This session invites contributions that advance understanding of the global nitrogen cycle, its regional and global budget closure, its interactions with carbon, water and climate, including studies that:
• Quantify nitrogen fluxes (N₂O, NH₃, NOx, N₂, BNF, lateral N) across atmosphere, vegetation, soil, and aquatic/marine systems.
• Reconcile regional and global nitrogen budgets using observations, inversions, process-based models, and data-driven approaches.
• Evaluate uncertainties, benchmarking strategies, and emergent constraints for nitrogen–carbon and nitrogen–climate interactions in ESMs and Integrated Assessment Models.
• Assess nitrogen’s role in regulating air and freshwater pollution, land carbon sinks, climate feedbacks, and mitigation pathways.
• Provide synthesis-level insights relevant to global assessments (e.g., IPCC).
By emphasizing budget closure, cross-domain integration, and benchmarking frameworks, this session provides a platform for advancing global nitrogen cycle research and strengthening its connections to Earth system modeling and sustainability challenges.
Orals: Mon, 4 May, 10:45–12:30 | Room 1.31/32
Terrestrial nitrogen cycling plays a vital role in the Earth system, influencing climate change and a myriad of dimensions of human well-being, yet remains poorly constrained in Earth system models (ESMs). In particular, terrestrial biological nitrogen fixation (BNF) is the dominant natural nitrogen source to the terrestrial biosphere and can alleviate nitrogen limitation of CO2 fertilization but is a key source of uncertainty in ESMs. When comparing terrestrial BNF from a CMIP6 ensemble of ESMs to a new global synthesis of observations across natural and agricultural biomes, ESMs are found to underestimate agricultural BNF but overestimate natural BNF by over 50% in the present day. Natural BNF is overestimated in the most productive ecosystems that contribute most to the terrestrial carbon sink (forests and grasslands). There is a positive correlation between modeled present-day natural BNF and the CO2 fertilization effect across ESMs, suggesting that overestimated natural BNF translates to an exaggerated CO2 fertilization effect of approximately 11%. Additionally, while the focus of terrestrial nitrogen cycling in ESMs has primarily been nitrogen limitation of CO2 fertilization, nitrogen losses from the terrestrial biosphere to the atmosphere and hydrosphere has been neglected. These include key flows of nitrogen, such as reactive nitrogen gas emissions from soils and wildfires as well as its transport along the land to ocean aquatic continuum, that are strongly influenced by human activities. ESMs with fully interactive nitrogen cycling could both improve climate change projections and be used to project nitrogen pollution and its impacts to inform planetary stewardship over the 21st century.
How to cite: Kou-Giesbrecht, S., Reis Ely, C., Perakis, S., Cleveland, C., Menge, D., and Reed, S. and the Terrestrial Biological Nitrogen Fixation USGS John Wesley Powell Center for Analysis and Synthesis Group: Terrestrial nitrogen cycling in Earth System Models: from biological nitrogen fixation to projecting pollution for planetary stewardship, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3617, https://doi.org/10.5194/egusphere-egu26-3617, 2026.
Atmospheric nitrogen deposition has long been recognized as an important external driver of terrestrial carbon uptake by alleviating ecosystem nitrogen limitation. However, it also enhances terrestrial nitrous oxide (N2O) emissions, leading to a potential climate trade-off under future mitigation pathways. Despite extensive research, the relative roles of anthropogenic emissions and climate change in regulating nitrogen deposition and their impacts on the terrestrial carbon sink and N2O emissions remain poorly constrained at the global scale. Here, we quantify the impacts of past and future nitrogen deposition pathways on terrestrial carbon cycling and N2O emissions from 1850 to 2100 by generating historical and future nitrogen deposition scenarios with the GEOS-Chem atmospheric chemistry transport model under the SSP1-2.6 and SSP3-7.0 pathways. We use these data and climate forcing from ISIMIP to drive a global carbon-nitrogen cycle model (ICON-Land in QUINCY configuration) in a factorial design to isolate climate and emission effects, while keeping the land cover fixed at 2014 land use conditions.
We find that increasing nitrogen deposition during the historical period (1850–2014) substantially enhanced terrestrial carbon uptake – contributing approximately 0.15 Pg C yr-1 to the global land carbon sink – but also accounted for about 0.82 Tg N yr-1 of terrestrial N2O emissions. In the future period (2015-2100), declining nitrogen deposition under strong mitigation (SSP1-2.6) leads to a decline of the terrestrial carbon sink and a reduction of terrestrial N2O emissions, whereas elevated nitrogen deposition under weak mitigation (SSP3-7.0) enhances both terrestrial carbon sequestration and N2O emissions. Climate change further modulates these responses by altering nitrogen deposition patterns, amplifying both positive and negative feedbacks. These results highlight a fundamental trade-off within the nitrogen–carbon–climate system and underscore the importance of explicitly representing nitrogen processes in earth system carbon budget assessments and mitigation strategies.
How to cite: Deng, J., Gong, C., Engel, J., Nabel, J., Slominska-Durdasiak, K., Nerobelov, G., Ninomiya, H., Zhang, L., and Zaehle, S.: Impact of Past and Future Nitrogen Deposition Pathways on the Terrestrial Carbon Sink and N2O emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18329, https://doi.org/10.5194/egusphere-egu26-18329, 2026.
Nitrous oxide (N2O) emissions from agricultural soils vary greatly in time and space, rendering detailed quantification challenging. Process models that have been used for that purpose are challenged by high computing resources and duration of model runs while providing modest improvement over data-driven approaches. In addition to the well-confirmed dependence on nitrogen input that also provides the basis for the IPCC emission factor to be applied to agricultural soils, multiple studies denoted a non-linear effect, such that excess fertilization provides over-proportionally high emissions. Directed towards effect-based consideration of sources and in order to better reflect mitigation measures, we have revised the N2O emissions calculation methodology for IIASA’s GAINS model to cover such non-linearities, which requires spatially explicit accounting of inputs and emissions. In a first step, emission sources (mineral N fertilizer application and manure N application taken from GAINS) were distributed on a 5’ grid globally using harvested areas from the M3 crop map and the gridded livestock of the world dataset, both updated using annual EUROSTAT data on NUTS2 level (for Europe) and FAOSTAT data for the rest of the world. In a second step, a data-driven approach was chosen reflecting enhanced emissions based on excessive nitrogen application to calculate N2O emissions. The spatially explicit representation of emissions allows to discern sub-regional hot spots of particularly high impact of this non-linearity such as the Indo-Gangetic plain in South Asia, Egypt’s Nile delta, the Yangtse river delta in China, with Northern France or also the Brazilian North-East tip to follow. Automatizing the calculations facilitates the development of a time series as well as the analysis of individual sources of nitrogen and different scenarios. Scenario analysis identifies the value of efficient N abating measures even before applying specific N2O reduction technology. These improvements in depicting N2O emissions in GAINS enhance the analysis of sub-regional emission patterns. Furthermore, they offer to cost-effectively address emission hotspots in more focused emission reduction policies and provide the foundation for fully assessing the impact of N2O abatement policies, both retroactively and in emission projections.
How to cite: Kaltenegger, K. and Winiwarter, W.: Global analysis of N2O emissions from agricultural soil surfaces considering non-linearity effects for the GAINS model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17628, https://doi.org/10.5194/egusphere-egu26-17628, 2026.
Nitrous oxide (N2O) is a major GHG and ozone-depleting substance which is produced by microbial processes in soils, with mineral nitrogen availability, carbon availability, soil moisture, soil temperature, oxygen availability and pH being important controlling factors. Emissions of N2O are notorious for being short-lived with the magnitude of emissions being difficult to predict due to the interplay of the aforementioned controlling factors. In Europe, the major share of anthropogenic N2O emissions result from fertilizer application to agricultural land. National reporting typically relies on so-called Tier 1 or 2 approaches which relate activity data (N inputs) to an emission factor to estimate a national total. However, this method does not consider the full set of spatially and temporally varying controlling factors, so that the latter approaches may be biased. For this reason, reconciliation with an independent, top-down method has large potential to improve national GHG budgets and to review mitigation strategies.
Here we present results from the Horizon Europe project Process Attribution of Regional emISsions (PARIS), where we calculate bottom-up and top-down N2O emission inventories for Germany, the UK and Switzerland at monthly time resolution for the timeframe 2018 – 2024. Bottom-up estimates are obtained using the biogeochemical model LandscapeDNDC and state-of-the-art European datasets. Top-down estimates are averaged results from three different inverse modeling systems: InTEM (UK MetOffice), RHIME (University of Bristol), ELRIS (EMPA) and two different atmospheric transport models: NAME-UM and FLEXPART-ECMWF.
We find the emission estimates from both top-down and bottom-up methods to be consistently higher than the corresponding national inventories, but bottom-up approaches are within the uncertainty of the top-down estimate. In terms of seasonality, bottom-up and top-down methods indicate a seasonal cycle, although its magnitude is country dependent. Across all countries, the discrepancy between bottom-up and top-down estimates is greatest in autumn, where LandscapeDNDC predicts an emission peak following planting of winter crops. Discrepancies regarding magnitude and seasonality of top-down and bottom-up approaches will be discussed considering controlling factors for N2O emissions simulated using LandscapeDNDC.
How to cite: Weber, C., Wolf, B., Chojnacki, L., Scheer, C., Kiese, R., Kraus, D., Haas, E., Smerald, A., Brito Melo, D., Henne, S., Manning, A., Redington, A., Ramsden, A., Andrews, P., Lugato, E., De Longueville, H., Danjou, A., Murphy, B., and Ganesan, A.: Reconciling bottom-up and top-down N2O emission inventories for Germany, Switzerland and the UK , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14527, https://doi.org/10.5194/egusphere-egu26-14527, 2026.
Quantifying lateral nitrogen (N) transfers and riverine N2O emissions is essential for closing the global N budget. We present ORCHIDEE3-Nlat, which couples lateral N routing with ORCHIDEE3 to simulate NH4+, NO3-, and DON fluxes through the land ocean aquatic continuum, from canopy to ocean. Aquatic transformations, including nitrification, denitrification and DON decomposition, occur within the routing framework, and riverine N2O emission is estimated to using an emission-factor scheme tied to nitrification and denitrification rates. Evaluation against global observation-based datasets shows that the model reproduces the global magnitudes and broad spatial patterns of DIN and DON concentrations and fluxes, as well as N2O emission rates across major river systems spread across the world. The model was then applied to reconstruct the historical evolution (1901–2020) of global N lateral transfers from land to rivers, and ultimately to the ocean, together with associated N2O emissions. Globally, DIN inflow to rivers and export to oceans increased by ~245% and ~151% from 1901–1920 to 2001–2020, whereas DON increased more modestly (~38% and ~32%), implying a century-scale shift towards inorganic N cycling. Riverine N2O emissions increased substantially, with a strong acceleration after the mid-1960s, with contemporary hotspots in intensively managed subtropical regions. Attribution analysis indicates that DIN trends were dominated by atmospheric deposition and sewage injection before the 1960s, while fertilizer inputs dominated the increase after the 1960s. The analysis also revealed that due to the fertilization effect on vegetation, increasing atmospheric CO2 decreased the DIN exports to the global river network. In contrast, DON variability and trends were governed primarily by manure application and hydroclimate, showing weaker sensitivity to anthropogenic N inputs than for DIN. Together, these results provide a comprehensive picture of how human activities have reshaped riverine N composition, downstream N export, and the spatial distribution of N2O emissions over the twentieth century, offering a robust baseline for global N-cycle assessments and mitigation planning.
How to cite: Ma, M., Vuichard, N., Zhang, H., Huang, T., and Regnier, P.: Anthropogenic Perturbations of Nitrogen Cycling and Budgets Across the Land–Inland Water Continuum: Insights from ORCHIDEE3_Nlat , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22032, https://doi.org/10.5194/egusphere-egu26-22032, 2026.
Maize and wheat are two major staple foods that collectively contribute two-thirds of the world’s grain supply. The extensive use of nitrogen (N) fertilizers during the cultivation of both crops leads to significant losses of reactive nitrogen (Nr) into the environment. Here, using machine learning algorithms, we generate high-resolution maps of crop-specific soil Nr losses based on global field measurements. We estimate that global annual soil Nr losses from the use of synthetic N fertilizer in 2020, including direct emissions of nitrous oxide (N2O), nitric oxide (NO), ammonia (NH3), N leaching and run-off, amount to 0.18, 1.62, 0.09, 1.47 and 1.10 million tonnes N for maize, and 0.12, 1.33, 0.07, 1.21 and 0.95 million tonnes N for wheat, respectively. The annual indirect N2O emissions induced by synthetic N fertilizer use from these soil Nr losses are estimated to be 45,000 and 37,000 tonnes for maize and wheat, respectively, with hydrologic pathways playing a predominant role. Enhancing N use efficiency up to 60% for regions below this value can achieve a total soil Nr loss mitigation potential of 4.00 million tonnes per year for the two crops, thereby reducing indirect N2O emissions by 49%. Our results contribute to constrain global N budgets from the use of fertilizer in agriculture, which then can help to improve projections of nitrogen cycle–climate feedbacks using modelling approaches.
How to cite: Liu, S.: Reducing soil nitrogen losses from fertilizeruse in global maize and wheat production, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1654, https://doi.org/10.5194/egusphere-egu26-1654, 2026.
Human activities have profoundly altered the global nitrogen (N) cycle, with far-reaching consequences for the environment and human well-being. By integrating data from multiple sources and employing advanced modeling techniques, here we present an up-to-date comprehensive assessment of the global nitrogen budget from 1980 to 2022, quantifying the major flows and redistributions of reactive nitrogen (Nr) among the atmosphere, terrestrial ecosystems, and aquatic systems. Our analysis reveals a 49% increase in anthropogenic Nr release over the past four decades, largely driven by agricultural intensification and industrial expansion. Emissions to the atmosphere (NH₃, NOₓ, N₂O) rose by 37%, while nitrogen losses to water bodies surged by 72%, intensifying air pollution, eutrophication and climate change. Regarding the terrestrial fate of Nr, we estimate that terrestrial ecosystems eliminate approximately 100 Tg N yr⁻¹ via denitrification to N2, while net accumulation in soils, biomass and industrial products accounts for 130-150 Tg N yr⁻¹. Hotspots of nitrogen accumulation and deficiency emerging in different regions, exacerbating regional and global inequalities. These findings underscore the urgency of coordinated global policies and region-specific strategies to mitigate nitrogen pollution and advance sustainable nitrogen management.
How to cite: Zhang, X., Xu, X., Winiwarter, W., and Gu, B.: Global Nitrogen budget 1980-2022, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3763, https://doi.org/10.5194/egusphere-egu26-3763, 2026.
Anthropogenic nitrogen (N) losses from croplands have risen alongside global food production and are a major driver of transgressed planetary boundaries. Price-based policy instruments are widely proposed to curb agricultural nitrogen pollution, yet their effectiveness and distributional consequences under market feedbacks remain insufficiently understood. Here we assess the global impacts of nitrogen pricing on cropland N losses, food security and economic outcomes. We extend the global land-use model GLOBIOM by endogenizing crop- and country-specific nitrogen balances and explicitly representing multiple N-loss pathways. Field-level mitigation technologies are incorporated, with adoption governed by marginal abatement costs, yield effects and economic affordability, allowing nitrogen taxation and subsidies to interact with production decisions, land allocation and international trade. Without additional intervention, global cropland N losses increase by 28% by 2050 relative to 2020. Nitrogen taxation reverses this trend, reducing N losses by 22% (12–29%) compared with business as usual, but at the cost of higher food insecurity. Field-level mitigation technologies provide a critical buffer, delivering additional abatement and offsetting nearly one-third of the food-security losses induced by taxation. In contrast, mitigation subsidies implemented alone yield limited net mitigation, as technology-driven reductions are partly offset by subsidy-induced cropland expansion. Combining taxation, subsidies and technologies yields the most balanced outcome, reducing global N losses by 23 Tg N by 2050 while moderating food-security impacts. Responses to nitrogen pricing vary strongly across regions. Under the combined policy scenario, South Asia, East Asia and Europe together account for about 58% of global mitigation, but through distinct pathways. Economically resilient regions mainly achieve mitigation through higher adoption of field-level technologies and declines in N-loss intensity, with mitigation shares exceeding their emission shares. Less affluent regions rely more on trade adjustments, shifting part of the mitigation burden to exporting regions through virtual N flows. These contrasts translate into marked distributional effects: technologies and subsidies offset more than half of taxation-induced farmer revenue losses in high-income regions, whereas buffering effects remain limited in some low-income regions, with mitigation costs increasingly borne by consumers and governments. Overall, price-based nitrogen mitigation can halt the long-term rise in global N pollution, but its effectiveness and equity critically depend on technology deployment and policy design and must be aligned with broader food-system transformations.
How to cite: Huang, W., Chang, J., Frank, S., Leclere, D., Kozicka, M., Havlík, P., and Zhou, F.: Price-based nitrogen mitigation from global croplands with uneven regional responses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7384, https://doi.org/10.5194/egusphere-egu26-7384, 2026.
Posters on site: Mon, 4 May, 08:30–10:15 | Hall X1
Nitrogen (N) is an essential element for life and a fundamental regulator of terrestrial ecosystem productivity, carbon sequestration, and climate feedbacks, yet it remains one of the most weakly constrained and uncertain components of Earth system models. Despite major advances in terrestrial biosphere modeling, large discrepancies persist in how models represent nitrogen inputs, internal cycling, losses, and their coupling to the carbon and water cycles. Here we present the first comprehensive, process-resolved benchmark of the global terrestrial nitrogen cycle based on coordinated simulations from the Nitrogen Model Intercomparison Project Phase 3 (NMIP3) combined with multiple independent observational constraints.
We trace the full nitrogen cascade across land ecosystems—from natural and anthropogenic inputs (biological nitrogen fixation, atmospheric deposition, and fertilizer and manure application), through plant uptake and soil–microbial transformations, to hydrological export to inland waters and gaseous losses to the atmosphere (N₂O, NH₃, NO, and N₂). This integrated framework allows us to evaluate not only individual fluxes and pools, but also the internal consistency of regional and global nitrogen budgets and their emergent coupling with carbon cycling.
Across models, we find broad agreement in the magnitude of total nitrogen inputs and in first-order global spatial patterns. However, models diverge strongly in how nitrogen is partitioned among vegetation, soils, and loss pathways. The largest spreads occur in biological nitrogen fixation, soil nitrogen turnover, nitrate leaching, and gaseous emissions, producing substantial inconsistencies in regional budget closure and large uncertainty in carbon–nitrogen feedback strength. These discrepancies are especially pronounced in intensively managed agricultural regions and climate-sensitive ecosystems, including the tropics and high latitudes, and they propagate directly into uncertainty in the magnitude and spatial distribution of the terrestrial carbon sink.
By systematically comparing model structures and process representations, we diagnose the dominant sources of these divergences and show that a small number of key processes control most of the uncertainty. Our analysis demonstrates that improving the representation and observational constraint of biological nitrogen fixation, soil organic matter turnover, and coupled nitrification–denitrification pathways can substantially reduce uncertainties in nitrogen budgets, N₂O and NH₃ emissions, and land carbon sink estimates.
More broadly, this work establishes a community framework for nitrogen cycle benchmarking that moves the field from qualitative model intercomparison toward quantitative, process-level accountability. Our results show that coordinated benchmarking can transform nitrogen–carbon–climate projections into more robust and policy-relevant tools, with direct implications for climate mitigation, air and water quality management, and integrated carbon–nitrogen stewardship.
How to cite: Tian, H. and the NMIP3 Participants: Where Does the Nitrogen Go? Model Intercomparison and Benchmarking of the Global Terrestrial Nitrogen Cycle and Carbon–Nitrogen Interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7379, https://doi.org/10.5194/egusphere-egu26-7379, 2026.
Nitrogen (N) addition from anthropogenic atmospheric deposition and fertilizer application is widely recognized to enhance terrestrial carbon (C) storage by alleviating ecosystem nutrient limitation. However, long-term N addition can also acidify soils and impair ecosystem functioning, an effect that is often overlooked in global assessments of terrestrial C cycling. Here, we performed a global meta-analysis to systematically quantify both the impacts of long-term N addition on soil pH and the responses of vegetation root growth and soil microbial respiration to soil pH changes. This data-driven understanding was then used to develop a parameterization for soil acidification and its impacts on vegetation and soil microbe within the C-N-coupled terrestrial biosphere model QUINCY. Model simulations show that present-day global N fertilization effects on terrestrial net ecosystem productivity (NEP) are around 240 Tg C yr-1, which are approximately 20% lower than the estimate when neglecting the long-term N-induced soil acidification. In the meanwhile, inclusion of soil pH effects increases the simulated soil carbon storage, consistent with patterns emerging from the meta-analysis. By explicitly incorporating soil acidification into terrestrial C–N interactions, our results reveal critical gaps in current representations of long-term ecosystem responses to N enrichment, with important implications for future sustainable N management and climate change mitigation.
How to cite: Gong, C. and Zaehle, S.: Overestimated nitrogen fertilization effects on global terrestrial carbon sinks due to neglect of long-term soil acidification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5298, https://doi.org/10.5194/egusphere-egu26-5298, 2026.
The mixing ratio of nitrous oxide (N2O), an important greenhouse gas and ozone-depleting substance, in the troposphere has increased by 25% (~336 ppb) since the preindustrial period, with increased emissions in the last few years showing that effective mitigation policies are urgently required. N2O is emitted from a range of anthropogenic sources, particularly fertilised agricultural soils. N2O sources and sinks can be constrained using measurements of four isotopocules: 14N15N16O (α), 15N14N16O (β), 14N14N16O, and 14N14N18O, and the site-specific relative isotope ratio differences (δ15Nα and δ15Nβ); however, N2O’s long tropospheric lifetime requires high precision (<0.1 ‰) to distinguish source signals from background variability. Existing preconcentration-laser spectrometry (TREX-QCLAS) systems lack the sufficient precision required for detailed tropospheric N2O budget studies, for example, resolving trends in site preference or the interhemispheric gradient in isotopic composition. In this project, we build upon preconcentration system development with key innovations: (1) a simplified single 6-port VICI valve design; (2) a system-wide reduction of dead volumes to minimise memory effects; (3) a smaller trap enabling faster heating/cooling without linear actuators; and (4) integration with MIRO Analytical's first commercial N2O isotope spectrometer featuring a temperature/pressure-controlled measurement cell. This system will measure N2O isotopic composition in flask samples from Jungfraujoch High-Altitude Research Station and other background sites, establishing global isotope scale compatibility through multi-site measurements and inter-laboratory comparisons. These advances will improve constraints on regional and temporal variability in the global N2O budget to support effective mitigation strategies.
How to cite: Agredazywczuk, P., Meier, R., Hlubucek, J., Bruckuisen, J., Espic, C., Wolf, B., Mohn, J., Aseev, O., and Harris, E.: Developing an enhanced preconcentration system (RAPTOR) for high-precision tropospheric nitrous oxide isotope measurements by laser spectroscopy , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-523, https://doi.org/10.5194/egusphere-egu26-523, 2026.
Imbalanced synthetic nitrogen fertilizer use remains a critical obstacle to global sustainable development. Excessive nitrogen application leads to environmental pollution in many world regions, whereas insufficient nitrogen input elsewhere constrains yields and exacerbates food insecurity. Resolving this spatial imbalance requires a comprehensive understanding of how nitrogen use can be more effectively redistributed, together with the associated economic costs and societal benefits to the achievement of Sustainable Development Goals (SDGs). We present a global analysis of synthetic nitrogen fertilizer redistribution among countries and its potential to contribute to multiple SDGs, particularly enhancing food security while mitigating nitrogen emissions to air and aquatic systems. The redistribution based on optimal regional nitrogen use efficiencies could increase global crop production by 14% while reducing global nitrogen fertilizer use by 11 million tonnes. This reduction would lower reactive nitrogen losses, decreasing emissions to the atmosphere and aquatic systems by 22% and 21%, respectively. The estimated implementation cost is US$21 billion, far below the projected social benefit of US$535 billion. Redistribution would improve 1-16% of multiple SDG performance, especially the SDG 2 (Zero Hunger). These findings offer a practical and cost-effective pathway to reconcile crop production with environmental sustainability, providing an evidence base for more equitable and efficient global nitrogen management.
How to cite: Qiu, Z. and Gu, B.: Redistributing 14% of global nitrogen fertilizer use advances multiple Sustainable Development Goals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4749, https://doi.org/10.5194/egusphere-egu26-4749, 2026.
Sustainable intensification of rice systems requires strategies that synergize productivity, environmental, and economic goals. This study presents a comprehensive, multi-dimensional evaluation of eight rice-based cropping systems (including straw-return and diversified green manure rotations) in the Yangtze River region, China. We uniquely integrated field measurements of greenhouse gases and reactive nitrogen (Nr) species (CH4, N2O, NH3, HONO) with agronomic and soil health indicators. The climate impacts were assessed using multi-temporal metrics (GTP20, GTP100). A Comprehensive Evaluation Index (CEI) quantified system-level synergies and trade-offs. The medium rate straw-return system (NPKS2) achieved the highest CEI score (0.63), representing the optimal balance among evaluated systems. A fundamental trade-off was identified: economic benefits and crop yield showed strong positive correlations with net GHG (r = 0.6 & 0.61, P ≤ 0.001) and Nr gas emissions (r = 0.54, P ≤ 0.001and r = 0.45, P ≤ 0.05, respectively), but were negatively linked to soil organic carbon (SOC) sequestration and biodiversity. This reveals an inherent conflict between short-term productivity and environmental sustainability. Critically, by including short-lived Nr species, our assessment shows that the climate impact is highly time-dependent. For instance, NH3-induced aerosol cooling offset 8–70% of N2O -induced warming over 20 years, but less than 0.1% over a century. We conclude that moving beyond single-gas or single-timescale assessments is essential to reveal the true costs and benefits of management practices, thereby informing strategies that are genuinely climate-smart and sustainable.
How to cite: Huang, J., Yue, L., Ding, Y., Wu, D., and Sha, Z.: Using half-straw return to tackle trade-offs among Grain Yield, Multiple Soil Gas Emissions, and Soil Health in Rice-Based Rotations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6898, https://doi.org/10.5194/egusphere-egu26-6898, 2026.
In recent years, emission factors published by the Intergovernmental Panel on Climate Change (IPCC) are widely used by national inventory compilers as a Tier 1 methodology for estimating N2O emissions at national levels. Whilst emission factors are straightforward to implement and offer several practical advantages, conventional emission factors tend not to account for the impacts of interannual climatic variability or spatial heterogeneity.
To investigate the added value of using spatially and temporally explicit processes included in land surface models, we assess the spatial and temporal variability of N2O emissions associated with land management and extreme weather events over Italy for the 2010-2021 period. We compare N2O emissions and N2O emission factors estimated from two process-based land surface models, LPJ-GUESS and ORCHIDEE, against those estimated using national inventory data and published emission factors from IPCC guidelines.
Inventory-derived emissions do not show a trend over the study period and have limited interannual variation. In contrast, both models show a positive trend in emissions over the study period with interannual variability that extends well beyond the variability suggested by the inventory. We investigate the variability in emissions simulated by both models and assess whether this is indicative of a sensitivity to climate that is largely muted in IPCC based emission factors.
Both models show higher emissions from croplands than grasslands (total and per square meter) but higher emission factors from grasslands than croplands, indicating that the addition of (organic) fertilisers to pastures is more likely to be emitted as N2O emissions than the same fertiliser added to croplands. We discuss key structural difference in how the models treat grasslands and pastures and how these discrepancies underscore the simplifications present in land surface model representations of these systems, especially regarding grazing, harvests, and manure management.
The substantial interannual variability in emission factors produced by both models exceed those estimated by inventory estimates and indicated by IPCC emission factors. These temporal patterns highlight the potential relevance of considering climate anomalies when using emission-factor methodologies, particularly with the increasing occurrence of extreme climate events.
How to cite: Lippmann, T. J. R., Lagergren, F., Naudts, K., Jönsson, A. M., and Fiore, A.: Large differences in variability between land surface models (LPJ-GUESS and ORCHIDEE) and inventory estimates: N₂O emissions and emission factors in Italy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8421, https://doi.org/10.5194/egusphere-egu26-8421, 2026.
Anthropogenic transformations to river systems are profoundly altering basin-scale nitrogen cycling globally, leading to long-term nitrogen accumulation that poses persistent and episodic threats to downstream water quality. Net nitrogen input (NNI) is a key integrative indicator that quantifies the cumulative influence of human activities on nitrogen budgets. This study constructed a comprehensive spatiotemporal NNI dataset for the Yangtze River Basin (YRB) between 1980-2020 and systematically examined its temporal dynamics, source composition, and landscape-driven controls. Results show that basin-wide NNI in the YRB followed a distinct three-stage trajectory during 1980–2020, characterized by a rapid increase, a high-level plateau, and a subsequent partial decline. Average NNI intensity typically increased along an upstream-downstream gradient, primarily governed by intense nitrogen fertilizer use and dense population pressures. Trend analyses revealed strong spatial asynchrony in NNI evolution, whereby: the downstream basin exhibited the earliest plateauing effect (c. 1994); the midstream basin experienced the longest period of sustained accumulation (1995–2010); and the upstream basin, despite possessing the lowest average NNI overall, displayed the fastest growth rate that highlights emerging nitrogen management challenges in upstream regions. Machine learning analyses demonstrated that these trends were primarily driven by agricultural land cover, whereas urban land and water bodies also exerted strong but nonlinear controls on long-term NNI evolution. This study thus provides novel and unique insights into long-term, large-scale nitrogen fluxes operating across one of the world’s mega-basins. By characterizing anthropogenic pressures governing these trends, this research could help underpin effective nutrient management efforts in the Yangtze River Basin and beyond.
How to cite: Wen, W., White, J., Xia, B., Zhuang, Y., Shen, W., Hannah, D., and Zhang, L.: Long-term trends in Net Nitrogen Inputs across the Yangtze River Basin and large-scale management implications, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20535, https://doi.org/10.5194/egusphere-egu26-20535, 2026.
Earth system models (ESMs) need to include nutrient limitation to predict realistic land carbon (C) uptake. In particular, Nitrogen (N) is a critical nutrient, that controls photosynthesis and decomposition processes. We have implemented an explicit N cycle in the land component of the CNRM-ESM model. Here we present an evaluation of the model using data from the Free-Air CO2 Enrichment (FACE) experiments conducted over 10 years in North America. We compare the reference version of the model without the N cycle (C) to the new version in which it is included (CN). We investigate the response of the Net Primary Prodcution (NPP) to elevated CO2 and confront our results to a multi-model analysis carried out on these two sites. Our results fall in the inter model range. We show that the CN version of the model performs better than the C version because NPP is reduced by N limitation. In the literature, diverging strategies are observed to overcome N limitation. We analyse the simulated N dynamics and show that the model reproduces well the main features but fails to represent some sites characteristics.
How to cite: Decayeux, J., Delire, C., and Decharme, B.: Evaluation of the Nitrogen Cycle in the Land Surface Model of CNRM, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11153, https://doi.org/10.5194/egusphere-egu26-11153, 2026.
To estimate N2O fluxes from groundwater due to N leaching from agricultural soils, an empirical parameter had been determined from the ratio of dissolved N2O-N to NO3--N (EF5(1), leading to a first estimate of IPCC-EF5g of 0.015 in 1998. While the data-set of dissolved N2O was steadily growing, the IPCC-EF5g was first lowered to 0.0025 in the 2006 guidelines, but raised back to 0.006 in the IPCC2019 guidelines based on a more recent review (Tian et al 2019). But it had previously been shown that the concept of EF5(1) must overestimate indirect N2O fluxes because it related N2O measured at a certain sampling point in groundwater to the NO3- concentration at that point (Well and Weymann, 2005). This neglects the fact that some of the NO3- leached to the groundwater surface is typically consumed by denitrification. Studies measuring N2O together with excess-N2 from denitrification and residual NO3- have shown that this overestimation can be highly relevant (Weymann et al., 2008). An alternative emission factor EF5(2) was thus proposed as the ratio between dissolved N2O-N and initial NO3--N, where the latter was calculated from the sum of excess N2 and residual NO3--N. Neglecting NO3- reduction in the EF5g concept had been justified by the wide lack of excess-N2 data in groundwater (Tian et al, 2019). But NO3- consumption in groundwater can also be estimated from the difference between NO3--N in leachate calculated from N budgets and the residual NO3--N in groundwater monitoring wells. For Germany, these data are widely available and could be used to correct current estimates of indirect N2O fluxes.
Here we present recalculations of indirect N2O fluxes using the EF5(2) concept. For the dataset of Tian 2019, we select data from regions where we can assume typical ranges of N fertilization together with the default IPCC factor for N leaching and typical ranges of seepage rates to estimate initial NO3--N at the groundwater surface. For Germany, we use respective data from inventories and spatial models. For both cases, indirect N2O fluxes based on EF5(1) and EF5(2) are compared. For Germany, we also estimate the lowering of currently reported indirect N2O fluxes with those based on EF5(2). We conclude that there is need for new research on indirect N2O fluxes from groundwater globally to avoid overestimation of this source.
References:
IPCC, 2019: 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, edited by E. Calvo Buendia, K. Tanabe, A. Kranjc, J. Baasansuren, M. Fukuda, S. Ngarize, A. Osako, Y. Pyrozhenko, P. Shermanau, and S. Federici, IPCC, Switzerland.
Tian, L., Y. Cai and H. Akiyama (2019), Environmental Pollution 245: 300-306.
Well, R. and D. Weymann (2005), 4th International Symposium on non-CO2/ greenhouse gases (NCGG-4), science, control, policy and implementation, Utrecht, Netherlands, 4-6 July 2005: 129-136.
Weymann, D., R. Well, H. Flessa, C. von der Heide, M. Deurer, K. Meyer, C. Konrad and W. Walther (2008). Biogeosciences 5(5): 1215-1226.
How to cite: Well, R., Fuß, R., Wolters, T., and Zinnbauer, M.: Overestimation of indirect agricultural N2O fluxes from the groundwater due to neglect of nitrate attenuation , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7363, https://doi.org/10.5194/egusphere-egu26-7363, 2026.
Nitrous oxide (N2O) production in the biosphere is traditionally attributed to microbial nitrification and denitrification. Recent studies suggest that N2O can be produced via chemodenitrification, i.e., the reduction of nitrite to N2O, which remains a major uncertainty in global N2O budget. By conducting 15N-tracer incubations, samples from a land–ocean continuum demonstrated that the significance of N2O production via chemodenitrification may be overlooked, particularly at metal-rich, acidic and anoxic conditions. Transition metals beyond iron, specifically manganese and zinc, drive abiotic N2O formation in both oxic and anoxic environments. And the rates are significantly enhanced under lower oxygen concentration. In natural estuarine waters, abiotic N2O production is modest but consistent (0.0001–0.0013 nmol N L-1 d-1). In contrast, acidic metal-rich mine wastewater stimulated abiotic N2O production up to 138 nmol N L-1 d-1. Furthermore, at the interface where mine drainage contaminating soils, N2O efflux reached 446 μmol N m-2 d-1, rivaling or exceeding emissions from many intensively managed croplands. In these hotspots, abiotic and biotic processes act in concert to sustain elevated N2O production, with microbial activity potentially modulating substrate availability for abiotic production. These findings highlight the necessity to integrate chemodenitrification into regional and global nitrogen assessments to improve the accuracy of N2O budget.
How to cite: Zheng, X. and Ji, Q.: Abiotic N2O Formation Across the Land–Ocean Continuum: An Overlooked Source of Nitrous Oxide via Abiotic Formation Across the Land–Ocean Continuum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6235, https://doi.org/10.5194/egusphere-egu26-6235, 2026.
Peatlands cover a small portion of the Earth's land area, but their impact on the carbon (C) and nitrogen (N) cycles at both regional and global scales is significant. The water regime of peatlands (as an indicator of oxygen content) and temperature are the main factors in peatland greenhouse gas (GHG) fluxes. Under high water tables, as well as very dry conditions, emissions of both carbon dioxide (CO2) and nitrous oxide (N2O) are low, but excess moisture and anoxic conditions increase methane (CH4) emissions. At moderate soil moisture and fluctuating water table, CO2 and N2O emissions are high. Peatland N2O emissions also depend significantly on availability of total mineral nitrogen (TIN). Permanently wet (i.e., natural) peatlands act as CO2 sinks, accumulating organic C in the soil. In drained peatlands, both gaseous and dissolved C losses are high. Artificial drainage and climatic drying induce approximately 70% of all N2O emissions from organic soils.
Tropical regions are some of the most important terrestrial sources of N2O. In drained tropical peatlands, N2O emissions are the second most important contributor to the GHG budget after CO2. Forests dominate tropical peatlands. These are more complex ecosystems than open peatlands, as the canopy (phyllosphere) may significantly influence GHG fluxes, especially during wet periods. Our studies show that large N2O fluxes from the soil can be absorbed by the canopy, although the underlying mechanisms remain unclear.
In our empirical process-based PeatN2O model, which simulates monthly N2O fluxes in peatlands, we integrate the following parameters: peat ammonium (NH4+) and nitrate (NO3–) content, C/N ratio, soil moisture level, rate of change in soil moisture, N and C cycle microbiome ratios, source (NH4+ and/or NO3–) partitioning based on N2O isotopologue signatures, a plant traits factor, and a canopy factor. The results of this model can be used to refine the global N2O estimates based on a combination of N2O emission estimates from the Global Peatlands Initiative map (2022) and the Major Land Cover Units map (MODIS, 2022). The sources are from our working group's global studies, IPCC emission factors, and other published studies. The main challenge in scaling future GHG fluxes to global change scenarios is predicting the spatial and temporal variability in environmental conditions that create hot spots and hot moments of fluxes.
How to cite: Mander, Ü., Pärn, J., Espenberg, M., Thayamkottu, S., Masta, M., Kazmi, F. A., Sagris, V., and Soosaar, K.: Modelling N2O Fluxes in Peatlands: From Process to Global Mapping, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2377, https://doi.org/10.5194/egusphere-egu26-2377, 2026.
The environmental problems caused by the overuse of nitrogen (N) fertilizer is well recognized. However, the complexity of the N cycle and its multiple pollution pathways have hindered the quantification of a safe operating space for N fertilizer use in China. We used a modeling approach and environmental thresholds for N deposition, N concentrations in surface water and groundwater, as well as for ammonia (NH3) volatilization and nitrous oxide (N2O) emissions to assess spatial patterns and quantify N use mitigation goals for different regions in China.
At the national scale, the results indicate that the safe operating space for N use can be achieved if total N deposition is reduced to 5.2 Tg N yr-1, total loading of N to surface water and groundwater are reduced to 5.4 and 13.9 Tg N yr-1, respectively, and total NH3 volatilization and N2O emissions are below 5.3 and 0.6 Tg N yr-1, respectively. Meeting these thresholds would require reductions of approx. 22%, 44%, 11%, 48%, and 30%, respectively. In total, this amounts to a reduction of 12.5 Tg N yr-1, or a 29% decrease from current levels of N inputs to the environment. Specifically, central China and southern China require higher emission reductions to meet the thresholds, particularly in provinces such as Henan, Shandong, and Sichuan. This study is the first to integrate multiple N indicators to determine a national reduction target for China. This approach provides a scientific basis for improving N management, mitigating its environmental impacts and identifying regional “low-hanging fruits” where targeted reductions could yield the greatest environmental benefits.
How to cite: Huang, J., Ti, C., Serra, J., Yan, X., and Butterbach-Bahl, K.: Integrated environmental thresholds for nitrogen in China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10815, https://doi.org/10.5194/egusphere-egu26-10815, 2026.
Nitrogen oxides (NOₓ ≡ NO + NO₂) play a central role in atmospheric chemistry, with direct impacts on human health through respiratory stress and indirect effects on climate via tropospheric ozone production, methane lifetime, and secondary aerosol formation. To study the impacts of NOₓ emissions on the atmospheric chemistry and the climate, we developed a version of the LMDZORINCA Chemistry-Transport model in which soil NOₓ emissions are computed by the ORCHIDEE land surface model, in complement of anthropogenic emissions provided by inventory data.
Current estimates place global total NOx emissions at about 45–50 Tg N yr⁻¹, dominated by fossil fuel combustion. Soils are a substantial source of NOₓ, with global emissions estimated at ~10–15 Tg N yr⁻¹, of which ~3 Tg N yr⁻¹ are attributable to fertilizer and manure inputs, the remainder arising from natural processes. Due to air-quality and climate policies reducing NOₓ emissions from transport and industrial sectors, the relative importance of soil NOₓ emissions is expected to further increase in the future. Currently, most atmospheric chemistry models take into account agricultural soil NOₓ emissions, using inventory-based approaches. These inventories rely on fixed emission factors or highly simplified parameterizations to calculate NOₓ emissions from nitrogen inputs, thereby neglecting, or overly simplifying, the strong non-linear dependence of emissions on climate, soil biogeochemistry, and vegetation type. Furthermore, natural soil NOₓ emissions are often neglected or calculated using simplified parametrizations.
In this work, we use soil NOₓ emissions estimated by the ORCHIDEE terrestrial biosphere model as an input to the LMDZINCA atmospheric chemistry model. ORCHIDEE simulates the carbon-nitrogen cycle as well as soil microbial nitrification and denitrification processes, thus offering a mechanistic and ecologically grounded description of soil NOₓ emissions. We first evaluate ORCHIDEE soil NOX emissions against three different datasets : CAMS-GLOB-SOIL product, which is based on empirical parametrizations, the inventory-derived dataset for anthropogenic NOₓ emissions CEDS, and the DESCO dataset using top-down constraints from satellite-based NO2. In the current configuration of LMDZINCA, soil NOₓ emissions are based on the CEDS anthropogenic emission inventory, therefore not taking into account NOₓ emissions from natural soils. Replacing these current CEDS soil NOₓ emissions with ORCHIDEE soil NOₓ emission includes the very substantial natural soil NOₓ component which has previously not been accounted for in LMDZINCA. The resulting changes on atmospheric NO2 in recent years are then analysed and compared with satellite derived NO2 columns from OMI and TROPOMI. These differences of soil NOX emissions and resulting tropospheric NO2 changes are studied over the last two decades.
The offline implementation of ORCHIDEE soil NOₓ in LMDZINCA represents a first step toward a fully coupled nitrogen cycle within the IPSL framework, enabling future assessments of feedbacks between terrestrial and atmospheric nitrogen reservoirs.
How to cite: Hanig, N., Lathiere, J., vuichard, N., Simpson, D., Cozic, A., and Hauglustaine, D.: Improving the representation of NOx emissions from soils in the LMDZORINCA model for global chemistry and climate purposes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18454, https://doi.org/10.5194/egusphere-egu26-18454, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 2
EGU26-13318 | ECS | Posters virtual | VPS5
Microbial breakthroughs in 2022 now allow us to link United Nations water volumes with EEA nitrates data, to reveal world nitrates processing loads in kilotons, including how much nitrate is from natural sources, and how much is from human activity.Tue, 05 May, 14:03–14:06 (CEST) vPoster spot 2
The European Environment Agency data on nitrates levels gives us a ratio of 8:1 for nitrates in groundwater versus river water, when we analyse the data across 27 countries. The “missing” nitrate, at an average of about 89%, matches the levels of “missing” nitrate due to capture of nitrate on the river bottom, by microbes known as diatoms, which take up 65-95% of the water nitrate load.
Diatoms convert nitrate to ammonium in daily cycles, that are linked to sunlight and Oxygen abundance, encountered in typical river and lake conditions.
We can identify that the major pathway of nitrate into rivers and lakes is through groundwater feeds, which average 25% of surface waterway volumes worldwide -because their nitrate levels dwarf those from any other source. We can also identify that the main mechanism of nitrates removal in river bottoms is diatom capture, where diatoms take up the bulk loads of nitrate arriving in the groundwaters beneath.
Diatoms' virtual monopoly on nitrates conversion may allow us to control N2O and global warming levels, by intercepting the conveyor belt system of nitrates to diatoms in waterways. We can capture and repurpose the nutrient for use as farm fertilizer and harvest diatom ammonium as a carrier for Hydrogen fuel. Diatoms are already farmed commercially for fish food, showing they are amenable to farming, and they are already a source of soil conditioner for farms. Ammonium is harvested in wastewater plants for Hydrogen fuel purposes already, and diatoms offer a low carbon method of ammonium production.
The junction between the UN, EEA and microbial data also allows us to calculate the world processing levels of nitrate in terms of both natural and human produced components. We obtain a range around 300,000 kilotons per annum as being processed by surface waters worldwide from all sources. About 120,000 kilotons of the load comes from human produced sources.
Ammonium nutrient from diatom nitrate conversion is quickly absorbed by aquatic plants and riverside trees, but there is a risk of high levels on hot days in lowered Oxygen conditions. Trees draw up around 1000 litres a day of groundwaters in river basins, so that ammonium and nitrates consumption by trees is additionally a main mechanism of Nitrogen reduction around the riverbed.
How to cite: Hall, C., Smith, D., Munro, A., and Sgroi, A.: Microbial breakthroughs in 2022 now allow us to link United Nations water volumes with EEA nitrates data, to reveal world nitrates processing loads in kilotons, including how much nitrate is from natural sources, and how much is from human activity., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13318, https://doi.org/10.5194/egusphere-egu26-13318, 2026.
