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SSS8.3

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

Public information:

Dear authors & colleagues,

We are looking forward to welcoming you all to our session next week- virtually and in person .

We plan to have a session dinner after the session, which is also open to all praticipants and people interested in our topics

on Wednesday, May 25 2022  at 20h

at the Brandauers Bierbögen,

(where we have been already some years ago)

 

If possible, please let me know if you like to join us:

Martin.maier@forst.bwl.de

 

 

Best 

 

Martin Maier

 

Co-organized by AS4/BG3
Convener: Bernard Longdoz | Co-conveners: Martin Maier, Jukka Pumpanen, Anna WalkiewiczECSECS, Nicholas Nickerson
Presentations
| Wed, 25 May, 15:55–18:28 (CEST)
 
Room D3
Public information:

Dear authors & colleagues,

We are looking forward to welcoming you all to our session next week- virtually and in person .

We plan to have a session dinner after the session, which is also open to all praticipants and people interested in our topics

on Wednesday, May 25 2022  at 20h

at the Brandauers Bierbögen,

(where we have been already some years ago)

 

If possible, please let me know if you like to join us:

Martin.maier@forst.bwl.de

 

 

Best 

 

Martin Maier

 

Wed, 25 May, 15:10–16:40

Chairpersons: Bernard Longdoz, Martin Maier

15:55–16:05
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EGU22-2027
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ECS
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solicited
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Highlight
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On-site presentation
Clément Lopez-Canfin et al.

The process of water vapor adsorption (WVA) by soil (i.e. water vapor movement from atmosphere to soil, forming liquid water on soil particles) is likely a substantial contributor to the water cycle in drylands. However, several gaps remain in our knowledge of WVA: (1) continuous in situ estimates of WVA are still very scarce; (2) the underlying mechanisms involved in its temporal patterns are still not well constrained, and (3) the understanding of its coupling with the carbon cycle and ecosystem processes remains at an incipient stage.

Here, we aimed to (1) identify periods of WVA and improve the understanding of the underlying mechanisms involved in its temporal patterns by using the gradient method (GM); (2) characterize a potential coupling between water vapor and CO2 fluxes, especially expected in drylands due to the water-limitation of ecosystem processes. In particular, we assumed that the nocturnal soil CO2 uptake increasingly reported in those environments (including at our study site) could come from WVA enhancing reactions with CaCO3; (3) explore the effect of soil properties and biocrusts ecological succession on fluxes.

To this end, in the Tabernas Desert (Almería, Spain), we measured continuously during ca. 2 years the relative humidity and CO2 molar fraction in soil and atmosphere, in association with below- and aboveground variables, in microsites representative of the biocrusts ecological succession. We estimated water vapor and CO2 fluxes with the GM, and cumulative fluxes over the study. Then, we used linear and non-linear statistical modelling to explain relationships between variables.

Our main findings are (1) WVA during hot and dry periods, and a new insight into the micrometeorological conditions triggering those fluxes; (2) a diel coupling between water vapor and CO2 fluxes (including the uptake of both gases by soil at night) and between cumulative fluxes, well predicted by our models; and (3) cumulative CO2 influxes increasing with specific surface area in early succession stages, thus mitigating CO2 emissions. We suggest that the GM is a suitable approach to monitor WVA in-situ since it offers several advantages such as providing direct low-cost measurements of water vapor fluxes with good spatio-temporal resolution and low soil disturbance. Over a year, the WVA represented between ca. 0.2% and 2.8% of the precipitation amount, depending on the microsite and the diffusion model that was used to estimate the fluxes.

Therefore, WVA constituted a non-negligible input of liquid water in this dryland. In particular, during summer drought, as WVA was the main water source, it probably maintained ecosystem processes such as microbial activity and mineral reactions. We propose that the nocturnal CO2 uptake reported in this dryland may arise from (i) WVA enhancing geochemical reactions involving CaCO3 and/or biological dark CO2 fixation; (ii) the co-adsorption of CO2. Further research is now needed to (1) disentangle those processes; (2) monitor soil water vapor and CO2 uptake by soils as those sinks could grow with climate change; (3) improve the accuracy of the water vapor fluxes estimated with the GM, for example by calibrating the GM with lysimeters.

How to cite: Lopez-Canfin, C., Lázaro, R., and Sánchez-Cañete, E. P.: The water vapor adsorption by dry soils potentially links the water and carbon cycles: insight from a semiarid crusted ecosystem , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2027, https://doi.org/10.5194/egusphere-egu22-2027, 2022.

16:05–16:11
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EGU22-1332
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On-site presentation
Ute Karstens and Ingeborg Levin

Quantitative understanding of the processes governing radon production and transport in soils and its exhalation rate into the atmospheric boundary layer are essential if we want to use this radioactive noble gas to assess above- and below-ground transport processes. While production of radon in soils is mainly governed by static soil properties such as texture and uranium content, the dominant parameter modulating its exhalation rate is volumetric soil moisture. Here we present an improved process-based high-resolution radon flux map for Europe, using up-to-date soil property maps, including updated uranium activity concentration data from the European Atlas of Natural Radiation. Daily radon exhalation is calculated based on high-resolution soil moisture estimates from the ERA5 and the GLDAS Noah land surface models.  Depending on the soil moisture model used, estimated radon fluxes show differences as large as a factor of two, but modelled soil moisture and corresponding modelled radon fluxes also differ from observations. This highlights the importance of accurate representative soil moisture observations for model validation. Although the fluxes of biogeochemical reactive trace gases at the soil-atmosphere interface are also driven by other variable parameters, such as temperature or microbial activity, their net fluxes can often also be limited by effective diffusivity in the upper soil layers, and thus by soil moisture. Estimating variability and uncertainty of biogeochemical active trace gas fluxes such as methane or hydrogen on the regional or continental scale could therefore benefit from experience with the noble gas radon.

How to cite: Karstens, U. and Levin, I.: Parameterisation of radon diffusivity and exhalation rate from soils – limitations and its applicability to other trace gases, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1332, https://doi.org/10.5194/egusphere-egu22-1332, 2022.

16:11–16:17
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EGU22-8713
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On-site presentation
Martin Maier et al.

Gas transport in the soil is dominated by molecular diffusion in the air-filled pore network. A study in the 1970s could show that Radon emissions from soil increased during the passage of a low-pressure system which temporarily enhanced soil gas transport rates (Clements & Wilkening, 1974). Enhanced wind speed near the soil surface was also found to speed up gas transport rates in the soil (Kimball & Lemon, 1971). Further studies followed confirming the observations that wind and substantial atmospheric pressure changes have the potential to affect soil gas transport, including studies conducted in snow and firn, deserts, forest soil, arid systems, and soils near water saturation. Especially during recent years, wind and air- pressure-related effects on soil gas transport received increasing attention, with diverse concepts and methodologies, and also a wider ecological relevance.

While the slow (hours) and relatively large atmospheric pressure changes (up to 50 hPa) reported in Clements & Wilkening (1974) cause a kind of steady piston flow in the soil, the effect in Kimball & Lemon, (1971) was explained as the result of dynamic wind-induced pressure fluctuations, which are much smaller in amplitude (2-20 Pa) and occur at higher frequencies (0.1-1.0 Hz). Although the effect of wind-induced pressure fluctuations on gas transport in the soil has been confirmed by a few studies, there is still only little knowledge about the underlying processes. Additional effects between the pure “static piston flow “and the dynamic pressure fluctuations certainly occur. Different approaches and methodologies were used to derive estimates for the impact (if quantified) of air pressure fluctuations on soil gas transport, which makes inter-study comparisons complicated and limits further progress.

We overview relevant studies, their methods, concepts and explanations to identify research gaps and develop a plan for further research concepts.

Clements, W. E., & Wilkening, M. H. (1974). Atmospheric pressure effects on 222 Rn transport across the Earth-air interface. Journal of Geophysical Research, 79(33), 5025–5029. https://doi.org/10.1029/jc079i033p05025

Kimball, B., & Lemon, E. (1971). Air Turbulence Effects Upon Soil Gas Exchange. Soil Science Societyof America Journal 35(1), 16–21. https://doi.org/10.2136/sssaj1971.03615995003500010013x

 

How to cite: Maier, M., Osterholt, L., and Schindler, D.: Blowing in the wind: a review of wind and air- pressure-related effects on soil gas transport , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8713, https://doi.org/10.5194/egusphere-egu22-8713, 2022.

16:17–16:23
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EGU22-3975
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ECS
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Virtual presentation
Navid Ahmadi et al.

The reactive transport of gas components in the subsurface significantly influences key biogeochemical processes. For instance, reactive transport of oxygen in soil influences mineral dissolution/precipitation and control pore water chemistry. The dynamics of such processes is affected by land-atmosphere interactions and controlled by the exchange processes occurring at the soil/atmosphere interface. One notable example is soil water evaporation that is driven by the exchange of water vapor and energy across the soil/atmosphere interface. This process creates a two-phase system in soil pores and induces a non-linear and complex distribution of the fluid phases (i.e., liquid and gaseous phase) and gas components in the individual phases. The spatiotemporal evolution of the fluid phases and the transport of gas components with and across the phases, in turn, exert important controls on key subsurface biogeochemical processes.

In this study, we explore the impact of evaporation on reactive transport of oxygen in soil using well-controlled laboratory experiments and numerical simulations. We performed a set of evaporation experiments in which an initially water saturated, anoxic soil column containing a layer of pyrite is exposed to a low-humidity atmospheric condition. This resulted in the formation of a partially saturated zone, the invasion of a drying front, and the penetration of oxygen into the porous medium, leading to oxidative dissolution of pyrite. In parallel, we also performed similar experiments under fully water-saturated conditions in order to compare the extent of mineral dissolution with and without evaporation. The spatiotemporal distribution of oxygen was measured using a non-invasive optode technique during the experiments and the concentration of dissolved reaction products (i.e., sulfate, iron and pH) was quantified at the end of the experiments. We developed a non-isothermal multiphase and multicomponent reactive transport model and applied the model to quantitatively interpret the experimental datasets and to understand the coupling between fluid displacement, component transport and geochemical processes.

How to cite: Ahmadi, N., Muniruzzaman, M., Battistel, M., and Rolle, M.: Multicomponent transport and geochemical reactions under evaporative conditions at the soil/atmosphere interface, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3975, https://doi.org/10.5194/egusphere-egu22-3975, 2022.

16:23–16:29
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EGU22-10393
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ECS
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On-site presentation
Valentin Gartiser et al.

The flux-gradient method (FGM) is a versatile approach for modelling soil gas fluxes from concentration profiles. It is especially useful for continuous and long-term estimations of gas fluxes based on concentrations from permanently installed probes or sensors, focussing on relative changes and trends in time. However, there are inherent uncertainties in the parametrisation, e.g. diffusivity estimates or installation depths of probes. This can make it challenging to estimate absolute fluxes, as small differences in some parameters can lead to disproportionately high changes in the model output. The relative uncertainty of the input parameters can be assessed by multiple replicate measurements. However, further analysis often requires the use of a single value, where usually the mean or median value is used. Yet, the “effective” parameter value that best describes real-world conditions can deviate from a mathematically precise mean value, so that rather than one-size-fits-all, a range of values (e.g. mean ± standard deviation) should be considered. This can be solved by calibration of FGM models on the basis of reference measurements.

The FGM requires estimation of both, gas concentration gradients and diffusivity in the soil. Gas concentration can be measured relatively easily and consistently, whereas diffusivity is often harder to estimate reliably. One possibility is in-situ measurement using a tracer gas. However, due to relatively high cost and work requirement, diffusivity is often modelled from air-filled pore space (AFPS) instead, using soil-specific transfer functions (TF´s). Modelling soil gas diffusivity in turn requires several input parameters, including porosity, soil water content, temperature and barometric pressure. While modelling diffusivity can have satisfactory results when analysed in the laboratory on soil cores, there are far more challenges in the field, which eventually result in a mismatch between the concentration profiles, diffusivity, and modelled efflux. As a result, FGM-modelled efflux may have an offset compared to more reliable chamber measurements.

Hence, rather than following a one-size-fits-all approach, the inherent uncertainties of diffusivity modelling should be accepted and compensated for by finding effective values of input parameters that close the gap between concentration and diffusivity measurements. Here, we introduce a procedure to run a sensitivity analysis on FGM models to identify the most influential input parameters, as well as find a suitable model parametrisation of effective values. Input parameters of FGM models are varied within a range around the original value and several quality parameters are calculated from the comparison of the model output to reference flux measurements and to the original gas concentration profile. The parametrisation with the “best” quality parameters are then used as “effective” values for the enhanced final model. The process was developed on a dataset of continuous gas concentration measurements in forest soils and is now being applied to long-term datasets as well. This may enhance the quality of FGM models and in turn help to balance gas fluxes in soils.

How to cite: Gartiser, V., Lang, V., Osterholt, L., Jochheim, H., and Maier, M.: Beyond one-size-fits-all: Estimating effective soil physical parameters for gas flux modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10393, https://doi.org/10.5194/egusphere-egu22-10393, 2022.

16:29–16:35
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EGU22-9503
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ECS
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Virtual presentation
Laurin Osterholt and Martin Maier

Gas transport in soils is generally dominated by molecular diffusion. Yet, several studies showed that other factors such as wind-induced pressure-pumping can substantially enhance soil gas transport for a certain time. The underlying processes behind wind-induced enhancement of soil gas transport are very complex and there is an ongoing discussion about it. It has been observed that turbulence associated with high above-canopy wind speed generates pressure fluctuations that propagate into the air filled soil pore network. The resulting 2D pressure field travels in wind direction over the ground and generates lateral pressure gradients in the soil (Laemmel et al., 2019). We hypothesize that the 2D oscillation of the pressure gradient in the soil significantly contributes to the pressure-pumping effect (PPE) compared to a purely 1D pressure oscillation.

Previous studies relied on a monitoring of gas transport rates in the soil, which needed to cover calm and windy periods. In order to quantify PPE at different soils and to investigate the influence of 2D versus 1D pressure fields we develop a large mobile chamber system (approx. 2 x 4 m) with separated compartments to simulate dynamic 2D fields of pressure fluctuations in the field. By alternately pumping air in and out of the chamber sinusoidal pressure fluctuations can be generated. Pressure fluctuations in the different compartments can be set with a time-lag to create a lateral gradient between the compartments and thereby simulate 2D pressure fields.

Combined with automated chamber measurements and soil gas profile measurements inside the chamber system the influence of pressure-pumping on soil gas efflux can be investigated while the influence of other environmental drivers can be excluded. In the natural environment windy periods often coincide with other parameters like precipitation or temperature which also influence gas transport in soil. Excluding these factors could allow a clearer quantification of PPE. With this chamber system also the influence of wind speed directly above the ground in comparison to the influence of pure pressure-pumping could be investigated. Artificially simulating pressure-pumping has the advantage over the monitoring of natural pressure-pumping events that different scenarios can be run under controlled conditions and with replications. Additionally, artificially simulating pressure-pumping saves a lot of time since there is no need to wait for the right wind conditions. We believe that this set up will help to gain a better understanding of wind-induced pressure-pumping on a process level.

Literature:

Laemmel, T., Mohr, M., Schack-Kirchner, H., Schindler, D., & Maier, M. (2019). 1D Air Pressure Fluctuations Cannot Fully Explain the Natural Pressure-Pumping Effect on Soil Gas Transport. Soil Science Society of America Journal, 83(4), 1044-1053.

How to cite: Osterholt, L. and Maier, M.: Towards a better understanding of wind-induced pressure-pumping - a chamber system to simulate dynamic fields of pressure fluctuations  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9503, https://doi.org/10.5194/egusphere-egu22-9503, 2022.

16:35–16:40
Discussion

Wed, 25 May, 17:00–18:30

Chairpersons: Martin Maier, Bernard Longdoz

17:00–17:10
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EGU22-6145
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solicited
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Virtual presentation
George Burba et al.

The N2O and CH4 soil flux studies traditionally consider certain time periods and certain ecosystems to be of low importance due to very small or negligible expected flux rates. Periods of such “negligible” fluxes are rarely reported because small fluxes are hard to resolve, measurements are costly, time-consuming, and often take a lot of power. “Negligible” flux sites are also rarely studied because small fluxes are hard to resolve, measurements are time-consuming and costly, and it is hard to get funding to measure something when the error bars cross zero.

However, such fluxes may not be negligible in time when multiplied by long time duration, for example, 340 out of 365 days per year. Similarly, these may not be negligible in space when multiplied by a large area. When GHG budgets are of interest, very small fluxes multiplied by hundreds of days or square kilometers, or both, could easily exceed large fluxes multiplied by a few days or square kilometers.

The new OF-CAES technology [1-7] has very low minimum detectable flux which helps make more of such measurements valuable and valid in both time and space. The presentation will demonstrate the field data on the N2O and CH4 soil flux performance of this new technology. Conceptual simulations will also demonstrate the significant advantages of using the technology when measuring small N2O and CH4 fluxes over time and space.

 

References:

[1] Burba, 2022. Eddy Covariance Method for Scientific, Regulatory, and Commercial Applications. LI-COR Biosciences, 660 pp (under review)

[2] Burba, 2021. Atmospheric Flux Measurements. In Advances in Spectroscopic Monitoring of the Atmosphere. Elsevier Science, 618 pp

[3] Koulikov and Kachanov, 2014. Laser-based cavity-enhanced optical absorption gas analyzer with laser feedback optimization. US Patent 8659758

[4] Leggett et al, 2019. Development of Trace CH4 and CO2 Analyzers: Performance Evaluation Studies, Gowers Integration, and Field Results. AGUFM

[5] Minish et al, 2019. New High-Precision Low-Power CO2 and CH4 Analyzers for Multiple Applications. Geophysical Research Abstracts, Vol. 21

[6] Romanini et al, 2014. Introduction to cavity-enhanced absorption spectroscopy. In Cavity-Enhanced Spectroscopy and Sensing. Springer, 546 pp

[7] Xu et al, 2020. How do soil temperature and moisture regulate N2O flux from an urban lawn? AGUFM

How to cite: Burba, G., Leggett, G., and Minish, K.: The Concept of Resolving Very Small Soil Fluxes of N2O and CH4 over Time and Space Using New OF-CEAS Technology  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6145, https://doi.org/10.5194/egusphere-egu22-6145, 2022.

17:10–17:16
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EGU22-5235
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On-site presentation
Jesper Christiansen and Klaus Steenberg Larsen

Exchange of greenhouse gases (GHG) between soils and the atmosphere are highly dynamic in space and time challenging prediction of how the fluxes from soils respond to environmental change. The soil hydrological and thermal regime are major drivers of the rates of biogeochemical processes producing or consuming GHG's in the soil, but how these factors interact to regulate net GHG fluxes is unclear.

Part of the reason is the lack of high frequency in situ GHG flux measurements in environments with gradients of the hydrological and thermal regimes. Disentangling the interactive effects of soil hydrology and temperature on GHG fluxes based on in situ observations is key for building more accurate biogeochemical models.

Here we present the results from a unique GHG flux observation campaign using the SkyLine2D automated chamber measurement system. Contrary to other automated chamber systems, the SkyLine2D uses one chamber moved along two ropes and lowered on to predefined collars on the ground which is ideal for studying environmental gradients. With the SkyLine2D we can study the complexity of the interactions of GHG fluxes and edaphic and dynamic factors.

We deployed the SkyLine2D with a total of 30 individual flux collars covering a soil hydrological gradient in a reestablished beech forest swap in Denmark, from well-drained upland to waterlogged and occasionally flooded soils. Along the transect automated measurements of groundwater depth (GWD), soil moisture (SM) and temperature (ST) were measured continuously together with climatic parameters (rain, humidity, wind and air temperature). Bulk density, pH and carbon/nitrogen pools were measured as well along the transect. Plants were excluded by clipping above ground parts in the collars to measure net soil GHG fluxes.

The campaign covered a 2-year period (2019 – 2021) with simultaneous measurements of net CO2, CH4 and N2O fluxes. With these data we will explore spatiotemporal patterns in GHG fluxes and relation of these to soil hydrology and temperature. We seek to present multi-factorial GWD/SM/ST -  GHG flux response functions nested within a soil type gradient (carbon/nitrogen pools, pH).

How to cite: Christiansen, J. and Steenberg Larsen, K.: Spatiotemporal variability of CO2, CH4 and N2O fluxes over a soil hydrological gradient reveal soil water-temperature interactions on biogeochemical pathways, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5235, https://doi.org/10.5194/egusphere-egu22-5235, 2022.

17:16–17:22
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EGU22-5959
A novel automatic chamber system for high to medium spatial and temporal resolution for the determination of CO2 (NEE & RECO), CH4 and N2O fluxes in ecosystems.
(withdrawn)
Tim Eickenscheidt et al.
17:22–17:28
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EGU22-13398
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On-site presentation
James Benjamin Keane et al.

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with a global warming potential 298 times that of carbon dioxide (CO2). Measurements of soil N2O emissions typically use manual chambers, with samples taken at low temporal resolution over long durations (months), or at higher temporal resolution (multiple samples per day) over short durations. Automated GHG flux systems have allowed the measurement of high frequency (sub-daily) N2O fluxes over longer periods (weeks to months), revealing that emissions can vary diurnally by up to 400% in agricultural soils.

Contributing approximately 70% of global anthropogenic N2O emissions, agriculture represents the largest area of uncertainty for GHG reporting and the most challenging sector for emissions reduction: global N2O emissions are increasing at double the rate estimated by the Intergovernmental Panel on Climate Change (IPCC). Improvements to agricultural GHG emission estimates have increased the accuracy of GHG reporting, but N2O emissions from agricultural soils still contribute 25% of the uncertainty of total GHG emissions across all sectors. Our project, diurnal variation in soil nitrous oxide emissions (DIVINE), combines field and laboratory experiments that exploit high-resolution, robotic and continuous N2O measurement technology, to investigate the drivers and mechanisms underpinning diurnal variation in N2O.

We will present work from a field study investigating the effect of soil properties and nitrogen (N) fertiliser management on diurnal variation in N2O emissions from a wheat crop. We assess how N fertiliser application (rate and frequency) and soil gas diffusivity (determined by bulk density and rain events), affect the depth of N2O production and N2O transport in the soil, and resultant impacts on the peak timing and amplitude of diurnal N2O emissions across the crop life cycle and seasons.

N2O emissions will be compared in paired transects with contrasting bulk density but similar soil texture and history, with three ammonium nitrate fertiliser scenarios. N2O is being measured continuously using SkyLine2D automated flux chamber technology. To resolve depth/gas transfer coefficients after N fertiliser and rain events, we will measure soil N2O concentration profiles across the rooting zone in discrete campaigns during the crop life cycle.

Further, we will discuss how our data will be used to improve the accuracy of N2O emission factors by accounting for environmental and diurnal variation. Bayesian statistical modelling will be used to represent the spatial and temporal distribution of emissions following fertilisation, and the effects of known environmental factors (e.g. temperature, soil moisture, light intensity), as well as the residual effect explicable by the diurnal cycle.

How to cite: Keane, J. B., McNamara, N. P., Whitaker, J., Moir, J., Levy, P. E., Robinson, S., Linnekogel, S., Walker, H., Storer, K., Berry, P., Toet, S., and Lee, S.: Diurnal variation in soil nitrous oxide emissions (DIVINE): drivers and mechanisms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13398, https://doi.org/10.5194/egusphere-egu22-13398, 2022.

17:28–17:34
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EGU22-9185
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On-site presentation
Bettina Weber et al.

Biological soil crusts (abbreviated as biocrusts) are composed of photoautotrophic cyanobacteria, algae, lichens, and bryophytes, growing together with heterotrophic bacteria, archaea and fungi and forming an intimate association with soil particles in the uppermost millimeters of the substrate. They occur globally in drylands, where they cover about 1/3 of the soil surface, corresponding to an area of about 18 x 106 km2. Biocrusts fix atmospheric nitrogen (N), which is needed for physiological processes and the formation of biomass. However, it recently was also shown that similar to bulk soil, N is cycled within biocrusts and major fractions of it are released as nitrous acid (HONO) and nitric oxide (NO) to the atmosphere.

Based on these initial results, we investigated the biologically mediated N-cycling processes in biocrusts as related to wetting and drying events. We investigated the microbial activity at different drying stages by means of transcriptome analysis and related these results to soil nitrite and nitrate concentrations over time. In addition, we utilized catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) to quantify the number of bacteria, archaea, and nitrite oxidizing bacteria in different strata over time.

Our results revealed that within less than 30 minutes after wetting, genes encoding for all relevant N cycling processes, including N fixation, ammonification, nitrification, denitrification, and assimilatory and dissimilatory N reduction were expressed. The most abundant transcriptionally active N-transforming microorganisms belonged to the Rhodobacteraceae, Enterobacteriaceae and Pseudomonadaceae within the Alpha- and Gammaproteobacteria. The soil nitrite contents increased significantly during the desiccation process, likely serving as a precursor for NO and HONO emissions, which peaked at relatively low water contents of ~20% water holding capacity. This nitrite accumulation was likely caused by a differential expression of nitrite as compared to nitrate reductase encoding genes over the course of desiccation. Additionally, our data suggest that ammonia-oxidizing organisms may have responded to changing local oxygen conditions during drying. These mechanisms are also supported by process-based modelling, which has been conducted by us. Thus, our results show that the activity of N-cycling microorganisms, as related to the water and oxygen conditions within the substrate, determines the process rates and overall quantity of reactive nitrogen emissions.

How to cite: Weber, B., Maier, S., Kratz, A. M., Weber, J., Kim, M., Leiva, D., Prass, M., Liu, F., Clark, A. T., Abed, R. M. M., Su, H., Cheng, Y., Eickhorst, T., Fiedler, S., and Pöschl, U.: Nitrogen cycling in biological soil crusts; microbial transformation processes and atmospheric nitrous acid and nitric oxide emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9185, https://doi.org/10.5194/egusphere-egu22-9185, 2022.

17:34–17:40
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EGU22-4585
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ECS
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On-site presentation
Line Vinther Hansen et al.

Nitrous oxide (N2O) emissions are notoriously variable at different spatial and temporal scales. As recognized in the literature, peaks in emissions of N2O occur after fertilization, precipitation and freeze-thaw events. Although the individual microbial processes have been extensively studied, the understanding of the underlying mechanisms behind the pulse emissions is still subject to many uncertainties. The N2O produced in connection with a rain event can either be entrapped in the soil matrix and be subject to N2O reduction or be released later when soil diffusivity increases as water infiltrate into the soil or evaporate.

To understand the mechanisms behind the observed flux emissions related to precipitation events, we are conducting a laboratory experiment to quantify the N2O movement in the soil. In 50 cm tall soil columns exposed to a simulated rain event, gas samples are extracted from the soil matrix at three depths via reinforced silicone tubes. At the surface, gas is sampled for flux estimates.

A common trigger of pulse emissions is a lowered soil oxygen content. Continuous monitoring of the soil oxygen with sensors at three depths provides measurements of O2 dynamics in the soil simultaneously with the N2O content. This can add to the understanding of how O2 relates to N2O production, reduction and movement. Tensiometers will additionally provide data on the soil water status during simulated precipitation events.

The experimental set-up can furthermore be used for studying the effects of other factors affecting N2O movement and emission in soil e.g., soil types, type of fertilizers, soil temperature etc. 

 

 

How to cite: Hansen, L. V., Brændholt, A., Tariq, A., Jensen, L. S., and Bruun, S.: Nitrous oxide emission peaks and distribution of nitrous oxide in the soil profile during rain events: A soil column experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4585, https://doi.org/10.5194/egusphere-egu22-4585, 2022.

17:40–17:46
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EGU22-5707
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ECS
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On-site presentation
Luisa I. Minich et al.

N2O is a stratospheric ozone depleting substance and a potent greenhouse gas which significantly contributes to global warming. Although soils are the largest source of N2O emissions, knowledge gaps in the understanding of N2O production and reduction processes in soils still exist. Here, we investigated N2O production and consumption processes along soil depth profiles in a mesocosm experiment using natural-abundance N2O and NO3- isotopic signatures as well as abundances of soil microbial genes associated with N2O production (nirK, nirS) and reduction (nosZ). Soil columns either displayed undisturbed soil stratification (control treatments), or contained an artificial clay layer at 35 cm depth (clay treatment), which acted as a diffusion barrier and thus induced O2-limited conditions in deeper strata. We collected soil pore gas, soil solution and soil samples at five depths of the soil columns over the course of four weeks. In addition, we continuously monitored N2O fluxes at the soil surface and soil environmental parameters (oxygen, moisture, temperature) along the soil depth profiles. Microbial gene analysis in soil samples revealed similar abundances of nirK, nirS and nosZ in the two treatments across the entire soil depth profiles. The distribution of the functional genes was thus not indicative of enhanced N2O production and/or reduction in O2-limited conditions. However, lowest O2 concentrations below the clay layer were associated with highest 15N and 18O enrichments in both NO3- and N2O, indicating N2O production by denitrification and fractional N2O reduction. In addition, we found higher N2O concentrations and surface fluxes for the clay treatment. Our observations imply a dominance of N2O production over N2O reduction, even under conditions most favorable for complete denitrification.

How to cite: Minich, L. I., Barthel, M., F. Conz, R., Hüppi, R., Wilde, B. C., Werner, R. A., Kuhn, T., Lehmann, M. F., Hagedorn, F., Hartmann, M., Scholten, T., and Six, J.: Elucidating soil pore N2O production and consumption processes using isotope and microbial gene analysis: A depth profile approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5707, https://doi.org/10.5194/egusphere-egu22-5707, 2022.

17:46–17:52
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EGU22-4511
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ECS
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Virtual presentation
Marcus Klaus et al.

Soils play an important role in the Earth's greenhouse gas cycle. The gas dynamics in soils are tightly coupled to gas dynamics in plants, trees, and surface waters. Riparian soils receive and process solutes leaching from upland areas and act as crucial buffers of land-use effects on various ecological and biogeochemical properties of surface waters. However, their role in greenhouse gas cycling is poorly understood. Forest clear-cutting often increases the leaching of organic carbon, nutrients and greenhouse gases in groundwater. Unfortunately, the fate of these substances on their way from upland clear-cut areas through riparian forest buffer zones left along streams after clear-cutting is unknown, but highly relevant for watershed-scale greenhouse gas budgets. Here, we performed a watershed-scale experiment to investigate the effect of clear-cutting on greenhouse gas dynamics in riparian forest buffer zones in a Swedish boreal headwater catchment. The experiment included weekly to monthly sampling during April-October before (2020) and after (2021) forest clear-cutting performed in February 2021, and included a treatment watershed and an untreated reference watershed. We measured concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in soils using gas probes installed at various depths within the zone of groundwater level fluctuations along four transects from the clear-cut area through riparian forest buffer zones to near-stream sites. We also measured fluxes of these gases between the atmosphere and the forest floor, as well as tree stems, using flux chamber techniques. Initial results suggest that the clear-cutting increased CO2 and CH4 concentrations in clear-cut soils and the center of riparian buffer zones, but not in near-stream sites. In contrast, the concentrations of N2O in soils were not affected by forest clear-cutting across the full transects. In terms of greenhouse gas exchange with the atmosphere, the clear-cutting did not affect CO2, CH4 and N2O fluxes at the forest floor. Tree stems were consistent emitters of CO2 and CH4 in 2021, but the clear-cut effect remains unclear due to missing reference data before the clear-cut. Together, these results suggest that the clear-cut induced excess of CO2 and CH4 in upland groundwater was likely consumed in riparian soils or emitted through tree stems, assuming that upland and riparian soils were hydrologically connected. Our results stress the potential importance of riparian buffer zones in mediating clear-cut effects on catchment-scale greenhouse gas budgets.

How to cite: Klaus, M., Machacova, K., Falk, A., Wallin, M., Soosaar, K., and Öquist, M.: Forest clear-cutting effects on greenhouse gas dynamics in riparian buffer zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4511, https://doi.org/10.5194/egusphere-egu22-4511, 2022.

17:52–17:58
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EGU22-13071
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ECS
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Virtual presentation
Duo Lou et al.

The increase of CO2 in the atmosphere has led to warming of the Earth’s surface and other climate changes. As heterotrophic respiration has great potential to increase atmospheric CO2 concentrations, it is important to quantify the variation in soil CO2 emission and to find its control factors under climate change. Though there are numerous studies about the warming effect on soil CO2 fluxes, the duration and variation of the effect remains unclear in subtropical forests. Here, we conducted a soil warming experiment with a multichannel automated chamber system in a secondary subtropical broad-leaved evergreen forest in Hong Kong. 15 chambers were set up in forest and were divided into 3 treatments, including a control, a root trenching, and an infrared-warming with root trenching chamber to determine the effect of warming on soil heterotrophic respiration in forest.

So far, after 3-year warming, soil temperature at 5 cm depth was increased by 2.47 °C, compared with the control chambers. Soil CO2 fluxes in experimental warming chambers have been significantly stimulated by 33.06%. There is significant relationship between soil temperature and soil CO2 fluxes in all the treatments, while in heating chambers, the relationship was weaker. The warming effect on soil CO2 emission was high in hot and humid summer, indicating that summer precipitation and the resulting soil moisture level also strongly influenced the soil warming effect in this forest. A moderately strong relationship was only found between soil moisture and temperature-normalized CO2 flux data in trenched chambers in 2020, when annual precipitation was the highest among 3 years. We found a significant reduction in the warming effect on soil respiration and highest Q10 values for soil respiration and its components in 2021, when annual precipitation was the lowest. Experimental warming significantly decreased Q10 value for heterotrophic respiration, which may be due to the reduction of soil moisture. Cross-correlation analysis showed that there was evident diel hysteresis between CO2 and soil temperature, while no significant seasonal hysteresis was observed. Longer-term monitoring on soil respiration under warming conditions is still needed to confirm if the reduction of warming effect is caused by microbial acclimation in our site.

How to cite: Lou, D., Liang, N., and Lai, D. Y. F.: Seasonal variability and magnitude of soil CO2 fluxes in a warming experiment in a secondary subtropical forest in Hong Kong, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13071, https://doi.org/10.5194/egusphere-egu22-13071, 2022.

17:58–18:04
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EGU22-9183
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ECS
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On-site presentation
Verena Lang et al.

As a reactive gaseous hydrocarbon, the phytohormone ethylene (Ethene, C2H4) influences root growth, senescence, and fruit ripening. While plants produce ethylene, microorganisms and fungi are also capable of degrading it. Ethylene therefore acts as an indicator for soil biological processes, but due to its reactivity it is hardly detectable in the atmosphere and soil air. In the 1970s to 1990s, studies were able to demonstrate that up to several ppm of C2H4 occur in soil under certain conditions. However, these studies were limited to laboratory experiments and have a limited transferabilty to undisturbed forest soils.

We investigated the occurrence of ethylene as well as the influencing environmental parameters in forest soils in southwestern Germany using long-term measurement series from the Forest Environmental Monitoring (ICP Forests), as well as from project studies over the past 30 years. In total, soil gas data were available from 24 sites covering a period from 1994 to 2021. Data from gas samplers were used which were installed at various soil depths, at which the soil gas concentration was determined at regular intervals.

The data analysis showed that ethylene in the forest soil very rarely reached the detection limit of our highly sensitive gas chromatography system and that the occurrence is not subject to a regular temporal pattern, but rather cluster in hotspots and hot moments. Ethylene is measured far more frequently under spruce than under deciduous trees. The observed tree species effect indicates a correlation between rooting intensity and ethylene occurrence, as revealed by the evaluation of the root profiles. Artificial soil compaction also leads to increased ethylene concentrations, whereas no effect of liming could be observed.

Thus, the extensive field measurements confirm the patterns known from laboratory studies and show that ethylene, despite its rare occurrence in forest soils, is potentially found at all sites. The accumulation of ethylene in soil air could be observed significantly more frequently in compacted soils than in well-aerated forest soils, where the faster exchange with ethylene free atmospheric air makes accumulation and thus detection difficult.

How to cite: Lang, V., Schneider, V., Schengel, A., Schäffer, J., Schack-Kirchner, H., and Maier, M.: Spotting C2H4 in forest soils- what influences the occurrence of the phytohormone? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9183, https://doi.org/10.5194/egusphere-egu22-9183, 2022.

18:04–18:10
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EGU22-11770
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ECS
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Highlight
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On-site presentation
Miriam Fuss et al.

Salt marshes are vegetated coastal habitats recognised for their great potential to act as effective soil organic carbon sinks, driven by high rates of photosynthetic CO2 uptake and effective long-term storage of organic matter under reducing soil conditions. However, it is poorly understood when and under which conditions salt marshes can act as sinks or sources of the powerful non-CO2 greenhouse gases CH4 and N2O. A complex interplay of environmental factors characterises the biogeochemistry of these ecosystems. This interplay is in turn controlled by elevation in respect to mean high water level and thereby inundation frequency, forming three vegetation zones, which are on average flooded twice daily with every high tide (pioneer zone), twice per month with every spring tide (low marsh) and sporadically during storm surges (high marsh).

We measured land atmosphere fluxes of CH4, N2O and CO2 at a salt-marsh site in Nordfriesland, Germany, combining a closed chamber approach with in situ measurements of portable infrared gas analysers. From June 2018 to September 2021 we conducted biweekly (Apr-Sept) and monthly (Oct-Mar) campaigns covering the elevational gradient throughout all vegetation zones from pioneer zone to high marsh.

All greenhouse gas fluxes indicated strong dependence on elevation. Ecosystem respiration CO2 fluxes showed highest values in the high marsh. CH4 emissions occurred mainly in the most frequently flooded pioneer zone (up to +0.60 µmol*h-1*m-2), whereas low and high marsh acted as net CH4 sinks (down to -2.0 µmol*h-1*m-2). Contrastingly, N2O mainly showed positive fluxes (up to +1.1 µmol*h-1*m-2) in the high marsh, and the more frequently flooded zones acted as net N2O sinks (down to  0.21 µmol*h-1*m-2). Further analysis of environmental variables like soil temperature, flooding frequency, groundwater level fluctuations and plant community composition will follow to identify drivers of varying greenhouse gas fluxes.

Our findings show that salt marshes are not only effective in assimilating CO2. They also show the ability to take up the strong greenhouse gases CH4 and N2O, emphasizing their important role in mitigating global warming.

How to cite: Fuss, M., Mueller, P., Rueggen, N., and Kutzbach, L.: Wadden Sea salt marshes - sinks or sources of methane and nitrous oxide?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11770, https://doi.org/10.5194/egusphere-egu22-11770, 2022.

18:10–18:16
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EGU22-9993
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ECS
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On-site presentation
Enrique Echeverría Martín et al.

Greenhouse gas (GHG: CO2, CH4 and N2O) concentrations continue to increase in the earth’s atmosphere and they are fully implicated in current global warming. There is a critical need to understand of the cause–effect relationships of GHG emissions and quantify their sources/sinks in the natural systems, as well as its main reservoirs and quantity. In particular, there is a need to understand and quantify GHGs within the vadose zone (as an unknown reservoir), because depending on its porosity it can store different amounts of these gases. The vadose zone, the space between the surface and the groundwater, has an important contribution to the global GHG due to both its high concentrations and the enormous capacity to store gases in its pore space.

At present, the measurements of these three GHGs have been widely studied mainly in the first few meters of the soil, not taking into account the transport and storage processes in deep areas. However, the study of the whole column of the vadose zone should not be neglected since it can make an important contribution to the global GHG balance.  

This study analyses GHG concentrations in the vadose zones of several aquifers of the Andalusian Mediterranean basins. For this purpose, air samples were taken from more than one hundred wells in a total of 22 aquifers with water table depths between 7-240 meters; samples were collected at different depths: 12.5, 25, 50, 100 and 200 meters and one sample was collected at the groundwater boundary; for these reasons, the number of samples per well varied depending on the depth to the water table. These samples and analyses provide profiles of GHG concentrations: with values for CO2 between 103-75030 ppm, for CH4 between 0.02-755 ppm and for N2O between 0.31-1504 ppm. The ultimate objective of the project is to know the GHG  profile, the porosity, depth to the water table, groundwater chemistry and aquifer extension, to estimate underground GHG storage.

How to cite: Echeverría Martín, E., Kowalski, A. S., Serrano-Ortiz, P., and Pérez Sánchez-Cañete, E.: Analyzing CO2, CH4 and N2O Concentrations in the Vadose Zone of Several Aquifers of the South of Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9993, https://doi.org/10.5194/egusphere-egu22-9993, 2022.

18:16–18:22
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EGU22-10407
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ECS
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On-site presentation
Yonatan Ganot and Helen Dahlke

Agricultural managed aquifer recharge (Ag-MAR) is an emerging method for groundwater replenishment, in which farmland is flooded during the winter using excess surface water to recharge the underlying aquifer. Successful implementation of Ag-MAR projects requires careful estimation of the soil aeration status, as prolonged saturated (waterlogged) conditions in the rhizosphere can damage crops due to O2 deficiency. We studied the soil aeration status under almond trees and cover crops during Ag-MAR at three sites differing in drainage properties. We used O2 and redox potential as soil aeration quantifiers to test the impact of forced aeration compared with natural soil aeration. Forced aeration treatments included air-injection through subsurface drip irrigation, or dissolution of calcium peroxide powder (scattered on the soil surface before flooding). Our results suggest that forced soil aeration methods have an average increase of up to 2% O2 compared to natural soil aeration. Additionally, only a minor impact on crop yield was observed between treatments for one growing season. Results further suggest that natural soil aeration can support crop O2 demand during Ag-MAR if flooding duration is controlled according to O2 depletion rates. According to this concept, we developed a simple model based only on soil texture and crop type, for estimating Ag-MAR flood duration with minimal crop damage.

How to cite: Ganot, Y. and Dahlke, H.: Natural and forced soil aeration during agricultural managed aquifer recharge (Ag-MAR), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10407, https://doi.org/10.5194/egusphere-egu22-10407, 2022.

18:22–18:28
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EGU22-2693
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ECS
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On-site presentation
Li Wan et al.

Vegetable production in solar greenhouses in Eastern China generally suffers from over-fertilization and unreasonable irrigation, which result in severe soil degradation and soil-borne pathogens occurrence. Anaerobic soil disinfestation (ASD), as a newly developed economic technique, can combat pathogens in greenhouse vegetable soils. The ASD can create strong reductive conditions through the decomposition of added fresh C sources (crop residues or livestock manure) under saturated irrigation and warm conditions induced by plastic coverage to kill soil pathogens. However, ASD-induced organic matters application may increase N leaching and greenhouse gas (GHG) emissions, which remains unknown. Here, we investigated the effects of combined application of two crop residues (rice shells/maize straw) with different amounts of dry chicken manure (0, 300, 600, 1200 kg N ha-1) on N leaching and GHG emissions losses in greenhouse vegetable production systems adopting ASD technique in Eastern China. Our results showed that seasonal N leaching and N2O emissions ranged from 144-306 kg N ha-1 and 3-44 kg N ha-1, respectively, which both significantly increased with manure application rate. Approximately 56-91% of seasonal N2O emissions occurred during the ASD period (5 weeks before vegetable transplantation), whereas 75-100% of total N leaching occurred in the following vegetable-growing season after ASD. The incorporation of crop residues significantly increased N2O emissions by 33-47% while decreasing N leaching by 26-27% compared with CK treatment. The application rate of chicken manure did not affect vegetable yield while significantly increasing the greenhouse gas intensity (GHGI) and reactive N losses intensity (NrI), with reducing 75% manure application significantly decreased 40-45% and 33-38% in GHGI and NrI, respectively. Our results demonstrate that overfertilization with conventional irrigation will not benefit the yield but at a high cost in environment N losses. Overall, current ASD schemes combined with additional manure and irrigation schemes need to be adapted to avoid GHG emissions and N leaching for reducing environmental pollution and improving the sustainability of greenhouse vegetable production systems.

How to cite: Wan, L., Zhao, Y., Xia, L., Hu, J., Xue, T., Lv, H., Butterbach-Bahl, K., and Lin, S.: Anaerobic soil disinfestation benefits soil health while at a high environmental cost in solar greenhouse vegetable production systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2693, https://doi.org/10.5194/egusphere-egu22-2693, 2022.