Displays

Soil respiration (Rs) is the soil‐to‐atmosphere CO₂ efflux produced by microbes and plant roots and is a critical component for the global carbon budget. We present state-of-the-art approaches to estimate global soil respiration at 1 km spatial resolution using the global Soil Respiration Database (GSRD) and machine learning techniques. Patterns of Rs are evident at the global scale and we report an annual estimate of 87.9 Pg C/year with an associated global uncertainty of 18.6 (mean absolute error) and 40.4 (root mean square error) Pg C/year. Global heterotrophic respiration (Rh), the microbial decomposition of soil organic matter, could be derived from empirical relationships with Rs with a global estimate of 49.7 Pg C/year. We discuss how these global estimates and patterns are influenced by adding new measurements as we compared the GSRD version 3 with version 4. This comparison raises challenges about how adding new information, within a multivariate space, influence model uncertainty and regional-to-global estimates. Finally, we discuss future approaches to estimate global Rs, network opportunities for expanding the GSRD, and where new measurements are needed across the world.

How to cite: Vargas, R., Warner, D., Stell, E., Bond-Lamberty, B., and Jian, J.: Global soil respiration: patterns, challenges and network opportunities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10965, https://doi.org/10.5194/egusphere-egu2020-10965, 2020.

Soil respiration causes one of the largest terrestrial carbon fluxes and its accurate prediction is still a matter of on-going research. Understanding the functional link between soil heterotrophic respiration and soil water content is relevant for the estimation of climate change impacts on soil CO₂ emissions. 
In order to quantify the effect of air-drying and sieving with 2 mm meshes on the soil heterotrophic respiration response to water content we incubated intact cores and sieved samples of two loamy and two sandy agricultural topsoils for six levels of effective soil water saturation. We further measured soil textural properties and the soil water retention characteristics of the soils with the aim to identify potential correlations between soil physical parameters and moisture sensitivity functions of heterotrophic respiration. 
The incubation of sieved and intact soils showed distinct differences in the response of soil heterotrophic respiration to soil water saturation. The sieved soils exposed threshold-type behaviour, whereas the undisturbed soils exposed a quadratic increase of heterotrophic respiration with increasing effective soil water content. Additionally, we found significant correlations between the moisture response functions of the undisturbed soils and soil textural properties.
From the comparison of intact and sieved soil incubations we conclude that the destruction of soil structure by sieving hampers the transferability of measured soil moisture response of heterotrophic respiration to real-world conditions. For modelling purposes we suggest the use of a quadratic function between relative respiration and effective saturation for soils with a clay fraction < 20 %.

How to cite: Herbst, M., Tappe, W., Kummer, S., and Vereecken, H.: The influence of soil structure on heterotrophic respiration response to soil water content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3365, https://doi.org/10.5194/egusphere-egu2020-3365, 2020.

Soil microbes are highly sensitive to changes in their environment, and rapidly measuring their responses is necessary to fully understand the biological processes. Drought is one of the most common environmental stresses that soil microbiomes experience, and it is important to understand the mechanisms by which the soil microbiome respond to soil dehydration. We used ¹³C as a tracer of nutrient fluxes in desiccated soil microbiomes after rewetting to simultaneously measure aerobic respiration and track the metabolic state of the community. Here, we describe a Real Time Mass Spectrometry (RTMS) approach for rapid gas monitoring combined with omics approaches to track ¹³C flow through a soil system.

The mechanism(s) behind the burst of rapid mineralization of soil organic matter and increased rate of CO₂ release upon rewetting dry soil (termed the ‘Birch Effect’) are yet to be fully defined. One known mechanism used by microbes to protect against dehydration is the production of intracellular compounds known as osmolytes. We evaluated metabolic mechanisms produced upon rewetting a marginal soil testing the hypothesis that the rapid release of CO₂ arises from the microbial processing of putative intracellular osmolytes that build up during desiccation. RTMS allows for the simultaneous, rapid and fine scale (every 2 sec) evaluation and deconvolution of the production and consumption of a number of gasses including ¹²CO₂,¹³CO₂, O₂, N₂ and H₂O.  We compared the hydration response (production of CO₂ in real time) between the addition of water and ¹³C labeled glucose dissolved in water. The initial burst of ¹²CO₂ followed by a leveling off was identical in both treatments with an additional larger increase in ¹³CO₂ about 20 minutes later in the ¹³C labeled glucose experiment. Examination of the two minutes after the water addition revealed a rapid rate of ¹²CO₂ (38 sec) and H₂O (47 sec) production and slow rate of ¹³CO₂ (56 sec) production followed by the consumption of O₂ (67 sec) and N₂ (73 sec).  Evaluation of the soil metabolomes at specified time points within 3 hours after wetting revealed the immediate release of sugars from the cells into the extracellular matrix. These results provide evidence for respiration of putative intracellular osmolytes as one driving mechanism of the Birch Effect. 

How to cite: Lipton, M., Smith, M., Weitz, K., Couvillion, S., Paurus, V., Metz, T., Jansson, J., and Hofmockel, K.: Unraveling the Molecular Mechanisms Underlying the Microbiome Response to Soil Rewetting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11994, https://doi.org/10.5194/egusphere-egu2020-11994, 2020.

Gaseous matter exchanges in soil are determined by the connectivity of the pore system which is easily clogged by fresh root exudates. However, it remains unclear how a hydrogel (e.g. mucilage) affects soil pore tortuosity when drying. The aim of this study is to obtain a better understanding of gas diffusion processes in the rhizosphere by explaining patterns formed by drying mucilage.

We measured oxygen diffusion through a soil-mucilage mixture after drying using a diffusion chamber experiment. Therefore we mixed soil with different particle size with various amounts of mucilage. Afterwards we saturated the soil and measured the gas diffusion coefficient during drying.

We found that mucilage decreases gas diffusion coefficient in dry soil without significantly altering bulk density and porosity. Electron microscopy indicate that during drying mucilage forms filaments and interconnected structures throughout the pore space. Exudation of mucilage may be a plant possibility to actively alter gas diffusion in soil.

How to cite: Haupenthal, A., Bentz, J., Brax, M., Schuetzenmeister, K., Jungkunst, H., and Kroener, E.: Plants possibility to control soil gas exchanges via mucilage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8447, https://doi.org/10.5194/egusphere-egu2020-8447, 2020.

Salt marshes are highly valuable Blue Carbon ecosystems in the transition zone between marine and terrestrial environments. They play an important role in mitigating climate change due to high carbon sequestration rates through photosynthetic CO₂ uptake. However, it is poorly understood when and under which conditions they act as sinks or sources for other greenhouse gases like CH₄ and N₂O.  A complex interplay of abiotic and biotic factors characterizes the biogeochemistry of these dynamic coastal wetland ecosystems. This interplay is in turn controlled by elevation in respect to mean high water level and the resulting inundation frequency.

We measured land‑atmosphere fluxes of CH₄, N₂O and CO₂ due to ecosystem respiration at Hamburger Hallig, North Frisia, Germany, combining a closed chamber approach with in situ‑measurements of a portable Fourier transform infrared absorption spectrometer (DX4015, Gasmet). Biweekly (Apr-Sept) and monthly (Oct-Mar) campaigns have started in December 2018 and cover the whole elevational gradient from the pioneer zone over the low marsh up to the high marsh.

While ecosystem respiration showed high variability over the seasonal course with fluxes up to +67 mmol*h^-1*m^-2, CH₄ and N₂O fluxes indicated a strong dependence on elevation and thus vegetation zone. Emissions of CH₄ occurred only in the most frequently flooded pioneer zone (+0.17 to +0.35 µmol*h^-1*m^-2), whereas the less frequently flooded zones of the low and high marsh acted as CH₄ sinks (down to -1.1 µmol*h^-1*m^-2). Contrastingly, N₂O solely showed positive fluxes (up to +1.0 µmol*h^-1*m^-2) in the high marsh and the more frequently flooded zones acted as sinks for N₂O (down to ‑0.21 µmol*h^-1*m^-2). Air temperature and tidal sea water level fluctuations could already be identified as additional environmental drivers of varying greenhouse gas fluxes. Further analysis of abiotic and biotic driver variables will elucidate their impact in detail.

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 in certain vegetation zones, emphasizing their important role in mitigating global warming.

How to cite: Fuss, M., Rueggen, N., Mueller, P., Nolte, S., and Kutzbach, L.: Greenhouse gas fluxes of Wadden Sea salt marshes strongly vary among different vegetation zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21621, https://doi.org/10.5194/egusphere-egu2020-21621, 2020.

Previously drained forested wetlands around the world are being restored for biodiversity, but our knowledge on the impact of restored hydrology on the total greenhouse gas (GHG) budget in these systems remains fragmented. Whereas the reduction in the net CO₂ emission upon rewetting is well documented, the magnitude of the effect on the microbial production of CH₄ and N₂O is much more uncertain. This is partly because GHG fluxes, especially for CH₄ and N₂O, exhibit a highly dynamic spatiotemporal variation tied to the soil hydrological regime. To capture this variation properly a high number of flux measurements in time and space is needed, but many field studies are still highly limited in terms of their spatio-temporal coverage. This hiatus of field data is a primary source of uncertainty in model projections of impacts on the GHG budgets when restoring natural hydrology in drained wetlands.

We use a novel automatic chamber measurement system (SkyLine2D) connected to a Picarro G2508 analyzer for CO₂, CH₄ and N₂O flux measurements in a rewetted Danish forest wetland. With this system, we wish to resolve the little known spatio-temporal patterns of these GHGs and their relationship with environmental drivers such as soil moisture, water table, temperature, and soil carbon content. A total of 30 measurement plots, each measured 5 times per day over a period approaching 1 year (> 40,000 measurements), were placed along a 30 meter transect covering a soil hydrological gradient including well-drained, waterlogged and open water conditions. The gradient also spans a soil carbon gradient increasing from well-drained mineral soils, over gleysols to waterlogged histosols.

Based on the novel, high-frequency flux data of CO₂, CH₄ and N₂O we will present a detailed analysis of the relationship with soil hydrology and temperature over periods spanning from hours to months. The data produced by this gradient approach combined with automated measurements represents an important step towards developing improved ecosystems models that can better predict the GHG effect of rewetting previously drained wetlands.

How to cite: Larsen, K. S. and Christiansen, J. R.: Rewet or not – insights on spatiotemporal patterns of greenhouse gas fluxes from soils in a rewetted Danish forested wetland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10997, https://doi.org/10.5194/egusphere-egu2020-10997, 2020.

Reliable models are required to estimate global wetland CH₄ emissions. This study aimed to test two process-based models, CH4MOD_wetland and TEM, against the CH₄ flux measurements of marsh, swamps, peatland and coastal wetland sites across the world; specifically, model accuracy and generality were evaluated for different wetland types and in different continents, and then the global CH₄ emissions from 2000 to 2010 were estimated. Both models showed similar high correlations with the observed seasonal CH₄ emissions, and the regression of the observed versus computed total seasonal CH₄ emissions resulted in R² values of 0.78 and 0.72 by CH4MOD_wetland and TEM, respectively. The CH4MOD_wetland predicted more accurately in marsh, peatland and coastal wetlands, with model efficiency (EF) values of 0.22, 0.55 and 0.72, respectively; however, the model showed poor performance in swamps (EF<0). The TEM model predicted better in peatland and swamp, with EF values of 0.77 and 0.71, respectively, but it could not accurately simulate the marsh and coastal wetland (EF<0). There was a good correlation between the simulated CH₄ fluxes and the observed values on most continents. However, CH4MOD_wetland showed no correlation with the observed values in South America and Africa. TEM showed no correlation with the observations in Europe. The global CH₄ emissions for the period 2000­­–2010 were estimated to be 105.31±2.72 Tg yr^-1 by CH4MOD_wetland and 134.31±0.84 Tg yr^-1 by TEM. Both models simulated a similar spatial distribution of CH₄ emissions across the world and among continents. Marsh contributes 36%–39% to global CH₄ emissions. Lakes and rivers and swamp are the second and third contributors, respectively. Other wetland types account for only approximately 20% of global emissions. Based on the models’ generality, if we use the more accurate model to estimate each continent/wetland type, we obtain a new assessment of 116.99–124.74 Tg yr^-1 for the global CH₄ emissions for the period 2000–2010.

How to cite: Li, T.: Evaluation of two process-based models used to estimate global CH4 emissions from natural wetlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1483, https://doi.org/10.5194/egusphere-egu2020-1483, 2020.

Rice production contributes roughly 11% of global CH4 anthropogenic emissions while producing food for over 3 billion people. The alternate wetting and drying (AWD) irrigation practice for rice has the potential to conserve water while reducing CH₄ emissions through the deliberate, periodic introduction of aerobic soil conditions. Our work in the US Mid-South rice production region has demonstrated, using the eddy covariance method on adjacent fields, that AWD can reduce field CH₄ emissions by about 66% without impacting yield. In any strategy, CO₂ and N₂O emissions should also be monitored to take advantage of the high carbon sequestration potential of rice and low potential N₂O emissions. Careful water and fertilizer management can theoretically keep N₂O emissions low. All three gases should be managed together, while sustaining or improving harvest yield, to create a sustainable rice production system.

We now present 5 years of closed chamber measurements of N₂O and CH₄ and compare them to the eddy covariance measurements of CH₄ and CO₂ to derive a more thorough perspective on the net greenhouse gas (GHG) emissions or global warming potential basis of rice production from the highly productive, mechanized, humid, US Mid-South. Global warming potential of GHG emissions from rice systems was dominated by CH₄ emissions (74 to 100%), hence mitigating efforts need to focus on CH₄ emissions. Greater reduction of CH₄ emissions can be achieved by proper AWD management practice combined with adequate N fertilization. We end with a comment on the upcoming challenge of how to sequester CO₂ uptake as soil organic matter via litter incorporation without increasing CH₄ emissions. 

How to cite: Runkle, B. R. K., Adviento-Borbe, A., Reba, M. L., Moreno-García, B., Karki, S., Iseyemi, O., Suvočarev, K., Reavis, C. W., and Barr, B. E.: Greenhouse gas emissions mitigation with alternate wetting and drying irrigation of rice agriculture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11643, https://doi.org/10.5194/egusphere-egu2020-11643, 2020.

Human activities implying land management are potential sources of greenhouse gases (GHGs) such as carbon dioxide (CO₂) and methane (CH₄). In addition, agricultural management practices enhances the presence of reactive gases in the atmosphere such as ammonia (NH₃).  Knowing the atmospheric variability of gases in relation to the different stages of the rice culture cycle and other anthropic activities could help to improve GHGs' mitigation strategies in deltas.

A mobile survey was undertaken through 2019 in the Ebro Delta as a part of the ClimaDat Network project (DEC station, www.climadat.es), to study the effect of land management in the spatial and temporal variability of greenhouse gases and NH₃ concentrations. We are broadening the scope of a survey undertaken in 2012 (Àgueda et al. 2017). In the new survey we increased the total number of transects and longitude every three weeks during a year, starting in December 2018.

Whereas atmospheric NH₃ concentration links with diurnal and seasonal cycles, the distribution of CO₂ and CH₄ shows a combination of spatial and temporal variability.   Our aim is to understand how we can use wind trajectories to find the principal sources of atmospheric variability. That is, can wind direction improve our comprehension of metabolic processes occurring in paddy lands? In this work, we use wind trajectories as means of spatial classification, to explore the spatiotemporal dynamic affecting the potential of CO₂ and CH₄ atmospheric concentration. 

How to cite: Estruch, C., Curcoll, R., Borrós, M., Àgueda, A., and Morguí, J.-A.: Ammonia, carbon dioxide and methane in Mediterranean paddy fields along the 2019 crop season, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12856, https://doi.org/10.5194/egusphere-egu2020-12856, 2020.

In the last two decades, acreage for biomass production has strongly increased in Germany due to the Renewable Energy Act. Recently, discussion about soil, climate, and biodiversity protection is receiving more and more public attention throughout broad parts of the society. The project BESTLAND focuses on the effect of land use change from the common annual maize cropping system to a perennial cropping system, as a measure against increasing environmental constraints in biomass production. A suitable perennial biomass crop as an alternative for maize is S. perfoliatum (cup plant). On one hand, the yellow flowering plant produces high biomass yields and on the other hand it provides a variety of ecosystems services. Field experiments were carried out in the Saar-Nahe mountain range in the state of Saarland on a fine textured planosol. The experimental sites are characterized by temporal waterlogging and slopes and therefore these sites are prone for soil compaction and soil erosion. Under these conditions perennial crops are assumed to have soil preserving benefits. Maize was compared to cup plant by establishing four paired sites, where each pair consisted of a maize and a cup plant field in close vicinity (< 500 meters) to each other. All sites are grower fields and were managed by the farmers according best management practices. Nitrous oxide and methane fluxes were measured weekly using the static chamber technique all year round. Besides greenhouse gas measurement, soil samples for determination of soil mineral nitrogen were taken at each gas sampling date. Furthermore, soil temperature and water content were continuously monitored using sensors. Biomass yields at each site were determined at harvest. In the first year average nitrous oxide emissions from cup plant fields were lower than from maize fields by more than 70 % on area and dry matter yield basis. These results indicate that perennial bioenergy crops not only offer a wider range of ecosystem services but can also decrease GHG emissions from bioenergy production.

How to cite: Kemmann, B., Ruf, T., Kirch, A., Emmerling, C., Fuß, R., and Well, R.: Land use change from an annual maize cropping systems to a perennial Silphium perfoliatum crop has unused potential to reduce GHG emission in biomass production, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4510, https://doi.org/10.5194/egusphere-egu2020-4510, 2020.

Agricultural greenhouse gas (GHG) emissions in Africa contribute 15 % to the global total agricultural emissions, which is in the same range as agricultural emissions from Europe. The majority of these agricultural GHG emissions is attributed to livestock farming (up to 80 % at national scale), of which 10-25 % originate from livestock manure. At the same time, livestock production is essential for the livelihoods of millions of people in Sub-Saharan Africa (SSA), where 45-80 % of livestock production occurs in smallholder systems. With the growing population in SSA, the demand for livestock products is expected to increase, and – without low-emission manure management – a rise in manure-borne GHG emissions will occur. However, reliable in situ measurements from SSA are scarce, leading to substantial uncertainties in agricultural GHG budgets and making assessments of potential mitigation options difficult.

Here we present results from two cattle manure incubation experiments in Kenya, using manure from Boran (Bos indicus) cattle, a breed common in East Africa that were fed with typical feeds used in SSA smallholder farms. Manure was collected and piled in heaps (solid storage), the most common form of manure storage in Kenyan smallholder systems, and CH₄ and N₂O emissions were measured over 140 days. In the first trial, cattle were fed a diet that either met their maintenance-energy requirements (i.e. animals received enough food to support their metabolism), or a diet at sub-maintenance energy levels to simulate common conditions in smallholder farming systems, particularly during the dry seasons. Cumulative manure N₂O emissions from the sub-maintenance diet (i.e. the “hungry” cows) were lower than from cattle fed at maintenance energy levels. These lower N₂O emission likely resulted from lower N concentration and a wider C:N ratio in the manure than in the “better fed” animals. Furthermore, the urine-N:faecal-N ratio in the “hungry” cows decreased, indicating a shift from urine-N (mostly inorganic N) to faecal-N (mostly organic N), which further backs the lower observed N₂O emissions. Both N₂O as well as CH₄ emissions from manure were lower than the IPCC default emission factors for solid storage in tropical regions across all diets tested.

In the second trial, Boran cattle were fed with three different tropical forage grasses common in Kenya: Napier (Pennisetum purpureum), Rhodes (Gloris gayana), and Brachiaria (Brachiaria brizantha). Manure from the Rhodes grass diet had the lowest N concentration and also the lowest cumulative CH₄ emissions, while N₂O emissions did not differ between diets. Similar to the sub-maintenance feeding trial, total CH₄ and N₂O emissions were lower than the IPCC default factors. Taken together, these results are an important step towards reducing the uncertainties in GHG emissions from agriculture in SSA. Furthermore, if African nations use IPCC default values for their national GHG reporting on livestock, emissions are likely to be overestimated, highlighting the importance and benefits of localized data from Africa.

How to cite: Leitner, S., Ring, D., Wanyama, G., Korir, D., Pelster, D., Goopy, J., and Merbold, L.: Nitrous oxide and methane emissions from cattle manure heaps in Kenya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21299, https://doi.org/10.5194/egusphere-egu2020-21299, 2020.

­­­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 might differ 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 (eddy covariance and automatic chambers) or short-term temporal variability (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 allowing to detect small-scale spatial heterogeneity and short-term temporal variability of CO₂ (as well as CH₄ and N₂O) flux dynamics for a range of different fertilization and tillage management practices. The system is equipped with two canopy chambers, CR6 data logger, CDM-A116 analog multiplexer and multiple sensors to measure plant activity/biomass development in parallel. The measurements of the gaseous C exchange is performed by moving the system along the tracks with each chamber along one half of the gantry crane. Thus, each chamber measures 18 plots, out of 36 plots (2x3m; 12 per soil type) established in the study area.

Here, we present first CO₂ flux measurement results (spring barley; 3 different soil types) using this novel system, to prove its overall accuracy and precision. Our results show clear small-scale/within field spatial pattern and short-term temporal dynamics regarding measured ecosystem respiration, net ecosystem exchange as well as derived gross primary productivity.

How to cite: Vaidya, S., Augustin, J., Sommer, M., Schmidt, M., Rakowski, P., and Hoffmann, M.: Detecting small scale spatial heterogeneity and short-term temporal variability of CO2 flux dynamics in agricultural used landscapes using a robotic chamber system , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-955, https://doi.org/10.5194/egusphere-egu2020-955, 2020.

Agriculture is globally a significant source of carbon emissions to the atmosphere. Main causes for these high emissions are conventional intensive management practices which include such as frequent ploughing, monocropping and high use of agrochemicals. These practices contribute to the loss of biodiversity and soil organic matter, as well as to the CO₂ emissions from land use. Recently, it has been recognised that agriculture functioning on the basis of regenerative practices is one of the most potential tools to mitigate climate change.

It is well known that topsoil layer and especially humus-rich soils can store more carbon than atmosphere and vegetation together. Therefore, increasing the amount of soil organic matter in the agroecosystems, by applying enhanced management practices such as reduced tillage, high biodiversity and cover cropping, agricultural soils would not only help to mitigate climate change but also to restore soil quality and fertility. To understand the carbon dynamics on different agricultural sites, factors affecting and comprising the carbon balance, and to verify soil carbon and ecosystem models, continuous long-term monitoring of the GHG fluxes is essential at such managed ecosystems. Here we present results from a new eddy covariance (EC) flux study site located in southern Finland.

Continuous CO₂ flux measurements using the EC method have been conducted at Qvidja farm on mineral (clay) soil forage grassland in Parainen, southern Finland (60.29550°N, 22.39281°E) since the spring 2018. Based on the flux and biomass data, the annual carbon balance was estimated to be negative, i.e. the site acted as an overall sink of carbon even in the dry and hot year 2018. However, the seasonal CO₂ fluxes were greatly dependent on weather conditions and management procedures. Results from 2019 show that the growing season accompanied with more mature and dense grass, a bit higher precipitation and lower temperatures, as well as higher cutting height was more favorable for carbon uptake in Qvidja as compared to year 2018.

How to cite: Heimsch, L., Lohila, A., Kulmala, L., Tuovinen, J.-P., Korkiakoski, M., Laurila, T., and Liski, J.: CO2 fluxes and carbon balance of an agricultural grassland in southern Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6618, https://doi.org/10.5194/egusphere-egu2020-6618, 2020.

The management of olive groves has a direct impact on the environment in the Mediterranean region since it is one of the most representative crops in this area. In order to prevent erosion and improve the physical-chemical conditions of the soil in these crops, the maintenance of weed cover in the alleys is an increasingly common practice. It increases the organic carbon content in the soil, improves biodiversity indices and enhances various ecosystem services such as pollination and infiltration. Now, the role of vegetation cover in olive groves on biogeochemical cycles is being studied. Although previous studies have quantified the combined effect of weed cover and olive trees on carbon and water at ecosystem level, the role of this conservation practice at the leaf level has not yet been explored.

The aim of this study is to quantify the effect of weed cover on the net CO₂ assimilation (A_n) and transpiration (T) rates in an irrigated olive grove. To do this, two plots of olive trees with irrigation (Olea europea L. "Arbequina") in southeast Spain were sampled. In the weed-cover one (WC), spontaneous vegetation is maintained until it is mechanically mowed and left in place. In the weed-free (WF) a glyphosate-based herbicide is applied. The data were taken with a portable gas analyzer (LI-6800, Li-Cor) controlling the following environmental variables on olive leaves: atmospheric CO₂, relative humidity, photosynthetic active radiation and temperature. One campaign per month was carried out (from January-2018 to January-2019) where 10 random trees were analysed in each treatment. In addition, an eddy covariance tower provided CO₂ and H₂O fluxes at ecosystem level and they were compared with the fluxes obtained from leaf-level campaigns.

The results shown significant differences for T only in the period after mowing with T_wc= 2.0 ± 0.7 mmol H₂O m^-2s^-1 vs T_wf = 2.5 ± 1.0 mmol H₂O m^-2s^-1. However, in this period ET is equal in both treatments, which suggests that the alleys with mowed weed has more ET than bare soil in the other treatment. On the other hand, there are significant differences for A_net only in the period before mowing with A_net-wc = 5.5 ± 3.1 μmol CO₂ m^-2s^-1 vs A_net-wf = 8.0 ± 3.6 μmol CO₂ m^-2s^-1. When the weeds are mowed, A_net is matched in both treatments. However, higher values of NEE_wc than NEE_wf  are observed in the period before mowing. This suggest that the weed-cover olive groves at ecosystem level take up more carbon when the weed-cover is established although the leaves of olive trees are capturing less CO₂.

How to cite: Aranda-Barranco, S., Kowalski, A. S., Serrano-Ortiz, P., and Sánchez-Cañete, E. P.: Influence of weed cover on leaf-level CO2 and H2O fluxes in an olive grove, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5181, https://doi.org/10.5194/egusphere-egu2020-5181, 2020.

Reactive nitrogen (N_r) compounds comprise essential nutrients for plants. However, a large supply of nitrogen by fertilization through atmospheric deposition may be harmful for ecosystems such as peatlands and may lead to a loss of biodiversity, soil acidification and eutrophication. In addition, nitrogen compounds may cause adverse human health impacts. Large parts of N_r emissions originate from anthropogenic activities.  Emission hotspots of ΣN_r, i.e. the sum of all N_r compounds, are related to crop production and livestock farming (mainly through ammonia, NH₃) and fossil fuel combustion by transport and industry (mainly through nitrogen oxides, NO₂ and NO). Such additional amount of N_r will enhance its biosphere-atmosphere exchange, affect plant health and can influence its photosynthetic capacity. Therefore, it is necessary to thoroughly estimate the nitrogen exchange between biosphere and atmosphere.

For measuring the nitrogen mixing ratios a converter for reactive nitrogen (TRANC: Total Reactive Atmospheric Nitrogen Converter) was used. The TRANC converts all reactive nitrogen compounds, except for nitrous oxide (N₂O), to nitric oxide (NO) and is coupled to a fast-response chemiluminescence detector (CLD). Due to a low detection limit and a response time of about 0.3s the TRANC-CLD system can be used for flux calculation based on the eddy covariance (EC) technique. Flux losses, which are related to the experimental setup, different response characteristics and the general high reactivity of most N gases and aerosols, occur in the high frequency range. We estimated damping factors of approximately 20% with an empirical cospectral approach.

For getting a reliable prediction of ΣN_r fluxes through deposition models, long-term flux measurements offer the possibility to verify the nitrogen uptake capacity and to investigate exchange characteristics of ΣN_r in different ecosystems.

In this study, we compare modelled dry deposition fluxes using the deposition module DEPAC (DEPosition of Acidifying Compounds) within the chemical transport model LOTOS-EUROS (LOng Term Ozone Simulation – EURopean Operational Smog) against ΣN_r flux measurements of the TRANC-CLD for a remote mixed forest site with hardly any local anthropogenic emission sources. This procedure allows to determine the background load and the natural exchange characteristics of nitrogen under low atmospheric concentrations. Therefore, the broad-scale dry deposition predicted directly by LOTOS-EUROS was compared to site-specific modelling results obtained using measured meteorological input data as well as the directly measured ΣN_r fluxes. In addition, the influence of land-use weighting in LOTOS-EUROS was examined. We further compare our results to ΣN_r deposition estimates obtained with canopy budget techniques. Measured ΣN_r dry deposition at the site was 4.5 kg N ha^-1 yr^-1, in close agreement with modelled estimates using DEPAC with measured drivers (5.2 kg N ha^-1 yr^-1) and as integrated in the chemical transport model LOTOS-EUROS (5.2 kg N ha^-1 yr^-1 to 6.9 kg N ha^-1 yr^-1 depending on the weighting of land-use classes).

Our study is the first one presenting 2.5 years flux measurements of ΣN_r above a remote mixed forest. Further verifications of long-term flux measurements against deposition models are useful to improve them and result in better understanding of exchange processes of ΣN_r.

How to cite: Wintjen, P., Schrader, F., Schaap, M., Beudert, B., and Brümmer, C.: Validation of nitrogen dry deposition modelling above a mixed forest using high-frequency flux measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3559, https://doi.org/10.5194/egusphere-egu2020-3559, 2020.

Wetlands cover an area of about 2% of the total land surface area of the world and are most common in the boreal and tundra zones. Northern wetlands are important sinks for carbon dioxide and sources of methane, but knowledge on their VOC emissions is very limited. Currently, we know that northern wetlands are high isoprene emitters (e.g. Holst et al., 2010), but very little is known on the emissions of other VOCs.

We have studied VOC emissions and their ambient concentrations at a sub-Arctic wetland (Lompolojänkkä) in Northern Finland, using an in situ TD-GC-MS. For the emission measurements, a dynamic flow-through FEP chamber was used.

Earlier studies have shown that isoprene is emitted from wetlands and it turned out to be the most abundant compound in the current study also. Monoterpene (MT) emissions were generally less than 10 % of the isoprene emissions, but sesquiterpenes (SQT) emissions were surprisingly high, exceeding MT emissions at all times. Both MT and SQT emissions were dependent on temperature.

Even with the higher emissions from the wetland, ambient air concentrations of isoprene were clearly lower than MT concentrations. This indicates that wetland was not the only source affecting atmospheric concentrations at the site, but surrounding coniferous forests, which are high MT emitters, contribute as well. In May concentrations of SQTs and MTs at Lompolojänkkä were higher than in earlier boreal forest measurements in southern Finland (Hellén et al., 2018). At that time, the snow cover on the ground was melting and soil thawing and VOCs produced under the snow cover, e.g. by microbes and decaying litter, can be released to the air. Daily mean MT concentrations were very highly negatively correlated with daily mean ozone concentrations indicating that vegetation emissions can be a significant chemical sink of ozone at this sub-Arctic area.

References

Hellén, H.et al. 2018, Atmos. Chem. Phys., 18, 13839-13863, https://doi.org/10.5194/acp-18-13839-2018.

Holst, T., et al. 2010, Atmos. Chem. Phys., 10, 1617-1634, https://doi.org/10.5194/acp-10-1617-2010.

How to cite: Hellén, H., Schallhart, S., Praplan, A. P., Tykkä, T., Aurela, M., Lohila, A., and Hakola, H.: Emissions and ambient air concentrations of isoprene, monoterpenes and sesquiterpenes at a Northern wetland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4938, https://doi.org/10.5194/egusphere-egu2020-4938, 2020.

Many management practices in cropland, forest and grassland ecosystems can extend forest area, increase carbon input or prevent C loss from vegetation and soil, and subsequently enhance C sinks and stocks. These management practices are considered as promising carbon sequestration measures. However, during implementation of these measures, the production, transportation and consumption of corresponding materials (such as synthetic fertilizers) and fossil fuel, the additional trace GHG emissions, and the processes taking place elsewhere as a result of the implementation activities may lead to GHG budget change other than the carbon stock, and form GHG leakage. Consequently, in order to reveal the true contribution of these practices to global warming mitigation and GHG reduction, full GHG budget need to be considered rather than the impact on soil and vegetation carbon alone. We built the frame of “Carbon Accounting and Net Mitigation (CANM)” and serious of CANM methods to investigate the GHG leakage and net mitigation of typical carbon sequestration practices in China's terrestrial ecosystem, including China’s national ecological restoration projects, and forest, cropland and grassland managements. The results showed large variations in carbon contributions, GHG leakages and their counteraction effects among different practices and ecosystems. The counteraction effects of GHG leakage from forest management and some forest-related ecological restoration projects were relatively small and could hardly exceed 25%. Meanwhile, the GHG leakage of some cropland management practice (e.g., straw return in rice paddies) could fully offset the carbon sequestration in soil. But reduction of synthetic fertilizer application in accordance with the national fertilization recommendations might own considerable net GHG mitigation potential. Grazing prohibition could sequester carbon in grassland ecosystem, but the transfer of grazing activity could offset about half of the carbon sequestration effect. Therefore, policies and technical approaches to minimize GHG leakage are necessary to enhance the GHG mitigation effect of the ecosystem carbon sequestration practices.

How to cite: Lu, F., Zhang, G., Liu, W., Liu, B., Zhao, H., Zhang, L., Wang, X., and Yuan, Y.: Greenhouse gas (GHG) leakage and net mitigation of typical carbon sequestration practices in China’s terrestrial ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21151, https://doi.org/10.5194/egusphere-egu2020-21151, 2020.

Forests play an important role in the exchange of radiatively important trace gases with the atmosphere. The past decade has seen remarkable growth in interest in this research area with studies yielding ever-greater insight into both the importance of these exchanges and the fundamental processes of exchange in ecosystems that are vulnerable and highly responsive to agents of global change. I will provide an overview of previous studies that are now global in coverage, which have shown that in both temperate and tropical wetland and upland forests, tree stems constitute significant surfaces of exchange of both methane (CH4) and nitrous oxide (N2O). Considering studies spanning diverse forest biomes across the full latitudinal range of forest extent, leads to emergent questions that this new and developing pan-disciplinary coalition of researchers are increasingly well able to address. Given that forests are both sensitive and highly responsive to agents of global change at a range of scales, there is a need to further characterise the fundamental functioning of exchange processes in forests e.g. with respect to hydrology, climate and the biology of microbes and the trees and soils they inhabit. Such insight will help with planning the next generation of integrative studies, at scale, to enable the role of forests in trace gas cycling in a changing world to be characterised.

How to cite: Gauci, V.: Where now for forest trace gas research?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18347, https://doi.org/10.5194/egusphere-egu2020-18347, 2020.

The role of vegetation on net methane fluxes from upland forest ecosystem has only recently been underlined and is still not fully understand and quantify. Indeed, influences of forest plants on the methane budget could be antagonist, being a net methane producer or emitter in some cases or enhancing the methane consumption in others. But the vegetation in upland forests decreases the net methane uptake by 0 to 63%, and in a few cases, increases the methane uptake up to twice. One of the mains source of methane emission related to the vegetation is the transport of methane from deep anoxic soil layers where the methane is produced to the atmosphere through plant stems.

In order to quantify if vegetation is a preferential way of methane emission in our field site, a ¹³CH₄ labelling had been undertaken in soil (at 40 cm depth) and ¹³CH₄ had been traced in upper soil layers (0, 5, 10, 25 cm depth), on the soil surface with soil chambers with or without herbaceous vegetation and in tree stem chambers for two days after the pulse labelling.

¹³CH₄ was recovered in all compartments even though the forest ecosystem was mainly a methane sink during this period when methane uptake dominated.

In our study, the vegetation (tree stems and herbaceous vegetation) have a limited contribution on the recovery of ¹³CH₄ at the forest scale, which is dominated by soil emissions.

How to cite: Plain, C. and Epron, D.: Contribution of vegetation to methane emission produced in the soil of an upland forest: a 13CH4-labelling approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13502, https://doi.org/10.5194/egusphere-egu2020-13502, 2020.

Methane (CH₄) is an important greenhouse gas, globally responsible for 17% of current radiative forcing. Soils can be important net sources or sinks of CH₄ depending on the net balance of two contrasting microbial processes - CH₄ production and CH₄ oxidation. In unsaturated soils, the aerobic methane oxidation process often dominates. These soils form the only global terrestrial CH₄ sink, but estimates are still highly uncertain, both spatially and temporally. Forest soils have shown some of the strongest net CH₄ uptake rates, but this is not consistent across sites and the controls are poorly understood.

In this field study, we focused on the effects of ectomycorrhizas on net CH₄ uptake in an unsaturated, sandy gley podzolic soil of a mature coniferous forest stand dominated by Lodgepole pine (Pinus contorta) in Northern England over three years. Methane fluxes were determined in cores with soil only (roots and ectomycorrhizal mycelium excluded using windows with 1 µm mesh in the cores) and cores with soil and ectomycorrhizal mycelium (only roots excluded with 41 µm mesh). Net CH₄ uptake rates in summer were higher when ectomycorrhizal mycelium was present, whereas the opposite was observed in winter. We will discuss mechanisms that may underpin these ectomycorrhizal impacts on net CH₄ uptake in unsaturated forest soils.

How to cite: Toet, S., Ma, R., Morton, P., and Ineson, P.: Unravelling controls on methane uptake in a temperate forest soil: impacts of ectomycorrhizas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11704, https://doi.org/10.5194/egusphere-egu2020-11704, 2020.

Current knowledge on methane (CH₄) sinks is limited to chemical processes in the atmosphere, and to methanotrophy in forest soils and peatlands. Recent discoveries have indicated that also tree branches, i.e. phyllosphere, may consume atmospheric CH₄, thus functioning as a novel CH₄ sink. However,  the process is not yet confirmed and the mechanism not resolved.

Here, we confirm that leaves and needles of boreal trees have the capacity to consume CH₄ with stable isotope enrichment studies in field and laboratory experiments, and that the consumption is a biological process. With molecular analyses, we confirmed that the activity of needle-associated proteobacterial methanotrophs increased sporadically under CH₄ and acetate enrichment. Our results indicate that CH₄ consumption can exist in the tree canopy, which is characterized by interspecies variation, spatial patchiness and small but significant microbial activity.

This is a novel symbiotic connection between microbes and plant cells, which can enhance overall carbon sequestration in the boreal forests.

How to cite: Siljanen, H., Laihonen, A., Aalto, S., Martikainen, I., Lamprecht, R., Biasi, C., and Tiirola, M.: Methane consumption by proteobacterial methanotrophs in boreal spruce phyllosphere activated with methane, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13072, https://doi.org/10.5194/egusphere-egu2020-13072, 2020.

Plant shoots can emit methane (CH₄) from multiple source processes (microbial methanogenesis in soils and core wood, aerobic CH₄ production in foliage). We constructed a chamber system to isolate these processes and study how leaf level CH₄ emissions respond to environmental factors like dark-light-cycles, temperature, drought, or CO₂ concentrations. Tree samplings are located in a FITOCLIMA D 1200 plant growth chamber for PAR, temperature and humidity control and equipped with a measurement chamber to quantify CH₄ exchange in a closed loop setup with a Picarro G2301 CH₄ analyser. The system was further customized to control temperature, CO₂, and humidity in the measurement chamber. The system allows the detection of CH₄ flux rates of on the order of 1 nmol CH₄ h^-1 and can conduct high frequency (< 15 min) measurements of CH₄ emissions rates from small shoots (<5g foliage biomass). Initial measurements were conducted with Scots pine and birch saplings. In addition, we measured conducted manual methane flux measurements on shoots of Scots pine saplings in two 24-hour campaigns.

These experiments demonstrated that the shoots of different tree species emit CH₄ from distinct sources. Scots pine shoots emitted CH₄ produced within the shoot, likely through aerobic CH₄ production, which showed a strong diurnal cycles that follows irradiation and photosynthesis rates. Shoot from some birch species, in contrast, showed emissions of soil-borne CH₄ that remained constant throughout day and nighttime. We expect that future experiment with this unique setup will allow to further disentangle shoot CH₄ emissions and characterize their response to environmental conditions including light, temperature, and relative humidity.

How to cite: Kohl, L., Koskinen, M., Mäkiranta, P., Polvinen, T., Patama, M., Tenhovirta, S., and Pihlatie, M.: High frequency measurements reveal distinct sources of shoot methane emissions. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12917, https://doi.org/10.5194/egusphere-egu2020-12917, 2020.

Trees have been demonstrated to play a role in the methane (CH₄) and nitrous oxide (N₂O) cycling in forests. Emissions of these two greenhouse gases have been observed from tree stems and shoots. The stem emissions of both CH₄ and N₂O have been suggested to originate from the soil, however, their transportation mechanisms might differ, and furthermore, at least the stem-emitted CH₄ can also be produced within tree tissue. Boreal forests are considered a sink of CH₄ due to predominant soil oxidation, but when CH₄ is taken up by the roots, it bypasses the CH₄-oxidation zone in the surface soil. The stem N₂O fluxes at the boreal zone have been shown to follow seasonal physiological activity of trees. However, studies on tree CH₄ and N₂O fluxes are scarce in the boreal zone.

We studied the tree stem CH₄ and N₂O exchange from the stems of Scots pine, downy birch, and Norway spruce – in total 47 trees, growing at six study plots with naturally different soil moisture and ground vegetation conditions (6–9 trees per plot). The measurements were performed during July–August 2017 at the Hyytiälä SMEAR II (Station for Measuring Ecosystem-Atmosphere Relations) ICOS (Integrated Carbon Observation System) research site, in southern Finland. In addition to the stems, we measured forest floor CH₄ and N₂O fluxes at all the plots, and shoot CH₄ fluxes from birch and pine at one plot. The stem chambers were installed at the tree bases, ca. 30 cm above the soil surface. Additionally, from the trees with the shoot measurements, we measured the stem fluxes from several heights in order to study the flux variation in the stem vertical profile. All the flux measurements were conducted with closed chambers – the stem and forest floor measurements were performed by using manual sampling and gas chromatography, while a portable greenhouse gas analyser was used for the shoot measurements. Soil moisture and soil temperature were monitored at the study plots throughout the measurement period.

The results show that all the studied tree species emit both CH₄ and N₂O from stems. Birches growing at one plot with waterlogging conditions stand out with the highest stem CH₄ emissions. Concerning the N₂O emissions, birch stems showed significantly higher emissions than pine stems. The results of the shoot measurements indicate that both birch and pine emit small amounts of CH₄ from their shoots, but the driving factors of the emissions may be different for the two species. Our aim is to model the spatial variability of the stem CH₄ and N₂O fluxes at the site, and to develop an upscaling method combining the stem and forest floor CH₄ and N₂O exchange, based on an existing modelling work on the forest floor CH₄ fluxes at the site.

Acknowledgements: This research was supported by the Academy of Finland (288494, 2884941), National Centre of Excellence (272041), ICOS-FINLAND (281255), Czech Science Foundation (17-18112Y) and National Sustainability Program I (LO1415), and the European Research Council (ERC) under Horizon 2020 research and innovation programme, grant agreement No (757695).

How to cite: Vainio, E., Galeotti, L., Ghasemi, H., Haikarainen, I., Machacova, K., Patama, M., Pyykkö, P., Rauna, L., and Pihlatie, M.: The role of trees in the CH4 and N2O exchange in boreal forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20506, https://doi.org/10.5194/egusphere-egu2020-20506, 2020.

Trees can exchange methane (CH4) with the atmosphere through their stems. However, the magnitudes, patterns, drivers and origin of these emissions as well as the biogeochemical pathways that might result in net CH4 production or uptake are still poorly understood. One of the most important constraints is the limited information on the spatial and temporal variability of these emissions. Manual measurements are useful for measuring spatial variability of stem emissions (both within and between trees), but their low temporal frequency hinders our understanding of temporal patterns. In contrast, high-frequency measurements capture temporal variability, but instrumentation cost and complex technical logistics preclude high number of spatial replicates. In this study we combined manual and automated measurements of tree stem emissions in 18 different bitternut hickory trees (Carya cordiformis) in an upland forest during one growing season. Methane emissions were measured at two stem heights (75 and 150 cm) in three trees every 30 min, whereas the other 15 trees were measured once every two weeks at three different stem heights (50, 110 and 170 cm). Additionally, sap flow, soil temperature, soil water content, ground water level, and CH4 concentrations in the heartwood and in the soil profile were measured. Finally, we performed incubations of stem cores to test its potential for producing CH4. All trees were net sources of methane during the experiment, but some of them showed sporadic capture of CH4. High-frequency measurements revealed large temporal variability of stem emissions even within hours. Trees showed a seasonal trend of CH4 emissions partially explained by sap flow, soil moisture and temperature, but the pattern and the magnitudes were not consistent between and within trees. Even when a larger number of trees were studied (15 trees with manual measurements every two weeks), no consistent spatial pattern emerged among trees or with stem height, with emissions differing up to two orders of magnitude among trees. We found high CH4 concentrations in the heartwood of the trees (up to 75,000 ppm), no relevant concentrations in the soil profile (<6 ppm in all cases), and methanogenic capacity in all trees (stem cores were able to produce CH4 in laboratory incubations), supporting the interpretation that CH4 emitted by treestems was likely produced in the heartwood of the trees rather than being produced in soils and transported by the roots. Our results provide evidence on the potential origin of CH4 emitted by tree stems, but also indicate that the spatial and temporal patterns of stem emissions should be better described in order to assess the role of trees in local-to-global CH4 budgets.

How to cite: Barba, J., Poyatos, R., Capooci, M., and Vargas, R.: Methane emissions and origin in tree stems in an upland forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-275, https://doi.org/10.5194/egusphere-egu2020-275, 2020.

The increase of greenhouse gas (GHG) emissions into the atmosphere is promoting and accelerating climate warming. Among GHG sources, soils are an important natural source of GHG to the atmosphere through aerobic soil respiration that release carbon dioxide (CO₂). However, in riparian areas, soils can also release relevant amounts of methane (CH₄) and nitrous oxide (N₂O) through anaerobic processes promoted by high groundwater levels or flooded conditions. Recent studies have highlighted the role of trees in CH₄ emissions, but little is still known about the origin of these emissions, the processes involved, and their contribution to the global carbon and nitrogen cycles. To shed light on this issue, we measured GHG emissions (i.e. CO₂, CH₄, and N₂O) from the stems of two riparian tree species (Fraxinus agustifolia and Quercus robur) located along a gradient of soil moisture conditions (i.e. from wet to completely flooded soils) in a Mediterranean floodplain forest. Moreover, we also analyzed the isotopic carbon signature of the GHG emitted and the microbial communities inhabiting within tree stems by 16S rRNA gene analysis. Our results showed that CH₄ emitted by riparian tree stems was 100-fold higher at the flooded than at wet soil locations, while CO₂ and N₂O emissions did not vary across moisture conditions. When considering together emissions form soil surface and tree stems under flooded conditions, riparian trees contributed up to 20%, 40% and 60% of the total CH₄, CO₂, and N₂O emissions, respectively. Keeling plots suggested that CO₂ emitted through tree stems was produced within the soil compartment and thus transported to the atmosphere through the tree stems, whereas CH₄ emissions may have a different origin. However, methanogens were almost absent on the wood microbiome. The substantially higher presence of methanotrophs on the wood than on the soil compartment suggested that, despite CH₄ emitted by stems could come from soil microbial activity, the microbial consumption of that CH₄ within the tree stem could have changed its isotopic signature. Overall, our findings suggest that the riparian trees growing in this Mediterranean floodplain forest may mainly act as passive transporters of GHG produced in soils instead of being active GHG producers.

How to cite: Poblador, S., Martínez-Sancho, E., Menéndez-Serra, M., Casamayor, E. O., Estiarte, M., Lupon, A., Martí, E., Peñuelas, J., Sabaté, S., and Sabater, F.: Greenhouse gas emissions from a Mediterranean floodplain forest: the role of tree emissions under a changing flooding regime., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19009, https://doi.org/10.5194/egusphere-egu2020-19009, 2020.

Peatlands are an enormous sink of carbon and nitrogen. Natural and human disturbances may release them as greenhouse gases (GHGs) or water pollutants. Tropical peatlands have especially intensive matter cycling. Amazonia holds almost a half of tropical peatlands. Most of it is inaccessible to current forestry and drainage machinery and thus untouched by man. Tropical rainforest has been labelled ’lungs of the Earth’. While photosynthesis in mature forests does sequester carbon in biomass, they respire an equal amount of carbon dioxide (CO₂). Only swamp forests may sequester carbon in wet anoxic peat for centuries. However, anoxic decomposition of peat yields methane (CH₄) and suboxic processes release nitrous oxide (N₂O). Both have high global warming potential. In undisturbed peatlands, carbon sequestration outweighs GHG emissions. GHG budgets are more complicated in disturbed peatlands.

With an objective to clarify the greenhouse gas budget of tropical peatlands, the Department of Geography, University of Tartu held a measurement campaign in Iquitos, Peruvian Amazon in September 2019. We observed fluxes of the three GHGs using opaque chambers and measured potential environmental factors in three sites under various disturbance histories: 1) a Mauritia flexuosa palm-dominated swamp forest, 2) toe-slope swamp forest grown in 12 years on fallow pasture and banana plantation, and 3) slash-and-burn cassava field.

The toe-slope swamp respired the largest amounts of CO₂ while site differences were small and may have been offset by photosynthesis (which we did not measure). The wet swamp forest sites, especially palm trunks, emitted large amounts of CH₄. The dry slash-and-burn cassava field emitted little methane. The CH₄ emissions were strongly correlated with nitrogen content of the peat. Previous literature links high soil nitrogen content with lability of soil organic carbon and high microbial activity. The swamp forest floor emitted an average of 390 µg N₂O-N m^–2 h^–1 after torrential rainfall. The downpour may have carried just enough oxygen into the peat to trigger N₂O production by nitrification or hamper the full pathway of denitrification to N₂. High peat Ca⁺⁺ and Mg⁺⁺ content and pH>4 favoured nitrification. High NH₄⁺-N concentration in the swamp peat (190 mg kg^–1), which can be related to N₂ fixation and litter from three species of leguminous trees, formed a solid base for nitrification. The slash-and-burn cassava field emitted a sizable 37 µg N₂O-N m^–2 h^–1. In conclusion, the variety of disturbances produced an interesting pattern of GHG emissions in relationship with environmental conditions. Thus, Amazonian peatlands demand elevated attention.

How to cite: Pärn, J., Soosaar, K., Schindler, T., Macháčová, K., Alegría Muñoz, W., Fachín Malaverri, L. M., Jibaja Aspajo, J. L., Negron-Juarez, R., Rengifo Marin, J. E., Tello Espinoza, R., Cordova Horna, S., Pacheco Gómez, T., Urquiza Muñoz, J. D., and Mander, Ü.: High CH4 and N2O emissions from soil and stems of disturbed swamp forests in Peruvian Amazon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21139, https://doi.org/10.5194/egusphere-egu2020-21139, 2020.

The importance of greenhouse gas (GHG) emissions in global climate change is undisputed, but our understanding of the daily and seasonal variations of the GHG fluxes is far from complete and detailed flux estimates are unequally distributed among ecosystems worldwide. Carbon dioxide (77%; CO₂), methane (14%; CH₄) and nitrous oxide (8%; N₂O) are the three main GHGs that trap infrared radiations and contribute to climate change. While CO₂ has been largely studied, a considerable effort is still required to quantify the magnitude and drivers of CH₄ and N₂O, which have radiative effects 25 and 298 times greater than CO₂, respectively. Tropical forests play a pivotal role in global carbon (C) balance and climate change mitigation, accounting for 68% of global C stock and representing up to 30% of total forest soil C sink. In the tropics, soils are main contributors to the ecosystem GHG fluxes. In fact, tropical forest soils are the largest natural source of soil CO₂ and N₂O and are overwhelmingly reported as important sink of CH₄. More recently, studies reported that tree stems can also emit CO₂, CH₄ and N₂O and act, via passive transport through the soil xylem stream, as a pathway for these gas emissions to the atmosphere.

Although accurate estimates of GHG sources and sinks are of great importance for reducing the uncertainties of C cycle - climate feed-backs, we are only just beginning to understand the role of tropical tree stems as producers and / or conduits of soil-produced GHG.

I present first results of soil and tree stem GHG fluxes estimated over a six-month period, including a dry and a wet season, of continuous high frequency measurements with automated GHG flux systems in a tropical rainforest, in French Guiana. We adapted and extended an existing soil GHG flux system, combining a commercial automated soil CO₂ flux chamber system (LI-8100A) and CH₄ and N₂O analyser (Picarro G2308), to include tree stem chambers. Different closure times were applied to ensure reliable flux estimates, especially for low CH₄ and N₂O fluxes. I show that the new automated system operated successfully, allowing for robust long-term measurements to examine temporal variations and ultimately calculate budgets of CO₂, CH₄ and N₂O fluxes at soil and tree stem levels. Our results indicated that soils and tree stems acted exclusively as source for CO₂, whereas soils and tree stems exhibited distinct patterns for both CH₄ and N₂O, which highlights the importance of partitioning GHG fluxes to better determine environmental controls regulating ecosystem GHG exchanges.

How to cite: Brechet, L., Daniel, W., Stahl, C., Burban, B., Goret, J.-Y., Salomόn, R. L., and Janssens, I. A.: Towards a better understanding of soil- and tree stem-atmosphere exchanges of greenhouse gases, i.e. CO2, CH4, N2O, in a tropical rainforest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11242, https://doi.org/10.5194/egusphere-egu2020-11242, 2020.

The vadose zone (VZ), found between the surface and groundwater level, can store massive amounts of CO₂, recording values greater than 60,000 ppm to depths of a few tens of meters. The CO₂ is produced mostly in the first meters of soil due to root respiration and microorganisms and, to a lesser extent, to geochemical reactions. Although commonly CO₂ is produced mostly near the surface, the concentration increases with depth, due mainly to transport in two phases: 1) infiltration of CO₂-enriched water followed by precipitation and CO₂ release in deeper layers, and 2) percolation of CO₂-rich air due to its high density. These transport process contribute to natural CO₂ accumulation in the VZ, whose storage capacity depends on its thickness and porosity. All this CO₂ storage can be exchange with the atmosphere mainly determined by differences in the temperature between the internal and external atmosphere.

Here we study a borehole located next to Nerja Cave (Málaga, Spain) developed within fissured and karstified Triassic dolomitic marbles. Our objective is to determine the main drivers involved in subterranean CO₂ exchange with the atmosphere. To do that, CO₂ molar fraction, air temperature, relative humidity, wind speed and direction were monitored in the top of the borehole, and were correlated with external variables as air temperature, relative humidity, atmospheric pressure, rain and sea tides. Results shown that within a few hours, the CO₂ molar fraction can increase ten times more, showing a pattern with two cycles per day. In periods with low CO₂ molar fraction the air penetrates into the borehole, on the other hand, periods with high CO₂ values are due to the borehole CO₂-rich air is moving toward the external atmosphere. We found that the CO₂ emitted to the atmosphere by this borehole is several orders of magnitude than the soil CO₂ fluxes in this area. Therefore, we need to produce accurate long-term estimates of borehole CO₂ fluxes to improve our understanding of its contribution to local carbon balance.

How to cite: Sanchez-Cañete, E. P., Benavente, J., Liñan, C., Ojeda, L., and Vadillo, I.: Patterns in CO2 exchange to the atmosphere from a borehole located in a Mediterranean karst system (Málaga, southern Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5650, https://doi.org/10.5194/egusphere-egu2020-5650, 2020.

The characterization of CO₂ transport, and other C compounds (CH₄, DIC, organic matter, etc.), in the vadose zone of a karst aquifer is key in order to quantify sources and sinks of carbon. In karst environments, most of the studies are focused on the dynamics of CO₂ in caves, but only a few studies are related to field measurements of the CO₂ content in boreholes, which provides direct insights about the vadose zone. Located at the east of the Nerja Cave (Malaga, Andalusia), one of the most important tourist caves in Spain, the vadose zone was accessed by 9 boreholes drilled into the vadose zone of a Triassic carbonate aquifer, with depths ranging between 15 and 30 m. The karst network in the study area is characterized by a great vertical heterogeneity, with significant cavities and voids at specific intervals. Groundwater levels at different altitudes are a consequence of this heterogeneity. Similarly, CO₂ distribution and transport are clearly determined by the complex karst network.

Our study aims to identify significant horizontal gradients of CO₂ in the karst vadose air, both spatial and temporally. We present monthly measurements of CO₂ concentration, relative humidity, air temperature and ²²²Rn inside boreholes. In addition, we present CO₂ results from an 18 hours-atmospheric air injection test. Linking them to the geophysical knowledge of voids in the study area, the results allow us to identify lateral fluxes of CO₂-rich air in the vadose zone and how these fluxes are favoured by the incidence of the main karst discontinuity orientations. We observe different ventilation patterns:  in spring the vadose air seems to be stored in specific orientations, while in summer there is a lower convective ventilation. The results contribute to explain the temporal variations of the chemical composition of recharge water in karst systems, as well as to support studies on the global carbon budget.

How to cite: Ojeda, L., Benavente, J., Vadillo, I., Liñán, C., and P. Sanchez-Cañete, E.: Borehole-based study of CO2-rich air transport in the vadose zone of a Mediterranean karst system (Malaga, southern Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7483, https://doi.org/10.5194/egusphere-egu2020-7483, 2020.

Karsts cover up to 25 % of the land surface and contain significant sedimentary deposits that become active cave-soils. Subterranean karst ecosystems play an active role in the global carbon cycle in terms of their contribution to the global GHG balance. They act alternately as a source or sink of CO₂ and as a rapid sink of CH₄. The most recent results indicate that microbiota must play a significant ecological role in the biogeochemical processes that control the subterranean atmosphere composition. Soils forming underneath the surface must host a large part of the subterranean microbiota. But to date, their behaviour concerning the production of gases and exchange with the “confined troposphere” has not been evaluated. Systematic direct estimates of CO₂ and CH₄ fluxes from cave-soils do not exist in literature. And they are needed before global generalizations can be made about the carbon budgets (emissions and sinks) of karstic ecosystems.

Here we present pioneering research to evaluate the carbon fluxes from the cave soils directly exchanged with the cave atmosphere. This preliminary study is the first approach to systematically characterize the role of cave-soils in the production and transport of CO₂ and CH₄ in the subterranean environment. We carried out automatic in situ and real-time monitoring of CO₂ and CH₄ diffusive fluxes from a sedimentary alluvial soil in Pindal cave for one year (north Spain). We developed seasonal campaigns for CH₄ and CO₂ fluxes daily continuous monitoring by a LICOR closed chamber-based gas exchange system, in conjunction with a compatible Gasmet FTIR gas analyser. Moreover, autonomous equipment monitored the main micro-environmental parameters of the local subsurface-soil-atmosphere system. To interpret gas exchange processes and rates, and to understand the underlying mechanisms in soils, we also carried out seasonal δ¹³C geochemical tracing by using Picarro cavity ring-down spectroscopy, through simultaneous cave atmosphere-soil-chamber air samplings. We also characterized the soil microbial communities related to the carbon cycle by meta-barcoding analyses of bacterial 16S rRNA genes and Shotgun Metagenomics.

Preliminary results show net CO₂ emissions from cave-soil on a daily scale, resulting from respiration by chemotrophic microorganisms. We detect significant magnitude variations along the day, reaching occasionally values close to zero. This is remarkable in such thermo-hygrometric stable environment and absence of light. Changes in the cave ventilation regime seems to be the determining factor just in some cases. Intrinsic microbial processes appear to be decisive in others. The results also reveal net CH₄ uptake from cave-soil on a daily scale, with no significant magnitude variations along the day. It seems to be linked to the metabolism of Nitrate-dependent methanotrophs belonging to the phylum Rokubacteria. Additionally, we detected significant variations in magnitude and different flow patterns in the cave-soils colonized by biofilms, most prominent in the case of moonmilk deposits.

These preliminary results confirm that cave-soil is playing an outstanding role in the processes of production, consumption and storage of CO₂ and CH₄ and may be partially determining the strong variations of these major GHGs in natural subterranean ecosystems.

How to cite: Cuezva, S., Martin-Pozas, T., Fernandez-Cortes, A., Canaveras, J. C., Janssens, I., and Sanchez-Moral, S.: On the role of cave-soil in the carbon cycle. A fist approach., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21793, https://doi.org/10.5194/egusphere-egu2020-21793, 2020.

Dissolution of CaCO₃ in calcareous soils is mainly governed by CO₂ which forms a weak but ubiquitous acid in the aqueous phase. Soil CO₂ concentrations are generally higher than atmospheric concentrations due to the CO₂ production in the soil. It is generally assumed, that it is mainly the CO₂ concentration in the soil and the discharge that control the re-location of CaCO₃, and thus the further formation of soil and karst. In most cases soil and karst systems are considered to be static and that the CaCO₃ dissolution process is a steady state process. However, we know that soil CO₂ concentrations can be highly dynamic and are affected by soil temperature and soil moisture. Our objective was to investigate whether this steady state assumption regarding carbonate dissolution and transport can be applied or whether we have to consider the dynamics and interaction of soil CO₂ and dissolution of CaCO₃ in the aqueous phase.

We report on insights from a 3 year field study in a calcareous soil in which soil CO₂ concentrations and its response to soil moisture and precipitation were investigated. Low intensity precipitation resulted in slow increase in soil CO₂ concentration, since increased soil water content blocks formerly air-filled pores. Intense precipitation events were followed by fast infiltration and probably preferential flow. Intense precipitation also resulted in temporary drops in soil CO₂. These drops can be explained by a relative under-saturation of the soil solution at a certain depth. The soil solution is mixed with infiltrating rain water, which is still equilibrated with the lower atmospheric CO₂ concentrations and thus drawing CO₂ from the surrounding soil air. These mechanisms should results in a much stronger dissolution of local CaCO₃ and net transport of dissolved CaCO₃.

A following laboratory experiment on mesocosms of natural soil and restructured soil was used to test and reproduce the observed CO₂ patterns as well as dissolution and transport of carbonate due to precipitation events. These experiments also showed that higher intensity of precipitation results in stronger drops in soil CO₂ concentration and higher transport rates of dissolved CaCO₃. Hydrus1D was used to model soil CO₂ dynamics and dissolution of CaCO₃ in the aqueous phase for the measured scenarios. The observed general pattern of the “drops” of soil CO₂ could be easily reproduced confirming the assumption of CO₂ undersaturated soil water right after the precipitation events. The natural soil mesocosm showed comparable patterns in all precipitations experiments. The restructured soil mesocosm showed a high mobilization and drainage during the first precipitations experiments which then fast declined to the level of the natural soil mesocosm. We interpret this as fast dissolution and washing off of carbonates attached to the macropore surfaces in which preferential flow occurs.

We conclude that dynamics and interaction of soil CO₂ and dissolution of CaCO₃ in the aqueous phase are highly dynamic and affected by preferential flow. It seems that general patterns can be reproduced using Hydrus 1D, with the hydrological parametrization as a major challenge.

This research was financially supported by DFG (MA 5826/2-1).

How to cite: Maier, M., Osterholt, L., and Hartmann, A.: Dynamics and effects of soil CO2 on carbonate dissolution and transport in response to precipitation events , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19189, https://doi.org/10.5194/egusphere-egu2020-19189, 2020.

Biochar (charcoal made from biomass in the pyrolysis process) has found broad application in agriculture. The research performed with biochar revealed the positive impact of biochar application for chemical and physical properties of soil. Biochar was also used as an material for decontamination of soil from heavy metals and pesticides. The improved water retention of soil after biochar application was shown as well. There are particular research concerning the usage of biochar as an material for decontamination of soil from anthropogenic radioactive material including Cs-137 and Sr-90 deposited after nuclear weapon test. However, the biochar find the most practical application in agriculture for improvement of crops efficiency and water retention of soils. The typical application amount of biochar for agricultural purpose varies from 40 to 100 Mg ha^-1.

Actually, there are numerous research activities focused on the direct impact of biochar on physical and chemical soil properties. Simultaneously lack of information are available for issue if and how biochar impact for environment radioactivity. As one of that impact could be  the influence on radon emission from soil surface. The aim of presented work was to investigate the impact of biochar application into the soil for the radon emission process.

The research objects were soil samples collected from experimental fields with biochar applied at doses from 1 to 100 Mg ha^-1. Two type of biochar were investigated – first biochar produced from sunflower husk at temperature of 650°C and second biochar produced from wood chips at temperature of 650°C. The radon emanation coefficient were assessed using active cumulative technique incorporating AlphaGUARD instrument equipped with sealed accumulation box.  In addition, we directly measured radon exhalation rate at the experimental fields. As the emanation coefficient calculation require the information on Ra-226 activity concentration, the gamma spectrometry analysis using HPGe detector were performed for samples collected on particular field.  

The results of activity concentration assessments shown that the most visible effect of biochar application into the soil is associated with the reduction of soil bulk density by this material. No significant changes in activity concentration depending on the biochar dose applied were observed for Ra-226. Fluctuation in radon exhalation rate as well as in emanation coefficient, depending on the biochar dose (from 1 to 100 Mg ha^-1) were observed and presented.

The research was partially conducted under the projects “Water in soil – satellite monitoring and improving the retention using biochar” no. BIOSTRATEG3/345940/7/NCBR/2017, which was financed by the Polish National Centre for Research and Development in the framework of “Environment, agriculture and forestry” – BIOSTRATEG strategic R&D programme.

How to cite: Szewczak, K., Wołoszczuk, K., Jednoróg, S., Rafalska-Przysucha, A., Gluba, Ł., and Lukowski, M.: Impact of soil incorporation of biochar on radon emission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6689, https://doi.org/10.5194/egusphere-egu2020-6689, 2020.

Accurate measurements of nitrous oxide (N₂O) fluxes from soils are necessary to understand dynamic changes in soil nitrogen cycles. Laboratory incubation experiments provide a controlled condition to measure these N₂O fluxes. Before incubation experiments, soils are often stored at certain conditions to minimize the microbial activities. However, the effect of soil storage on N₂O emission has been poorly studied. A laboratory incubation experiment was conducted using disturbed soils to study the storage effect. The soil was sieved to 2mm and the following four treatments were tested: fresh undisturbed (FU), fresh sieved (FS), fridge stored at 4ºC (ST), and stored at room temperature after drying (PI). After soil samples were brought to 60% water-filled pore space (WFPS), ¹⁵N labelled urea (1 At%) was applied at the rate of 50 mg N kg^-1 soil and the soil was incubated at room temperature (23 ºC). The N₂O fluxes were measured for 7 weeks using off-axis integrated cavity output spectroscopy (OA-ICOS, Los Gatos Research, California, USA). Cumulative N₂O fluxes and Keeling plot intercepts (δ¹⁵N source) were calculated. The results showed that soil storage has a significant effect on N₂O emission. Over the 7-week period, ST produced the highest cumulative N₂O emissions (2.70 µg N g^-1 soil) as well as the largest amount of N derived from fertiliser (Ndff) (1.4 µg N g^-1 soil). FU produced the lowest cumulative N₂O emissions (1.0 µg N g^-1 soil) but the largest amount of N derived from soil (Ndfs) (0.6 µg N g^-1 soil). The daily N₂O fluxes of FS and FU declined rapidly after the peak emissions, but the fluxes of PI and ST fluctuated after the peaks. These results indicate that soil storage affects microbial processes and therefore N₂O emissions. Our results suggest using fresh soil to avoid storage effects. If this is not possible the effect of soil storage should be considered before the experiment.  

How to cite: Ding, Y., Heiling, M., Zaman, M., Resch, C., Dercon, G., and Heng, L. K.: Use of laser spectroscopy to evaluate the influence of soil storage on N2O emission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4570, https://doi.org/10.5194/egusphere-egu2020-4570, 2020.

Greenhouse gas emission from agricultural ecosystems are one of major environmental issue, recently. Our research aim is improving greenhouse gas flux measurement method precisely, inexpensively and automatically in agricultural ecosystems. Measurement method for CO₂, CH₄ and N₂O simultaneous analysis (3GHG-GC) was firstly launched in 2005 followed by automatic gas sampling system (AGSS) in 2006, automatic injector for GC (RoVi) in 2013 and nitrogen generation system from compressed air for precise GC analysis in 2011, respectively. 3GHG-GC was recently further improved that the carrier gas of this method was changed from helium to nitrogen or argon to meet global requirement to save helium consumption. In "3GHG-GC", 3 stages of packed separation column using Porapak Q (Waters Co. Ltd. USA) and Unibeads C (GL Science Co. Ltd. Japan). Shimadzu GC-2014 gas chromatograph equipped with thermal conductivity detector (TCD), flame ionization detector (FID) and electron capture detector (ECD). The carrier gas was purified nitrogen generated by compressed air. The impurity of methane in the carrier nitrogen was eliminated by catalytic chemical treatment to measure precise atmospheric level of CH₄. Finally the system "3GHG-GC" achieved three gas combined precise measurement with standard error of  within 1% without gas cylinder for carrier gases.  

How to cite: Sudo, S.: Development of combined measurement method for methane, nitrous oxide and carbon dioxide without gas cylinder by gas chromatography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10266, https://doi.org/10.5194/egusphere-egu2020-10266, 2020.

Gas fluxes between soil and atmosphere play an important role for the global greenhouse gas budgets. Several methods are available to determine soil gas fluxes. Besides the commonly used chamber methods the gradient method becomes more and more important. Chamber methods have the disadvantage that the microclimate can be influenced by the chamber which can affect gas fluxes. This problem does not occur with the gradient method. Furthermore the gradient method has the advantage that it can provide information about the depth profile of gas production and consumption in the soil.

The concept of the gradient method is to calculate gas fluxes by the vertical concentration gradient of a gas in the soil. For the calculation of the flux the effective diffusivity coefficient of the soil is needed. This can be approximated by models or by lab measurements. However, both of these approaches often fail in explaining site specific characteristics and spatial variability. Another way to determine soil gas diffusivity is to apply the gradient method using a tracer gas. By the injection of a tracer gas with known flux soil gas diffusivity can be measured in-situ.

We developed an innovative sampling set-up to apply an improved gradient method including the possibility to determine soil gas diffusivity in situ. We designed a sampler with build-in CO₂ sensors in multiple depths that can easily be installed into the soil. With this sampler CO₂ concentrations can be measured continuously in several depths. This enables the identification of short-time effects such as the influence of wind-induced pressure pumping on gas transport. The sampler allows tracer gas injection into the soil for in-situ diffusivity measurement. We decided for CO₂ as a tracer gas because it can be measured with small sensors which keep the set-up simple. To account for the natural CO₂ production in the soil we developed a differential gas profile approach. Using an additional reference sampler allows measuring the natural CO₂ gradient without the tracer signal, and thus subtracting the tracer CO₂ signal from the natural CO₂ signal.

The sampler consists of one 3D print segment per depth each containing one CO₂ sensor. These parts can be combined to a sampler with flexible amount of measurement depths. The construction with individual segments allows a better maintenance in case of sensor defects. For the installation of the sampler a hole has to be drilled, into which the sampler is inserted. To prevent gas bypassing along the wall of the drill hole we equipped each segment with an inflatable gasket between the measurement locations.

In a next step we will evaluate the sampler and test it in the lab and under different environmental conditions. We expect that with this sampler we will be able to run gas transport experiments in the field with a high temporal resolution and relatively low effort.

Acknowledgements

We thank Alfred Baer and Sven Kolbe for the technical support.

How to cite: Osterholt, L. and Maier, M.: Development of an in-situ CO­2 gradient sampler, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7272, https://doi.org/10.5194/egusphere-egu2020-7272, 2020.

Soil respiration is one of the most significant carbon fluxes in terrestrial ecosystems. The analyses and quantification of soil CO2 production and its influencing factors play a crucial role in the understanding of the global carbon budget.

To investigate CO₂ efflux from terrestrial soils under field conditions, manual or automated soil chambers are the most common methods. The flux-gradient approach (FGA) as an alternative method applies Fick’s law to vertical profiles of soil CO₂. The FGA uses the soil gas diffusivity to calculate vertical fluxes of soil CO₂ and the CO₂ efflux from soil. The vertical partitioning the production of CO₂ in different soil layers can be regarded as an option and an advantage of FGA as compared to chamber methods.

This investigation aims at clarifying whether a spline or an exponential function is more suitable for fitting vertical distributions of measured CO₂ concentrations. We compared simulation results on the CO₂ efflux and the vertical distribution of CO₂ production within the soil when applying an exponential function or a spline function, respectively. Soil CO₂ concentrations were measured at the soil surface and at 0, 0.1, 0.2, 0.3 and 1.0 m soil depth of a Scots pine and a European beech forest stand of the Northeast German Lowlands. Additionally, the CO₂ efflux was estimated by applying the manual chamber method. The results suggest that vertical distribution function of soil CO₂ affects both the calculated CO₂ efflux and the production of soil CO₂. The CO₂ efflux from the chamber method fits best with the CO₂ efflux from spline function. We discus some effects with the application of the spline function on the calculated vertical distribution of CO₂ production.

How to cite: Jochheim, H., Wirth, S., Paulus, S., Maier, M., Haas, C., and Gerke, H. H.: The effect of vertical distribution functions on CO2 efflux and production calculated with the flux gradient approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17686, https://doi.org/10.5194/egusphere-egu2020-17686, 2020.

The interface of the Earth’s critical zone is the place where organic carbon is dramatically decomposed and transformed．The dynamics and fate of organic carbon serve as an important foundation to reveal the material transportation in the Qinghai-Tibet Platea critical zones. This research analyzed temperature, soil moisture and stable carbon isotope values (δ¹³C) of CO₂ in different soil layers, measure soil surface respiration using soil respiration measurement system (LI-8100) , and analyzed carbon storage , carbon dynamics and its controlling factors in critical zones in seven typical ecosystems of the Qinghai-Tibet Platea. The results found that the underground carbon content and its controlling factors were very different in different ecosystems on the Qinghai-Tibet Plateau. The main controlling factor of carbon changes was water in alpine steppe and desert ecosystem while it was temperature in alpine meadow. In the meanwhile, this research also measured the maximum carboxylation rate (V_cmax) of dominant plants in each ecosystem, trying to explore the different carbon inputs in different ecosystems. Understanding the impacts of environmental changes on the geochemical cycling of critical zone’s organic carbon in the Qinghai-Tibet Platea would benefit the optimization of carbon cycling model and climate change predictions．

How to cite: Yao, H., Wang, P., Yang, C., Xu, X., Wei, J., Shi, F., Guo, N., Yao, H., and Li, X.: Soil organic carbon dynamics and controlling factors in typical ecosystems of the Qinghai-Tibet Platea critical zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20806, https://doi.org/10.5194/egusphere-egu2020-20806, 2020.

Atmospheric emissions and concentrations of CH₄ are continuing to increase, making CH₄ the second most important human-influenced greenhouse gas in terms of climate forcing, after CO₂. Previous studies indicated that wetland CH₄ emission is not only the single largest but also the most uncertain natural source in the global CH₄ budget. Furthermore, the strong sensitivity of wetland CH₄ emissions to environmental conditions has raised concerns on potential positive feedbacks to climate change. Therefore, evaluation of the process-based land surface models of earth system models (ESMs) in simulating CH₄ emission over wetlands is needed for more precise future predictions. In this work, a set of high-latitude wetland sites with various nutrient conditions are studied. The wetland CH₄ fluxes are simulated by the land surface model JULES of the UK Earth System model and the Helsinki peatland methane emission model (HIMMELI), which is developed at Finnish Meteorological Institute and Helsinki University. The differences between the modelled and observed CH₄ fluxes are analyzed, complemented with key environmental variables for interpretation (e.g. soil temperature and moisture, vegetation types, snow depth, NPP, soil carbon). In general, the simulated CH₄ fluxes by HIMMELI is closer to the observed CH₄ fluxes in magnitude and seasonality at sites than those by JULES. The inter-annual variability of simulated CH₄ fluxes by HIMMELI depends on the simulated anoxic soil respiration, which serves as the substrate of the CH₄ fluxes in HIMMELI. The anoxic soil respiration is calculated based on the simulated soil respiration and water table depth in JULES. More accurate simulation of soil carbon pool and water table depth in JULES will lead to improvement in the simulated anoxic soil respiration.

How to cite: Gao, Y., Burke, E., Chadburn, S., Raivonen, M., Vesala, T., Aurela, M., Lohila, A., Yang, H., Li, T., and Aalto, T.: Evaluation of modelled methane emissions over high-latitude wetlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12686, https://doi.org/10.5194/egusphere-egu2020-12686, 2020.

The aim of this study was to investigate the spatial heterogeneity of CO₂ emission of two different croplands in Croatia (Šašinovec, 45° 50´ N; 16° 11´ E; soil type - Stagnosols) and in Hungary (Józsefmajor, 47° 40´ N; 19° 36´ E; Chernozems). The measurements of the soil water content (SWC), soil temperature (Ts), organic matter (OM) and CO₂ flux was executed after the harvest of the soybean in both fields. In a regular grid (2 x 2 m and 2 x 3 m) 44 and 170 samples were collected from Croatian and Hungarian site, respectively. At Hungarian site Ts and SWC showed relatively high spatial heterogeneity, ranging from 19.4 to 24.6 ^oC, and from 7.5 to 34.1%, respectively. Content of soil OM had lower variability ranging from 2.0 to 2.4 % at Croatian and from 3.2 to 4.5 % at Hungarian site, respectively. CO₂ efflux was 0.125 ± 0.078 and 0.060 ± 0.088 mg m^{- 2} s^-1 in average at Croatian and Hungarian field, respectively. Investigated properties did not follow normal distribution, so logarithm transformation were applied before modelling. Kriging interpolation model for mapping soil properties is tested to compare the prediction accuracy. Soil maps showed sufficient concentrations of soil OM at Hungarian site and insufficient concentrations of OM at Croatian site. Soil CO₂ efflux map showed that the largest part of the investigated area in Hungary have low loss of C, while loss of C at Croatian site is high. There are areas, especially wheeled rows, where CO₂ emission is lower than the average value of the field at both investigated site. These low CO₂ emission areas coincide with the compacted row of wheel tracks. For future management it is necessary to provide better conditioning of soil at Croatian site and adopt environmental friendly soil management at both sites. 

This work is supported by the Croatian-Hungarian Bilateral Project (2018-2.1.12-TÉT-HR-2018-00007) and the PD116084  and NKFIH131792 reseach project.

How to cite: Toth, E., Dencső, M., Gelybó, G., Mészáros, J., Bakacsi, Z., Horel, Á., Josip Telak, L., Galic, M., Kisic, I., and Bogunovic, I.: Spatial heterogeneity of CO2 emission in Hungarian and Croatian arable fields – preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19704, https://doi.org/10.5194/egusphere-egu2020-19704, 2020.

This study focuses on the soil N₂O emission of arable fields. We initially set up several soil column experiments in laboratory and based on these findings we started field measurements in a long term tillage experiment at Józsefmajor Experimental and Training Farm, Hungary. For the column experiments we collected undisturbed soil columns (d=10 cm, h=10 cm) from mouldboard ploughing (P) and no-till (NT) treatments.  We investigated the effect of different fertilizer doses (40, 80, 160, 240 kg h^-1 N), soil water content (SWC) and different tillage methods on soil N₂O emission.

We found a nonlinear response of N₂O emission on the applied fertilizer doses. The moderately fertilized (80-160 kg ha^-1 N) samples had the highest N₂O emissions. Samples from NT had higher N₂O emission than samples from P. We found better correlation between N₂O emission and SWC in NT (R² is between 0.47 and 0.62) than in the P (R² is between 0.01 and 0.35).  The N₂O emission values showed high spatial variability. The field measurements showed similar findings of N₂O emission compared to the column experiments. In 2020 we intend to continue the field measurements and include further investigations of governing factors of soil N₂O emission.

How to cite: Dencső, M., Baklanov, S., Horel, Á., Gelybó, G., and Tóth, E.: N2O emission and governing factors on arable fields, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-388, https://doi.org/10.5194/egusphere-egu2020-388, 2020.

Increase in the concentration of greenhouse gases (GHGs) in the atmosphere threatens the existence of many ecosystems and their inhabitants. Agricultural activities contribute up to 70 % of total anthropogenic emission of nitrous oxide (N₂O), one of the GHGs, which is characterized with the highest global warming potential and contributes to stratospheric ozone depletion. Our study presents the results obtained from the recent field and lab activities carried out in order to obtain better insight into the factors that define the presence of N₂O in groundwater. Previous large scale investigations, performed in the Hesbaye chalk aquifer in Eastern Belgium, suggested that the concentration of N₂O in the aquifer depends on different, possibly overlapping biochemical processes such as nitrification, denitrification and/or nitrifier-denitrification. This study explored the occurrence of biochemical stratification in the same aquifer and its impact on N₂O production and consumption mechanisms. For this purpose low flow sampling technique was applied at different depth intervals to obtain better insight into the extent of oxic and anoxic zones and variability of concentrations of GHGs along the vertical profile. Collected groundwater samples were analyzed for the range of hydrochemical parameters as well as NO₃^-, N₂O, H₂O and B isotopes signatures and N₂O isotopomers. Afterwards, rates of nitrification and denitrification processes were estimated based on short-term incubations of collected groundwater amended with NO₃^- and NH₄⁺ compounds labeled with heavy ¹⁵N isotope. In addition, in order to characterize the dynamics of ongoing biogeochemical processes, polymerase chain reaction (PCR) tests for detection of the activity-specific enzymes in the aquifer were performed. Such studies help to clarify which conditions are more prone to the accumulation of high concentrations of GHGs in aquifers and better constrain models which estimate local and regional GHGs budgets.

Acknowledgments

This project has received funding from the European Union’s Horizon 2020 research and innovation  programme under the Marie Skłodowska-Curie grant agreement No 675120.

How to cite: Nikolenko, O., Morana, C., Taminiau, B., Borges, A. V., Robert, T., Goderniaux, P., Duvivier, M., and Brouyѐre, S.: Vertical interval dynamics of greenhouse gases in groundwater (Hesbaye chalk aquifer, Belgium) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4958, https://doi.org/10.5194/egusphere-egu2020-4958, 2020.

Ammonia (NH₃) emissions from farmlands and livestock are attracting more and more attention. There is an urgent need for ground-based instruments that can acquire the spatial and temporal variability in NH₃ concentrations and emissions, particularly in field environments where power and shelter are not readily available. However, accurate measurements of atmospheric NH₃ is of great challenges due to its reactive nature. Conventional NH₃ instruments are subject to drawbacks, such as slow response time, limited precision, intensive maintenance, or high power consumption due to the use of the closed-path tube, optics, and vacuum pump.

We have developed an open-path instrument for fast (10 Hz) and sub-ppbv sensitivity measurements of atmospheric NH₃ concentration. The instrument is based on second-harmonic (2f) wavelength modulated laser absorption spectroscopy technique (WM-LAS), which employs a distributed-feedback semiconductor quantum cascade laser (DFB-QCL) and a HgCdTe (MCT) photodetector. An open-path Herriott cell configuration with a 0.5 m physical path and 46 m optical path-length is used for selective and sensitive detection of the mid-infrared absorption transition of NH₃ at 9.06 μm [1]. There is no delay due to sample adsorption. The instrument has a precision (1σ noise level) of 0.53 ppbv and 0.15 ppbv at a sampling frequency of 10 Hz and 1 Hz, respectively. The entire NH₃ instrument has a weight of ~7 kg and dimensions of 84 cm (length) and 20 cm (diameter). It can be powered by rechargeable lithium batteries, with a total power consumption of as low as 50 W. The instrument has strong environmental adaptability and is suitable for field deployment in various environments. It can be used in ground-based or vehicle-based measurements of atmospheric NH₃ concentration.

With the good performance in terms of response time and precision, this instrument is an ideal tool for NH₃ flux measurements based on the eddy covariance (EC) technique [2]. An EC flux system was built based on the open-path ammonia instrument, which also included a CSAT3 sonic anemometer (Campbell Scientific®) and LI-7500 (LICOR®) for water vapor (H₂O) and carbon dioxide (CO₂) measurements. The system was installed at a rice paddy field with a typical Chinese-style rice-duck symbiosis system in Jiangsu province, China. Experiments showed that the lower detection limit of the EC system for NH₃ flux was around 17ng m^-2 s^-1.

References:

[1] Miller, D. J., Sun, K., Tao, L., and Zondlo, M. A.: Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements, Atmos. Meas. Tech., 7, 81–93,2014.
[2] McDermitt, D., Burba, G., Xu, L., Anderson, T., Komissarov, A., Riensche, B., Schedlbauer, J., Starr, G., Zona, D., Oechel, W., Oberbauer, S., and Hastings, S.: A new low-power, open-path instrument for measuring methane flux by eddy covariance, Appl.Phys. B, 102, 391–405, 2011.

How to cite: Wang, Y., Wang, K., Kang, P., Lu, Y., Zhen, X., Liu, G., and Zheng, X.: An open-path QCL-based instrument with sub-ppbv sensitivity for NH3 eddy covariance measurement, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6223, https://doi.org/10.5194/egusphere-egu2020-6223, 2020.

Inverse dispersion modelling (IDM) using a backward Lagrangian stochastic (bLS) dispersion model has been successfully applied to quantify emissions from confined ground sources e.g. as for ammonia (NH₃) loss after manure spreading. The most widely used bLS model for emission measurements of NH₃ and methane (CH₄) from agricultural sources such as lagoons and livestock buildings is based on Flesch et al. (2004). For such applications, the model assumptions of a diffusive ground source within a homogeneous turbulence field, which implies absence of obstacles as e.g. buildings disturbing the flow, is clearly not fulfilled. It remains unclear to what extend these violations introduce bias into the emission estimates. Further, the model by Flesch et al. does not include deposition removal, which for NH₃, can induce an underestimation of the emission from the source (Häni et al., 2018). Häni et al. extended the standard bLS calculation model with an optional dry deposition mechanism.

In a field campaign between mid-September and mid-December 2018, CH₄ and NH₃ emissions from a natural ventilated dairy housing with 40 cows were quantified using the IDM method with the bLS model by Häni et al. (2018). From the three-month period, results for 63 measurement days at 30-minute resolution were evaluated and thereof 71% of the data points were discarded from the emission calculation due to inapplicable turbulence conditions or instrument failure.

NH₃ and CH₄ concentrations were analysed with open-path instruments (NH₃: miniDOAS,; CH₄: GasFinder, Boreal Laser, Inc., Edmonton, Alberta, Canada) (aligned in parallel) with 50 m path lengths (distance between sensor and reflector). During part of the field campaign (24 days), simultaneous in-house measurements of CH₄ and NH₃ emissions using the tracer ratio method (iTM) (SF₆ and SF₅CF₃, Mohn et al., 2018) were conducted and results compared with the estimates retrieved by the IDM method. Overall, the results from the IDM method compare well to the results of the in-house measurements, with mean daily emissions of 18.3 kg CH₄/d (IDM) and 17.9 kg CH₄/d (iTM) and 1.08 kg NH₃/d (IDM) and 1.56 kg NH₃/d (iTM), respectively. Regarding NH₃, the IDM method was run without the inclusion of a dry deposition mechanism. First results from IDM calculations with the inclusion of dry deposition indicate, that dry deposition modelling may explain the difference in NH₃ emissions between the IDM method and the iTM.

References

Flesch, T. K., Wilson, J. D., Harper, L. A., Crenna, B. P., and Sharpe, R. R.: Deducing ground-to-air emissions from observed trace gas concentrations: A field trial, J. Appl. Meteorol., 43, 487–502, 2004.

Häni, C., Flechard, C., Neftel, A., Sintermann, J., and Kupper, T.: Accounting for Field-Scale Dry Deposition in Backward Lagrangian Stochastic Dispersion Modelling of NH3 Emissions, Atmosphere, 9, 146, 2018.

Mohn, J., Zeyer, K., Keck, M., Keller, M., Zähner, M., Poteko, J., Emmenegger, L., and Schrade, S.: A dual tracer ratio method for comparative emission measurements in an experimental dairy housing, Atmospheric Environment, 179, 12–22, 2018.

How to cite: Häni, C., Bühler, M., Schrade, S., Zähner, M., Wyss, S., Mohn, J., and Kupper, T.: Quantifying NH3 and CH4 emissions from a dairy housing using backward Lagrangian stochastic modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13487, https://doi.org/10.5194/egusphere-egu2020-13487, 2020.

As a central process in the hydrological system and the climate system, terrestrial evapotranspiration is a key factor furthering our understanding of the climate change processes. Knowledge of factors controlling the variability in evapotranspiration is crucial for the prediction of the fate of terrestrial ecosystems under environmental changes. Based on long-term (2005-2014) eddy covariance flux data observed at a rainfed maize site in northeast China, the purpose of this study was to clarify the environmental regulation of actual evapotranspiration (ET) and the extent to which the regulatory effects on ET are directly or indirectly mediated by changes in biotic factors, using the structural equation modeling (SEM) method. The results showed that annual total ET was 397 ± 35 mm for the rainfed maize site in comparison with 575 ± 169 mm of precipitation (Prec), with an ET/Prec ratio ranging from 0.43 (2012) to 1.14 (2014). It was revealed that net radiation (Rn) was the primary controlling factor of the maize ET, followed by leaf area index (LAI), vapor pressure deficit (VPD), air temperature (Ta), and soil water content (SWC). The adjusted SEM models explained 71%, 67%, and 67% of the variation in daily ET of the maize growing season (ET_gs) for dry, normal, and moist years, respectively. Rn and VPD dominated ET_gs in an increasing order of dry, normal, and moist years. Conversely, the effects of LAI and Ta on ET_gs followed the opposite trend. This indicated that drought may increase the sensitivity of maize ET to temperature changes, and decrease the sensitivity of maize ET to radiation changes. In SEM analysis, LAI played an important mediating role in the relationship among climate, soil variables, and ET_gs. Rn, VPD, Ta, and SWC all had significant indirect effects on ET_gs mediated through LAI. At the annual scale, it was identified that most active days could be a robust predictor of annual ET.

How to cite: Zhou, L., Wang, Y., and Zhou, G.: Evapotranspiration over a rainfed maize field in northeast China: how are relationships between the environment and terrestrial evapotranspiration mediated by leaf area?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9837, https://doi.org/10.5194/egusphere-egu2020-9837, 2020.

Crop residues are a significant source for soil N₂O emissions and major component affecting the C storage in arable soils. The balance between C sequestration and N₂O emissions is delicate and depends on the type of residues and its management. Thus, residue management might be a feasible option to reduce the GHG footprint of crop production. However, the mitigation potential of residue management is highly variable and strongly affected by the crop residue quality (C and N content, C:N ratio, concentrations of lignin, cellulose and solutes), field management (incorporation depth, amount applied) as well as soil physical and soil biogeochemical properties. In the frame of the EU-ERAGAS project RESIDUEGAS, we investigated the impact of different crop residue qualities on soil respiration and reactive N fluxes as well as soil ammonium (NH₄⁺) and nitrate (NO₃^-) concentrations in order to test and possibly improve existing IPCC emission factors for GHG emissions from crop residue management.

In this study, we used sieved and homogenized soil columns of 8 cm height and 12 cm diameter filled with arable soil taken from a site near Gießen, Germany. Soil columns were incubated in the laboratory for 60 days at constant soil temperature (15°C) and water-filled pore space (60 %). Residues from nine different crops (oilseed rape, winter wheat, field pea, maize, potato, mustard, red clover, sugar beet, ryegrass) were re-wetted according to field moisture level and incorporated over approx. 0-4 cm topsoil layer one week after soil re-wetting and start of the measurements. The CO₂, N₂O (as well as NO and NH₃) fluxes were measured automatically using a dynamic chamber approach. Soil samples were additionally analyzed for soil NH₄⁺ and NO₃^- concentrations at specific time steps during the experiment.

Re-wetting of the dry soil immediately resulted in a sharp increase of soil N₂O and CO₂ emissions, which, however, was less pronounced than peak emissions following residue incorporation. Those were 4-5 times higher as compared to soil cores without residue amendment. Elevated emissions were short-lived and declined to background levels within 10 days for N₂O and within 30 days for CO₂. However, a small but significant period of higher than background N₂O emissions was observed in the second half of the incubation period, which might be directly related to the decomposition of slower decomposable organic matter such as lignin and cellulose from crop residues. Generally, the emission magnitude was strongly affected by the crop residue quality, with highest N₂O as well as CO₂ emissions being calculated for residues with a narrow C:N ratio. However, C:N ratio was not the single explaining factor. The range of calculated emission factors (fraction of cumulatively emitted N₂O-N to crop residue N input) over a 60 day period was larger than the range given by IPCC in 2006.

How to cite: Havermann, F., Butterbach-Bahl, K., Janz, B., Engelsberger, F., Ernfors, M., Laville, P., Lashermes, G., Petersen, S. O., Taghizadeh-Toosi, A., Bleken, M. A., and Olesen, J. E.: Effect of crop residue incorporation and crop residue quality on soil N2O emissions and respiration - A laboratory measurement approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17716, https://doi.org/10.5194/egusphere-egu2020-17716, 2020.

Arthropods are a major soil fauna group, and have the potential to substantially influence the spatial and temporal variability of soil greenhouse gas (GHG) sinks and sources. The overall effect of soil-inhabiting arthropods on soil GHG fluxes still remains poorly quantified since the majority of the available data comes from laboratory experiments, is often controversial, and has been limited to a few species. The main objective of this study was to provide first insights into field-level carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions of soil-inhabiting larvae of the Scarabaeidae family. Larvae of the genus Melolontha were excavated at various grassland and forest sites in west-central and southern Germany, covering a wide range of different larval developmental stages, and larval activity levels. Excavated larvae were immediately incubated in the field to measure their GHG emissions. Gaseous carbon emissions of individual larvae showed a large inter- and intra-site variability which was strongly correlated to larval biomass. This correlation persisted when upscaling CO₂ and CH₄ emissions to the plot scale. Field emission estimates for Melolontha spp. were subsequently upscaled to the European level to derive the first regional GHG emission estimates for members of the Scarabaeidae family. Estimates ranged between 10.42 and 409.53 kt CO₂ yr^-1, and 0.01 and 1.36 kt CH₄ yr^-1. Larval N₂O emissions were only sporadically observed and not upscaled. For one site, a comparison of field- and laboratory-based GHG emission measurements was conducted to assess potential biases introduced by transferring Scarabaeidae larvae to artificial environments. Emission strength and variability of captive larvae decreased significantly within two weeks and the correlation between larval biomass and gaseous carbon emissions disappeared, highlighting the importance of field measurements. Overall, our data show that Scarabaeidae larvae can be significant soil GHG sources and should not be neglected in soil GHG flux research.

How to cite: Görres, C.-M. and Kammann, C.: First field estimation of greenhouse gas emissions from European soil-dwelling Scarabaeidae larvae targeting the genus Melolontha, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19924, https://doi.org/10.5194/egusphere-egu2020-19924, 2020.

Using animal waste (manure) for soil amendments have been recognized as an efficient strategy for farm management, as well as for soil preservation and greenhouse gas (GHG) emissions mitigation. It is believed that manure can improve soil quality, increase soil organic carbon (SOC) level and therefore potentially mitigate GHG emissions. However, recent studies reported that use of manure in the field can cause large amount of nitrous oxide (N₂O) emissions which in many cases offset the amount of SOC sequestered in agricultural ecosystems and eventually lead to net GHG emissions. In this report, we intended to investigate this management related mitigation option holistically, by modeling the full GHG budgets from a life cycle perspective. GHG emissions and some reactive gases (e.g., VOCs, NO) were specifically included in the manure life cycle. By re-examining the system boundary in previous studies, we show that use of manure does not necessarily cause large GHG emissions as previously reported. Net GHG emissions or mitigation potentials depend on not only SOC and N₂O emissions in situ, but also emissions and reactive gases beyond the farmgate and those would have been released anyway.

How to cite: Qin, Z.: Manure happens: re-examining mitigation potential from waste-to-resource in agricultural ecosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1345, https://doi.org/10.5194/egusphere-egu2020-1345, 2020.

Di Carlo et al. (2004) identified a discrepancy between measured total hydroxyl radical (OH) reactivity and the OH reactivity derived from the known air chemical composition in a forested environment. This missing reactivity has also been observed in the boreal forest (Sinha et al., 2010; Nölscher et al., 2012; Praplan et al., 2019). It remains ambiguous (e.g. Nölscher et al., 2013) if this missing reactivity stems from unknown primary emissions of volatile organic compounds (VOCs) from vegetation or from other sources (e.g. soil).

In order to further investigate emissions from a boreal forest, we applied the Comparative Reactivity Method (CRM; Sinha et al., 2008; Praplan et al., 2017) to emission measurements. Simultaneously, the emissions were chemically characterized with on-line gas chromatography coupled to mass spectrometery (GC/MS) methods.

In a first stage of the study (May to October 2017), measurements alternated between seedlings of Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and downy birch (Betula pubescens). They were placed in pots outside of the container were the instrumentation was placed at the SMEAR II station in Hyytiälä, Finland. In a second stage (May to September 2019), emissions from forest trees (Norway spruce and Downy birch) for in situ conditions were analysed.

The results show large variations of emission profiles and amounts throughout the year. In particular seedling were subject to periods of high stress which saw a large fraction of Green Leaf Volatiles (GLVs) contributing to the reactivity and a general increase of the emissions and the total observed reactivity. Trees from the forest were less prone to such stress and their emissions are higher in the spring and early summer compared to later summer and autumn.

While the presented dataset is limited and difficult to extrapolate from, it highlights important factors that need to be taken into account when modelling emissions: variability between tree species and individual trees, seasonal variations (slow changes) and stress factors (rapid changes), for instance.

References:

• Di Carlo et al. (2004), Science, 304, 722–725, doi:10.1126/science.1094392.
  
• Nölscher et al. (2012), Atmos. Chem. Phys., 12, 8257–8270, doi:10.5194/acp-12-8257-2012.
• Nölscher et al. (2013), Biogeosciences, 10, 4241–4257, doi:10.5194/bg-10-4241-2013.
• Praplan et al. (2017), Atmos. Env., 169, 150–161, doi:10.1016/j.atmosenv.2017.09.013.
• Praplan et al. (2019), Atmos. Chem. Phys., 19, 14431–14453, doi:10.5194/acp-19-14431-2019.
• Sinha et al. (2008), Atmos. Chem. Phys., 8, 2213–2227, doi:10.5194/acp-8-2213-2008.
• Sinha et al. (2010), Environ. Sci. Technol., 44, 6614–6620, doi:10.1021/es101780b.

How to cite: Praplan, A. P., Schallhart, S., Tykkä, T., Bäck, J., and Hellén, H.: The complexity of biogenic boreal emissions through the lens of hydroxyl radical (OH) reactivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13057, https://doi.org/10.5194/egusphere-egu2020-13057, 2020.

Soils play an important role of atmospheric methane sink, consuming about 30 Tg year^-1. Methane consumption is carried out by methanotrophic bacteria whose activity can be affected by different environmental factors. One of the most important factors that impact on methane consumption is the air-filled porosity of soil (AFP), which depends on its total porosity (P) and its water content (SWC). A high AFP enhances gas diffusion in soil, and therefore methane consumption. In forests, P is thought to increase with stand age because of soil decompaction by tree roots and SWC is thought to decrease because of a high evapotranspiration. Another factor that can affect methane consumption and thought to decrease with the aging of forest stands is mineral nitrogen (Nmin) and particularly ammonium that competes with methane for the active site of methane monooxygenase, thus reducing methane oxidation. However only few studies have addressed the effects of stand aging on soil methane consumption.

Our objective was to confirm the hypothesis that methane consumption by forest soil increases with stand age, in relation with an increase AFP and a decrease Nmin. We carried out this study in a chronosequence of 16 stands of sessile oak divided into six age classes (20-30, 40-60, 60-70, 85-90, 125-130 and 140-145). Three sampling campaigns were conducted in late summer 2018 and 2019 (periods of maximum AFP) and in early spring 2018 (period of minimum AFP). Soil methane consumption was measured by incubating the five first centimetres of soil cores at 20°C and by measuring the decrease of CH₄ concentration in the incubation chamber with a laser-based CH₄ analyser.

In contrast to our hypothesis, we did not find any significant effect of stand age on Nmin, P, SWC and AFP, nor on methane consumption. However, methane consumption was higher in stands with high values of AFP and low value of SWC, whatever their age. AFP, through differences in SWC, appeared to be the main driver of soil methane consumption in our study site, explaining both seasonal variations and variations among stands, that could not however be related to their age.

How to cite: Bras, N., Plain, C., and Epron, D.: Does stand age affect methane consumption of forest soil? A study in a chronosequence of sessile oak., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6896, https://doi.org/10.5194/egusphere-egu2020-6896, 2020.

Living trees are recognized as sources of greenhouse gases carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). However, less is known about greenhouse gas exchange in deadwood during its decay, and especially in logging residue. During the logging process, logging residue is produced in large amounts. Even though residue can be harvested for energy production, significant amounts of logging residue is still left in forests. In Finland, 30 % of the logging residue is recommended to be left on the logging site. It has been estimated, that in the European Union, annually over 200 million cubic meters of logging residue is produced, which of approximately one sixth is produced solely in Finland. As an example, only 2.7 million cubic meters of logging residue was recovered from Finnish forests and used for energy production in 2018.

We hypothesized that logging residue left in forests produces various greenhouse gases – CO₂, CH₄ and N₂O – during its decay. We studied greenhouse gas exchange in logging residue of spruce (Picea abies) and birch (Betula sp.) with focus on logs with average diameter of 5 – 10 cm. Residue was collected from 18 different research areas, covering approximately 47 hectares of spruce-dominated forest in Central Finland. All research areas were clear cuts, with known cut ages; the studied logs had decayed between 0 and 10 years. The study was carried out in 2019 during an eight-month period from May to December. In addition to greenhouse gas flux, dry matter content of logs was determined. All studied logs were a source of CO₂, with CO₂ flux correlating with log decay time and dry matter content. CO₂ emission was observed to be dependent on ambient temperature. In general, we detected low CH₄ emissions from logging residue; opposite to CO₂, no clear trend was found between CH₄ flux and log decay time or dry matter content. N₂O results were similar to CH₄, with low overall emissions. Dry matter content of logs correlated well with log decay time, with dry matter content decreasing as the logs were more decayed. Our study is an important step in understanding greenhouse gas exchange in logging residue and decaying wood in forests.

How to cite: Laihonen, A. and Tiirola, M.: Logging residue produces greenhouse gases in boreal forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5094, https://doi.org/10.5194/egusphere-egu2020-5094, 2020.

Woody plants are known to emit methane (CH₄) as an important greenhouse gas into the atmosphere. Recent studies show that tree stems might be also sinks for CH₄; however, the mechanisms of CH₄ uptake and its fate are unknown. Norway spruce (Picea abies) is characterised as negligible CH₄ source in boreal forests. Even though spruce trees have been widely planted for its wood in large-scale monocultures in European temperate forests, no studies have focused on their CH₄ exchange potential in the temperate zone.

We determined stems of Norway spruce growing in a temperate zone aiming to find out whether the tree stems exchange CH₄ with the atmosphere and how they contribute to the forest trace gas exchange.

The measurements were performed at the experimental station of the ‘Kranzberg Forest Roof Experiment’ near Freising, Germany, in June 2019. Fluxes of CH₄ in mature tree stems were measured using non-steady-state stem chamber systems (n=32) installed in stem vertical profile approx. two weeks prior to measurements using a portable greenhouse gas analyser. Moreover, resins sampled from spruce stems were investigated for their CH₄ exchange potential. Control measurements were performed to ensure that the fluxes do not originate from used chamber materials, in particular silicones used for chamber installation.

Our preliminary results show that the spruce stems can be a strong sink for CH₄ (-0.288 ± 0.053 mg CH₄ m^-2 stem area h^-1, mean ± s.e.), even if a small amount of resin is present on the bark. The stems exuded resins to different extent (covering 4.8 ± 1.3% of the stem surface area in chambers), partly as a result of smoothening of rough surface layers of dead bark for chamber installation. However, even spruce stems without obvious “injuries” released small amounts of resins for unknown reasons (response to drought, bark-beetle attack, etc.?). The incubated resin samples consistently consumed CH₄ (-12.0 ± 1.7 mg CH₄ m^-2 resin area h^-1). Moreover, the detected stem CH₄ uptake negatively correlated with the resin occurrence in the stem chambers (R² = 0.884). After re-calculation of the stem fluxes to resin area, the CH₄ consumption rates of stems and resin samples were in the same order of magnitude at median level (-13.2 and -12.0 mg CH₄ m^-2 resin area h^-1, resp.).

Concluded, the spruce resins appear to be a very strong and until now undiscovered sink for CH₄. Even one small droplet of resins on bark can turn the known negligible CH₄ exchange of intact spruce stems into strong CH₄ sinks, having thus severe impact on the overall forest CH₄ balance. This consumption potential of fresh resins should be considered by estimation of forest ecosystem CH₄ balance especially in areas, where resin bleeding is widely spread or is to be expected (bark-beetle areas, drought events, tree harvest, clear-cutting).

Acknowledgement

This research was supported by the Czech Science Foundation (17-18112Y) and National Sustainability Program I (LO1415). We thank Prof. Thorsten Grams for all his kind support, and Jan Hrdlička and Thomas Feuerbach for their technical support.

How to cite: Machacova, K., Schindler, T., Mander, Ü., and Soosaar, K.: Spruce resins constitute a strong sink for methane (CH4), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2892, https://doi.org/10.5194/egusphere-egu2020-2892, 2020.

Upland forest soils are typically a net methane (CH₄) sink, while trees may act as CH₄ sources. Studies on tree CH₄ exchange in boreal forests, especially regarding canopies, are rare. We aimed to quantify the contribution of trees to the forest CH₄ budget during spring leaf-out period and to reveal the role of microbes in the CH₄ exchange of trees. We measured stem and shoot fluxes of two common boreal tree species at a fen and at an upland site at Hyytiälä, southern Finland, together with soil CH₄ flux, environmental variables and the abundances methanogens and methanotrophs within the forest. Both birch (Betula pubescens) and spruce (Picea abies) trees emitted CH₄ from their aboveground surfaces, with significantly higher stem emissions detected from the birch and higher shoot emissions from the spruce. The shoot CH₄ exchange had no clear link to the vertical profile of the canopy or the progress of the leaf-out. The stem CH₄ emissions from birches at the fen were high (mean 45 µg h⁻¹ m⁻²) and decreased drastically with stem height. Their dynamics followed soil temperature, suggesting the emitted CH₄ originated from the soil. A lack of similar pattern in the fen spruces and in the upland birch indicates other processes behind the stem CH₄ fluxes of these trees. The lack of detection of methanogens or methanotrophs in the aboveground plant tissues suggest that the observed tree-derived CH₄ fluxes were not induced by these microbes. The emitted CH₄ from the tree stems may, however, be produced microbially in the soil indicating that physiological differences in tree anatomy or adaptation to different belowground conditions might be a key factor explaining the differences between the tree species.

Acknowledgements: This research was supported Academy of Finland (288494, 2884941), National Centre of Excellence (272041), ICOS-FINLAND (281255), Helsinki Institute of Life Science (HiLIFE), Czech Science Foundation (17-18112Y) and National Sustainability Program I (LO1415), and the European Research Council (ERC) under Horizon 2020 research and innovation programme, grant agreement No (757695).

How to cite: Pihlatie, M., Vainio, E., Haikarainen, I., Putkinen, A., Santalahti, M., Koskinen, M., and Machacova, K.: Contribution of tree stem and canopy fluxes to the CH4 budget of a boreal birch and spruce forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9001, https://doi.org/10.5194/egusphere-egu2020-9001, 2020.

Riparian forest ecosystems have been considered to be a natural source of nitrous oxide (N₂O) and a natural sink of methane (CH₄), both of which are important greenhouse gases (GHG) originating from microbiological processes. Wetland trees may also contribute to the GHG exchange by the release of both gases to the atmosphere or uptake therefrom. Recent studies have investigated the role of tree stems, underlining their importance in understanding forest GHG dynamics, focussing on various tree species, soil conditions or seasonal dynamics. However, knowledge about the short-termed day and night-time distributed GHG exchange of tree stems with the atmosphere is still scarce. We studied stem fluxes in a riparian forest ecosystem aiming to investigate the diurnal pattern and predict the potential influence of solar radiation.

The diurnal flux measurements were performed at 40-year-old grey alder (Alnus incana) forest stand in Estonia with 12-hour interval during July-September 2017 and May-September 2018 (n=16). The exchange of N₂O and CH₄ was measured from 12 trees at profile height up to 5 m (0.1, 0.8, 1.7, 2.5, 5.0 m) using non-steady state stem chamber systems and gas chromatography. Simultaneously, soil fluxes were automatically quantified using a dynamic chamber system (Picarro 2508); piezometers, automatic groundwater level wells, soil temperature and moisture sensors were installed to determine coherent soil conditions.

Our preliminary results showed N₂O and CH₄ emissions from alder tree stems during daytime (4.91 ± 0.15 µg m^-2 h^-1 and 66.38 ± 16.02 µg m^-2 h^-1, mean ± s.e.) and lower during nighttime (3.65 ± 0.22 µg m^-2 h^-1 and 51.49 ± 13.83 µg m^-2 h^-1, mean ± s.e.) at 0.1 m stem height, revealing a likely link to solar-driven physiological tree activity. Further, with increasing stem height, the relation of night to daytime fluxes diminished. However, the day-wise variation, including a minor GHG uptake indicates a fast response to changing micro-spatial environmental conditions like water regime in the soil and temperature.

Our study demonstrates the GHG exchange between tree stems and atmosphere occurs both in day- and night-time, showing slightly higher values in day-time, probably due to the trees’ physiological activities. Furthermore, our findings provide the potential to predict reaction kinetics in future modelling of flux pathways in forest ecosystems.

Acknowledgement

This research was supported by the Ministry of Education and Science of Estonia (SF0180127s08 grant), the Estonian Research Council (IUT2-16, PRG-352, and MOBERC20), the Czech Science Foundation (17-18112Y), the Czech National Sustainability Program I (LO1415), and the EcolChange Centre of Excellence, Estonia.

How to cite: Schindler, T., Machacova, K., Mander, Ü., and Soosaar, K.: Nighttime doesn’t stop N2O and CH4 exchange from riparian forest tree stems with the atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13438, https://doi.org/10.5194/egusphere-egu2020-13438, 2020.

Methane (CH₄) is the second most important long-lived anthropogenic atmospheric greenhouse gas. Despite its importance, natural sources of methane, such as tropical wetlands, are still not well understood and a large source of uncertainty to the global CH₄ budget. The Amazonian rain forest is estimated to hold 90-120 Pg of carbon, which is approximately 14-27% of the carbon stored in vegetation worldwide. The region is characterized by high precipitation rates and large wetlands, and it has been estimated that the Amazon basin emits 7% of the annual total CH₄ emissions. Due to its remote location, micro-meteorological measurements are rare and absent for other gases than CO₂.

The 50 m high K34 tower (field site ZF2) is located in a pristine tropical forest region 60 km northwest of Manaus (Brazil), and is located next to a waterlogged valley, a possible location for anaerobic CH₄ production. In October 2018, in addition to the existing EC CO₂ system, a Relaxed Eddy Accumulation (REA) system was set up at this tower, connected to an in-situ FTIR-analyzer. This set up continually measures fluxes and concentration profiles of CO₂, CO, CH₄, N₂O and δ¹³CO₂. In addition, CH₄, CO₂, and N₂O uptake and emission processes were studied by flux chamber measurements in the footprint of the REA tower, focusing on different possible sources (soil, stream, trees and termites). In this presentation, an overview of the measured CH₄ and N₂O forest concentrations and fluxes will be shown.

How to cite: van Asperen, H., Warneke, T., Carioca de Araújo, A., Rider Forsberg, B., Ramos de Oliveira, L., de Lima Xavier, T., de Oliveira Sá, M., Ricardo Teixeira, P., Azevedo de Oliveira, R., Sousa de Moura, V., do Socorro Monteiro Leal, L., Botia, S., Lavrič, J., Komiya, S., Frumau, A., Hensen, A., van den Bulk, P., van Dinther, D., and Notholt, J.: Tropical forest CH4: from flux chambers to micrometeorological tower measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6139, https://doi.org/10.5194/egusphere-egu2020-6139, 2020.