SSS8.6

EDI
Soil gases : production, consumption and transport processes

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

Co-organized by BG3
Convener: Martin Maier | Co-conveners: Bernard Longdoz, Nicholas Nickerson, Jukka Pumpanen, Anna Walkiewicz
vPICO presentations
| Tue, 27 Apr, 09:00–10:30 (CEST)

Session assets

Session materials

vPICO presentations: Tue, 27 Apr

Chairpersons: Martin Maier, Bernard Longdoz, Anna Walkiewicz
09:00–09:10
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EGU21-8449
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solicited
Noam Weisbrod, Maria Dragila, and Elad Levintal

Gas movement within the earth’s subsurface and its exchange with the atmosphere are some of the principal processes in soil, ecosystem, and atmospheric environments. For a decade, our group has explored the roles played by atmospheric conditions and matrix properties in gas transport at the earth-atmosphere interface, where surface discontinuities, such as fractures, boreholes and aggregated soils, exist and may affect the process.

The gas transport mechanisms, resulting from the development of a thermal gradient and surface wind, were analyzed both independently and in combination. Two types of experiments were carried out: (1) under field conditions and (2) under highly controlled laboratory conditions. During all studies, temperature and wind conditions across the media and at the media-atmosphere interface were monitored. Results show that the magnitudes of thermal- and wind-induced convection were directly related to the media permeability, given favorable ambient conditions at the media-atmosphere interface. Such ambient conditions included high diurnal temperature amplitude (~± 10 ᵒC) or high surface wind (~2 m/s measured 10 m above ground). In addition, specific results from the field experiment were used to establish an empirical model that predicts gas transport magnitude as a function of wind speed and media permeability.

With respect to other discontinuities, such as boreholes and fractures, the effect of atmospheric conditions was investigated, namely atmospheric pressure and temperature, on air, CO2, and radon transport. Using high-resolution spatiotemporal measurements, it was concluded that diurnal atmospheric pressure oscillations (barometric pumping) and borehole-atmospheric temperature differences (thermal-induced convection) controlled the air transport within the boreholes. For one of the boreholes monitored, the air velocities and CO2 emissions to the atmosphere were quantified (up to ~6 m/min and ~5 g-CO2/min, respectively). This reveals the role of boreholes as a source of greenhouse gas emissions.

The results and conclusions derived from our studies are expected to improve our understanding of the governing mechanisms controlling gas movement in porous media, fractures, and boreholes, and their functions in gas exchange across the earth-atmosphere interface.

How to cite: Weisbrod, N., Dragila, M., and Levintal, E.: How fast the earth surface breathe? Gas transport in high permeability soils and earth surface discontinuities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8449, https://doi.org/10.5194/egusphere-egu21-8449, 2021.

Carbon dioxide
09:10–09:12
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EGU21-434
Marie Spohn and Stefan Holzheu

The factors that control the soil CO2 concentration are not yet well understood. Therefore, the objective of this study was to explore what factors control the soil CO2 concentration and its dynamic in a desert soil. For this purpose, CO2 concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a deeply weathered, coarse-textured desert soil in the North of Chile at high frequency (every 60 minutes) together with precipitation and air temperature for one year. The mean CO2 concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm soil depth. We observed a diel oscillation of the CO2 concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO2 concentration and both air and soil temperature. A small precipitation event increased the CO2 concentrations in 15, 30, and 50 cm soil depths for several days but did not alter the amplitude of the diel oscillation of the CO2 concentration. The diel oscillation was very likely caused by strong differences between the soil and the air temperature at night, in particular in summer, causing transport of topsoil air to the atmosphere by thermal convection. Our results have important implications as they show that the soil CO2 concentration can be controlled by air temperature through thermal convection, rather than by soil temperature, and that the hysteretic relationship between soil CO2 concentration and temperature can be caused by physical factors alone.

 

How to cite: Spohn, M. and Holzheu, S.: Air temperature controls diel oscillation of the CO2 concentration in a desert soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-434, https://doi.org/10.5194/egusphere-egu21-434, 2021.

09:12–09:14
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EGU21-2487
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ECS
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Highlight
Clément Lopez-Canfin, Roberto Lázaro, and Enrique Pérez Sánchez-Cañete

Biological soil crusts (biocrusts) have been reported to play a considerable role in the global carbon budget through CO2 uptake by photosynthesis. However, it is still unclear if ecosystems dominated by biocrusts are net carbon sinks. That is mainly because so far, most research have focused on characterizing photosynthesis ex-situ, neglecting the underlying soil component, and particularly the in-situ spatio-temporal variability of soil CO2 fluxes, which can be substantial. Moreover, it is still unknown how those CO2 fluxes evolve during the ecological succession of biocrusts and which are the biophysical and geochemical factors that control them. Therefore, this research aimed to (1) identify those factors and (2) describe and explain the evolution of annual cumulative soil CO2 fluxes over ecological succession in a dryland.

To this end, we conducted continuous measurements over 2 years of the topsoil CO2 molar fraction (χs) in association with below- and aboveground microclimatic variables in 21 locations representative of the ecological succession of biocrusts, characterized by 5 stages: (1) physical depositional crust; (2) incipient cyanobacteria; (3) mature cyanobacteria; (4) lichen community dominated by Squamarina lentigera and Diploschistes diacapsis and (5) lichen community of Lepraria isidiata. Those measurements were also conducted under plants (Macrochloa tenacissima, Salsola genistoides, and Lygeum spartum). Using spatio-temporal statistics, an explanatory model of χs dynamics was calibrated on the first year of data and cross-validated to test prediction on the second year. An explanatory model of annual cumulative fluxes was also developed.

The biocrust type, soil water content (ϑ) and temperature (Ts) and interactions between those variables explained and predicted efficiently the χs dynamics. Among those factors, the effect of ϑ was preponderant and dependent on Ts and antecedent soil moisture conditions. The magnitude of the ϑ effect tended to increase in late successional stages, producing greater CO2 emissions, most likely as a result of progressive soil organic carbon accumulation resulting in greater substrate availability for microbial respiration, and higher porosity enhancing CO2 diffusion. The calcite content (and potentially indirectly the pH through a buffering effect of CaCO3) also played a role in explaining annual cumulative CO2 fluxes. Those fluxes were particularly mitigated where CaCO3 was abundant, apparently due to a substantial nocturnal uptake of atmospheric CO2 by soil (influx) throughout the study. The cumulative annual influx represented up to 115% of the cumulative annual efflux, generating a net annual carbon uptake by soil in some locations. Influxes have been increasingly reported recently from drylands soils, which are now regarded as potential carbon sinks. Those influxes have been attributed to different abiotic processes which are still debated. In this ecosystem, in the light of our observations, we assume that a geochemical process of CO2 dissolution in soil water followed by CaCO3 dissolution that consumes CO2 might be involved. If this assumption could be verified, this geochemical process consuming CO2 would need to be separated from biocrust photosynthesis and respiration, when measuring soil surface CO2 fluxes, to not overestimate and underestimate respectively the biotic contribution to the global carbon budget.

How to cite: Lopez-Canfin, C., Lázaro, R., and Pérez Sánchez-Cañete, E.: Biophysical and geochemical processes control antagonistically the soil-atmosphere CO2 exchange during biocrust ecological succession in the Tabernas Desert, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2487, https://doi.org/10.5194/egusphere-egu21-2487, 2021.

09:14–09:16
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EGU21-789
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ECS
Yihan Cai, Takahiro Nishimura, Hideyuki Ida, and Mitsuru Hirota

 Soil respiration (Rs) is the second largest carbon flux between the atmosphere and terrestrial ecosystem. Because of the large proportion, even small change in Rs would considerably impact the global carbon cycle. Therefore, it is important to accurately estimate Rs by taking its spatial and temporal variation into consideration. While the temporal variation of Rs and its controlling factors have been well-described, large unexplainable part still has been remained in the spatial variation of Rs especially in the forest ecosystems with complex structures. The objective of this study is to fill the knowledge gap about spatial variation of Rs and its controlling factors in a typical mature beech forest in Japan. Hypotheses of this study were, 1) Rs would show large spatial variation in the mature beech forest, 2) the spatial variation of Rs was mainly influenced by soil water content (SWC) and soil temperature (ST), 3) the two key factors were determined by the forest structures. This study was conducted in a 1- ha permanent study plot in the mature beech forest with significant gap-mosaic structures. To examine these hypotheses, Rs, SWC, ST and parameters related to forest structure, i.e. sum of basal area, diameter at breast height, number of trees, number of species within a radius of 5 m from the Rs measurement points, and canopy openness were measured at 121 points in different season between 2012 to 2013. In this study, all the measurements of Rs were conducted by using alkali-absorption technique.

 Coefficient of variation of Rs was between 25 - 28 % which was similar to that of SWC in all the measurements. The spatial variation of Rs was relatively higher in July, August and September than that in June and October. There was no significant relationship in the spatial variation between Rs and ST in all the measurements, meanwhile, Rs was well explained by SWC in measurements conducted in August, September and October. Multiple linear regression analysis indicated that canopy openness and sum of basal area showed significant positive and negative correlation with SWC, respectively. And canopy openness explained SWC much more than sum of basal area did. This result suggested that SWC, the key factor determined the spatial variation of Rs, cannot be only explained by stems distribution and their characteristics, but also canopy architecture in the forest ecosystem.

How to cite: Cai, Y., Nishimura, T., Ida, H., and Hirota, M.: Spatial variation in CO2 efflux from the soil in a mature beech forest ecosystem., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-789, https://doi.org/10.5194/egusphere-egu21-789, 2021.

09:16–09:18
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EGU21-2530
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ECS
Anna Walkiewicz, Piotr Bulak, Mohammad Ibrahim Khalil, Bart Kruijt, Pia Gottschalk, Katja Klumpp, and Bruce Osborne

Forests play a key role in the global carbon (C) balance. On the one hand, a large amount of C is sequestered in soils, and on the other hand, the forest soils are also a significant source of carbon dioxide (CO2). Soil respiration includes anaerobic and aerobic microbial respiration, and root respiration which may contribute even more that half of the total soil respiration. Assessment of the contribution of forest soils to CO2 emissions, in addition to C sequestration, is worth special attention in the context of increasing climate change. To address this field experiments were carried out to assess the CO2 fluxes of 10 different forest soil types with different tree species (deciduous, coniferous, and mixed) in Poland (using static chamber method). The highest CO2 emissions were observed for a silty soil under the youngest deciduous forest (12 y.) with a  daily average of 1.66 ± 0.7 g CO2 m-2 d-1. The lowest daily mean CO2 flux was associated with a sandy soil in a mature stand of a predominantly coniferous forest (0.87 ± 0.3 g CO2 m-2 d-1). Annual averages were in the range 3.21 t C ha-1 to 6.06 t C ha-1 for a mature and young forest, respectively. The main factor causing differences in CO2 emissions could have been the contribution of both trees and soil properties to hydrological conditions. The young forest was covered with trees with a lower root system forest and the young trees could have a lower demand for water resulting in a higher soil moisture content than in a mature forest soil. Different CO2 fluxes could be also a result of a higher water storage capacity in silty soil in the young forest than that of a sandy soil under mature stand. In addition to water supply, the activity of soil microorganisms is also regulated by C availability which was about 30% lower in sandy soil than in silty soil. The two-yearly measurements showed seasonal variations in CO2 fluxes depending on the soil type, age and tree species. Regardless of the characteristics of the forest being studied, the highest CO2 emissions occurred in the summer or spring and the lowest CO2 emissions were found  in winter as a result of a strong influence of temperature on the biological processes under investigation. The observed seasonality in CO2 emission may be attributed to changes in soil moisture during the measurement periods since soil water content regulates microbial activity and gaseous diffusion. Statistical analyses, however, imply that temperature could have  a stronger control over CO2 emissions from the soils studied than soil moisture.

Research was conducted under the project financed by Polish National Centre for Research and Development within of ERA-NET CO-FUND ERA-GAS Programme (ERA-GAS/I/GHG-MANAGE/01/2018) “GHG-Manage”.

How to cite: Walkiewicz, A., Bulak, P., Khalil, M. I., Kruijt, B., Gottschalk, P., Klumpp, K., and Osborne, B.: Variability in soil CO2 fluxes across a range of forest types and edaphic conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2530, https://doi.org/10.5194/egusphere-egu21-2530, 2021.

09:18–09:20
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EGU21-12366
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ECS
Carmen Telser, Eliza Harris, David Reinthaler, and Michael Bahn

Climate change is expected to lead to an increase in frequency and severity of extreme climatic events like summer drought. Drought and rewetting have strong impacts on soil respiration, which constitutes the largest flux of CO2 from terrestrial ecosystems to the atmosphere. However, little is known about the role of biotic and abiotic factors in driving CO2 production and transport across the soil profile and how these processes are affected by repeated drought events. Soil CO2 transport can be assessed using the flux-gradient approach, a method which assumes that diffusion is the only transport mechanism for CO2 through soil, with diffusion rates primarily dependent on air-filled pore space. It is therefore generally assumed that the calculated soil CO2 concentration gradient translates directly into soil CO2 efflux, however, a discrepancy between measured soil CO2 efflux and modeled soil CO2 concentration gradients can indicate presence of non-diffusive transport mechanisms.

In a multiyear drought and rewetting experiment at a mountain meadow in the Austrian Alps, we compared soil CO2 production, transport and efflux for plots which were exposed to two and twelve subsequent years of experimental summer drought, respectively, versus plots with ambient precipitation and soil moisture. We measured soil respiration using automated chambers and assessed the production and transport of CO2 using the flux-gradient approach on data obtained with solid-state sensors in three soil depths through the soil profile. We tested the hypothesis that drought-driven reduction in soil respiration will be more intense for the 12-year drought treatment, but the CO2 pulse induced by rewetting will be higher. We furthermore expected that non-diffusive transport mechanisms would play a crucial role during drought and would be more pronounced in the 12-year drought treatment compared to the 2-year drought treatment. Data analysis is currently in progress, the findings will be presented at the conference.

How to cite: Telser, C., Harris, E., Reinthaler, D., and Bahn, M.: Legacy effects of multiyear summer drought on soil CO2 production, transport and efflux in a sub-alpine grassland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12366, https://doi.org/10.5194/egusphere-egu21-12366, 2021.

Oxygen
09:20–09:22
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EGU21-8036
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ECS
Caitlin Hodges, Susan Brantley, and Jason Kaye

Soil CO2 and O2 are coupled in some processes (e.g. respiration) but uncoupled in others (e.g. mineral weathering), such that simultaneous measurement of these two gases can yield insight into an array of soil chemical reactions and biogeochemical processes. Because soil CO2 production and O2 consumption are tightly coupled when aerobic respiration and diffusion persist in the soil system, the deviations from that coupling can be interpreted to signify various biotic and abiotic reactions. Here, we used such measurements as a function of depth to understand mineral, hillslope, and seasonal controls on soil pCO2 relative to pO2 in three watersheds of different bedrock lithology. We made our measurements over a growing season in three neighboring humid, temperate watersheds underlain by three different sedimentary bedrocks – acidic shale, calcareous shale, and acidic sandstone. Across these three watersheds, we expected to observe different soil pCO2 vs. pO2 patterns. For example, in calcareous soils we anticipated to observe a greater signature of soil CO2 consumption through weathering reactions than in silicate-dominated systems. Additionally, based on prior work, we anticipated a strong metal oxidation signature in the acidic soils.

Our results point to the strong control of parent material on the deviation of soil pCO2 from the theoretical values for aerobic respiration and diffusion. In the two acidic parent materials we observed a signature of seasonal metal redox cycling, with metal oxidation in the early growing season as soils drain and reoxygenate, and metal reduction in the late growing season when warm moist soils drive soil respiration rates to higher than the diffusion rate of O2. On the other hand, in the calcareous watershed, soil pCO2 and pO2 measurements did not suggest a seasonal redox cycle and instead indicate a consistent deficit of CO2 relative to the O2 consumed through aerobic respiration. Corresponding measurements of porewater chemistry indicate that this deficit is not solely attributable to carbonate mineral weathering, but also from consistent dissolution and transport downslope of respired CO2. We calculate that the effects of these processes can impact soil CO2 efflux to the atmosphere by up to 35%. Such results challenge our understanding of the soil carbon cycle. Employing coupled pCO2 and pO2 measurements in other systems will deepen understanding of soil C fluxes by identifying where and when factors other than aerobic respiration and diffusion control C flux out of the soil.

 

How to cite: Hodges, C., Brantley, S., and Kaye, J.: Soil carbon dioxide and oxygen concentrations indicate mineralogy plays a key role in controlling soil pCO2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8036, https://doi.org/10.5194/egusphere-egu21-8036, 2021.

09:22–09:24
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EGU21-7442
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ECS
Valentin Gartiser, Verena Lang, and Martin Maier

Soils act as bioreactors for the production and consumption of different gases. CO2 is usually produced in soils due to the oxidation of organic material. Under aerobic conditions, this production is coupled to a consumption of O2 resulting in concentration profiles that increase with depth for CO2 and decrease for O2. Depending on the organic material present, the exchange of O2 and CO2 is approximately equimolar in well aerated soils. This can be deduced from vertical gradients of both gases which should reflect the ratio of their diffusion coefficient (Massmann 1998). The ratio between the CO2 and O2 flux is often called the respiratory coefficient. However, certain soil types or conditions may invoke anaerobe processes that may lead to a decoupling of CO2 production and O2 consumption. Such a decoupling can also result from oxidation of minerals or dissolution and relocation of carbonates.

Here we present long-term data of soil CO2 and O2 concentrations from forest sites in South West Germany. Gas samples were collected passively starting 1998 until now using permanently installed gas wells at different depths. The samples were then analysed using gas chromatography for CO2 and O2 (and additionally N2, Ar, N2O, CH4, and C2H4).

CO2 and O2 fluxes were calculated using the gradient approach (Maier et al 2020). At sites with well aerated soils, the observed CO2 and O2 fluxes followed a clear linear relationship, with high effluxes of CO2 corresponding to high influxes of O2. The exchange was furthermore approximately equimolar with the calculated fluxes following a -1:1 trend.

We will compare these data from well aerated soils to concentration data of CO2 and O2 from less well-aerated soils with temporally suboxic conditions to further analyse the respiratory coefficient under oxygen limited conditions. Furthermore, diffusion-coefficient-normalised gradients are calculated to obtain information about the stoichiometry of the production and consumption patterns involved.

 

Literature:

Maier M, Gartiser V, Schengel A, Lang V. Long Term Soil Gas Monitoring as Tool to Understand Soil Processes. Applied Sciences. 2020; 10(23):8653.

Massman, W J. A review of the molecular diffusivities of H2O, CO2, CH4, CO, O3, SO2, NH3, N2O, NO, and NO2 in air, O2 and N2 near STP. Atmospheric Environment 1998; 32(6), 1111–1127

 

How to cite: Gartiser, V., Lang, V., and Maier, M.: Analysing the relationship of CO2 and O2 concentrations and flux patterns in forest soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7442, https://doi.org/10.5194/egusphere-egu21-7442, 2021.

09:24–09:26
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EGU21-9996
Moshe Shenker and David Yalin

Soil oxygen has been recognized as a potential limiting factor in plant production second only to water and nutrients. While it is widely accepted that soil gaseous oxygen levels below 10% V/V are detrimental to plant production, there are currently no accepted indices to quantify the effect of different agricultural practices on soil oxygen supply and availability. To address this challenge, a new approach is introduced, whereby indices describing the soil oxygen dynamics are determined using data from continuous in-situ soil oxygen measurements. To give the measurements a mechanistic interpretation, we developed a conceptual model describing the soil oxygen dynamics as a simplified mass balance between oxygen supply rate and oxygen consumption rate. The approach was applied to analyze field measurements of soil oxygen and water tension at 35 cm depth in avocado orchards irrigated with either Fresh Water (FW) or Treated Wastewater (TWW) in clay soil (~60% clay). The reliability of the method was shown, as soil respiration rates equivalent to 1-2 g O2m-2 d-1 were established, in line with previous reports for evergreen trees. The model defines the soil water tension at which oxygen supply to the measurement depth after irrigation surpasses the oxygen consumption rate as the critical soil water tension, and a value of ~50 mbar was established for the experiment site, again within the range described in the literature for soils with similar properties using other methodologies. Using the new approach, it was established that more hypoxic conditions occur in TWW irrigated plots as compared to FW irrigated plots due to a difference in the time required to reach the critical soil water tension – TWW irrigated plots took nearly 50% longer to reach a soil water tension of 50 mbar after each irrigation in the height of the irrigation season. This delay in TWW irrigated plots was directly related to the soil drying rate, which was lower in the TWW irrigated soils in both night and day periods, indicating both a hindering of drainage and of plant water uptake. In a second study site, the values describing the soil oxygen dynamics were found to relate to the soil stone content (particles>2mm), a known effector of soil aeration. By utilizing in-situmeasurements, the method aims to represent the intricate interrelations occurring in the field which may be missed using methods focusing on the individual factors affecting soil oxygen. The insights gained can provide the basis for designing management techniques to resolve unfavorable low oxygen levels in agriculture, as well as in natural environments where hypoxia affects soil carbon turnover, the evolution of greenhouse-gasses, and the fate of toxic elements in soils.

How to cite: Shenker, M. and Yalin, D.:  Analysis of soil oxygen dynamics as a diagnostic tool of the soil oxygen status in-situ, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9996, https://doi.org/10.5194/egusphere-egu21-9996, 2021.

Nitrogen dioxide & Nitrogen
09:26–09:28
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EGU21-1948
Ryosuke Kitamura, Chiho Sugiyama, Kaho Yasuda, Arata Nagatake, Yiran Yuan, Jing Du, Norikazu Yamaki, Katsuro Taira, Masahito Kawai, and Ryusuke Hatano

Appropriate application of organic fertilizer is required to reduce environmental impact from grassland and to achieve sustainable livestock production. However, N2O fluxes from soil increase mainly due to changes in soil environmental factors such as temperature, moisture, soil pH and soil mineral nitrogen content, immediately just after fertilization, and it may be different among the types of fertilizer. In this study, we investigated that how N2O fluxes are influenced by the application of three types of organic fertilizer (manure, slurry, and digestive fluid) for 4 years in a grassland on Andosol in southern Hokkaido, Japan. Five treatment plots: no fertilizer, chemical fertilizer, manure, slurry, and digestive fluid were established in a managed grassland in Shizunai Livestock farm, Hokkaido University. Fertilizers were applied in late April every year from 2017 to 2020. Organic fertilizers were applied such that the NPK not exceed the regional recommendation rate, and the shortage was compensated by chemical fertilizer. N2O flux was measured by using a closed chamber method. At the same time of the flux measurements, soil temperature at 5 cm soil, and soil moisture (WFPS), soil pH, NO3-N contents in 0-5 cm soil were measured to see the relationship with N2O fluxes.

In 2017, a large peak of N2O flux was observed in slurry plot (195.8μg m-2h-1) and digestive fluid plot (347.8 μg m-2h-1), whereas in 2018 and 2019, there were no large peak after the fertilization at all plots, however, in 2020, a large peak of N2O flux was observed in manure plot (472.7 and 475.7μg m-2h-1) and slurry plot (194.9μg m-2h-1). These peaks of N2O flux were significantly larger than those in no fertilizer and chemical fertilizer plots. All N2O flux peaks were observed when the soil temperature ranged 10-14 ℃. In 2017 and 2020, a large peak of N2O flux was observed although WFPS was always above 80% which is the soil moisture level leading to the complete denitrification. There was a negative relationship between N2O flux and soil pH. Low soil pH might reduce the N2O reductase activity, leading to the large peak of N2O flux at high WFPS above 80%. In addition, there was a positive relationship between N2O flux and soil NO3--N contentin 2017 and 2020. However, in 2018 and 2019, when WFPS was below 80% in most days, there was no positive relationship between N2O flux and soil NO3--N content. In conclusion, the peak of N2O flux was different depending on the year and fertilizer, In order to reduce N2O flux just after fertilization, it is especially important not to lower the soil pH and not to increase the WFPS.

 

How to cite: Kitamura, R., Sugiyama, C., Yasuda, K., Nagatake, A., Yuan, Y., Du, J., Yamaki, N., Taira, K., Kawai, M., and Hatano, R.: Influence of soil environmental factors on N2O fluxes just after application of three types of organic fertilizers - 4 years study in a grassland on Andosol in southern Hokkaido, Japan , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1948, https://doi.org/10.5194/egusphere-egu21-1948, 2021.

09:28–09:30
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EGU21-13220
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ECS
Kate Kuntu-Blankson, Johan Six, Lena Barczyk, Christof Ammann, and Pierluigi Calanca

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) with a global warming potential about 300 times that of carbon dioxide (CO2). In Switzerland, N2O emissions contribute to about 6% of the total GHG emissions, agriculture being responsible for more than 60% of the former. Understanding the processes driving N2O emissions from agricultural land is therefore of paramount importance for developing national GHG emissions inventories. Of relevance in this respect is the fact that about two-thirds of the agricultural lands are grasslands, part of which are managed as pastures.

Urine deposited by grazing animals has high N loads and induce increased nitrification and denitrification. Urine patches are hence hotspots for N2O emissions. In the IPCC Tier 1 method still in use in Switzerland for quantifying N2O emissions, a default EF3 value of 2% is assumed for excreta (dung and urine). This does not properly account for the spatial heterogeneity of N returns from grazing animals. Recent studies have indeed shown that country-specific EF3 are typically much lower than the default IPCC value. These results suggest that the use of IPCC Tier 2 and Tier 3 methods, that rely on the application of process-based models, is to be preferred for estimating countrywide N2O emissions.

In this work, we will apply the comprehensive process-based model ecosys to simulate N2O emissions from urine patches in a Swiss grazing system. We report on preliminary results from experiments aiming at modelling artificially applied urine patches. After showing that the model is able to reproduce the emission rates measured in a companion field trial, we use ecosys to examine N fractions lost to direct (N2O emissions) and indirect (ammonia volatilization, nitrate leaching and runoff) pathways for urine-N input rates varying from 500-2000 kg N ha-1. We also apply the model to understand the effects of seasonal variations in the environmental drivers on N2O EF. This work is part of a PhD conducted by the first author that aims at developing the scientific basis for establishing country-specific EFs for grazing-related N2O emissions in Switzerland.

How to cite: Kuntu-Blankson, K., Six, J., Barczyk, L., Ammann, C., and Calanca, P.: Process-based model estimation of N2O Emission factors for urine patches in a Swiss grazing system , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13220, https://doi.org/10.5194/egusphere-egu21-13220, 2021.

09:30–09:32
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EGU21-7835
Reinhard Well, Dominika Lewicka-Szczebak, Martin Maier, and Amanda Matson

Common field methods for measuring soil denitrification in situ include monitoring the accumulation of 15N labelled N2 and N2O evolved from 15N labelled soil nitrate pool in soil surface chambers. Bias of denitrification rates derived from chamber measurements results from subsoil diffusion of 15N labelled denitrification products, but this can be corrected by diffusion modeling (Well et al., 2019). Moreover, precision of the conventional 15N gas flux method is low due to the high N2 background of the atmosphere. An alternative to the closed chamber method is to use concentration gradients of soil gas to quantify their fluxes (Maier &  Schack-Kirchner, 2014). Advantages compared to the closed  chamber method include the facts that (i) time consuming work with closed chambers is replaced by easier sampling of soil gas probes, (ii) depth profiles yield not only the surface flux but also information on the depth distribution of gas production and (iii) soil gas concentrations are higher than chamber gas concentration, resulting in better detectability of 15N-labelled denitrification products. Here we use this approach for the first time to evaluate denitrification rates derived from depth profiles of 15N labelled N2 and N2O in the field by closed chamber measurements published previously (Lewicka-Szczebak et al., 2020).

We compared surface fluxes of N2 and N2O from 15N labelled microplots using the closed chamber method. Diffusion–based soil gas probes (Schack-Kirchner et al., 1993) were used to sample soil air at the end of each closed chamber measurement. A diffusion-reaction model (Maier et al., 2017) will be  used to fit measured and modelled concentrations of 15N labelled N2 and N2O. Depth-specific values of denitrification rates and the denitrification product ratio will be obtained from best fits of depth profiles and chamber accumulation, taking into account diffusion of labelled denitrification products to the subsoil (Well et al., 2019).

Depending on the outcome of this evaluation, the gradient method could be used for continuous monitoring of denitrification in the field based on soil gas probe sampling. This could replace or enhance current approaches by improving the detection limit, facilitating sampling and delivering information on depth-specific denitrification.  

References:

Lewicka-Szczebak D, Lewicki MP, Well R (2020) N2O isotope approaches for source partitioning of N2O production and estimation of N2O reduction – validation with the 15N gas-flux method in laboratory and field studies. Biogeosciences, 17, 5513-5537.

Maier M, Longdoz B, Laemmel T, Schack-Kirchner H, Lang F (2017) 2D profiles of CO2, CH4, N2O and gas diffusivity in a well aerated soil: measurement and Finite Element Modeling. Agricultural and Forest Meteorology, 247, 21-33.

Maier M, Schack-Kirchner H (2014) Using the gradient method to determine soil gas flux: A review. Agricultural and Forest Meteorology, 192, 78-95.

Schack-Kirchner H, Hildebrand EE, Wilpert KV (1993) Ein konvektionsfreies Sammelsystem für Bodenluft. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde, 156, 307-310.

Well R, Maier M, Lewicka-Szczebak D, Koster JR, Ruoss N (2019) Underestimation of denitrification rates from field application of the N-15 gas flux method and its correction by gas diffusion modelling. Biogeosciences, 16, 2233-2246.

 

 

How to cite: Well, R., Lewicka-Szczebak, D., Maier, M., and Matson, A.: Quantifying soil denitrification in situ from depth profiles of 15N labelled denitrification products by diffusion-reaction modelling , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7835, https://doi.org/10.5194/egusphere-egu21-7835, 2021.

09:32–09:34
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EGU21-1415
Joseph Tamale, Roman Hüppi, Marco Griepentrog, Laban Frank Turyagyenda, Matti Barthel, Sebastian Doetterl, Peter Fiener, and Oliver van Straaten

The exchange of the climate-relevant greenhouse gases (GHGs) at the soil-atmospheric interface is regulated by both abiotic and biotic controls. However, evidence on nutrient limitations of soil GHG fluxes from African tropical forest ecosystems is still rare. Therefore, an ecosystem-scale nutrient manipulation experiment (NME) consisting of nitrogen (N), phosphorus (P), N + P, and control treatments was set up in a tropical forest in northwestern Uganda. Soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were measured monthly using static vented chambers for 14 months. A root trenching treatment was also done in all the experimental plots in order to disentangle the contribution of root and microbial respiration to total soil CO2 effluxes. In parallel to soil GHG flux measurements, soil temperature, soil moisture, and mineral N were determined. Lifting the N limitation on the soil nitrifiers and denitrifiers through N fertilization significantly increased N2O fluxes in N, and N + P addition plots in the transitory phase (0-28 days after N fertilization, p < 0.01). However, sustained N fertilization did not significantly affect background (measured more than 28 days after fertilization) N2O fluxes. Alleviation of the P limitation on soil methanotrophs through P fertilization marginally and significantly increased CH4 consumption in the transitory (p = 0.052) and background (p = 0.010) phases, respectively. Simultaneous addition of N and P (N + P) significantly affected transitory soil CO2 effluxes (p = 0.010), suggesting a possible co-limitation of N and P on soil respiration. Microbial CO2 effluxes were significantly larger than root CO2 effluxes (p < 0.001) across all treatment plots so was the contribution of microbial respiration to the total soil CO2 effluxes (about 70 %, p < 0.001). Despite the fact that soil respiration was affected through N + P fertilization, neither heterotrophic nor autotrophic respiration significantly differed in either the N + P or the other treatments. Overall, the study findings suggest that the contribution of tropical forests to the global soil GHG budget could be altered by changes in N and P availability in these biomes.

Key words: Soil greenhouse gas fluxes, nutrient manipulation experiment, soil nutrient limitation, and Ugandan tropical pristine forest.

How to cite: Tamale, J., Hüppi, R., Griepentrog, M., Turyagyenda, L. F., Barthel, M., Doetterl, S., Fiener, P., and van Straaten, O.: Evaluating the role soil nutrients play in regulating soil greenhouse gas fluxes from the pristine tropical forests: evidence from a nutrient manipulation experiment in Uganda, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1415, https://doi.org/10.5194/egusphere-egu21-1415, 2021.

Methods & Materials
09:34–09:36
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EGU21-16474
Shahar Baram, Asher Bar-Tal, Alon Gal, and David Russo

Static chambers are frequently used to evaluate greenhouse gas (GHG) emissions from agro-systems. However, the effects of such chambers on water and nutrient distribution within and under the chamber’s base (i.e., anchor) in drip irrigation and its effects on GHG emissions is not well understood. This study aimed to shed some light on the topic by using field measurements and physically based, three-dimensional (3-D) simulations of flow transport and nitrogen transformations in variably saturated, spatially heterogeneous flow domain. GHG fluxes [methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O)] were measured in the field for two years using a portable FTIR gas analyzer. The main findings of this study suggest that: (i) the chamber’s base modifies the water and nutrient distribution within it. Placement of the dripper inside the base leads to higher water contents, higher nitrate and ammonium concentrations, and higher N2O fluxes relative to an undisturbed area. In contrast, placement of the dripper outside the chamber base reduces all of these parameters, including the N2O fluxes, relative to an undisturbed area. (ii) The dripper’s location relative to the chamber’s base had minor to no effect on CO2 fluxes. The effect on the CH4 fluxes was not conclusive, yet suggested higher emissions when the dripper was located inside the base. (iii) A minimal disturbance is achieved when the dripper is located within a base, and the base’s radius equals the capillary length of the soil.

How to cite: Baram, S., Bar-Tal, A., Gal, A., and Russo, D.: The use of static chambers in drip irrigation: what should be considered?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16474, https://doi.org/10.5194/egusphere-egu21-16474, 2021.

09:36–09:38
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EGU21-1256
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ECS
Mathias Hoffmann, Shrijana Vaidya, Marten Schmidt, Norbert Bonk, Peter Rakowski, Gernot Verch, Michael Sommer, and Jürgen Augustin

Improved agricultural practices sequestering additional atmospheric C within the soil are considered as one of the potential solution for mitigating global climate change. However, agricultural used landscapes are complex and their capacity to sequester additional atmospheric C differs substantially in time and space. Hence, accurate and precise information on the complex spatio-temporal CO2 flux pattern is needed to evaluate the effects/benefits of new agricultural practices aiming towards increasing soil organic carbon.

To date, different approaches are used to measure and quantify CO2 flux dynamics of agricultural landscapes, such as e.g. eddy covariance, as well as manual and automatic chamber systems. However, all these methods fail to some extend in either accounting for small scale spatial heterogeneity (e.g., eddy covariance and automatic chambers) or short-term temporal variability (e.g., manual chambers). Although, automatic chambers are in principle capable to detect small-scale spatial differences of CO2 flux dynamics in a sufficient temporal resolution, these systems are usually limited to only a few spatial repetitions which is not sufficient to represent small scale soil heterogeneity such as present within the widespread hummocky ground moraine landscape of NE-Germany.

To overcome these challenges, we developed a novel robotic chamber system. This system was used to detect small-scale spatial heterogeneity and short-term temporal variability of CO2 flux dynamics in a full factorial experimental setup for a range of three different soil types, two N fertilization forms (2; mineral vs. organic) and two soil manipulation status, representing two different tillage practices. Here, we present measured CO2 flux dynamics and cumulative emissions for the 3 repetitions of the 12 randomized treatments (36 subplots) directly following soil manipulation and N fertilization during summer 2020. Our results show distinct differences between the three measured soil types as well as a clear response of all three soil types to conducted soil manipulation, yielding in significantly lower ecosystem respiration (Reco) and net ecosystem exchange (NEE) for manipulated vs. non-manipulated subplots. No clear difference, however, was obtained in case of N fertilization.

How to cite: Hoffmann, M., Vaidya, S., Schmidt, M., Bonk, N., Rakowski, P., Verch, G., Sommer, M., and Augustin, J.: Using an advanced robotic chamber system to detect spatio-temporal short-term responses in measured CO2 exchange to soil manipulation and N fertilization, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1256, https://doi.org/10.5194/egusphere-egu21-1256, 2021.

09:38–09:40
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EGU21-4222
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ECS
Isidoro Gutiérrez Álvarez, José Luis Guerrero, José Enrique Martín, José Antonio Adame, and Juan Pedro Bolívar

A common method to measure radon exhalation rates relies on the accumulation chamber technique. Usually, this approach only considers one-dimensional gas transport within the soil that neglects lateral diffusion. However, this lateral transport could reduce the reliability of the method. In this work, several cylindrical- shaped accumulation chambers were built with different heights to test if the insertion depth of the chamber into the soil improves the reliability of the method and, in that case, if it could limit the radon lateral diffusion effects. To check this hypothesis in laboratory, two reference exhalation boxes were manufactured using phospho- gypsum from a repository located nearby the city of Huelva, in the southwest of Spain. Laboratory experiments showed that insertion depth had a deep impact in reducing the effective decay constant of the system, extending the interval where the linear fitting can be applied, and consistently obtaining reliable exhalation measurements once a minimum insertion depth is employed. Field experiments carried out in the phosphogypsum repository showed that increasing the insertion depth could reduce the influence of external effects, increasing the re- peatability of the method. These experiments provided a method to obtain consistent radon exhalation mea- surements over the phosphogypsum repository.

How to cite: Gutiérrez Álvarez, I., Guerrero, J. L., Martín, J. E., Adame, J. A., and Bolívar, J. P.: Influence of the accumulation chamber insertion depth to measure surface radon exhalation rates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4222, https://doi.org/10.5194/egusphere-egu21-4222, 2021.

Methane & VOC´s
09:40–09:42
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EGU21-3912
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ECS
Hiyori Namie, kasane Shimada, Shuang shuang Zhao, Munehide Ishiguro, and Ryusuke Hatanano

 Generally, during the paddy rice cultivation period, CH4 produced in the soil is reported to be released to the atmosphere through three pathways: diffusion (<1%), bubbles (<10%), and via rice (> 90%). However, there are few studies have measured gas diffusion coefficient for soil below surface of the water, and there is no study has provided an accurate understanding of CH4 dynamics in paddy fields. Furthermore, there are few studies that understanding the CH4 dynamics in fertilizer-free and pesticide-free paddy fields, which is mainly controlled by inter-tillage practices. Therefore, this study aimed to clarify the effects of tillage and the number of inter-tillage and the presence or absence of fertilizer and pesticide on the CH4 dynamics in rice paddy soil. This study compared three types of CH4 flux, which were total CH4 flux from rice paddy field measured by transparent chamber with plants, and soil derived CH4 flux measured by dark chamber without plants, and gas diffusion flux calculated as a product of the gas diffusion coefficient and measured soil gas concentration gradient at the depths of 0-5 and 5-10cm. And they were compared with in the five rice cultivation periods (flooding, mid-drying, intermittent irrigation, drainage, and fallowing) and in the four treatment plots (conventional farming (CF), and fertilizer- and pesticide-free farming with zero-inter-tillage(T0), two-inter-tillage(T2), and five-inter-tillage (T5)). The CF was conducted according to the regional recommendation for tillage, fertilization and pest and weed control. The results showed that the peak of total CH4 flux was observed in the mid-drying and intermittent irrigation periods in all treatments, and that the CH4 flux via rice plant accounted for 60-90% of the total CH4 flux. The CF showed significantly highest CH4 emission during the periods, and the increase of the number of inter-tillage tended to increase the CH4 emission. In the drainage period, the CH4 flux by bubbles in the CF and T5 accounted for more than 80% of the total CH4 flux. In the fallowing period, the diffusion CH4 flux at the depth of 5-10cm increased in all treatments, but the low total CH4 emission and increased CO2 emission. This study revealed that incorporation of organic matter into soil in conventional rice farming tended to increase CH4 emission. The main pathway of CH4 emission from rice paddy field was via rice, and it was influenced by tillage significantly. The decomposition of organic matter from rice straw and weeds incorporated into soil was the source of the bubble of CH4. Furthermore, it seemed that the most of diffusively transferred CH4 was easily oxidized to CO2.

How to cite: Namie, H., Shimada, K., Zhao, S. S., Ishiguro, M., and Hatanano, R.: Influence of tillage practice on major pathways of CH4 emission in rice paddy field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3912, https://doi.org/10.5194/egusphere-egu21-3912, 2021.

09:42–09:44
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EGU21-9088
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ECS
Qiong Liu, Marco Romani, Jiajia Wang, Britta Planer-Friedrich, Johanna Pausch, and Maxim Dorodnikov

Alternate wet-drying (AWD) and sulfate fertilization have been considered as effective management practices for lowering CH4 emissions from paddy soils. However, the effects of management practices on in situ belowground CH4 turnover (production and oxidation) are not yet fully understood. Here, soil CO2 and CH4 concentrations and their C isotope compositions were measured at three rice growing stages in straw-amended paddy soils with and without sulfate fertilization under continuously flooded conditions and two wet-dry-cycles. CH4 concentration reached 51.0 mg C L-1 at flowering stage under flooded conditions, while it decreased to 0.04 mg C L-1 under AWD. Relative enrichment of δ13C in CH4 and depletion of δ13C in CO2 under AWD indicated CH4 oxidation. Sulfate addition had no significant effect on CH4 concentration. The ample substrate supply might have prevented sulfate-reducing bacteria from out-competing methanogenic archaea and could therefore explain the absence of a fall in CH4 production. The δ13C-CO2 enrichment over time (7 ‰ and 5‰ with and without sulfate fertilizer, respectively) under flooded conditions likely indicates an increasing contribution of hydrogenotrophic methanogenesis to CH4 production with ongoing rice growth. Overall, the results showed that AWD could more efficiently reduce CH4 production than sulfate fertilization in rice-straw-amended paddy soils.

 

How to cite: Liu, Q., Romani, M., Wang, J., Planer-Friedrich, B., Pausch, J., and Dorodnikov, M.: Alternating wet-dry cycles rather than sulfate fertilization control pathways of methanogenesis and methane turnover in rice straw-amended paddy soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9088, https://doi.org/10.5194/egusphere-egu21-9088, 2021.

09:44–09:46
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EGU21-15077
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ECS
Giovanni Pugliese, Johannes Ingrisch, Thomas Klüpfel, Kathiravan Meeran, Gemma Purser, Juliana Gil Loaiza, Joost van Haren, Jürgen Kreuzwieser, Nemiah Ladd, Laura Meredith, Christiane Werner, and Jonathan Williams

Volatile organic compounds (VOC) play an important role in determining atmospheric processes that control air quality and climate. Although atmospheric VOC concentrations are mostly affected by plants, soils are significant contributors as they are simultaneously a source, a sink and a storage of atmospheric VOCs. The aim of the present study was to assess the effects of a prolonged drought condition on VOC soil fluxes in the tropical rainforest mesocosm of Biosphere 2 (B2; Tucson, Arizona, USA). The absence of atmospheric chemistry due to UV light filtering by the glass and the possibility to control and manipulate the conditions of the ecosystem make the B2 an ideal set-up to study the rainforest VOC dynamics.

The experiments were conducted over the 4 months B2WALD campaign during which the rainforest was subjected to a controlled drought period of about 10 weeks followed by a rewetting period. Soil VOCs fluxes were measured continuously by means of a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) that was connected to 12 automated soil chambers (LI 8100-104 Long-Term Chambers, Licor Inc.) placed in 4 different locations within the B2 rainforest.

The B2 rainforest soil acted as a strong sink for all isoprenoid species. The isoprene sink steadily weakened during drought period, but increased sharply back to the pre-drought levels after the rain rewet. In contrast, the monoterpene soil sink became slightly stronger during the mild drought period (up to 5 weeks after the last rainfall) but weakened during the severe drought period (up to 10 weeks after rainfall). A huge increase in monoterpene uptake was observed after the rain rewet. The oxidation products of isoprene (methacrolein, methyl vinyl ketone and isoprene peroxides) showed a similar trend to the monoterpenes, even in absence of atmospheric chemistry. The species with molecular formula C5H8O was taken up by the soil during predrought, which was reduced during mild drought period but increased again during the severe drought period.Sulfur-containing compounds including DMS and methanethiol all showed a significant emission peak immediately after the rain rewet.Oxygenated VOCs such as methanol and acetone were taken up by the soil in wet conditions. The uptake of both compounds strongly decreased with the drought and in severe drought conditions they were even emitted by the soil.

In summary, soil VOC fluxes changed markedly with the onset and development drought stages (pre, mild and severe drought) of the B2 rainforest, mirroring atmospheric VOC concentrations and soil microbial activity changes related to overall ecosystem response to drought and recovery.

How to cite: Pugliese, G., Ingrisch, J., Klüpfel, T., Meeran, K., Purser, G., Gil Loaiza, J., van Haren, J., Kreuzwieser, J., Ladd, N., Meredith, L., Werner, C., and Williams, J.: Effects of drought conditions on VOC soil fluxes within the rainforest mesocosm of Biosphere 2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15077, https://doi.org/10.5194/egusphere-egu21-15077, 2021.

Gas transport
09:46–09:48
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EGU21-9313
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ECS
Asma Parlin, Noriaki Watanabe, Mizuki Yamada, Kengo Nakamura, and Takeshi Komai

Investigation of the transport behaviors of volatile organic compounds (VOCs) in contaminated soils has previously been conducted in various environments. Accordingly, the present study focuses on specific phenomena in the near-surface soil environment where dynamic temperature affects the diffusive flux of VOC vapor phase as previous studies have suggested that temperature variations significantly influence such transport behaviors near-surface soils, but the nature of those influences and their mechanisms have remained unclear because of unexpected correlation of flux with the temperature that impacts on VOC vapor transport. More specifically, current practices report on a set of experiments into the vertical and upward vapor phase diffusive transport of benzene and trichloroethylene (TCE) in sandy soils that were conducted in soil column with water content conditions of up to 10 wt% and sinusoidal temperature conditions ranging from 20 to 30°C. This studies experimentally investigated that in all conditions tested, the top (outlet) flux change correlated positively with temperature change, while the bottom (inlet) flux change showed negative correlations. These results are consistent with previous observations showing that, at relatively deeper locations, there is little correlation between near-surface vertical VOC flux and soil temperature levels, and that VOC concentrations can be independent of the soil temperature at those locations. The present study's results highlighted for the first time that the negative correlation impact of temperature on VOC transport may occur frequently at deeper locations of subsurface soil. This occurs because the VOC concentration gradient is reduced by VOC desorption and the evaporation of water containing VOCs that accompany increasing temperature levels. However, our results also show that such mechanisms have a positive impact on VOC emissions from the upper part of subsurface soils to the atmosphere that can act as a low concertation boundary.

How to cite: Parlin, A., Watanabe, N., Yamada, M., Nakamura, K., and Komai, T.: Dynamic temperature effects on diffusive transport behaviors of VOC vapors in unsaturated soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9313, https://doi.org/10.5194/egusphere-egu21-9313, 2021.

09:48–09:50
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EGU21-13442
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ECS
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Highlight
Taryn Thompson, Ryan Stewart, Daniel McLaughlin, and Madeline Schreiber

Gas diffusion is a primary driver of carbon dioxide (CO2) movement through unsaturated soils. In typical soils, high soil concentrations of CO2 caused by autotrophic and heterotrophic respiration cause the gas to primarily diffuse upward. However, karst landscapes can have subsurface CO2 sinks, both due to CaCO3 weathering and losses via underlying caves and fracture networks. In this study our objective was to quantify the magnitude and direction of CO2 fluxes in a pastured karst system located in Southwest Virginia (James Cave). Our hypotheses were: 1) the zero-flux plane, or location of maximum CO2 concentration within the soil profile, is located at deeper depths, ≥60 cm depth during warmer months of the year and located at shallower depths, ≤60 cm, during the colder months of the year, 2) the zero-flux plane will exist ˂60 cm depth at the sinkhole location more often than at the upslope locations, and 3) CO2 fluxes will be primarily upward during the growing season and primarily downward during the colder months of the year. We installed paired CO2 and soil moisture sensors at 20 cm, 40 cm, and 60 cm depths, with profiles installed in the shoulder, midslope, and bottom (i.e., sinkhole) of a hillslope adjacent to the cave entrance. The sensors recorded hourly data between 7 February 2017 and 13 September 2019. The depth of the zero-flux plane was identified by the depth of maximum CO2 concentration for each profile, while the measured concentration gradient from 20 to 60 cm was used to estimate CO2 flux with Fick’s Law. Our findings support our hypotheses that the relative location of the zero-flux plane was located more often at deeper depths during warmer months of the year and located at shallower depths, i.e. ˂60 cm, during colder months of the year. The zero-flux plane was more frequently shallow (i.e., ˂60 cm) at the sinkhole location compared to the upslope profiles. The CO2 fluxes reflected upward movement during the growing season and downward movement during the colder months of the year. We speculate that these processes reflect the influence of the underlying cave system, which may serve as a CO2 sink during colder months, when the cave becomes vented via natural convection. Altogether, these findings suggest that downward diffusion may be an important yet oft-overlooked component of carbon fluxes in karst landscapes.

How to cite: Thompson, T., Stewart, R., McLaughlin, D., and Schreiber, M.: Assessing magnitudes and directions of CO2 fluxes within a karst landscape, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13442, https://doi.org/10.5194/egusphere-egu21-13442, 2021.

09:50–09:52
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EGU21-6101
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ECS
Ana M. C. Ilie, Tissa H. Illangasekare, Kenichi Soga, and William R. Whalley

Understanding the soil-gas migration in unsaturated soil is important in a number of problems that include carbon loading to the atmosphere from the bio-geochemical activity and leakage of gases from subsurface sources from carbon storage unconventional energy development. The soil water dynamics in the vadose zone control the soil-gas pathway development and, hence, the gas flux's spatial and temporal distribution at the soil surface. The spatial distribution of soil-water content depends on soil water characteristics. The dynamics are controlled by the water flux at the land surface and water table fluctuations. Physical properties of soil give a better understanding of the soil gas dynamics and migration from greater soil depths. The fundamental process of soil gas migration under dynamic water content was investigated in the laboratory using an intermediate-scale test system under controlled conditions that is not possible in the field. The experiments focus on observing the methane gas migration in relation to the physical properties of soil and the soil moisture patterns. A 2D soil tank with dimensions of 60 cm × 90 cm × 5.6 cm (height × length × width) was used.  The tank was heterogeneously packed with sandy soil along with a distributed network of soil moisture, temperature, and electrical conductivity sensors. The heterogeneous soil configuration was designed using nine uniform silica sands with the effective sieve numbers #16, #70, #8, #40/50, #110, #30/40, #50, and #20/30 (Accusands, Unimin Corp., Ottawa, MN), and a porosity ranging in values from 0.31 to 0.42. Four methane infrared gas sensors and a Flame Ionization detector (HFR400 Fast FID) were used for the soil gas sampling at different depths within the soil profiles and at the land surface.  A complex transient soil moisture distribution and soil gas migration patterns were observed in the 2D tank. These processes were successfully captured by the sensors. These preliminary experiments helped us to understand the mechanism of soil moisture sensor response and methane gas migration into a heterogeneous sandy soil with a view to developing a large-scale test in a 3D tank (4.87 m × 2.44 m × 0.40 m) and finally transition to field deployment.

How to cite: Ilie, A. M. C., Illangasekare, T. H., Soga, K., and Whalley, W. R.: A laboratory study of the effect of soil-water dynamics on the migration of gases from subsurface sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6101, https://doi.org/10.5194/egusphere-egu21-6101, 2021.

09:52–10:30