BG3.21 | Soil gases: production, consumption and transport processes
EDI PICO
Soil gases: production, consumption and transport processes
Convener: Jukka Pumpanen | Co-conveners: Bernard Longdoz, Martin Maier, Anna Walkiewicz, Nicholas Nickerson
PICO
| Thu, 27 Apr, 16:15–18:00 (CEST)
 
PICO spot 3b
Thu, 16:15
Soils sustain complex patterns of life and act as biogeochemical reactors producing and consuming a large amount of gas molecules. They play a fundamental role in the temporal evolution of the atmospheric gases concentration (greenhouse gases, biogenic volatile organic compounds, nitrous acid, isotopic composition…) and they modulate the soil pore gas concentrations affecting many soil functions, such as root and plant growth, microbial activity, and stabilization of soil organic carbon. Gases production, consumption and transport in the different soil types have then some important ecological implications for the earth system.
The factors affecting the soil gas processes range from physical soil structure (porosity, granulometry,…), type and amount of living material (microbiota, root systems), soil chemistry properties (carbon and nitrogen contents, pH,…) and soil meteorological conditions (temperature, water content,…). A large mixing of different scientific backgrounds are therefore required to improve the knowledge about their influence which is made even more difficult due to the very large spatial heterogeneity of these factors and the complexity of their interactions.
This session will be the place to present and exchange about the measurement techniques, data analyses and modelling approaches that can help to figure out the temporal and spatial variability of the production/consumption and transport of gases in soils. In addition to mechanisms related to carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), including the geochemical ones, the abstracts about volatile carbon compounds produced by plant and microbial or Helium and Radon geogenic emissions production are welcome
A special attention will be given to the researches including special water situations as edaphic drought or waterlogged soils

Session Dinner on Thursday evening at Gasthaus Schosztarich, 

https://www.gasthof-schosztarich.at/english/

( please contact Martin.Maier@uni-goettingen .de for furtehr details)

PICO: Thu, 27 Apr | PICO spot 3b

Chairpersons: Jukka Pumpanen, Anna Walkiewicz, Martin Maier
16:15–16:20
16:20–16:30
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PICO3b.1
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EGU23-8257
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solicited
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Virtual presentation
Rodrigo Vargas and Huong Le

A fundamental question for any sampling design is identifying where and when to measure. Technological advances allow us to measure multiple greenhouse gases (GHGs) simultaneously, and now it is possible to provide complete GHG budgets from soils (i.e., CO2, CH4, and N2O fluxes). We present a data-driven method for identifying optimized samples from times series (1D approach) or spatial arrays (2D approach) of information on soil gases. The autocorrelated conditioned Latin Hypercube Sampling (acLHS) combines a conditioned Latin Hypercube (cLHS) to obtain a representative sample of the joint probability distribution function and an autocorrelation model to ensure a reproducible spatial or temporal dependency function (i.e., temporal or spatial variability). The results show a conflict between the convenience of simultaneously measuring multiple soil GHG fluxes at fixed time intervals (e.g., once or twice per month) and the intrinsic temporal variability in and patterns of different GHG fluxes. Furthermore, the acLHS is more efficient than other sampling methods (i.e., fixed sampling, cLHS) as it can better reproduce the joint probability distribution and the temporal or spatial variability of the variables of interest. We test this approach using time series and spatial arrays to evaluate the relationship between soil CO2 efflux and temperature. These results have implications for assessing gas fluxes from soils and consequently reduce uncertainty in the role of soils in biogeochemical cycles.

How to cite: Vargas, R. and Le, H.: When and where to measure soil gases: an optimization approach for time series and spatial information, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8257, https://doi.org/10.5194/egusphere-egu23-8257, 2023.

16:30–16:32
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PICO3b.2
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EGU23-4787
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ECS
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On-site presentation
Elad Levintal

The development of new affordable sensors and hardware, and the ability to log high-resolution data for long periods of time can enhance the ability to capture soil gas process-related heterogeneity. The use of novel open-source sensors, defined as hardware whose design is made publicly available, lowers the cost dramatically compared to commercial solutions and allows implementing higher spatiotemporal resolution sensor grids that are imperative for modeling and mechanistic understandings. Here, I will present the basic concepts, advantages, and challenges of using open-source, low-cost, do-it-yourself hardware for soil gas monitoring (mainly O2, CO2, CH4, and N2O), including examples in which this type of sensors was utilized to solve soil-related research questions. For example, the development of a low-cost wireless underground sensor network for O2/CO2 monitoring under waterlogged conditions using the relatively new low-power long-range (LoRa) communication protocol. Another example is a portable, low-cost incubation chamber for quantifying soil microbial activity using in-situ sensors for measuring O2, CO2, CH4, and air temperature at high temporal resolution (<1 min). In all the presented studies, only readily buyable hardware is used, and complete technical guides on design, assembly and installation are provided. By doing so, the adoption and cost barriers can be reduced, allowing easier reproducibility and opening the technology for new applications in soil gas monitoring studies.

How to cite: Levintal, E.: The use of open-source, affordable hardware in soil gas research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4787, https://doi.org/10.5194/egusphere-egu23-4787, 2023.

16:32–16:34
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PICO3b.3
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EGU23-11650
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ECS
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On-site presentation
Anna Walkiewicz, Adrianna Rafalska, Adam Kubaczyński, Victor Rolo, Maria Vivas, Gerardo Moreno, and Bruce Osborne

Soils may act as a biological sink for methane (CH4) through methanotrophic activity. This process is particularly important in the farming sector, as CH4 emissions from livestock and manure storage often dominate the greenhouse gas (GHG) budget. This places a particular emphasis on the identification of management practices that may increase the capacity of soils to absorb CH4. In this study we examined  practices with the potential to improve the CH4 balance at farm level, including the effect of biochar as a soil additive, and the potential of silvopasture systems. Experiments conducted under controlled laboratory conditions revealed that the addition of biochar increased the rate of CH4 oxidation in the mineral and manure-fertilized silty soil, although such effect has not been confirmed in all soil types. Using biochar produced from crop by products  may also provide a way of managing agricultural wastes with concomitant practical benefits. Silvopastoral systems can also alter the CH4 balance of farms because of the effect of the presence of trees on microclimate and soil conditions. However, relatively few studies have assessed the potential of trees to improve CH4 budgets at the farm level in Mediterranean silvopastoral systems. In-situ measurements of soil-atmosphere CH4 fluxes were undertaken to evaluate the CH4 uptake potential of pastures below and beyond tree canopies. Preliminary results showed CH4 emissions in open tree-less pastures, but not under trees, which showed mainly CH4 uptake. This result highlights the potential of silvopastoral systems to improve the CH4 balance at farm level perhaps in combination with biochar additions. Nevertheless, the mitigation potential of different soil additives and silvopastoral  practices at farm level are still a subject of research in need of further studies.

This work was funded by the National Centre for Research and Development within GHG Manage (ERA-GAS/I/GHG-MANAGE/01/2018) and ReLive (CIRCULARITY/61/ReLive/2022); Joint Call of the Co-fund ERA-Nets Programme, SusCrop (Grant N° 771134), FACCE ERA-GAS (Grant N° 696356), ICT-AGRI-FOOD (Grant N° 862665) and SusAn (Grant N° 696231), Spanish Ministry of Science and Education (PCI2021-122100-2A).

How to cite: Walkiewicz, A., Rafalska, A., Kubaczyński, A., Rolo, V., Vivas, M., Moreno, G., and Osborne, B.: The role of soil methanotrophy in offsetting methane emissions at farm level – the potential contribution of silvopastoral systems and biochar additions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11650, https://doi.org/10.5194/egusphere-egu23-11650, 2023.

16:34–16:36
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PICO3b.4
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EGU23-17596
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Virtual presentation
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Verena Lang, Peter Hartmann, Alexander Schengel, and Martin Maier

Methanotrophic bacteria are capable to uptake methane (CH4) from the atmosphere. They are mainly found in forest soils, making them the most important terrestrial sink for methane. While agricultural soils have partially lost their methane sink function due to the negative effect of nitrogen fertilization on methanotrophy, the methane sink function of forest soils is considered to be intact. Differences in sink capacity of different land use types and short-term factors influencing methane uptake are well studied. Since the most commonly used methodology to measure methane fluxes are energy- and personnel-intensive chamber measurements, there are only few long-term measurements, especially of forest soils. Therefore, little is known about long-term effects and climate change impacts on methane sink function.

In the long-term forest environmental monitoring of the Forest Research Institute (FVA-BW), soil air including methane content has been measured at different depth levels at a monthly interval on 13 forest monitoring plots (ICP Forest Level II) in southwestern Germany for more than 20 years. This method, which is well suited for long-term monitoring, allowed continuous sampling since 1998 and 2010, respectively. From the concentration gradients, the methane flux can be determined using the gradient method. To make these calculated fluxes more precise, chamber measurements were carried out over 1.5 years in 2021/2022 in parallel with the collection of gas samples. By comparing the fluxes of both measurement methods, a validation of the long-term measurement series is possible.

First evaluations of our sites show so far insignificant changes in methane fluxes over the last 20 years. This contrasts our results with study results (Ni & Groffman, 2018), which report a dramatic 53-89% decrease in methane uptake in forest soils observed at four sites in the USA over the last 20 years. Trend estimates of our monitoring sites and the analysis of significant factors influencing long-term methane trends are presented.

References:

Ni, X., Groffman P.M.2018. Declines in methane uptake in forest soils. PNAS 115 (34) 8587-.

How to cite: Lang, V., Hartmann, P., Schengel, A., and Maier, M.: Methanotrophic bacteria in forest soils – should I stay or should I go?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17596, https://doi.org/10.5194/egusphere-egu23-17596, 2023.

16:36–16:38
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PICO3b.5
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EGU23-9590
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ECS
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On-site presentation
Xuefei Li, Maxim Dorodnikov, Lukas Kohl, and Timo Vesala

Boreal peatlands emit a substantial amount of CH4, a potent greenhouse gas, to the atmosphere. Despite decades of effort made on studying CH4 efflux to the atmosphere, understanding the dynamics of the different co-occurring processes underlying CH4 emission remains a challenge in peatland CH4 modeling, especially during the non-growing seasons. Stable isotope signatures of the soil pore water and emitted CH4 can provide information on these processes. To this end, we conducted a first systematic study using stable isotope methods on in-situ major CH4 turnover processes along a peat profile in a typical boreal peatland (Siikaneva fen) in Southern Finland.

We run a cavity ring-down spectrometer continuously in 2022 to capture the dynamics of belowground dissolved CH4 and CO2 concentrations and their δ13C natural abundance signatures at 10, 30 and 50cm. Same variables were measured at 40cm above peatland surface to estimate ecosystem-scale average δ13C value of the emitted CH4 using nocturnal boundary-layer accumulation approach. These data were used to indicate CH4 production pathways, in-situ CH4 oxidation and transport pathways on an annual basis. Additionally, 13C pulse labelling experiments targeting acetoclastic methanogenesis, hydrogenotrophic methanogenesis and methanotrophy were performed both in-situ and in the lab condition to trace all these processes which cannot be separated by the isotope natural abundance approach alone.

Preliminary results indicated a successful implementation of these novel methods. Continuous measurement of soil gas showed systematic differences in the vertical profile of soil pore water isotopes between winter and summer. δ13C-CH4 values were highest in the deepest layer during winter but they were the lowest in summer. As expected, CH4 production pathway moved towards acetoclastic methanogenesis through winter-summer transition. In winter, the δ13C-CH4 values from emitted CH4 was higher than those from the soil which indicating CH4 oxidation, while in summer the opposite was found due to CH4 diffusive plant transport. CH4 concentrations were higher in summer than in winter from all the depths, while at -30cm had the highest concentration. In-situ labelling experiments showed a higher rate of acetoclastic methanogenesis at -30cm than at -50cm, while hydrogenotrophic methanogenesis was similar at both depths. Experiments also demostrated that there was substantial methanotrophy in the soil as deep as 50cm belowground.

 

How to cite: Li, X., Dorodnikov, M., Kohl, L., and Vesala, T.: Temporal and vertical variation of in-situ methane turnover from stable isotope studies at a boreal peatland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9590, https://doi.org/10.5194/egusphere-egu23-9590, 2023.

16:38–16:40
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PICO3b.6
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EGU23-16463
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On-site presentation
Ype van der Velde, Merit van der Berg, Jim Boonman, Tanya Lippman, and Jacobus van Huissteden

Measuring carbon dioxide (CO2) exchange between ecosystem and atmosphere is a widely used method to determine peat oxidation from drained peat soils. The net ecosystem carbon balance (NECB), which is the net CO2 flux over a year with accounting for harvest (C-export), is taken as an estimate for peat oxidation. This might be the case if the short-term carbon cycle, dominated by vegetation, is in balance within one year. Carbon processes are, however, often complex determined by weather conditions and interactions between different carbon pools. To better estimate the contribution of the soil carbon pools, including peat oxidation, to the measured CO2 fluxes within a season or a year, a reliable model is needed. 

PEATLAND-VU is a 1D process based model, consisting of four submodels for 1) soil physics (water table, soil temperature and soil moisture), 2) biomass production, 3) CH4 production, oxidation and transport, and 4) CO2 production. CO2 production is the sum of decomposition from different soil organic matter (SOM) pools, like litter, root exudates, microbial biomass and peat. We improved the PEATLAND-VU model and calibrated it for two intensively used drained peat meadows in the Netherlands, that are equipped with sensors for measuring continuously CO2 fluxes and all environmental variables related to that. These sites have a reference field and a field with elevated groundwater level.

In this presentation, we discuss the model performance on these sites. We will show the contribution of the different sources to the ecosystem respiration, and how the modelled peat oxidation relates to the measured NECB.

How to cite: van der Velde, Y., van der Berg, M., Boonman, J., Lippman, T., and van Huissteden, J.: Extracting peat oxidation from ecosystem respiration with the PEATLAND-VU model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16463, https://doi.org/10.5194/egusphere-egu23-16463, 2023.

16:40–16:42
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PICO3b.7
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EGU23-11821
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On-site presentation
Bogdan Chojnicki, Patryk Poczta, Kamila Harenda, Paweł Dłużewski, and Damian Józefczyk

The soil CO2 emission is one of the most important parts of forest carbon balance, and accurate estimation of this flux is fundamental for appropriate forest management aimed at adaptation and mitigation of climate change. The soil carbon dioxide flux density is determined by different factors, e.g. soil temperature, humidity, and C-content. The Polish forest habitats classification (based on the climate and soil conditions) provides the practical basis for the effective extrapolation of local carbon dioxide emission observations to larger areas. Thus, the main goal of this study was the estimation of the annual dynamics of the soil CO2 emission at three of the most common forest habitats and to select the most reliable model that can be commonly applied to managed forests. There were three experimental sites selected for this study, and they represented the following forest habitats: optimal conditions for pine forest (OP), rich conditions for pine forest (RP) optimal conditions for mixed oak and pine forest (OOP). These three habitats represent 66% of forested areas in Poland. The sites were located in Oborniki Forest Inspectorate in the Greater Poland Voivodship, Western Poland. The CO2 emission was measured by means of the manual dynamic opaque chamber attached to the infrared gas analyzer (LI-840 LI-COR, USA). There were 3 collars (25 cm diameter) inserted about 15 cm depth into the ground at each site, and the measurement campaigns were carried out from 16th of March 2022 8th of March 2023, at 3-week intervals. The soil measurement system (TMS-4, TOMST, Czechia) was applied for discrete (15-minute interval) measurements of the air and soil temperature and soil water content at each collar. Additionally, soil analysis was made at each site. The initial analysis of obtained results shows that the model based on both soil temperature and soil water content can be considered the most accurate and reliable. The richest forest habitat (OOP) with the highest soil C-content is characterized by the highest annual soil CO2 emission.

How to cite: Chojnicki, B., Poczta, P., Harenda, K., Dłużewski, P., and Józefczyk, D.: The soil CO2 emission at the three most common forest habitat types in Poland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11821, https://doi.org/10.5194/egusphere-egu23-11821, 2023.

16:42–16:44
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PICO3b.8
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EGU23-9145
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On-site presentation
Martin Maier, Laurin Osterholt, Hubert Jochheim, and Helmer Schack-Kirchner

Soils are important terrestrial biological reactors and play a central role in the global carbon (C) and nitrogen (N ) cycle. Soils can store large amounts of C and N, but they also can be a major source (or sink) of greenhouse gases. The highest C and N concentrations are usually found in the topsoil, which is also the biologically most active soil layer, and the origin of most soil respiration. Subsoil (>0.5m depth) usually has lower C and N contents, and the contribution to the soil surface gas fluxes, e.g. soil respiration is low. Nevertheless, the total amount of C and N stored in the subsoil (e.g. 0.5-3m) can be large. Slow changes due to global climate change (e.g. in subsoil moisture or temperature) might affect subsoil respiration, i.e. subsoil C mineralization, and thus, might have a substantial long-term effect on subsoil C and N storage.

While gas fluxes from soil surfaces are usually measured by chamber methods or the Eddy-covariance method, these methods are not suitable to assess subsoil gas fluxes. The gradient method allows calculation of gas fluxes in a soil profile, that means also in the subsoil, based on a measured soil gas profile and a known soil gas diffusivity (Maier & Schack-Kirchner, 2014). Estimating the latter is a major challenge, especially in subsoils, and the (unreflective) application of a general soil gas diffusivity model without prior knowledge of the soil physical characteristics of the subsoil can result in large uncertainties.

We present soil CO2 data from a deep soil profile (1m) of a forest site (Jochheim et al., 2022) from which we chose special and typical situations of daily CO2 cycles at different soil depths. We used time-dependent Finite Element Modelling (COMSOL) to run different scenarios to investigate the phase shift and damping of diurnal CO2 cycles in the atmosphere/topsoil and subsoil, which allows to derive soil gas diffusivity of the subsoil. We tested the susceptibility of the approach to misinterpretation due to possible inaccurate assumptions by further scenarios. To evaluate the effect on the derived subsoil gas flux, we will use diffusivity values from this new in situ approach and known general soil gas diffusion models as well.

How to cite: Maier, M., Osterholt, L., Jochheim, H., and Schack-Kirchner, H.: Estimating subsoil diffusivity and respiration by inverse modelling: results from first case studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9145, https://doi.org/10.5194/egusphere-egu23-9145, 2023.

16:44–16:46
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PICO3b.9
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EGU23-13572
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ECS
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On-site presentation
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Enrique Echeverría Martín, Ángel Fernández-Cortés, Andrew S. Kowalski, Penélope Serrano-Ortiz, and Enrique Pérez Sánchez-Cañete

It is crucial to understand the cause-effect relationships of greenhouse gas (GHG: CO2, CH4 and N2O) concentrations and quantify their sources and sinks in natural systems, including their main reservoirs. This is particularly important when it comes to the vadose zone, which has the potential to store large amounts of GHGs in its pores. Currently, GHG measurements are mainly limited to the top few meters of soil, ignoring transport and storage processes in deeper areas. As a result, the vadose zone, with high concentrations of GHGs and a significant capacity for gas storage, is an enormous but unknown GHG reservoir.  

To improve knowledge of GHGs in the vadose zone, the air column of boreholes, soils and the atmosphere were sampling over the course of a year, with three sampling campaigns, generating depth profiles of GHG concentrations down to 150 meters. This study shows the behavior of GHG concentrations found in the vadose zone of several sampling campaigns carried out in boreholes of different aquifers in the south of Spain. Also, we focus on two with results showing fluctuating concentrations of CO2 (419-8452 ppm), CH4 (0.56-63 ppm) and N2O (0.33-1504 ppm). The carbon isotopic signature for CO2 was -9 and -10 ‰ for the atmosphere, between -22 and -25 ‰ for the soil and between -10 and -22 depending of the air column of the borehole. The isotopic composition of CO2 from sectors closer to surface results from a mixing process between the soil-derived CO2 and the local atmosphere. The 13C enrichment of CO2 in some deeper sector of the air columns denotes the CO2 contribution by outgassing of water reservoirs within the vadose zone that has experienced a high interaction with the host-rock. The carbon isotopic signature for CH4 was especially surprising with values fluctuating between -9.76 and -100 ‰. The 13C enrichment of CH4 with concentrations above 50 ppm CH4 may indicate a particular case in which intense production coexists with a high consumption by methanotrophic bacteria and the 13C depletion of CH4 shows a biotic generation of methane. Although the complexity of these values may involve other processes that will be discussed.

These results reveal great variability in concentration and origin of the underground atmosphere, indicating the need for further investigation in order to accurately characterize this significant reservoir of greenhouse gases.

This work was supported by the OAPN through the project PN2021-2820s (IBERALP).

How to cite: Echeverría Martín, E., Fernández-Cortés, Á., Kowalski, A. S., Serrano-Ortiz, P., and Pérez Sánchez-Cañete, E.: What is the source of CO2 and CH4 at 150 meters depth? Studying CO2, CH4 and N2O concentrations and carbon isotopic signatures in the air of the Vadose Zone in Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13572, https://doi.org/10.5194/egusphere-egu23-13572, 2023.

16:46–16:48
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PICO3b.10
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EGU23-9913
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ECS
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On-site presentation
Elizabeth Lunny, Joseph Roscioli, and Joanne Shorter

Soil biogeochemical processes produce greenhouse gases which can have significant environmental impacts when exchanged with the atmosphere. The magnitude of surface fluxes is driven by vertical concentration gradients, thus understanding drivers of below-ground N2O production and consumption pathways is critical to atmospheric greenhouse gas mitigation strategies. We present subsurface gas composition and surface flux measurements in laboratory soil mesocosms to understand how depth-dependent soil processes impact surface fluxes over a range of soil moisture conditions. Diffusive gas probes are buried at three depths in three mesocosms of Northeastern agricultural soil and the columns are capped for surface flux measurements. We measure N2O (14N15NO, 15N14NO, 14N14NO, N218O), NO, CO2 (12CO2, 13CO2), and O2 coupled with soil moisture and temperature measurements using a Tunable Infrared Laser Direct Absorption Spectrometer (TILDAS). Isotopically resolved maps of trace gases in response to 15N-labled N2O dosing under a range of soil moisture conditions at various subsurface depths provides insight into the impact of soil moisture and oxygen content on subsurface transport, abiotic transformations and biological processes impacting surface fluxes.

How to cite: Lunny, E., Roscioli, J., and Shorter, J.: Linking subsurface biogeochemical nitrogen cycling to surface fluxes over a range of soil moisture conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9913, https://doi.org/10.5194/egusphere-egu23-9913, 2023.

16:48–16:50
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PICO3b.11
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EGU23-6786
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ECS
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On-site presentation
Yi Jiao, Magnus Kramshøj, Cleo L. Davie-Martin, Christian Nyrop Albers, and Riikka Rinnan

Volatile organic compounds (VOCs) is a group of highly reactive gaseous species in the atmosphere with significant environmental implications, such as influencing air quality and Earth’s radiation balance. Natural ecosystems constitutes a large part of VOCs inventory with vegetation as well-known sources and soils as potential unidirectional interface yet relatively less studied. Here, we collected soil samples from two representative temperate ecosystems: beech forest and heather heath, and incubated them under manipulated conditions, such as at different temperatures,  and/or exposed to different ambient VOC levels, using a dynamic flow-through system coupled with a PTR-ToF-MS, from which production and/or uptake rates of some selected VOCs were measured and calculated. Results showed that these soils were natural sources of a variety of VOCs, and their emission strength and profile were influenced by soil biogeochemical properties (e.g., soil organic matter, moisture) and temperature. These soils were switched to natural sinks of most VOCs when supplying VOC substrates to the headspace of the enclosed soils at parts per billions level, and the sink size positively responded to the amount of VOCs available in the ambient air. Further analysis indicated that the observed VOC uptake by soils were likely driven by microbial metabolism plus a minor contribution from physical adsorption to soil particles. Overall, our study suggests that soil uptake of VOCs may conceal the simultaneous production and turn it into VOC sinks when ambient VOCs become readily available, such as significant VOC sources existing near surface, thereby regulating the net performance of ecosystem exchange of these environmentally important trace gases.

How to cite: Jiao, Y., Kramshøj, M., Davie-Martin, C. L., Albers, C. N., and Rinnan, R.: Soil uptake of VOCs exceeds production when ambient VOCs are readily available, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6786, https://doi.org/10.5194/egusphere-egu23-6786, 2023.

16:50–16:52
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PICO3b.12
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EGU23-6568
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ECS
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On-site presentation
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Zeina Bourhane, Pierre Amato, and Barbara Ervens

Gases can partition between soil and the atmosphere, depending on their physicochemical properties. They can be degraded in both compartments by chemical or microbial processes. Polycyclic aromatic hydrocarbons (PAHs) are among such gases that are ubiquitous in the atmosphere and soils. They result mainly from the incomplete combustion or pyrolysis of organic matter; they are of concern due to their toxic, mutagenic and carcinogenic properties. PAHs are semivolatile, highly lipophilic and persistent organic pollutants.

The biodegradation of PAHs and other semivolatile compounds in soil has been extensively studied. Their chemical processing in the atmosphere has also been addressed by means of many model studies. However, even though the existence of bacteria in the atmosphere is well known, the role of atmospheric biodegradation has not been extensively studied.

We present a new model that includes explicit chemical processes in the atmospheric gas and aqueous phases, as well as by biodegradation in fog droplets, coupled to a soil module by volatilization and deposition processes. PAHs in soil are transported between three aerobic layers where they can be degraded by chemical and bacterial processes.

Even though PAH lifetimes in soil and the atmosphere might be similar, our initial model results suggest that degradation in soil represents the major sink for PAHs. While biodegradation in soil is predicted to be the main loss process of PAHs, oxidation processes in the atmospheric gas phase also contribute significantly to overall PAH loss.

Our model represents a new tool to assess the relative and absolute sink strengths of pollutants and other compounds in soil and the atmosphere. We will give an outlook on planned model studies for other compounds and discuss reasons for their choice.

How to cite: Bourhane, Z., Amato, P., and Ervens, B.: Comparing the loss of polycyclic hydrocarbons (PAHs) in soil and the atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6568, https://doi.org/10.5194/egusphere-egu23-6568, 2023.

16:52–18:00