Billions of tons of dimethylsulfoniopropionate (DMSP) are produced every year in marine and coastal ecosystems such as saltmarshes and estuaries. DMSP has far-reaching roles in global carbon and sulfur cycling, also as an osmotolerant and signalling molecule. Furthermore, the microbial degradation of DMSP contributes significantly to the formation of dimethylsulfide (DMS) and methanethiol (MT), other abundant organosulfur compounds with ecological significance. Particularly, in anaerobic sediments, microbial DMS and MT degradation leads to the formation of methane, a powerful greenhouse gas. However, research to date has predominantly focused on aerobic settings, revealing diverse groups of microbes and enzymes mediating DMSP degradation. DMSP concentrations in anaerobic ecosystems and microbial populations underlying DMSP breakdown have never been studied, prohibiting improvements in our understanding of global carbon and sulfur cycles. To address this key knowledge gap, we applied stable-isotope probing combined with 16S rRNA sequencing to identify the active DMSP-degraders in anaerobic saltmarsh sediments.

We collected sediments from a 5-10 cm depth of Medway Saltmarshes (UK) using 3.5cm Perspex corers. We transferred the samples to the laboratory and measured in situ DMSP concentrations of 7.7 (±0.5) μmol g⁻¹ wet sediment. In line with the in situ concentrations, we set up replicated incubations anaerobically with 8 μmol g⁻¹¹³C- and ¹²C-labelled DMSP, and applied stable-isotope probing combined with 16S rRNA sequencing.

We observed immediate degradation of DMSP in the sediment incubations and DMS production, suggesting the existence of a resident microbial community actively carrying out this process. A total of 48 μmol/g ¹³C- or ¹²C-DMSP was amended and a total of 34 (±3.2) μmol/g DMS was produced in the incubations over 12 days.  DNA was extracted and ultracentrifugation was applied to separate heavy and light DNA fractions for downstream analysis. 16S rRNA sequencing of the fractions from ¹³C and ¹²C-labelled DNA demonstrated significant enrichment of the family Nitrincolaceae within the order Oceanospirillales in ¹³C-heavy fractions compared to ¹³C- light and ¹²C-heavy fractions (P<0.05). Their relative abundance increased from 2% (±1.3) to 27.2% (±9.1). This demonstrates that they are the active DMSP degraders in anaerobic saltmarsh sediments.

This is the first study quantifying significant concentrations of DMSP in anaerobic saltmarsh sediments and demonstrating Nitrincolaceae to be the active DMSP-degraders. Our findings not only broaden our understanding of microbial carbon and sulfur cycling but also highlight a previously overlooked route to methane formation in anaerobic saltmarsh sediments.  Our study underscores the need to identify microbial communities and pathways of DMSP breakdown across diverse anaerobic settings.

How to cite: Eyice, Ö., Hawthorne, S., Tsola, S., Carrión, O., and Todd, J.: Stable-isotope probing identifies microorganisms actively degrading DMSP in anaerobic saltmarsh sediments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5799, https://doi.org/10.5194/egusphere-egu24-5799, 2024.

Lompolojänkkä is a nutrient-rich fen located in western Lapland. The site has been the focus of detailed methane flux measurements, which revealed high spatial variability along a transect from the central stream to the edge of the peatland. Surprisingly, the highest fluxes did not occur in the center of the peatlands, but rather at the halfway point between the center and the edge of the peatland, likely due greater oxygen transport by turbulent water flow at the center of the peatland. In this study, we aim to quantify the contribution of hydrogenotrophic and acetoclastic methanogenesis, the fraction of methane oxidized prior to emission to the atmosphere, and the location (depth) of these processes in the peat profile. We further investigate if these processes differ in space along a the stream-to-edge transect and time with the progress of the growth season. To quantify these processes, we collected pore water samples from 15 depth profiles at 20 to 100 cm depth. In these samples we quantified concentrations of dissolved methane, its carbon and hydrogen isotope values, and a suite of geochemical measures. We find that locations close to the central stream are characterized by high methane concentrations at depth, which decrease steeply towards the surface, indicating that high rate of methane are produced at depth but oxidized prior to reaching the surface. Sites located at the edge of the peatland, in contrast, show low methane concentrations throughout the peat profiles, indicating that small amounts of methane are produced relatively close to the surface. Stable carbon and hydrogen isotope values add additional complexity to our understanding of the methane dynamics. Methane oxidation is associated with strong increases in both δ13C and δ2H values in the residual methane and would therefore be indicated by an increase in both isotope values from deep to shallow peat layers. Such a pattern, however, was only detected close to the central stream, where approximately 50% of methane was oxidized prior to reaching the surface. In most other transect points, we found that δ13C increased from deep to shallow layers, whereas δ2H showed the opposite trend, indicating the mixing of hydrogenotrophic methane produced in deep peat layers with acetoclastic methane produced in the rooting zone. An isotope mixing model indicated that that the fraction of hydrogenotrophic methane increased from center to edge of the site (from 45 to 30% at 100 cm depth in June) and with the advancing growth season (32 to 0% in September). In contrast, we typically find less than 15% hydrogenotrophic methane in shallow layers. We note that these numbers are associated with significant external uncertainty stemming from poor certainty about mixing model parameters. Overall, our data demonstrates high and temporal spatial heterogeneity of methane production and oxidation within a single site. We demonstrate the additional information gained methane dual isotope analysis, and reveals how δ13C profiles alone can be ambiguous and misleading.

How to cite: Kohl, L., Tenhovirta, S. A. M., Haikarainen, I., Pihlatie, M., Greule, M., Keppler, F., and Lohila, A.: Belowground methane cycling along a stream-to-edge transect in the Lompolojänkkä fen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13087, https://doi.org/10.5194/egusphere-egu24-13087, 2024.

The dynamics of soil carbon (C) emissions along with their biogeochemical and environmental control have garnered increasing attention. However, the role of methane (CH₄) in soil organic carbon (SOC) modelling has been relatively underexplored compared to carbon dioxide (CO₂), and the omission of microbial processes may prevent us from accurately modelling CH₄ dynamics under environmental changes. Here, we incorporated an explicit microbial CH₄ module into the Microbial-ENzyme Decomposition (MEND) model and evaluated it against a sub-version with the first-order kinetics (First-order) and the previous MEND (MEND_old) model. We conducted a rigorous calibration and validation of MEND with high-resolution CO₂ and CH₄ efflux observations across two soil types and five different oxygen (O₂) fluctuation conditions. Beyond precisely capturing soil CO₂ and CH₄ effluxes, the model could also effectively simulate the relative contents of microbial biomass and enzymes. The multi-model comparison further revealed that the inclusion of new processes did not necessarily enhance model performance if microbes were not perceived as explicit state variables. Our results demonstrated that adopting microbial functional groups as drivers of soil CH₄ cycle could provide a basis for testing hypotheses on microbially mediated CH₄ processes and their responses to environmental changes. With the availability of diverse data and the development of genetic technologies, our modelling framework present here will empower ecologists and governments to perceive and intervene in global warming from underlying biogeochemical mechanisms rather than predictions.

How to cite: Wang, G. and Zhou, S.: Representing explicit microbial processes enhances methane modeling under oxygen fluctuation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9741, https://doi.org/10.5194/egusphere-egu24-9741, 2024.

The decomposition of buried straw in rice fields during post-harvest generates volatile fatty acids (VFA), thus activating methanogenesis (1). In this study, bioelectrochemical biosensors were used to measure the in-situ electrical current produced by electroactive microorganisms, related to the biodegradation of buired straw,  in outdoor mesocosms containing rice paddy soil from the Ebro Delta (Spain) .

Three  biosensors (BS1-BS3), based on bioelectrochemical cells buried in the water saturated soil (at a -10 cm), were used in 3 rice paddy soil mesocosms, with a poised working electrode (graphite) potential at +0.2V vs Ag/AgCl, by using a potentiostat. During 5 months (November 2022-March 2023), the production of electrical current (I) in the soil mesocosms was monitored using chronoamperometry. The presence of electroactive microbial biofilms on the electrodes was assessed by cyclic voltammetry (CV). Simultaneously, soil chemical parameters were monitored (total and soluble COD, VFA and CH4 emission), and microbial diversity (bacteria and archaea) in  the soil and the electrodes biofilms was assessed by 16S rRNA-metabarcoding.

Chronoamperometry data in BS1-BS3 showed a marked current production curve from the day 3 to 5 after straw addition, with an I max of 110-180µA (4.26-6.91 µA cm^-2) at day 10, remaining higher than the baseline for 30-45 days, and concomitant with VFA accumulation  (69-28 mg-eq Acetic kg^-1 soil , 7-40 days) and a high emission rate of CH4 (198.1±101.0 mg C-CH4· m^-2 soil · h^-1 7 days after straw addition. The CV revealed electroactive profiles in the 3 biosensors, similar in BS1-BS2 (oxidation peak -0.16/-0.22 V vs Ag/AgCl, similar to Geobacter), and different in BS3 (oxidation peak +0.26 V vs Ag/AgCl), revealing different electroactive microbial communities. 16S-based metataxonomy revealed an enrichment of well known electroactive bacteria on the three anode biofilm but with different relative predominances, encompassing mainly Desulfobulbus in BS1-BS3,  Geobacter mainly in BS1, but in less predominance in BS2 and BS3, Proteiniclasticum solely in BS3, and Clostridium in BS2 and BS3.  Methanogenic archaea such as Methanosarcina and Methanobacterium were also depicted on the anode, but at lower relative abundance than observed in the soil, where ammonium oxidizing archaea (Nitrososphaera and candidatus Nitrosocaldus) were also predominant.

The results showed the capacity of the bioelectrochemical-based biosensors for real time detection of microbial in-situ degradation processes of buried edible organic carbon (straw) in the soil of rice  paddy fields, also linked to methane emissions.

Aknowledgements
This research was funded by Agencia Estatal de Investigación (PID2019-111572RB-I00/AEI/10.13039/501100011033 ) from Spain.

References
1. Martínez-Eixarch, M., Alcaraz, C., Viñas, M., Noguerol, J., Aranda, X., Prenafeta-Boldú, F. X., Saldaña-De la Vega, J.A., Català, M.M. & Ibáñez, C. (2018). Neglecting the fallow season can significantly underestimate annual methane emissions in Mediterranean rice fields. PLoS One, 13(5), e0198081. DOI: 10.1371/journal.pone.0202159

How to cite: Viñas, M., Martínez-Eixarch, M., Esteve-Núñez, A., Berna, A., Fernández, B., Lucas, Y., Medina-Armijo, C., Guivernau, M., Jornet, L., Noguerol, J., and Alcaraz, C.: Bioelectrochemical biosensors for in-situ monitoring microbial activity in outdoor soil mesocosms from postharvest rice field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19680, https://doi.org/10.5194/egusphere-egu24-19680, 2024.

Nitrogen cycling, a critical biogeochemical process in ecosystems, involves a complex microorganism network. In nitrification, ammonia oxidation is mainly governed by ammonia-oxidizing archaea (AOA) in acidic soil. Limited information exists about these taxa in tropical peatlands. This genome-centric metagenomic study aimed to identify key taxa and their functional potential driving nitrification in tropical peatlands. After cleaning Illumina reads, draft bins were created, refined, reassembled, and decontaminated through various strategies, involving both semi-supervised and unsupervised binners, including deep-learning-based approaches. This process resulted in 271 medium to high-quality archaeal metagenome-assembled genomes (MAGs). Five near-complete high-quality AOA MAGs were constructed. Phylogenomic analyses placed the AOA MAGs in the Nitrosotalea genus within the Nitrosopumilaceae family. Comparisons to reference genomes using average amino acid identity (AAI) and average nucleotide identity (ANI) suggested these MAGs might represent separate Nitrosotalea species. Besides core ammonia monooxygenase (amoCAB), these Nitrosotalea MAGs also encoded for nitrite reductase (nirK), ferredoxin-nitrite reductase (nirA) and nitric oxide reductase (norQ) that could also lead to the production of nitrous oxide (N₂O), a potent greenhouse gas. These tropical peatland autotrophic Nitrosotalea MAGs fixed carbon with the hydroxypropionate/hydroxybutyrate pathway and survive in low pH environments through flagellar motility, various transport proteins, substrate acquisition and pH regulation systems for oxidising ammonia. Genomic analyses of candidate taxa can provide a thorough understanding of important biogeochemical functions as critical baseline information to assess microorganism resilience and response to anthropogenic-induced land use change.

How to cite: Midot, F., Goh, K. M., Liew, K. J., Lau, S. Y. L., and Melling, L.: Genome-resolved metagenomics of tropical peatland ammonia-oxidising archaea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17269, https://doi.org/10.5194/egusphere-egu24-17269, 2024.

Wetting of dry soil after prolonged drought triggers emissions of N-oxides (nitric oxide; NO and nitrous oxide; N₂O) and this post-wetting burst may contribute disproportionately to annual soil N-oxides emissions in drylands. During the wetting, nitrification and denitrification were shown to be the major sources of soil N-oxides emissions. Several abiotic reactions involving the nitrification intermediates- e.g. nitrite (NO₂^-), however, may also contribute to the production of N-oxides in soils. The contribution of these abiotic reaction to N-oxides emissions, despite potential importance is not well quantified. To quantify and partition the contribution of abiotic and biotic processes to post-wetting N-oxides emissions in drylands, we measured soil NO and N₂O production in a laboratory incubation with live and gamma-irradiated soils. Samples were collected under canopies of dominant local (Acacia tortilis) and invasive (Prosopis juliflora) trees, as well as from bare soils outside the canopy cover.

We found that that while the overall dynamics of soil NO and N₂O emissions were similar in gamma irradiated and live soils under both P. juliflora and A. tortilis trees, as well as in bare soils, the magnitudes and rates of emissions exhibited significant disparities. In particular, gamma irradiated soils under A. tortilis canopies after eight hours’ incubation, emitted ~10 times less NO (~5 ng N g^-1) and ~4 times less N₂O (~10 µg N g^-1) compared to the live soils. While gamma irradiated soils under P. juliflora canopies emitted ~2 times less NO (~7 ng N g^-1) and similar N₂O (~7 µg N g^-1) compared to the live soils, and in the bare soils, ~9 times less NO (~5 ng N g^-1) and similar N₂O (~10 µg N g^-1). Our findings suggest that both biotic and abiotic pathways contribute to N-oxides production following dry soil wetting, however, the relative contribution is dependent on the landscape position and affected by plant presence and species. Specifically, abiotic processes contributed 10% to soil NO and 25% to N₂O production in soils beneath A. tortilis canopies and between 10% and 75% in the bare soils. In soil under P. juliflora canopies abiotic processes contributed five times more to the NO production (50%) while N₂O production was solely from abiotic activity.

How to cite: Yagle, I. and Gelfand, I.: Quantification and partitioning the contributions of abiotic and biotic processes to soil N-oxides emissions in the Dead Sea valley, Israel., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16201, https://doi.org/10.5194/egusphere-egu24-16201, 2024.

Denitrification, the reduction of nitrogen oxides (NO^3-and NO^2-) to NO, N₂O and, ultimately, to N₂ gas in soils, is classified as a microbiologically ‘broad process’ which can be conducted by a wide array of microbes belonging to remote phylogenetic groups. Further, understanding how environmental and management factors drive denitrification is challenging because they are scale-dependent, with large scale drivers affecting denitrification fluxes both directly and through drivers working at detailed small scales. 

Despite of this, we hypothesized that denitrification processes, although highly complexes due to the multiple processes and environmental conditions involved, they could present a functional convergence at the microbial community level explained by a short list of microbial groups or functions.  

On the other hand, different methodological approaches to assess soil microbial diversity are currently used; among them are multiple substrate-induced respiration by MicroResp™, enzymes activities and functional genes abundance and structure by GeoChip 5S microarray. We applied all those methods to study functional diversity in 5 different soils from 5 countries: Finland, Belgium; France, Switzerland and Italy. Studied soils have a wide range of soil pH, organic Carbon and Nitrogen content, and texture. Soils were sampled at Hot Moment and Low flux emission of N₂O.   

The main objective of this study was to explore possible convergences in terms of functional microbial diversity in contrasting N₂O emission events (low emission versus hot moments).  

Result showed that MicroResp™ , enzyme activities and GeoChip 5S microarray were reliable ecological indicator to evaluate soil microbial functionality diversity. Results stressed the importance to study soil microbiome at different magnitude of N₂O emission with the aim to gain a deeper knowledge of nitrifiers community. Reciprocal relationship of those methodologies, soil proprieties and magnitude of flux emission of N₂O are discussed.   

How to cite: Mattana, S., Sabaté, C., Tallec, T., Boland, F., Manise, T., Heinesch, B., Feigenwinter, I., Turco, F., Rautakoski, H., Lohila, A., Guerrieri, R., Janssens, I., Roland, M., Poblador, S., Magliulo, E., Vitale, L., Wu, L., Zhou, J., Peñuelas, J., and Ribas, A.: Soil microbial functional diversity changes under contrasting N2O emission events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20187, https://doi.org/10.5194/egusphere-egu24-20187, 2024.

Nitrous oxide is a potent greenhouse gas which is involved in stratospheric ozone depletion. Even though nitrogen cycle has been studied for a long time, it is still challenging to understand specific N₂O production and consumption processes. This is due to the complexity and heterogeneity of soil, wherein multiple processes can take place simultaneously. Isotopic composition of N₂O can help us solve this and provide useful information on evaluating N₂O sources and calculate global budgets. N₂O is a linear molecule and its understanding at molecular scale can provide major insights into partition of its source processes. The N₂O site preference (SP), which is the difference in δ¹⁵N between N₂O molecules substituted with ¹⁵N at the central and the peripheral position, has proved to be a major tool to tackle this problem. The objective of this study is to use isotopic and microbial research for N₂O sources and process partitioning. We will bring some examples from our recent studies in the lab and in a drained peatland forest.

During our lab study based on peat soil from a floodplain fen, we observed bacterial denitrification was a major source of N₂O emissions under flooded conditions. We observed this using ¹⁵N isotopic mapping technique, which helped separate multiple active processes. We applied a similar method in-situ on a drained peatland in southeastern Estonia and described hybrid N₂O formation, where one N atom of the N₂O molecule was taken from NH₄ and the other N molecule from another source such as organic N, was the dominant source of N₂O emissions. The isotopic mapping and molecular enrichment of ¹⁵N during our experiment showed that. The isotopic mapping initially suggested nitrification as a major source, but on further investigation of ¹⁵N enrichment, we found the presence of hybrid processes (¹⁵N nitrogen from two pools or processes). Furthermore, we studied the genetic potential for major N₂O processes (denitrification, nitrification, dissimilatory nitrate reduction to ammonium (DNRA)) and combined these with the isotope results, and this integrated approach is an important tool to partition N₂O processes. When using ¹⁵N tracers, the isotopic technique can partition the sources (nitrate or ammonia) of N₂O. Hence, using the isotopic mapping of natural abundances and ¹⁵N tracers to partition the source, we can get initial insights into N₂O sources and processes together. Isotopic mapping is still under development and further research is required as it also has a problem of overlapping of processes.

How to cite: Masta, M., Espenberg, M., Pärn, J., and Mander, Ü.: Using 15N isotope and microbiome analysis to understand N2O production and consumption processes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8889, https://doi.org/10.5194/egusphere-egu24-8889, 2024.

Containing about three times more carbon (C) than the atmosphere (600-800 PgC) or the Earth’s vegetation, soils are crucial C pools for climate change mitigation. The CO₂ flux (~110 PgC yr⁻¹) from soils is the largest terrestrial C source to the atmosphere and is about ten times the annual emissions from burning fossil fuels (IPCC 2021). A small change in soil CO₂ flux can significantly alter the atmospheric CO₂ concentrationand potentially amplify global warming.A complete and reliable identification of soil processes likely to affect soil C balance and CO₂ flux is essential to predict future atmospheric CO₂ concentrations.

The current scientific consensus is that the dominant component of the soil CO₂ flux is heterotrophic microbial respiration. However, this paradigm is challenged by recurrent observations of substantial and persistent CO₂ emissions in soil microcosms where sterilization treatments (e.g. γ-irradiations) reduced microbial activities to an undetectable level. To address this shortcoming, we postulated that non-cellular respiratory pathways in soils are capable of performing the complete oxidation of organic matter to CO₂. This hypothesis was enhanced (i) by the detection of an isotopic signature of soil CO₂ flux (δ¹³C-CO₂ up to −75.4 ± 2.8 ‰) incompatible with a cell-derived respiration and (ii) by the release of ¹³C-CO₂ in sterilized soils supplied with ¹³C-glucose (Maire et al. 2013; Kéraval et al. 2016; 2018).

Overall our work highlights that non-cellular respiration accounts for 16 to 48 % of CO₂ fluxes from sterilized soils worldwide with contrasted physical and chemical properties. We have also demonstrated that sterilized soils have a high and persistent potential for electron transfer and form self-sustaining systems that can maintain CO₂ emissions for more than 6 years without external input. Furthermore, untargeted metabolite profiling carried out using proton nuclear magnetic resonance (¹H NMR) spectroscopy revealed that non-living soils have an orderly exometabolome dynamics supporting the idea that non-stochastic scenarios mimicking biochemical transformations (i.e. Krebs cycle, fermentation) occurred in sterilized soils (Bouquet, Keraval et al. in prep).

• Maire, V. et al, 2013. An unknown oxidative metabolism substantially contributes to soil CO₂emissions, Biogeosciences, 10, 1155–1167, https://doi.org/10.5194/bg-10-1155-2013,
• Kéraval, B., et al, 2016. Soil carbon dioxide emissions controlled by an extracellular oxidative metabolism identifiable by its isotope signature, Biogeosciences, 13, 6353–6362, https://doi.org/10.5194/bg-13-6353-2016, 2016
• Kéraval, B. et al, 2018. Cellular and non-cellular mineralization of organic carbon in soils with contrasted physicochemical properties. Soil Biol. Biochem. 125, 286–289. doi:10.1016/j. soilbio.2018.07.02
• Bouquet, C., et al. in prep. Non-living respiration : another breath in the soil

How to cite: Bouquet, C., Keraval, B., Alvarez, G., Traïkia, M., Perrière, F., Revaillot, S., Le Jeune, A.-H., Billard, H., Fontaine, S., and Lehours, A.-C.: Non-living respiration: another breath in the soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-197, https://doi.org/10.5194/egusphere-egu24-197, 2024.

Carbon capture and storage (CCS) projects aim to capture carbon dioxide (CO2) from hard-to-abate industries and the existing energy industry, for permanent storage in suitable geological formations. CCS technologies offer promising solutions to achieve net-zero emissions and ease the transition towards clean energy. Environmental monitoring is employed to demonstrate minimal influences on the near-surface environment by the CCS operation and provides assurance to the regulators and local communities. Soil gas monitoring is one of the techniques available for monitoring onshore sequestration sites.

The Otway International Test Centre (OITC), Australia’s first demonstration site for deep-well CO2 injection, has demonstrated over 95,000 tonnes of CO2 sequestration into a depleted gas reservoir and a deep saline aquifer. Due to the unique regulatory framework under which the site is permitted, a requirement of the site’s EPA license for the injection of CO2 into the subsurface is soil gas monitoring, which commenced prior to the first injection in 2008. At the OITC, soil gas samples were collected at more than 100 sites across a study area of 3.8 km2 from a 1-meter depth, with soil gas baseline values established in 2007 and 2008. The samples were analysed for major gas concentrations (i.e., oxygen (O2), nitrogen (N2), CO2 and methane (CH4)), 13C analysis on CO2, and selected samples were tested for tracer, including sulphur hexafluoride (SF6), Krypton (Kr) and Xeon (Xe). Based on available data, the injection operations at the OITC have no undesirable impacts on the near-surface environment and, when managed appropriately, CCS operations can be conducted with a high level of confidence.

The 17-year soil gas data from the OITC shows high year-to-year variabilities in soil gas CO2 concentrations, posing a major challenge to ensure robust soil gas baseline monitoring. For this reason, the use of soil gas monitoring for regulatory processes is not supported, however, as a general site check and as a means to garner community confidence, it has proven to be useful. To address the challenge of this naturally occurring variability, a multi-step verification process has been implemented to enhance confidence in identifying or ruling out anomalies. This process incorporates tracer analysis, baseline analysis, and adapted analysis methodologies demonstrated in research papers, such as the process-based analysis. Furthermore, research was conducted to review the evolution of soil gas science in the CCS industry and to optimise the monitoring strategies with data collected from the OITC as a case study.  Valuable lessons highlighted the efficacy of risk-based monitoring adjacent to identified storage formations. For example, monitoring near relatively high-risk legacy wells with compromised well integrity or for highly faulted regions with great geological uncertainty. Risk-based monitoring that includes several locations with higher temporal resolution is supported for future large-scale CCS sites.

How to cite: Zhang, K., Stevanovic, S., Zhou, Z., and Timms, W.: 17-Years of Soil Gas Sampling for Assurance Monitoring at an Onshore CCS Demonstration Site in Victoria, Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13690, https://doi.org/10.5194/egusphere-egu24-13690, 2024.

Drylands, constituting approximately 56% of the Earth's terrestrial surface, stand as the largest biome. Despite their vast expanse, our understanding of soil trace gas emissions from these regions remains limited. This knowledge gap arises from an uneven distribution of soil trace gas flux measurements across continents. While North American and East Asian drylands have been extensively studied, reports from other drylands are scarce. This lack of information hinders our ability to effectively constrain the atmospheric budget of reactive carbon and nitrogen gases and to develop predictive models for changes in soil trace gas emissions amid ongoing global environmental changes.

To address this gap, we conducted a comprehensive study in the Negev Desert, Israel, utilizing an array of seven automatic soil static chambers coupled to two infrared gas analyzers. This allowed us to measure soil emissions of methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) near-continuously every 15 minutes over three rainless months, measuring ~5000 individual soil fluxes. Our focus was on bare soils with varying organic carbon content (0.2%, 0.5%, and 0.6%) and nitrogen content of ~0.1%.

Our findings reveal significant diurnal variations in both CO₂ and N₂O emissions. CO₂ emissions peaked at noon (1318.2±440.4 µg C m^-2min^-1) and reached their lowest point at midnight (373.4±228.8 µg C m^-2min^-1). In contrast, soil N₂O flux was highest at 9:00 (0.07±0.02 µg N m^-2min^-1) and lowest at 21:00 (0.03±0.01 µg N m^-2min^-1). Soil CH₄ flux exhibited minimal variation, with maximum and minimum emissions of 0.43±0.24 and 0.16±0.09 µg C m^-2min^-1, respectively.

Notably, the distinct peak emission times for CO₂ and N₂O suggest different underlying mechanisms for the production of these gases in the soil. Furthermore, we observed a strong correlation between soil CO₂ emissions and soil water fluxes, while all gaseous fluxes correlated with the organic carbon content of soils. This emphasizes the role of water and soil organic carbon as primary driving factors for trace gas production in desert soils during rainless periods. Specific mechanisms of soil trace gases production in dry desert soils, however, will require further research.

How to cite: Gelfand, I. and Grabovsky, V. I.: During the rainless season, arid soils exhibited large diurnal fluctuations in carbon and nitrous oxides emissions, while displaying a uniform pattern of methane emissions throughout the day. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10301, https://doi.org/10.5194/egusphere-egu24-10301, 2024.

Methane is the second highest contributor to human greenhouse gas emissions. In Ireland, it represented 29% of the total CO₂ equivalent emissions in 2022. A drastic reduction methane emissions is thus crucial to meet the Paris Agreement commitment of 30% reduction of emissions between 2005 and 2030. It is, however, challenging as more than half of anthropogenic methane emissions are produced at concentrations below 5%. At such low concentrations, methane cannot be efficiently recovered or even flared as it is lower than its flammability level in air. In Ireland, this concerns mainly the agriculture and the waste sector. In terms of wastewater treatment, on-site domestic wastewater treatment systems serve approximately one third of the households in Ireland and so represent a significant source of methane coming from the anaerobic processes (mainly septic tanks).

A promising alternative way to treat methane is microbial oxidation by methanotrophs grown on a suitable porous media. Such a passive biofilter could be easily placed on top of septic tank gas vents, capturing the emitted methane before it is released into the atmosphere. The methane-oxidizing bacteria will then convert it into carbon dioxide, which is approximately thirty times less potent greenhouse gas in terms of global warming potential.

Multiple questions must be addressed to confirm the practical feasibility of this methane biofilter concept. The environmental conditions in the filter must allow the methanotrophs to thrive and outcompete other bacteria, thus ensuring an efficient methane oxidation, without obstructing the airflow. In addition to methane, an adequate supply of oxygen is necessary. This requires complex simulations of both the fluid dynamics involved as well as microbial growth and other kinetic dynamics. To investigate these different physical and biological aspects, a numerical study has been conducted combining computational fluid dynamics (CFD) modelling and multispecies biofilm modelling.

The CFD approach is carried on at the system level, producing velocity fields in the septic tank and the different pipes and vents. Knowledge of the gas flow in the full wastewater treatment system is essential to estimate the inlet flow conditions the biofilter will be subjected to depending on the wind weather. The information obtained on the gas phase, especially oxygen and methane levels, is then fed into a multispecies biofilm model. At this local level, we model the methanotrophs as well as the other bacteria expected to grow, compete for space and oxygen, and decay in the biofilter environment: heterotrophs, nitrifiers and Sulphate Reducing Bacteria. The results show that the methanotrophs should not be outcompeted. Moreover, the model enables the height of the filter to be estimated such that it should reach the target of 90% of methane consumption. Finally, transient simulations give insight into the expected time of usage of the filter before it needs to be regenerated.  

How to cite: Bellec, M., Picioreanu, C., Ali, M., and Gill, L.: Numerical investigation of methanotrophs in a biofilter for methane emission mitigation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18734, https://doi.org/10.5194/egusphere-egu24-18734, 2024.

Biogenic volatile organic compounds (BVOCs) released by boreal vegetation have a net cooling impact on climate, both in the boreal and Arctic regions. While boreal forests play a major role in this process, the release and uptake of BVOCs in peatlands is poorly understood, even though they cover up to 28% of the boreal region. Furthermore, soil BVOC sinks and sources are an understudied component of the boreal BVOC budget. Recently, microbial uptake of BVOCs has been found to regulate BVOC release from the soil into the atmosphere. In peatlands, methane emissions from the peat are known to be controlled by microbial oxidation within the living mosses, but it is unknown whether similar uptake occurs with BVOCs.

Our aim was to quantify the release and uptake of BVOCs across different boreal peatland habitats. We collected peat samples, including the living moss layer, from four peatland habitats varying in fertility, wetness, and vegetation composition (bog hollow, bog hummock, fen, bog peat). The samples were split into the living moss layer, as well as the oxic and anoxic peat layers, above and below the water table, respectively. First, we investigated the potential uptake of peat-derived BVOCs in the living moss layer by incubating the peat and moss layers in glass jars both separately and together with other layers from the same habitat. Next, we quantified the uptake of four specific compounds by introducing ¹³C-labeled BVOCs into jars containing peat or moss layers. The magnitude and compound composition of BVOCs was measured with proton transfer reaction–time of flight–mass spectrometry (PTR-TOF-MS).

Contrary to our expectations, BVOC uptake of peat-derived compounds was observed in the living moss layer, as well as in the oxic and anoxic peat layers. The most important layer for BVOC release and uptake varied between the peatland habitats. For example, the number of released compounds and the total BVOC emissions were largest for anoxic peat in the fen, while it was the living mosses in the bog hollow. Anoxic bog peat had the largest BVOC uptake of all of the habitats and layers. BVOC uptake varied between the studied compounds; while ethanol was taken up by all layers in every habitat, we observed no uptake of acetic acid. Acetone was mostly consumed in the peat layers, while acetaldehyde uptake occurred in bog hummock and fen habitats, regardless of the layer. According to our results, BVOC emissions from boreal peatland soil into the atmosphere are a net outcome of production and consumption both in the peat and moss layers. As these patterns vary even within habitats of the same site, changes in vegetation have the potential to modify BVOC fluxes in boreal peatlands.

How to cite: Korrensalo, A., Davie-Martin, C., Männistö, E., Blande, J., and Rinnan, R.: Differences in the uptake of biogenic volatile organic compounds (BVOCs) between habitat types and peat layers in boreal peatlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17493, https://doi.org/10.5194/egusphere-egu24-17493, 2024.

Carbon dioxide is the most important among all greenhouse gases and microbial respiration is one of the fundamental soil processes, that contribute to atmospheric CO₂ pool. Many factors influence the respiration of soil microbiota. With regard to agricultural soils, the most discussed are the type of cultivation and fertilisation. Much less attention is paid to herbicides, which are widely used and comprise a frequent contaminant of the soil environment. The most commonly used herbicide worldwide is glyphosate (GFP). In 2018, annual  GFP consumption exceeded 8.25 x 10⁸ kg and is still increasing. GFP is a foliar herbicide that is used in agriculture in the form of commercial formulations (GFC). Due to imprecise dosing, leaf washoff or with plant necromass, GFC reaches the soil environment where can potentially modulate activity and abundance of soil microorganisms. Possible modes of action include toxicity (e.g. due to inhibition of the shikimate pathway) or stimulation due to the fact that GFP is biodegradable and can potentially be a source of all major biogenic elements C, N and P. Due to the widespread use of GFC in agriculture, it may be an important driver of soil-related CO₂ emissions, but knowledge in this area is still fragmentary.  

In the current study, a wide range of GFP and GFC (0 – 10 000µg g^-1) doses were used to determine its effect on microbial respiration in two agriculturally used soils (histosol and fluvisol). In parallel, the qualitative and quantitative composition of the soil microbial community was studied. Pure glyphosate (GFP) and a commercial formulation (GFC) containing adjuvants in addition to glyphosate were tested.

For both soils, the exposure to GFP and GFC resulted in an increase in microbial respiration. However, this effect was greater for GFC, indicating the important role of adjuvants in shaping the environmental effect of the herbicides used. In accordance with the respiration results, a significant increase in the total bacteria count was found in both studied soils. Qualitatively, communities' structures were not significantly transformed, even under the influence of high doses of the tested preparations.

How to cite: Furtak, A., Szafranek-Nakonieczna, A., Górski, A., and Pytlak, A.: The influence of glyphosate on soil CO2 respiration and microbial communities structure in histosol and fluvisol, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5323, https://doi.org/10.5194/egusphere-egu24-5323, 2024.

This research investigates the complex dynamics of how soil NO concentrations and soil moisture affect the exchange of greenhouse gases between soils and the atmosphere. To this end, we have developed and tested an automated soil mesocosm system (AU-MES), which allows for dynamically change of headspace and soil NO concentrations, measures trace and greenhouse gas fluxes based on a dynamic chamber approach, and observes and manipulates key soil and environmental metrics such as temperature, light conditions, or moisture.

Initial a brief phase of soil-only incubation experiments demonstrated the influence of soil moisture and soil and headspace NO concentrations of 400 ppbv on gas emissions. We observed that under low soil moisture conditions (30% water-filled pore space), nitrification was favored, as indicated by increased emissions of NO (at zero NO concentration 0.191 kg N ha^-1 and at high NO concentration 0.180 kg N ha^-1) and NO₂ (at zero NO concentration 0.002 kg N ha^-1 and at high NO concentration 0.001 kg N ha^-1). In contrast, under higher soil moisture conditions (50% water-filled pore space), we observed increased N₂O (at zero NO concentration 0.149 kg N ha^-1and at high NO concentration 0.147 kg N ha^-1) and CO₂ (at zero NO concentration 0.122 t C ha^-1 and at high NO concentration 0.110 t C ha^-1)fluxes, suggesting that denitrification may become more important. These results, particularly under soil rewetting and fertilizer application, illustrate the complex interplay between soil nitric oxide concentrations, moisture levels, microbial activities, and gas emissions.

In summary, the AU-MES system is a valuable tool for investigating soil-atmosphere gas interactions and the effects of various environmental elements on these processes. Our research provides important insights into how nitric oxide may affect soil processes and trace gas exchange at the soil-atmosphere interface.

Keywords
Automated soil mesocosm system, nitric oxide, gas concentrations, headspace purging, soil purging

How to cite: Subramaniam, L., Engelsberger, F., Wolf, B., Dannenmann, M., and Butterbach-bahl, K.: An innovative soil mesocosm system for studying the effect of soil moisture and background NO contribution on soil surface trace gas fluxes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2201, https://doi.org/10.5194/egusphere-egu24-2201, 2024.

To date, extensive field measurements of nitrogen oxide (N₂O) exchanges in soils across diverse terrestrial ecosystems, complemented by controlled laboratory incubation studies, have unveiled considerable variability in N₂O soil fluxes. This variability arises from the intricate interplay of various factors. Notably, soil N₂O emissions display significant spatiotemporal fluctuations, including extreme events. The primary objective of this study is to enhance our understanding of the environmental factors influencing soil N₂O fluxes and to characterize instances of pronounced N₂O emissions, hereafter termed "hot-moments."

Our investigation encompassed six distinct sites of the Integrated Carbon Observation System (ICOS) network including agricultural systems, sylvicultural systems, and unmanaged forests spanning the northern hemisphere. To identify and categorize hot-moments events, we standardized N₂O values and considered events greater than or equal to 4, or -4-fold standard deviations from the mean of each site.

We then conducted wavelet coherence analyses to delve into the patterns of N₂O fluxes. In the biwavelet plots, our variable of interest was juxtaposed with each soil environmental variable, illustrating the distribution of correlations in the time-frequency domain of our signals. Employing this advanced approach, we explored N₂O patterns and their variability in relation to specific environmental characteristics (soil water content, soil temperature, and CO₂ flux) within the six temporal series (different soil types).

Our analyses revealed a recurring pattern across all time series, with a frequency of approximately 24 hours for the N₂O vs. CO₂ plots, indicating a daily correlation between the emissions of both gases. This correlation may be linked to seasonality in certain sites. Soil temperature emerged as a leading factor in shaping the daily patterns of N₂O fluxes in most sites, exhibiting also a 24-hour pattern. Although the periodicities related to soil water content were less clear, a discernible pattern persisted with variations within sites. However, we will deepen into the discussion of these results and their implications in our EGU presentation.

Key words: N₂O fluxes, hot-moments, soil environmental variables, temporal series, wavelet coherence analysis

How to cite: Sabaté Gil, M. C., Peñuelas, J., Fernandez-Martinez, M., Mattana, S., Tallec, T., Boland, F., Heinesch, B., Freigenwinter, I., Rautakoski, H., Lohila, A., Magliulo, E., Jansens, I., Roland, M., Poblador, S., and Ribas, À.: Dynamics of soil N2O fluxes and hot-moments typification: How are they related to environmental characteristics?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20747, https://doi.org/10.5194/egusphere-egu24-20747, 2024.

Soil structures regulate the production and emission of N₂O from soils mainly through influencing substrate availability and gas diffusion. However, the respective impacts of substrate availability and gas diffusion and their response to moisture changes remain elusive. This study conducted laboratory incubation experiments with disturbed (sieved) and undisturbed (intact) soil cores under different soil moisture levels (i.e., 40, 60, 80 and 100% water filled pore space (WPFS)). Soil N₂O fluxes were continuously monitored over a 21-day incubation period, during which O₂ concentration profile was occasionally measured and relative soil gas diffusivity was measured at the end of experiments. The results show that the N₂O fluxes from the disturbed soil cores were 2~25 times higher, respectively, than those from undisturbed cores, which are similar to field observations. Nevertheless, the difference in the relative soil gas diffusivity between them was not obvious, especially under high moisture conditions. Therefore, the overestimated soil N₂O emission from sieved soil experiments was attributed to increased C availability caused by disturbance rather than changes in gas diffusivity. Additional incubation experiments with ¹⁵N tracing further demonstrated the key impacts of soil microsites on N₂O production and emission. Overall, this study highlighted the physical protection of soil microsites on carbon sequestration and N₂O mitigation.

How to cite: Yan, Z. and Chang, B.: Soil microsites controls N2O production and emission in undisturbed soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4353, https://doi.org/10.5194/egusphere-egu24-4353, 2024.

Nitrous oxide (N₂O) contributes to increasing the greenhouse effect and is also involved in stratospheric ozone depletion. In soil and water, N₂O reductase catalyses the reduction of N₂O into the inert form N₂ and is then considered as a key environmental enzyme. N₂O reductase activity is known to be affected by acidic conditions (Samad et al. 2016) and the application of liming materials to acidic soils is now proposed as a solution for mitigating soil N₂O emissions (Barton et al. 2013).

During a one-year laboratory experiment, we studied the functioning of N₂O reductase after the application of calcium carbonates to an acidic soil with initially a very low capacity to reduce N₂O. The functioning of N₂O reductase was characterised through anaerobic incubations using the acetylene inhibition technique combined with a logistic model to determine the main enzyme functioning characteristics (latency, maximal rate).

Both changes in soil pH and soil capacity to reduce N₂O were rapidly observed after the application of lime materials. The activity of N₂O reductase was observed to be efficient throughout the experiment even when the soil had returned to initial acidic conditions, revealing a hysteretic response of N₂O reductase to pH variations. Nevertheless, some signs of lower N₂O reductase activity over time were observed mainly after 200 days of applying lime materials. Altogether, these results suggest that, in this soil condition, the beneficial impact of the application of liming materials on N₂O emissions could last longer than this on soil pH.

Keywords: Climate change mitigation · N₂O reductase · Soil · pH · Lime application · Logistic modelling

References:

Barton, L. et al. (2013) Is liming soil a strategy for mitigating nitrous oxide emissions from semi-arid soils? Soil Biology and Biochemistry 62, doi: 10.1016/j.soilbio.2013.02.014

Samad, M. S. et al. (2016) High-resolution denitrification kinetics in pasture soils link N₂O emissions to pH, and denitrification to C mineralization. Plos One 11, doi: 10.1371/journal.pone.0151713  

Acknowledgements: The authors gratefully acknowledge funding for the NatAdGES project from the “Investissement d’Avenir” program, ISITE-BFC project (contract ANR-15-IDEX-0003), the European Regional Development Fund (FEDER), the public investment bank (BPI France) and the CMI-Roullier.

How to cite: Rousset, C., Ouerghi, I., Bizouard, F., Brefort, H., Ubertosi, M., Arkoun, M., and Hénault, C.: Hysteretic response of N2O reductase activity to soil pH variations after application of lime to an acidic agricultural soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7425, https://doi.org/10.5194/egusphere-egu24-7425, 2024.