Methane emission from wetland trees is an overlooked source of methane, with poor resolution of their global significance and mechanisms. Our ongoing work in the Amazon basin has revealed that wetland trees are the largest source of methane, emitting the equivalent of all the methane emitted from the Arctic. Factors controlling and mechanisms driving these emissions remain unclear. Tree stem surfaces are no longer considered passive conduits for soil-produced methane; instead, they are active surfaces driving both methane production and oxidation.

Over the past five years, using methane flux measurements, wood incubation experiments, stable carbon isotopic composition of methane measurements and wood structure and traits analysis, we attempt to unravel the following questions:  Where is methane produced? How is methane transported and emitted from the tree stems? What controls the flux strength of methane eventually released at the stem surface?

So far, results suggest that soil is the predominant source of tree stem-released methane; however, certain tree species display strong internal methane production, increasing from the wet to dry season. The methane transport pathway is also tree species-specific, with some trees showing strong evidence of diel variability and others displaying minimal to zero diel variability. Internal wood methane concentration and stable isotopic measurements corroborate this. A strong presence of tree-methane oxidation was observed, which again was tree species-specific, despite the net fluxes measured at the stem surface always being positive. Methane oxidation within the tree stems was dominant, with methane oxidation in the bark only playing a minor role. Wood structure and traits analysis revealed that wood density could be used as a proxy to predict stem methane fluxes at an ecosystem level. However, species-level variability was controlled by other species-specific wood traits, making it harder to fully explain the variability we observe in methane emitted at the stem surface. 

How to cite: Pangala, S., Nunes-Sousa, R., Blincow, H., Gomez, C., and Reis, L. P.: Stem-methane emissions from the Amazon floodplains: controls and variability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9990, https://doi.org/10.5194/egusphere-egu23-9990, 2023.

Trees are understood to emit large quantities of methane, particularly in tropical wetland environments; however, little is known about the source of tree methane emissions. We aim to understand the form of methanogenesis behind tree methane in the Brazilian Amazon and the source of this methane. In order to compare methanogenesis between different systems, isotope samples were taken from trees, soil and flood water at two sites. Initial isotopic analysis shows that there is no significant difference between soil and tree methane samples, whereas water-sampled methane was significantly different from both soil and tree samples. Hydrogen isotope analysis will further our understanding of the specific methanogenesis process in the soil-tree-atmosphere continuum. These preliminary results suggest tree methane is soil derived, which is critical in enhancing our understanding of both the global methane budget and the role trees play in methane emissions.

How to cite: Blincow, H., Pangala, S., McNamara, N., and Hoyt, A.: Tree methane: Getting to the root of it., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1783, https://doi.org/10.5194/egusphere-egu23-1783, 2023.

Floodplain forests as wetlands are characterized by methane (CH₄) emission. Methane, after carbon dioxide (CO₂) is the second main driver of global climate change. The magnitude of CH₄ emission is site specific and depends on environmental factors like water table level and soil temperature. The standard method to quantify ecosystem-scale CH₄ exchange is the eddy covariance (EC) method. Gap-filling procedures, however, are manifold and not standardized yet.

The main aim of our study was to quantify the CH₄ emission on the floodplain forest ecosystem level using the EC method, with special emphasis on environmental conditions, turbulence development and footprint. Furthermore, the ecosystem-scale CH₄ fluxes shall be analysed with regards to the CH₄ emissions of water bodies within the EC footprint.

The studied floodplain forest represents nowadays relatively dry conditions. Consequently, we initially hypothesized that ecosystem-scale CH₄ exchange will be negligible.

First results, however, showed, that the whole ecosystem is a small but constant CH₄ source as we observed an average emission flux of 11.7 mg CH₄ m^-2 day^-1 over the period June to December 2021.  In parallel, CH₄ fluxes from a stream located within the footprint of the EC tower were measured using the floating chambers and bubble traps. Stream was substantial source of CH₄ with mean CH₄ fluxes of 260 ± 107 mg CH₄ m^-2 day^-1, respectively, over the period from April to December 2021. Both, the EC and floating chamber measurements of CH₄ were conducted also in 2022 and results will be presented.

In the future, the ecosystem-scale CH₄ measurements shall be connected not only with the CH₄ measurements from the water bodies, but also with stem CH₄ efflux measurements conducted at the study site. Finally, an overview of all relevant CH₄ sources in the studied ecosystem shall evolve including their relative importance for ecosystem CH₄ exchange.

How to cite: Kowalska, N., Jocher, G., and Bednařík, A.: Ecosystem-scale floodplain forest methane exchange, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6417, https://doi.org/10.5194/egusphere-egu23-6417, 2023.

Agricultural soils are a major source of the potent greenhouse gas nitrous oxide (N₂O). However, these emissions have high spatial variability and are highly heterogeneous in their distribution in agricultural landscapes. In Eastern Denmark, N₂O “hotspots” or disproportionately high emission zones, have been observed in the vicinity of glacial depressions. These depressions form a topographical slope, where the base of the slope is typically inundated for 1-3 months over the winter and spring seasons. Preliminary work showed that the highest N₂O emissions have been observed at the base of the slope, along the perimeter of the ponding zone of these depressions. In the present study we now aim to identify the mechanistic drivers of these N₂O hotspots.

N₂O emissions were measured weekly at four positions along a gradient from upslope to the centre of a glacial depression over a winter to spring wheat growth season, at a farm in Eastern Denmark. The potential driving factors were  measured weekly along the slope: soil moisture at depths of 10 cm, 20 cm and 100 cm; soil solution nitrates and DOC at these same depths; and root growth using photographs at different depths using minirhizotrons to a depth of 100 cm. Additionally the groundwater level was monitored using a well and pressure logger. To underpin the results of this core site, further N₂O measurements and soil samples were taken along the slope of three additional glacial depressions nearby with comparable topography and soil properties .

The N₂O emissions were found to be highest at the base of the slope, around the perimeter of the depression. We were able to demonstrate that root growth is directly linked to the moisture regime and thus the overall fate of nitrate and N₂O emissions.

Given the locally high N₂O emissions of these hot spots, this study provides a lens into an important source of N₂O emission heterogeneity in the Danish agricultural landscape.

How to cite: Poultney, D. M.-N., Liu, Y., Ambus, P., Elberling, B., Thorup-Kristensen, K., and Müller, C. W.: N2O emissions from emission hotspots in agricultural soils – linking crop root growth and distribution with soil moisture and nitrate dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9406, https://doi.org/10.5194/egusphere-egu23-9406, 2023.

Nitrous oxide (N₂O) is a potent greenhouse gas (GHG) with a global warming potential 265 times that of carbon dioxide (CO₂) over 100 years. Contributing approximately 70% of global anthropogenic N₂O emissions, agriculture represents the largest area of uncertainty for GHG reporting and the most challenging sector for emissions reduction: global N₂O emissions are increasing at double the rate estimated by the Intergovernmental Panel on Climate Change (IPCC). The largest source of agricultural N₂O emissions is from application of inorganic-N fertilisers, the manufacture of which produces more than 1% of global CO₂ emissions and consumes 1% of global energy output.

However, typical crop N uptake efficiency (NupE) means approximately half the fertiliser doesn’t reach the target plant, causing further ecological problems, such as biodiversity loss from eutrophication and atmospheric deposition. The extent to which microbial immobilisation of fertiliser N contributes to the NupE value of ca. 60% is currently unknown. If N immobilisation is found to be a large contributor to reducing N available to crops, this offers new opportunities to better manage fertiliser N inputs. Critically, with a growing global population, it is vital that we can increase food crop yields, and more efficient use of water and nutrients could help close the 70% ‘yield gap’ between potential and actual crop yields. Finally, inorganic N is the largest single cost in gross margins for wheat production and prices are rising. Increased NupE therefore represents a key opportunity for farmers to increase their financial sustainability. 

We hypothesised that under the conventional management of three applications of inorganic N in the spring, crops do not have the ability to outcompete the fast-growing soil microbial community for N, and that by supplying N to the crop in a ‘little and often’ approach, we could increase NupE by reducing immobilisation, and consequentially reduce N₂O emissions. We conducted a field study of a winter wheat crop on a northern UK farm to investigate this, which compared conventional N fertiliser management (220 kg N ha^-1 over three applications) of ammonium nitrate, to a little and often approach (220 kg N ha^-1 over six applications) and an untreated (0 kg N ha^-1) control. We followed the crop until harvest, and continuously measured N₂O emissions and net ecosystem exchange of CO₂ using a skyline2D automated flux system and also measured C and N pools in soil, plants and microbial biomass to assess changes in N uptake and allocation.

We will present data which shows the outcome of plant-microbe competition for N in our agricultural system, and discuss the implications of different N fertiliser management for yield, profitability and GHG mitigation.

How to cite: Keane, J. B., Lee, S., McNamara, N., Whitaker, J., Moir, J., Levy, P., Robinson, S., Linnekogel, S., Walker, H., Storer, K., Berry, P., Bentley, M., Howarth, S., and Toet, S.: The outcome of plant-microbial competition for N in a wheat system and the implications for yield and N₂O mitigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15717, https://doi.org/10.5194/egusphere-egu23-15717, 2023.

China contributes the largest share of cropland’s greenhouse gas (GHG) emissions globally. Processed-based biogeochemical models are useful tools to simulate GHG emissions from cropping systems. However, model comparisons are necessary to provide information for the application of models under different climate, soil, and crop conditions. In this study, two widely-used models (DayCent and DNDC) were evaluated and compared under four main cropping systems in China. The field observations from nine experiments were used for model calibration and validation.  The DayCent and DNDC models simulated daily and seasonal CH₄ emissions from early rice-late rice and rice-wheat cropping systems reasonably well (r²≥0.49 for daily simulation and nRMSE≤52.9% for seasonal simulation). Both models were able to satisfactorily predict seasonal N₂O emissions from maize-wheat fields (0.6≤d≤0.8), but overestimated most daily N₂O fluxes at fertilisation and irrigation events. Significantly positive relationships were found between simulated and observed cumulative N₂O fluxes in spring maize growing season (0.61≤ r²≤0.85). The DNDC showed smaller differences in simulated and observed cumulative GHG emissions for spring maize and double rice, while DayCent showed better performance on estimating N₂O and CH₄ for maize-wheat and rice-wheat. This study shows that both models have strengths and weaknesses under a variety of cropping systems and growing regions, which are important to consider when choosing a model for a crop/region-specific simulation.

How to cite: Wang, J., Kuhnert, M., Abdalla, M., Smith, P., Ding, W., Yan, X., Zou, J., Guo, S., Fan, J., Jiang, Y., Hu, R., Li, F., Guo, Y., Chen, Z., Zhao, X., and Xie, Y.: A comparison of DNDC and DayCent to evaluate GHG emissions from China’s main cropping systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9893, https://doi.org/10.5194/egusphere-egu23-9893, 2023.

There is hot debate about whether grassland-based livestock production can be climate-smart or not. Greenhouse gas (GHG) emissions from livestock (primarily from enteric methane [CH₄] and manure CH₄ and nitrous oxide [N₂O]) stand vis-à-vis vegetation CO₂ uptake and soil carbon sequestration. In sub-Saharan Africa (SSA), livestock are a precious good that ensures the livelihoods of millions of people, which often belong to marginalized groups such as pastoralists. To protect their animals from predation and theft, livestock are secured in overnight enclosures (“bomas” in Kiswahili), which form the center of many pastoral settlements. However, in these enclosures manure accumulates for months or even years, making them a potential hotspot for GHG emissions. Here, we present the first year-long measurements of GHG emissions from active and inactive (abandoned) bomas from an African rangeland at the ILRI Kapiti Research Station in Kenya.

We found that active bomas were continuous sources for CO₂, CH₄ and N₂O emissions, with flux peaks of up to 1940 mg CO₂-C m^‑2 h^‑1, 1600 μg N₂O-N m^‑2 h^‑1 , and 6690 μg CH₄-C m^‑2 h^‑1. Even after their abandonment, fluxes from bomas continued to be elevated compared to savanna soil background emissions for all GHGs. When calculated over a full year and put in context with manure deposition rates into the bomas (GHG emission factors), we found that 12.6 ± 5.3 % manure-C was emitted as CO₂, 2.4 ± 0.4 % manure-N was emitted as N₂O, and 0.5 ± 0.1 % manure-C was emitted as CH₄. GHG emissions from active bomas were not affected by rainfall seasonality or temperature, presumably because the moisture content of the fresh manure was always high due to urine input, and because temperature did not vary much during the year. In abandoned bomas, GHG emissions were driven by rainfall events that triggered emission pulses, leading to higher emissions during the wet season.

The high N₂O and CH₄ emissions we found have implications for global GHG inventories, which currently do not have a category for overnight livestock enclosures and therefore do not account for these emissions. Furthermore, hotspots for GHG emissions such as these livestock enclosures need to be included to assess the full GHG budget of pastoral livestock systems and to develop management interventions for low-emission livestock production in developing countries.

How to cite: Leitner, S., Carbonell, V., Butterbach-Bahl, K., Barthel, M., Mhindu, R. L., Mutuo, P., Buchmann, N., and Merbold, L.: Traditional livestock enclosures are greenhouse gas hotspots in the African savanna landscape: The case of a rangeland in Kenya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14773, https://doi.org/10.5194/egusphere-egu23-14773, 2023.

Nitrous oxide (N₂O) is a strong greenhouse gas, and its atmospheric concentration is rising. Anthropogenic N₂O emissions stem mostly from agricultural activities, especially the fertilization of fields. There is an urgent need to reduce the emissions of N₂O from agriculture, but so far well documented mitigation options remain scarce.

Here we present data from the first year of a series of field trials which aim to test if N₂O emissions from Danish winter wheat fields can be reduced by optimizing the fertilization strategy. The field trials were located at three different locations in Denmark with different soil types and climatic conditions. All treatments received 200 kg N/ha except the 0 N treatment (giving the background N₂O emissions). The treatments were: (1) ammonium nitrate split in three applications, (2) ammonium nitrate coated with a nitrification inhibitor (3,4-Dimethylpyrazole phosphate, DMPP) split in three applications, (3) ammonium sulfate coated with DMPP split in three applications, (4) liquid fertilizer split in three applications, and (5) ammonium nitrate split in four applications. Nitrous oxide emissions were measured by manual chambers throughout the growing season in 2022 (22 days of measurements).

The highest emissions and cumulative emissions were observed in the treatment with liquid fertilizer, and in two of the trials the emissions from the liquid fertilizer treatment were higher than emissions from the treatment with ammonium sulfate coated with DMPP. However, the nitrification inhibitor did not significantly decrease N₂O-emissions when compared to the same fertilizer type without inhibitor. In the treatment with ammonium nitrate split in four applications, we did not find significant reductions in N₂O emissions. Generally, nitrous oxide emissions from all sites were low (cumulative fluxes of 0.14 – 0.31 kg N₂O-N/ha for the growing season) due to a dry spring with a few peaks mainly due to precipitation events. Therefore a preliminary conclusion after the first year of field trials is that in a dry year, with low emissions, the selected fertilization strategies seem to have limited capacity for reducing N₂O emissions.

How to cite: Skov Nielsen, C., Schrøder Baggesen, N., Nair, D., Taghizadeh-Toosi, A., and Værge, A. B.: Can improved fertilization strategies reduce N2O emissions from winter wheat?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8205, https://doi.org/10.5194/egusphere-egu23-8205, 2023.

Agriculture is the main contributor to anthropogenic emissions of nitrous oxide (N₂O) and methane (CH₄). Greenhouse gas (GHG) mitigation options in agricultural ecosystems are therefore urgently needed. In contrast to carbon dioxide (CO₂), continuous measurements of N₂O and CH₄ fluxes are still scarce. In this study, we investigated management and environmental drivers of N₂O and CH₄ fluxes, which were measured using eddy covariance in a predominantly mown temperate grassland. A N₂O mitigation experiment took place at the site where two parcels surrounding the eddy station were managed differently: at the experimental parcel, organic fertilizer was replaced by an increased legume (clover) proportion while the other parcel was still fertilized with slurry. Random forest gap-filling models were able to capture intermittent emission peaks well, with a better performance for half-hourly N₂O than for CH₄ fluxes. The unfertilized clover parcel showed reduced N₂O emissions (4.4 and 2.7 kg N₂O-N ha^-1 yr^-1) compared to the fertilized parcel (6.9 and 5.9 kg N₂O-N ha^-1yr^-1) over two years, which confirmed the results from the first years of the experiment. The net ecosystem CO₂ exchange (NEE) showed high interannual variability, which had a substantial influence on the grassland GHG budget. Overall, reducing fertilization and increasing the legume proportion were effective N₂O reduction measures. N₂O and CH₄ fluxes play an important role in the GHG budget of agricultural ecosystems as they can partly offset the ecosystem CO₂ uptake.

How to cite: Feigenwinter, I., Hörtnagl, L. J., and Buchmann, N.: Greenhouse gas (CO2, N2O, CH4) fluxes from intensively managed grassland during a N2O mitigation experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17103, https://doi.org/10.5194/egusphere-egu23-17103, 2023.

Agricultural management has recently drawn substantial attention as regenerative practices are showing their potential in enhancing soil quality and fertility, biodiversity, and carbon uptake from the atmosphere into the soil. In Nordic countries, there is a great number of farmers farming regeneratively. However, they are still a minority, and we are lacking scientific studies on the effects of various improved practices and their combination and use in practice in northern growing conditions.

We conducted a long-term study of an agricultural grassland ecosystem in southern Finland where regenerative management practices were implemented from 2018 onwards. We monitored H₂O and CO₂ fluxes with the eddy covariance method, and additionally, CH₄, N₂O and CO₂ with flux chambers. We also measured meteorological variables and several soil and vegetation parameters. We studied the impacts of different cutting heights for the silage grass on the ecosystem carbon sequestration. Furthermore, we utilised the data in model simulations with the grassland model BASGRA to study the carbon dynamics of the agricultural ecosystem in various weather conditions and with different management decisions. Our results indicate that the studied years, which were differing greatly from the long-term average weather, may have had a great impact on carbon dynamics on the grassland. Both empirical data and modelling demonstrated net carbon accumulation into the ecosystem under the selected improved practices.

How to cite: Heimsch, L., Vira, J., Fer, I., Vekuri, H., Tuovinen, J.-P., Nevalainen, O., Kuvaja, K., Lohila, A., and Kulmala, L.: Impact of weather and management practices on GHG dynamics on an agricultural grassland in southern Finland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7822, https://doi.org/10.5194/egusphere-egu23-7822, 2023.

Agricultural sources of atmospheric ammonia after slurry application vary over space and time, which makes it difficult to accurately quantify emissions. Different methods for concentration and emission estimation have been used by different institutions for many years, and these differences may contribute to variability in measurements. There is an need for commonly acceptable and reliable measurement methods.

Ammonia emission measurements show a strong connection to the group that conducted them, suggesting effects of local soil properties, application techniques, or measurement method biases. The aim of this work was to clarify one source of these institutional effects related to applied measurement methods. Emission measurements with several common measurement methods were compared by three different research institutions simultaneously in the same field plots. This approach eliminates any variation from soil properties and application technique, making it possible to obtain new insight into the effect of measurement technique on model ammonia flux estimates.

Two joint experiments were conducted at Research Center Foulum, Aarhus University (AU), Denmark, and one at Wageningen University and Research (WUR), the Netherlands. The four measurement methods included in the first experiment in Denmark were the backwards Lagrangian model (bLS) with online concentration measurement and wind tunnel measurements conducted by a AU group, while a group from Thünen Institute for Climate-Smart Agriculture conducted measurements with the Dräger Tube Method (DTM) and ALPHA passive diffusion samplers combined with bLS. The second experiment in the Netherlands included the integrated horizontal flux (IHF) method conducted by a WUR group using impingers as ammonia traps, while AU conducted bLS and wind tunnel measurements again. Furthermore, emission from both experiments were also estimated with the ALFAM2 model (v2.10, https://github.com/sashahafner/ALFAM2) based on the specific slurry and climatic parameters after slurry application.

The difference in season and application method between the two experiments caused large differences in emissions as expected. The low time resolution measurements methods (DTM, ALPHA samplers with bLS, and IHF) tended to have lower emissions compared to the online and high time resolution methods (bLS and WT). More comparative measurements are needed to allow for more complete assessment of different methods.

How to cite: Kamp, J. N., Pedersen, J., Huijsmans, J., Götze, H., Pacholski, A., and Hafner, S.: Measurement methods for ammonia emissions after field application of slurry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12920, https://doi.org/10.5194/egusphere-egu23-12920, 2023.

Emission of ammonia from agriculture is a problem due to the negative effects on human health and natural ecosystems. Additionally, ammonia is a precursor for production of N₂O in the atmosphere and is therefore an indirect greenhouse gas. A large part of ammonia emissions from agriculture originate from manure handling, which also reduces manure fertilizer value. Therefore, more knowledge on emissions from different types of manure and the effect of manure treatments are necessary to develop new measures to reduce ammonia emissions. Separating liquid manure (slurry) into a liquid and solid fraction can be used as a reduction technique for field application. The lower dry matter content of the liquid fraction may increase infiltration and decrease emission. Because separation might influence emissions during the storage period, this period must be considered along with the potential increased emissions from field application of the fiber fraction, when assessing the ammonia mitigation effect of separation. Here, data on ammonia emissions from storage and field application of raw and separated manure is presented. The manure types investigated were anaerobically digested manure and pig manure. Ammonia emissions from storage were measured with 1 m³ tanks constructed as dynamic flow chambers, and emissions after field application were measured with wind tunnels. Online measurements of ammonia concentrations were done with cavity ring-down spectrometry.   
    How the fiber fraction from the manure separation is utilized is important for the overall ammonia loss. Fiber can be stored in a pile and subsequently spread in the field. Another way to treat the fiber is to pyrolyze it into biochar which can be incorporated into the field as a strategy for long term carbon sequestration. It has been suggested to mix the biochar and manure prior to field application to limit operating costs with field driving. Therefore, during the field application experiments, a treatment with biochar added to the liquid fraction of manure was also investigated.

How to cite: Holm Støckler, A., Pedersen, J., Nørlem Kamp, J., Feilberg, A., and D. Hafner, S.: Effect of manure separation on ammonia emission during storage and subsequent field application., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12913, https://doi.org/10.5194/egusphere-egu23-12913, 2023.

Concerns about ammonia (NH₃) emission from agriculturre have increased in recent years due to its contribution to atmospheric fine particulate matter formation (PM2.5 and PM10). To reduce NH₃ losses a wide range of techniques has been reported, from the management of livestock and storage of excreted animal manure to the types and methods of application of organic and mineral fertilizers. The successful implementation of such techniques requires following a collaborative bottom-up approach that engages farmers and practitioners to the full technology valuation. Bayesian Belief Networks (BBNs) are probabilistic models that represent expert knowledge in any particular situation –e.g. in the agroecosystem– and evaluate the potential effects of different management scenarios. By linking multiple variables in a cause-and-effect relationship, BBNs can provide both diagnosis and prognosis aiding the decision-making process. In this work, a BBN was built to integrate quantitative experimental data and quali-quantitative stakeholder assessment. The aim was to provide recommendations to policy makers and practitioners about the most promising best available techniques (BAT) that combine environmental effectiveness in reducing NH₃ emissions with economic and sociocultural acceptability by farmers at the regional scale. The variability of the livestock sector (swine, cattle and dairy cows) and agricultural systems (climate, soils, crops, etc.) across the Veneto region, NE Italy, was included in the BBN model. For the livestock sector management practices such as those related to feeding (e.g., precision feeding), overcrowding (e.g., breeding density), healthcare (e.g., infirmary spaces), etc. were considered. Estimates of NH₃ losses from N fertilizer application techniques (e.g., closed slot injection Vs. surface distribution, N fertilizer in conservation vs conventional tillage) came from the integration of experimental, literature, and modelling data by using the modified version of DNDC v.CAN biogeochemical model. Stakeholders were engaged in evaluating the NH₃ mitigation effectiveness of the proposed techniques. Perceptions about economic attractiveness and sociocultural acceptability were enquired, and results were introduced in the BBN as utility nodes to determine BATs. Results showed that the BBN model was able to embed into a single network quantitative outcomes from technical solutions with quali-quantitative assessment by stakeholders. By combining social and economic valuation with the technical potential of NH₃ reduction, the BBN model acted as an effective tool to recommend the most promising BAT that should be supported by policy makers. The greatest room for improvement was found in the livestock supply chain, from the stable management to the manure distribution in the field. In contrast, stakeholders were unfamiliar with the most innovative techniques (e.g. precision farming, closed slot injection of mineral fertilizers), whose uncertainty in the costs and difficulties in the implementation would hinder their application despite their environmental benefits.

How to cite: Dal Ferro, N., Mencaroni, M., Fabbri, G., Gottardo, F., Lazzaro, B., and Morari, F.: How to select Best Available Techniques to reduce NH3 emissions from the agricultural sector? Results from integrating the pillars of sustainability into a Bayesian Belief Network model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11378, https://doi.org/10.5194/egusphere-egu23-11378, 2023.

Trace gases of nitrogen (N), such as NO_x (nitric oxide, NO + nitrogen dioxide, NO₂) have a negative impact on human health and the environment. Although NO_x are naturally produced in volcanic eruptions, forest fires and biotic nitrification and denitrification in soils, human activity is a major source of these contaminants via e.g. the combustion of fossil fuels. Additionally, N fertilization in agricultural soils is also an important source of NO_x emissions. These emissions involve a loss of soil N to the atmosphere and have a negative impact in air quality. The abiotic part of the N cycle in terrestrial ecosystems has not received as much attention as the biotic part and certain abiotic reactions could play a key role in regulating NO_x emissions. Photocatalysis is an example as this is used to abate NO_x gases in urban and industrial areas. This reaction requires the presence of a catalyst (e.g. titanium oxide), oxygen, water, and energy from the sun (UV-visible light) to transform NO from the atmosphere into innocuous inorganic N forms (mainly nitrate, NO₃^-). There is a continuous investment in the production of catalysts by the industry. However, a variety of soil minerals such as anatase or rutile (titanium oxides), hematite and goethite (iron oxides), are found in soils and they could act as catalysts; however, the occurrence of photocatalysis in soils has not been evaluated so far. In this study, we assess (i) the potential of a selection of soils with different mineralogy and a wide variety of soil properties to fix or emit NO_x through photocatalysis, and (ii) the possible alterations in the fixation or emission of other N gases from the soil, i.e., nitrous oxide (N₂O) and ammonia (NH₃), when photocatalysis is induced. Around thirty agricultural soils were selected to meet the first objective and irradiated for 1 hour with UV-visible light under a constant flux of air and NO (100 ppm). Similar experiments were carried out with a selection of soils, whose potential to fix NO was different and tested in the previous experiment, to satisfy the second objective. However, only air (without NO) was pumped within the soil chamber in this case and the soils were previously fertilized with different N fertilisers (urea or KNO₃^-) and rates (0 to 250 mg N kg^-1 soil). Our experiments show that weathered soils (with a high content in titanium and iron oxides) were able to fix more atmospheric NO through photocatalysis (objective i), and that NO and NH₃ fixation and emissions after N fertilization depended not only on the N fertilizer and rate but also on soil properties, mainly soil pH and N content (objective ii). Soil mineralogy and properties play a key role in soil photocatalysis, and this abiotic reaction should be considered in order to design more sustainable strategies for agriculture.

How to cite: Sánchez-Rodríguez, A. R., Gómez-Álvarez, E., Méndez, J. M., Skiba, U., Jones, D. L., Chadwick, D. R., del Campillo, M. C., Fernandes, R. B., Kleffmann, J., and Barrón, V.: Photocatalysis in agricultural soils: Mineralogy and soil properties control the fixation and emission of NOx and other trace gases of N, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1139, https://doi.org/10.5194/egusphere-egu23-1139, 2023.

Nitrogen compounds such as nitrogen dioxide (NO₂) and ammonia (NH₃) contribute significantly to air pollution and environmental degradation. Fine-grained networks of sensors for ambient nitrogen compounds can be used to inform policy makers and farmers about the effectiveness of techniques to reduce emissions of nitrogen compounds. We are developing a low-cost self-sustaining sensor system that can be deployed outdoors in large numbers in and around agricultural areas to measure the concentration of NH₃, NO₂, temperature and humidity with a high spatiotemporal resolution. We use off-the-shelf electrochemical sensors to measure nitrogen compounds. A preliminary comparison between the NH₃ measurements taken by our sensor system and by a differential optical absorption spectroscopy instrument (miniDOAS) demonstrate encouraging results. After calibration, the measurements from our system show fairly good agreement with hourly-averaged miniDOAS measurements, at concentrations down to ~20 µg/m³. We are currently setting up a larger validation study to further assess the performance and robustness of our system in different outdoor agricultural environments. Our sensor system has the potential to greatly expand the availability and affordability of NH₃ monitoring across wide areas, enabling farmers and policymakers to gain insights on the effectiveness of potential nitrogen reduction measures.

How to cite: Fabius, J. H., Celikkol, B., Rai, U., Vonk, J., Suer, R., and Zhuang, S.: Low-cost sensor system for measuring ambient nitrogen compounds in agricultural areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7381, https://doi.org/10.5194/egusphere-egu23-7381, 2023.

Ammonia is an atmospheric pollutant precursor of inorganic fine particles (sulphate and ammonium nitrate particles) that are particularly harmful to human health. Ammonia and particulate matter (PM) are responsible for severe pollution outbreaks over Europe (LCSQA, LCSQA 2019), during springtime of 2012 (Kutzner et al., 2021), 2014 (Fortems-Cheiney et al., 2016), 2015 (Petit et al., 2017), 2016 (Tournadre et al., 2020: Viatte et al., 2020) and 2020 (Viatte et al., 2021). Despite this major societal and scientific interest, there is a crucial lack of routine ammonia and aerosol speciation observations. One of the scientific reasons comes from the difficulty to measure atmospheric ammonia due to its sticky, volatile, and reactive nature (von Bobrutzki et al., 2010).

The objective of the Multi-Instrumental Analysis of Ammonia Concentrations (AMICA) project is to compare the response of different available systems for measuring atmospheric ammonia at a rural site in the Île-de-France region. The 14 instruments based on different NH3 measurement techniques are compared over a wide range of ammonia concentrations from ambient atmospheric to boosted concentrations (10 to 600 ppbv) using an innovative 400 m² ammonia emission system. They are all synchronized with a cross-correlation function based on the median value. At elevated concentrations all inlet-based instruments sampling to the same manifold performed very well on precision, even at high temporal resolution monitoring (1 min) that highlights a great progress for current in situ NH₃ analysers. By comparing with the data from a mini Differential Optical Absorption Spectrometer (miniDOAS) and a sequential acid trap-IC (ROSAA), we demonstrated that inlet design perturbs the response time of the instruments connected to the manifold, which was already mentioned in literature. This measurement campaign is part of a series of ammonia projects that have recently taken place in France.

References

Fortems-Cheiney, A., et al., Geophys. Res. Lett., 43, 5475–5482, https://doi.org/10.1002/2016GL069361, 2016.

Kutzner, R. D., et al., Atmos. Chem. Phys., 21, 12091–12111, https://doi.org/10.5194/acp-21-12091-2021, 2021.

LCSQA, Le Laboratoire Central de Surveillance de la Qualité de l'Air, Bilan des travaux 2018-2019 du programme CARA, Ref. INERIS : DRC-19-181155-02828A, 2019.

Petit, J.-E. , et al., T, Atmospheric Environment, Volume 155, 2017, Pages 68-84, ISSN 1352-2310, https://doi.org/10.1016/j.atmosenv.2017.02.012.

Tournadre, B., et al., Atmos. Meas. Tech., 13, 3923–3937, https://doi.org/10.5194/amt-13-3923-2020, 2020.

Viatte, C., et al., Atmos. Chem. Phys., 20, 577–596, https://doi.org/10.5194/acp-20-577-2020, 2020.

Viatte C., et al., Atmosphere, 2021, 12, 160, https://doi.org/10.3390/atmos12020160.

von Bobrutzki, et al., Atmos. Meas. Tech., 3, 91–112, https://doi.org/10.5194/amt-3-91-2010, 2010.

How to cite: Chelin, P., Caville, S., Guendouz, N., Michoud, V., Bergé, A., Fortineau, A., Decuq, C., Buysse, P., Loubet, B., Esnault, B., Génermont, S., Ciuraru, R., Burban, M., Depuydt, J., Durand, B., Viatte, C., Cailteau-Fischbach, C., Petit, J.-E., Crunaire, S., Espina, P., Redon, N., Joly, L., Cousin, J., Parent, F., Bonne, J.-L., Flechard, C., Fauvel, Y., Romain, A.-C., and Scheuren, M.: Measurements of ammonia in ambient air and over a controlled artificial source during the AMICA field campaign at a rural site in the Ile-de-France region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4564, https://doi.org/10.5194/egusphere-egu23-4564, 2023.

Non-methane volatile organic compounds are important air pollutants that contribute to tropospheric ozone production in combination with nitrogen oxides (NO_x) and sunlight. Ozone is an important but often overlooked greenhouse gas with adverse effects on human health and crop yields as well as climate. Due to these indirect effects, there is a need for knowledge on emissions and potential mitigation strategies for NMVOC from key sources. Agricultural activities have recently been assessed to be a major source of non-methane volatile organic compounds (NMVOC) with particular importance in regions with intensive livestock production and manure management. In e.g. Denmark, recent assessments indicate that agriculture is the dominant source of NMVOC exceeding emissions from industry, transportation and residential heating. However, estimates of NMVOC emissions from agriculture are based on very limited realistic data and obtained by e.g. indirect calculations relative to ammonia. According to estimates for 2020 (EMEP Centre on Emission Inventories and Projections), around 25% of NMVOC in EU are from agriculture with livestock production and manure management being the dominant sources. These emission inventories are, however, quite uncertain and only based on measured data to a very low degree. Only very few studies have actually attempted to quantitatively measure NMVOC emissions from agricultural facilities and activities. In addition, little is known about the NMVOC composition and how composition varies with sources and conditions. Here, data on emissions from field application of manure based on a number of wind tunnel experiments are presented and used to estimate the contribution to national NMVOC emissions. NMVOC were quantified by proton-transfer-reaction mass spectrometry (PTR-MS) and simultaneous measurement of ammonia was used to achieve national emission estimates from field application of manure. Measurements were performed by placing a series of wind tunnels with realistic air flow rates in agricultural fields following application of liquid manure (slurry) and analyzing emissions over one week with a time resolution of typically 1 – 2 hours. The results demonstrate that emissions are significant and consist mainly of carboxylic acids with smaller contributions from phenols. Highly dynamic diurnal variations are identified. Impacts of different source types and manure treatments are discussed together with recommendations for future investigations.

How to cite: Feilberg, A., Lemes, Y. M., Kamp, J. N., and Pedersen, J.: Emissions of NMVOC from field application of manure measured by PTR-MS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11693, https://doi.org/10.5194/egusphere-egu23-11693, 2023.

Plants are the primary worldwide source of Volatile Organic Compounds (VOCs) on Earth and therefore play a significant role in the atmosphere's gas composition. While emissions from foliage have been well documented for decades, emissions from soils with living roots and associated microorganisms are not well understood. In particular, field studies show a wide and inconsistent range of soil-derived VOC net fluxes, possibly due to the variable abiotic and biotic conditions during measurements. In order to figure out the main drivers of soil VOC exchanges, studies under controlled experimental conditions are necessary. 

We developed a new experimental dynamic chamber, allowing to monitor the gas emissions from 1-9 plants simultaneously, both in the aboveground and belowground compartments. Aside from providing controlled experimental conditions, this setup allows to compare the net VOC, CO₂, and H₂O flux dynamics from soil to that from the aboveground plant organs at a high time resolution.

Using a Proton Transfer Reaction – Time Of Fly – Mass Spectrometer, constitutive emissions from soil-grown rapeseed and tomato plants were recorded over 24h. Methanol was the main VOC emitted by both species, followed by, at one order of magnitude lower, methanethiol and monoterpenes for rapeseed and tomato plants, respectively. Although root-derived VOC emissions were generally much lower than shoot-derived ones, belowground DMDS emissions from rapeseed plants were twice higher than those from aboveground.  Interestingly, a negative correlation was observed between several root-derived VOC and root/soil respiration, suggesting a shift in the carbon allocation to specific metabolic pathways in roots or root-associated microorganisms. This experimental approach opens new perspectives for understanding the specific contributions of VOC emissions from soils and roots in agricultural ecosystems, and how these emissions may be linked to plant carbon budget.

How to cite: Voyard, A., Ciuraru, R., Staudt, M., Loubet, B., and Rees, F.: Are crops significant sources of Volatile Organic Compounds? A bi-compartmented chamber setup for investigating VOC emissions from aboveground and belowground, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5752, https://doi.org/10.5194/egusphere-egu23-5752, 2023.