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.

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.

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.

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.

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.

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 16^th of March 2022 8^th 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.

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.

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.

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.