry 14%). Waste from CAFOs contribute substantially to nutrient pollution when spread on fields, often at higher N and P application rates than those of commercial fertilizer. Managing the runoff associated with fertilizer use has improved with best management practices, but reducing the growing waste from CAFO operations is essential if eutrophication and its effects on fresh and marine waters-namely hypoxia and harmful algal blooms (HABs)-are to be reduced.

Best Management Practices for Diffuse Nutrient Pollution: Wicked Problems Across Urban and Agricultural Watersheds

Extensive time and financial resources have been dedicated to address nonpoint sources of nitrogen and phosphorus in watersheds. Despite these efforts, many watersheds have not seen substantial improvement in water quality. The objective of this study is to review the literature and investigate key factors affecting the lack of improvement in nutrient levels in waterways in urban and agricultural regions. From 94 studies identified in the academic literature, we found that, although 60% of studies found improvements in water quality after implementation of Best Management Practices (BMPs) within the watershed, these studies were mostly modeling studies rather than field monitoring studies. For studies that were unable to find improvements in water quality after the implementation of BMPs, the lack of improvement was attributed to lack of knowledge about BMP functioning, lag times, nonoptimal placement and distribution of BMPs in the watershed, postimplementation BMP failure, and socio-political and economic challenges. We refer to these limiting factors as known unknowns. We also acknowledge the existence of unknown unknowns that hinder further improvement in BMP effectiveness and suggest that machine learning, approaches from the field of business and operations management, and long-term convergent studies could be used to resolve these unknown unknowns.

Factors driving nutrient trends in streams of the Chesapeake Bay watershed

Despite decades of effort toward reducing nitrogen and phosphorus flux to Chesapeake Bay, water-quality and ecological responses in surface waters have been mixed. Recent research, however, provides useful insight into multiple factors complicating the understanding of nutrient trends in bay tributaries, which we review in this paper, as we approach a 2025 total maximum daily load (TMDL) management deadline. Improvements in water quality in many streams are attributable to management actions that reduced point sources and atmospheric nitrogen deposition and to changes in climate. Nutrient reductions expected from management actions, however, have not been fully realized in watershed streams. Nitrogen from urban nonpoint sources has declined, although water-quality responses to urbanization in individual streams vary depending on predevelopment land use. Evolving agriculture, the largest watershed source of nutrients, has likely contributed to local nutrient trends but has not affected substantial changes in flux to the bay. Changing average nitrogen yields from farmland underlain by carbonate rocks, however, may suggest future trends in other areas under similar management, climatic, or other influences, although drivers of these changes remain unclear. Regardless of upstream trends, phosphorus flux to the bay from its largest tributary has increased due to sediment infill in the Conowingo Reservoir. In general, recent research emphasizes the utility of input reductions over attempts to manage nutrient fate and transport at limiting nutrients in surface waters. Ongoing research opportunities include evaluating effects of climate change and conservation practices over time and space and developing tools to disentangle and evaluate multiple influences on regional water quality.

Economic Valuation of Earth’s Critical Zone: A Pilot Study of the Zhangxi Catchment, China

Earth’s critical zone is the physical layer contained between the top of the vegetation canopy and the depth of the circulating groundwater below the land surface. The critical zone is defined within the study of Earth natural sciences as the unique terrestrial biophysical system that supplies most life-sustaining resources for humans. A feature of this specific physical system that is defined by geographical locale is the interactions of people with the vertically-connected biophysical flows and transformations (energy, material, biodiversity) that contribute to human welfare by delivering, both directly and indirectly, critical zone services to humankind. We have characterized these interactions by considering the full extent of the critical zone through the application of economic valuation methods. We estimated the current economic value of 14 critical zone services for 5 biophysical components of Earth’s critical zone, based on data collected from the Zhangxi catchment of Ningbo city located in the Yangtze River Delta region of China and from several additional published studies. For the full vertical extent of Earth’s critical zone bounded by the Zhangxi catchment, the value, most of which is outside the market, was estimated to be USD 116 million in 2018. Valuation of goods and services was delineated for benefits arising from key components of the critical zone physical system. The estimated value of the atmospheric component of Earth’s critical zone was USD 5 million; the vegetation component value was USD 96 million; the soil component value was USD 8 million; the surface water component value was USD 5 million; and the groundwater component value was USD 2 million. Because of the nature of the uncertainties and lack of data for the full range of identified services, these values are considered a minimum estimate. Gross domestic product in the Zhangxi catchment was around USD 431 million in 2018. These results illustrate, for one location, the range of services that arise when considering the full depth of Earth’s critical zone, the data needs for valuing this range of services, and the conceptual and potential methodological advances, and the challenges, that exist at the disciplinary interface between Earth natural sciences and applied economics.

Calculating socially optimal nitrogen (N) fertilization rates for sustainable N management in China

Current nitrogen (N) fertilization rates in China have incurred high social costs in the drive to achieve higher yields and economic returns. We conducted an intensive nation-wide investigation to estimate the socially optimal N rate (SOR) for Chinese maize, rice and wheat as a balance between crop productivity, farm income, ecological health and human health. The social cost of N impacts (SCN) was calculated based on 2210 field observations reported in 264 publications. The estimated SCN for three cereal crops grown in China was in the range $142-218 ha^-1 at medium N fertilization rates (173-204 kg N ha^-1). The net benefits of N use were calculated as the differences between private profitability and the SCN. The minimum N application rate with maximized net benefit was estimated as the SOR calculated from data compiled from 27,476 on-farm year-site trials. The average SOR was in the range 149-160 kg ha^-1; values in this range were 18.1-23.7% lower than the privately optimal N rate (POR). The yield losses associated with implementation of the SOR were not significant (p < 0.01) compared with the yield of POR implementation. The POR calculates the minimum N application required to maximize private profitability, i.e., traditional N recommended practice. Compared with the POR, implementation of SOR reduced reactive N losses by 17.8-39.0%, and the SCN by 18.8-30.9%. Finally, we simulated the SOR at the county level for each soil type based on data collected from no-N control plots yields and maximum achieved yields (p < 0.01). Thus, we estimated the SOR at the Chinese county level for three cereal crops using direct on-farm measurements. This study provide updated estimates of optimizing N management to simultaneously address production and pollution problems in China and other similar regions of the world.

Microbes and the Next Nitrogen Revolution

The Haber Bosch process is among the greatest inventions of the 20th century. It provided agriculture with reactive nitrogen and ultimately mankind with nourishment for a population of 7 billion people. However, the present agricultural practice of growing crops for animal production and human food constitutes a major threat to the sustainability of the planet in terms of reactive nitrogen pollution. In view of the shortage of directly feasible and cost-effective measures to avoid these planetary nitrogen burdens and the necessity to remediate this problem, we foresee the absolute need for and expect a revolution in the use of microbes as a source of protein. Bypassing land-based agriculture through direct use of Haber Bosch produced nitrogen for reactor-based production of microbial protein can be an inspiring concept for the production of high quality animal feed and even straightforward supply of proteinaceous products for human food, without significant nitrogen losses to the environment and without the need for genetic engineering to safeguard feed and food supply for the generations to come.

Assessing the Social and Environmental Costs of Institution Nitrogen Footprints

This article estimates the damage costs associated with the institutional nitrogen (N) footprint and explores how this information could be used to create more sustainable institutions. Potential damages associated with the release of nitrogen oxides (NOx), ammonia (NH₃), and nitrous oxide (N₂O) to air and release of nitrogen to water were estimated using existing values and a cost per unit of nitrogen approach. These damage cost values were then applied to two universities. Annual potential damage costs to human health, agriculture, and natural ecosystems associated with the N footprint of institutions were $11.0 million (2014) at the University of Virginia (UVA) and $3.04 million at the University of New Hampshire (UNH). Costs associated with the release of nitrogen oxides to human health, in particular the use of coal-derived energy, were the largest component of damage at UVA. At UNH the energy N footprint is much lower because of a landfill cogeneration source, and thus the majority of damages were associated with food production. Annual damages associated with release of nitrogen from food production were very similar at the two universities ($1.80 million vs. $1.66 million at UVA and UNH, respectively). These damages also have implications for the extent and scale at which the damages are felt. For example, impacts to human health from energy and transportation are generally larger near the power plants and roads, while impacts from food production can be distant from the campus. Making this information available to institutions and communities can improve their understanding of the damages associated with the different nitrogen forms and sources, and inform decisions about nitrogen reduction strategies.

The economic and environmental consequences of implementing nitrogen-efficient technologies and management practices in agriculture

Technologies and management practices (TMPs) that reduce the application of nitrogen (N) fertilizer while maintaining crop yields can improve N use efficiency (NUE) and are important tools for meeting the dual challenges of increasing food production and reducing N pollution. However, because farmers operate to maximize their profits, incentives to implement TMPs are limited, and TMP implementation will not always reduce N pollution. Therefore, we have developed the NUE Economic and Environmental impact analytical framework (NUE) to examine the economic and environmental consequences of implementing TMPs in agriculture, with a specific focus on farmer profits, N fertilizer consumption, N losses, and cropland demand. Our analytical analyses show that impact of TMPs on farmers' economic decision-making and the environment is affected by how TMPs change the yield ceiling and the N fertilization rate at the ceiling and by how the prices of TMPs, fertilizer, and crops vary. Technologies and management practices that increase the yield ceiling appear to create a greater economic incentive for farmers than TMPs that do not but may result in higher N application rates and excess N losses. Nevertheless, the negative environmental impacts of certain TMPs could be avoided if their price stays within a range determined by TMP yield response, fertilizer price, and crop price. We use a case study on corn production in the midwestern United States to demonstrate how NUE can be applied to farmers' economic decision-making and policy analysis. Our NUE framework provides an important tool for policymakers to understand how combinations of fertilizer, crop, and TMP prices affect the possibility of achieving win-win outcomes for farmers and the environment.

Reducing Nitrogen Pollution while Decreasing Farmers' Costs and Increasing Fertilizer Industry Profits

Nitrogen (N) pollution is emerging as one of the most important environmental issues of the 21st Century, contributing to air and water pollution, climate change, and stratospheric ozone depletion. With agriculture being the dominant source, we tested whether it is possible to reduce agricultural N pollution in a way that benefits the environment, reduces farmers' costs, and increases fertilizer industry profitability, thereby creating a "sweet spot" for decision-makers that could significantly increase the viability of improved N management initiatives. Although studies of the economic impacts of improved N management have begun to take into account farmers and the environment, this is the first study to consider the fertilizer industry. Our "sweet spot" hypothesis is evaluated via a cost-benefit analysis of moderate and ambitious N use efficiency targets in U.S. and China corn sectors over the period 2015-2035. We use a blend of publicly available crop and energy price projections, original time-series modeling, and expert elicitation. The results present a mixed picture: although the potential for a "sweet spot" exists in both countries, it is more likely that one occurs in China due to the currently extensive overapplication of fertilizer, which creates a greater potential for farmers and the fertilizer industry to gain economically from improved N management. Nevertheless, the environmental benefits of improving N management consistently dwarf the economic impacts on farmers and the fertilizer industry in both countries, suggesting that viable policy options could include incentives to farmers and the fertilizer industry to increase their support for N management policies.

Hidden cost of U.S. agricultural exports: particulate matter from ammonia emissions

We use a model of agricultural sources of ammonia (NH3) coupled to a chemical transport model to estimate the impact of U.S. food export on particulate matter concentrations (PM2.5). We find that food export accounts for 11% of total U.S. NH3 emissions (13% of agricultural emissions) and that it increases the population-weighted exposure of the U.S. population to PM2.5 by 0.36 μg m(-3) on average. Our estimate is sensitive to the proper representation of the impact of NH3 on ammonium nitrate, which reflects the interplay between agricultural (NH3) and combustion emissions (NO, SO2). Eliminating NH3 emissions from food export would achieve greater health benefits than the reduction of the National Ambient Air Quality Standards for PM2.5 from 15 to 12 μg m(-3). Valuation of the increased premature mortality associated with PM2.5 from food export (36 billion US$ (2006) per year) amounts to 50% of the gross food export value. Livestock operations in densely populated areas have particularly large health costs. Decreasing SO2 and NOx emissions will indirectly reduce health impact of food export as an ancillary benefit.

Consequences of human modification of the global nitrogen cycle

The demand for more food is increasing fertilizer and land use, and the demand for more energy is increasing fossil fuel combustion, leading to enhanced losses of reactive nitrogen (Nr) to the environment. Many thresholds for human and ecosystem health have been exceeded owing to Nr pollution, including those for drinking water (nitrates), air quality (smog, particulate matter, ground-level ozone), freshwater eutrophication, biodiversity loss, stratospheric ozone depletion, climate change and coastal ecosystems (dead zones). Each of these environmental effects can be magnified by the 'nitrogen cascade': a single atom of Nr can trigger a cascade of negative environmental impacts in sequence. Here, we provide an overview of the impact of Nr on the environment and human health, including an assessment of the magnitude of different environmental problems, and the relative importance of Nr as a contributor to each problem. In some cases, Nr loss to the environment is the key driver of effects (e.g. terrestrial and coastal eutrophication, nitrous oxide emissions), whereas in some other situations nitrogen represents a key contributor exacerbating a wider problem (e.g. freshwater pollution, biodiversity loss). In this way, the central role of nitrogen can remain hidden, even though it actually underpins many trans-boundary pollution problems.

Consequences of human modification of the global nitrogen cycle

The demand for more food is increasing fertilizer and land use, and the demand for more energy is increasing fossil fuel combustion, leading to enhanced losses of reactive nitrogen (Nr) to the environment. Many thresholds for human and ecosystem health have been exceeded owing to Nr pollution, including those for drinking water (nitrates), air quality (smog, particulate matter, ground-level ozone), freshwater eutrophication, biodiversity loss, stratospheric ozone depletion, climate change and coastal ecosystems (dead zones). Each of these environmental effects can be magnified by the 'nitrogen cascade': a single atom of Nr can trigger a cascade of negative environmental impacts in sequence. Here, we provide an overview of the impact of Nr on the environment and human health, including an assessment of the magnitude of different environmental problems, and the relative importance of Nr as a contributor to each problem. In some cases, Nr loss to the environment is the key driver of effects (e.g. terrestrial and coastal eutrophication, nitrous oxide emissions), whereas in some other situations nitrogen represents a key contributor exacerbating a wider problem (e.g. freshwater pollution, biodiversity loss). In this way, the central role of nitrogen can remain hidden, even though it actually underpins many trans-boundary pollution problems.

Costs and benefits of nitrogen for Europe and implications for mitigation

Cost-benefit analysis can be used to provide guidance for emerging policy priorities in reducing nitrogen (N) pollution. This paper provides a critical and comprehensive assessment of costs and benefits of the various flows of N on human health, ecosystems and climate stability in order to identify major options for mitigation. The social cost of impacts of N in the EU27 in 2008 was estimated between €75-485 billion per year. A cost share of around 60% is related to emissions to air. The share of total impacts on human health is about 45% and may reflect the higher willingness to pay for human health than for ecosystems or climate stability. Air pollution by nitrogen also generates social benefits for climate by present cooling effects of N containing aerosol and C-sequestration driven by N deposition, amounting to an estimated net benefit of about €5 billion/yr. The economic benefit of N in primary agricultural production ranges between €20-80 billion/yr and is lower than the annual cost of pollution by agricultural N which is in the range of €35-230 billion/yr. Internalizing these environmental costs would lower the optimum annual N-fertilization rate in Northwestern Europe by about 50 kg/ha. Acknowledging the large uncertainties and conceptual issues of our cost-benefit estimates, the results support the priority for further reduction of NH3 and NOx emissions from transport and agriculture beyond commitments recently agreed in revision of the Gothenburg Protocol.

A post-Kyoto partner: considering the stratospheric ozone regime as a tool to manage nitrous oxide

Nitrous oxide (N2O) is the largest known remaining anthropogenic threat to the stratospheric ozone layer. However, it is currently only regulated under the 1997 Kyoto Protocol because of its simultaneous ability to warm the climate. The threat N2O poses to the stratospheric ozone layer, coupled with the uncertain future of the international climate regime, motivates our exploration of issues that could be relevant to the Parties to the ozone regime (the 1985 Vienna Convention and its 1987 Montreal Protocol) should they decide to take measures to manage N2O in the future. There are clear legal avenues to regulate N2O under the ozone regime as well as several ways to share authority with the existing and future international climate treaties. N2O mitigation strategies exist to address the most significant anthropogenic sources, including agriculture, where behavioral practices and new technologies could contribute significantly to reducing emissions. Existing policies managing N2O and other forms of reactive nitrogen could be harnessed and built on by the ozone regime to implement N2O controls. There are several challenges and potential cobenefits to N2O control which we discuss here: food security, equity, and implications of the nitrogen cascade. The possible inclusion of N2O in the ozone regime need not be viewed as a sign of failure of the United Nations Framework Convention on Climate Change to adequately deal with climate change. Rather, it could represent an additional valuable tool in sustainable development diplomacy.

Chesapeake Bay nutrient pollution: contribution from the land application of sewage sludge in Virginia

Human health concerns and the dissemination of anthropogenic substances with unknown consequences are the reasons most often given why disposal of municipal sewage sludge in landfills or using the organic waste as biofuel is preferable to land application. But no "fertilizer" causes more nitrogen pollution than sludge when applied according to Virginia law. Poultry litter is the only other "fertilizer" that causes more phosphorus pollution than sludge. Cost savings by the few farmers in Virginia who use sludge are far less than the costs of the nitrogen pollution they cause. A ban on the land application of all forms of animal waste is very cost-effective and would reduce Chesapeake Bay nutrient pollution by 25%.

Atmospheric reactive nitrogen in China: sources, recent trends, and damage costs

Human activities have intensely altered the global nitrogen cycle and produced nitrogenous gases of environmental significance, especially in China where the most serious atmospheric nitrogen pollution worldwide exists. We present a comprehensive assessment of ammonia (NH(3)), nitrogen oxides (NO(x)), and nitrous oxide (N(2)O) emissions in China based on a full cycle analysis. Total reactive nitrogen (Nr) emission more than doubled over the past three decades, during which the trend of increase slowed for NH(3) emissions after 2000, while the trend of increase continued to accelerate for NO(x) and N(2)O emissions. Several hotspots were identified, and their Nr emissions were about 10 times higher than others. Agricultural sources take 95% of total NH(3) emission; fossil fuel combustion accounts for 96% of total NO(x) emission; agricultural (51%) and natural sources (forest and surface water, 39%) both contribute to the N(2)O emission in China. Total atmospheric Nr emissions related health damage in 2008 in China reached US$19-62 billion, accounting for 0.4-1.4% of China's gross domestic product, of which 52-60% were from NH(3) emission and 39-47% were from NO(x) emission. These findings provide policy makers an integrated view of Nr sources and health damage to address the significant challenges associated with the reduction of air pollution.