Displays

Ecosystems play a fundamental role in climate change mitigation by taking up carbon from the atmosphere and storing it for a period of time in organic matter. Although climate impacts of carbon emissions can be quantified by global warming potentials, there is not a formal metric to assess climate benefits of carbon removals by sinks. We introduce here the Climate Benefit of Sequestration (CBS), a metric that quantifies the radiative effect of taking up carbon dioxide from the atmosphere and retaining it for a period of time in an ecosystem before releasing it back to the atmosphere.  To quantify CBS, we also propose a formal definition of carbon sequestration (CS) as the integral of a sequestered amount of carbon over the time horizon it remains stored in an ecosystem. Both metrics incorporate the separate effects of i) inputs (amount of atmospheric carbon removal), and ii) transit time (time of carbon retention) in carbon sinks, which can vary largely for different ecosystems or management types. In three separate examples, we show how to compare different carbon management practices in forestry and soils using CS and CBS. We believe these metrics can be useful in resolving current controversies about the management of ecosystems for climate change mitigation. 

How to cite: Sierra, C., Crow, S., Heimann, M., Metzler, H., and Schulze, E.-D.: The Climate Benefit of Carbon Sequestration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5062, https://doi.org/10.5194/egusphere-egu2020-5062, 2020.

Legumes facilitate soil carbon (C) sequestration and mitigation of nitrous oxide (N₂O) emissions. They have an important role in improving model predictions of future feedbacks from the high-latitude carbon dioxide (CO₂) and N₂O fluxes and climate driving the response of northern ecosystems to warming. Legume based grasslands are an important part of the economy as high protein fodder for the cattle and thus, they are crucial for meat and dairy industries in Europe. However, there is a lack of regionally based, ecosystem scale field experimental data on legume based grasslands. Therefore, using the eddy covariance technique, we measured CO₂ and N₂O fluxes from a grassland site, growing timothy (Phleum pratense L.) and red clover (Trifolium pratense L.), treated with mineral nitrogen (MinN) or with digestate residue (OrgN) in eastern Finland during two growing seasons (May – Sep 2017 and 2018). Results showed that higher mean seasonal temperature (2018) increased net ecosystem CO₂ exchange (NEE) and total dry matter (DM) and decreased N₂O emissions. Specifically, NEE was 8.3 and 12.1 Mg ha^-1 in 2017 and 2018, respectively with no differences between treatments over the two years. The DM yield was 5.9 and 4.9 Mg ha^-1 for MinN and OrgN, respectively, in 2017, while it was 6.3 and 6.8 Mg ha^-1 in 2018. Cumulative N₂O fluxes were 0.01 (100-year global warming potential CO₂-equivalent) and -0.6 Mg CO₂ ha^-1 in 2017 and 2018, respectively. Summing up the seasonal NEE, N₂O flux and DM yield, the seasonal C balance was 2.1 and -1.3 Mg ha^-1 for MinN and OrgN treatments in 2017, and it was -2.5 and -3.5 Mg ha^-1, respectively, in 2018. Our observations from two climatically contrasting seasons suggest that the legume based grasslands in the boreal region have a strong C sequestration potential and the addition of organic fertilizer turns the systems to a larger sink in in the warmer year.

How to cite: Li, Y., Korhonen, P., Virkajärvi, P., and Shurpali, N. J.: Carbon dioxide and nitrous oxide fluxes from a legume-based grassland during contrasting seasons in eastern Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8788, https://doi.org/10.5194/egusphere-egu2020-8788, 2020.

The recent research and policy efforts on climate change mitigation highlight the need for proper understanding of the effects of many types of land management interventions on greenhouse gas exchange processes. The complexity of carbon and nitrogen cycles, which is the case also for agricultural ecosystems, call for model-based research approaches. These can make the decision-making applications easier as well. The agricultural use of sewage sludge is widespread in many countries. There are a number of case studies about its possible effects on greenhouse gas fluxes under different climatic conditions, but there are not many experiences in relevant model-based assessments. In our contribution, the Biome-BGC MuSo (v.6.) model was used for the investigation of the main characteristics of ecosystem exchange of carbon in arable land of warm dry temperate climate in the Great Plain of Hungary. The Biome-BGC is one of the most widely used biogeochemical models, it is capable of handling different land management activities, have a multilayer soil module and enable a quite detailed ecophysiological parameterization, which make it suitable for the targeted study. The results of laboratory analyses of soil profiles of the study area were used for the parameterization (element contents, organic matter, etc.). The poster presents the first results of the integrated measurement and modelling research work.

How to cite: Kiss, M., Barta, K., Gulyás, Á., Krajcsi, E., and Farsang, A.: Modelling possibilities of the effects of sewage sludge deposition on ecosystem carbon exchange processes - a case study on arable lands in Southeast Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11415, https://doi.org/10.5194/egusphere-egu2020-11415, 2020.

Nitrous oxide (N₂O) is a very potent greenhouse gas, and the majority of the emissions are associated with intensive livestock production. The magnitude of the emissions depends on the nitrogen (N) input to the soil, and on grazed pastures the largest share of the emissions is typically originating from the N applied via fertilization and excreta of the grazing animals. The uneven spatial distribution of the excretion leads to emission hot spots on grazing systems and makes the quantification of the gaseous emissions difficult. Micrometeorological methods like the eddy covariance (EC) that integrate emissions over a larger area method are well suited to quantify total field-scale N₂O emissions of grazed pastures. But the partioning of emissions for different sources and the determination of source-specific emission factors is still a challenge.

We present results of a 5-year field experiment carried out in western Switzerland. The investigated pasture was grazed by dairy cows in an intensive rotational management. The field was additionally fertilized with organic and mineral fertilizer each year, according to the N requirement of the grassland. The field-scale N₂O fluxes were quantified with the EC technique using a fast response Quantum cascade laser spectrometer for N₂O concentration measurements. The experimental setup and the environmental conditions resulted in high temporal and spatial dynamics of the N₂O fluxes with highest values typically occurring after mineral fertilization events in the summer month. Using N₂O background parametrizations retrieved from chamber measurements in one year and subtracting the background emission from the measured N₂O fluxes allowed us to calculate excreta-related emission factors (EFs) according to the IPCC guidelines. EFs for fertilizer N input were calculated using a pre-defined time window after the fertilizer was applied. The subtracted background emissions during the fertilization events were calculated from the EC measurements outside this time window. We attribute the observed emissions to the different N inputs and discuss potential reasons for the supposedly higher emissions after mineral fertilizer applications in comparison to organic fertilizer emissions.

How to cite: Ammann, C. and Voglmeier, K.: Partitioning of eddy covariance derived pasture N2O emissions for different sources and respective emission factors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11792, https://doi.org/10.5194/egusphere-egu2020-11792, 2020.

Agricultural and animal production are normally considered activities that degrade soils and are sources of greenhouse gases (GHG), such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). Here, we present a detailed description of the carbon (C), nitrogen (N) and phosphorus (P) stocks in croplands (CR), grasslands (GR), native shrublands (NS) and invasive shrublands (IS) at three locations of northern Chiloé Island, southern Chile. Also, using a portable chamber system (1 m³), the three GHG fluxes were measured one day per month, for one year (2018). The results showed that the larger total stocks of C and N were found at the NS sites, with values of 50.5 ± 4.3 kg m^-2 and 2.96 ± 0.54 kg m^-2, respectively. In contrast, the larger stock of P was observed at the GR sites, with a value of 0.51 ± 0.08 kg m^-2. Comparisons of the total ecosystem stocks showed no significant differences among  the agroecosystems but differed from values reported for a forest in Chiloé, which revealed a significant loss in C (58.6%) and N (11.1%) stocks in the agroecosystems, while the P stock increased by 92% compared to the forest. As net sources of CO₂ acted the CR sites; net sources of CH₄ were the CR, GR and IS sites; and net sources of N₂O were the CR sites. The GHG balance showed that the CR sites behaved as a net source (388 g CO₂-eq m^-2 year^-1), while GR (-1248 g CO₂-eq m^-2 year^-1), NS (-1097 g CO₂-eq m^-2 year^-1) and IS (-1928 g CO₂-eq m^-2 year^-1) acted as sinks. This indicates that croplands could make an important contribution to local and regional GHG emissions. In a wider context, these results indicate that the regulation of land use conversions for agricultural use might be an effective tool to combat climate change, potentially reducing GHG emissions.

How to cite: Perez-Quezada, J., Cano, S., Ibaceta, P., Aguilera, D., Salazar, O., Galleguillos, M., and Osborne, B.: Land use effects on C-N-and P stocks and greenhouse gas fluxes in agroecosystems in southern Chile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12052, https://doi.org/10.5194/egusphere-egu2020-12052, 2020.

The N₂O emission change by biochar addition in soils showed inconsistent trends depending on biochar types, soil properties, environmental conditions, and soil management practices. Especially in non-flooded upland agricultural soils, due to the complexity of N₂O emission processes, which include nitrification, nitrifier-denitrification, and denitrification, there are still many gaps in the mechanistic understanding of biochar effects. In order to maximize climate change mitigating effect of biochar, the biochar application guidelines that consider N₂O emission change need to be offered to farmers. However, the current lack of knowledge makes it challenging to create mechanistic models, and new approaches are needed. Machine learning techniques can be a solution because we can find the relationship between input and output variables without explicit mechanistic understanding and mathematical description. We aimed at developing a deep neural network (DNN) model to predict the N₂O emission change from upland agricultural soils by biochar application. Among all the papers published between Jan 2007 ~ Jul 2019 collected from Web of Science Core Collection, 65 papers were chosen which report changes in N₂O emissions by biochar addition in upland agricultural soils. Eleven variables, which have been reported as important factors influencing N₂O emission, were selected as input parameters. These include 5 soil properties (Total carbon and nitrogen content, sand and clay content and pH), 3 biochar properties (Feedstock type, pyrolysis temperature and biochar application rate), and 3 agricultural practices (Fertilizer type, number of fertilization and N application rate). The output parameter is the ratio of the cumulative N₂O emission of biochar treatment and control. Using 85% of the compiled dataset (training set), the DNN model was trained to predict the changes in N₂O emission by biochar addition. The rest of the dataset (validation set) was used to validate the DNN model. As a result, the DNN model predicted the decreasing and increasing patterns of biochar driven N₂O emission change in 84% of the validation data. This preliminary result could be a basis for developing practical biochar use guidelines. Further studies will be conducted to improve the prediction accuracy of the DNN model by combining principal component analysis.

How to cite: Hyun, J., Park, E., and Yoo, G.: Deep neural network model to predict N2O emission change by biochar amendment in upland agricultural soils , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12135, https://doi.org/10.5194/egusphere-egu2020-12135, 2020.

Since January 2008 the first eddy covariance (EC) ecosystem station in Polish forests was set up in a 54-year-old homogenous Scots pine stand near Tuczno (north-western part of the country).  Almost 40-m tall steal scaffold tower ensures obtaining CO₂ and H₂O fluxes from the area extending to 500 m in the prevailing wind direction most of the time. Until now measurements carried out in Tuczno forest are the only direct, real-time and long-term studies of this type in the Poland. In comparison with other European pine forests, investigated using the same technique, this site is very productive, annually sequestering about 16 t of CO₂ per hectare. There were many other comprehensive studies done nearby the main EC tower, which were the part of the common project founded by the State Forests since the very beginning e.g.: dendrometry and typical forest biometrics, hydrological and soil investigations, etc.

The results of EC measurements of CO₂ fluxes from Tuczno site together with data from two others pine forest sites: Tlen I (5-year-old forest, 6 years of data) and Mezyk (25-year-old forest, 2 years of data) allowed to create the cumulative NEP over the chronosequence. This is the first chronosequence curve for one tree species in this part of Europe. Since the climate and soil conditions at all three sites are very similar (there is no significant statistical difference), the current research at all site will be continued until 2025 and we do expect a full chronosequence curve very soon. These results were also compared with models (mainly CBM) and we would like to extend our results to the whole territory of Poland where it is a dominant species (about 60% of total forest area is covered by Pinus Silvestris).

How to cite: Olejnik, J., Ziemblinska, K., Urbaniak, M., and Malek, S.: Towards the first Scots pine chronosequence studies in Poland , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16123, https://doi.org/10.5194/egusphere-egu2020-16123, 2020.

There is evidence of increasing severity of extreme meteorological events, which due to climate warming are also more frequent than in the past few decades. Any disturbances (either natural or anthropogenic) exert a significant influence on the forest’s functioning. In Canada and the USA, fires and insect outbreaks cause the greatest damage while in Europe wind disturbances are the main threat. Since in Poland the majority of forests are managed by the State Forests, after such events disturbed areas are almost immediately designated for reforestation. While natural regeneration still contributes the least to forest restoration, the most common practices in our country include harvesting, soil preparation (ploughing) and manual seedlings introduction, which in this sense is similar to clear-cut’s management. 

Once such an event happened in Poland two EC stations were set up in the area of an 80-year old pine forest, which had been wiped out by a tornado in July 2012, to asses the impact of forest management. To date, there have been more than 5 full years of continuous carbon and energy fluxes measurement, allowing insight into forest regeneration patterns due to manual reforestation, as well as differences in CO₂ losses connected to chosen treatments. The two sites (Tlen I and Tlen II) differ mostly in terms of soil preparation – at Tlen I site soil was ploughed before replanting and at Tlen II soil cover remained almost intact. Additionally, at the second location, only trunks and main branches were harvested, while all uprooted stumps were left to decompose. Both meteorological and soil conditions have been investigated, with most of them not being significantly different, which allowed drawing the conclusion that observed differences in GHGs balance are most likely related to chosen forest management practices. Thorough analysis of quality checked EC data revealed that in 5-year perspective the application of traditional method (Tlen I site), mainly due to soil ploughing, resulted in much less total CO₂ loss to the atmosphere, reaching C-neutrality point in only 6 years after the damage as well as better seedling growth in general in comparison to the technique, where the soil cover was not disrupted. Moreover, it seems that furrows created at the conventionally managed forest site (“double” organic layer) serve as crucial water reservoirs during water shortage periods, preventing from the pine plantation damage caused by prolonged droughts.

This work advances our understanding of how different forest management practices can help to sustain the least CO₂ losses on the example of wind-disturbed forests. Although, it has to be remembered that long-term studies are needed to point the best option from the perspective of climate change mitigation. 

How to cite: Ziemblinska, K., Olejnik, J., Urbaniak, M., and Malek, S.: Different management practices impact on CO2 and H2O budget of wind disturbed forest sites- 5-year dataset, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20452, https://doi.org/10.5194/egusphere-egu2020-20452, 2020.

Nitrogen (N) added through atmospheric deposition or as fertilizer in boreal forests may alter their carbon (C) sequestration potential and sensitivity to climatic changes. While previous studies have primarily explored the responses of individual ecosystem components such as stem biomass production and soil carbon changes following N addition, the long-term impacts of N addition on the ecosystem-scale C balance of boreal forests still remain unclear. Here, we use data from eddy-covariance measurements in a fertilized Scots pine (Pinus sylvestris L.) forest (i.e. 16 ha receiving 100 and 50 kg N ha^-1 yr^-1 since 2006 and 2012, respectively) and an adjacent unfertilized control stand in boreal Sweden to investigate how one decade of N addition affected the net ecosystem productivity (NEP), gross primary production (GPP) and ecosystem respiration (ER) over five fertilization years (2015-2019). Results showed that N fertilization increased GPP in all five years with by 18% at average to 1183±41 g C m^-2 yr^-1 in the N-fertilized stand compared to 1003±56 g C m^-2 yr^-1 in the control stand. ER was also increased from 744±29 g C m^-2 yr^-1 in the control stand to 875±37 g C m^-2 yr^-1 in the fertilized stand. As a result, fertilization increased NEP from 259±28 g C m^-2 yr^-1 in the control stand to 308±20 g C m^-2 yr^-1 in the N-fertilized stand. Our results further suggested that the annual NEP was similar between stands during years with normal weather conditions (2015-2016) while NEP diverged due to a larger reduction in the control stand in years with environmental constraints (i.e. a cool summer in 2017 and droughts in 2018 and 2019). These findings indicate that enhanced N input to boreal forests increases and stabilizes their C sequestration potential under future climate conditions.

How to cite: Zhao, P., Chi, J., Nilsson, M., Ottosson.Lofvenius, M., Linder, S., Lundmark, T., Marshall, J., Näsholm, T., and Peichl, M.: Long-term impact of nitrogen addition on the carbon balance of a boreal pine forest in Northern Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21293, https://doi.org/10.5194/egusphere-egu2020-21293, 2020.

A managed boreal forest landscape is a diverse successional mosaic of clear-cuts to old-growth stands of different species growing on a variety of soil types. Consequently, this high spatial heterogeneity strongly impacts the forest net ecosystem production (NEP) across the managed landscape. However, the quantification of the variability of NEP and its component fluxes across forested landscapes is currently highly uncertain due to the complex interactions between forest structure and physiological processes and their changes over time.

Here, we assessed the spatial variability of NEP and its component fluxes during a 3-year period (2016-2018) over a boreal forest landscape (ca. 68 km²) located within the Krycklan catchment (64°14′N, 19°46′E) in northern Sweden. For this purpose, we selected 50 representative forest plots (10 m radius) across the catchment spanning various tree species (pine- and spruce-dominated stands) and forest age classes (from clear-cuts to old-growth forests). In each plot, forest floor CO₂ fluxes were manually measured with custom-made closed chambers in monthly intervals during the growing seasons 2016-2018. Measurements were carried out across natural (both light/dark measurements) and trenching/vegetation removal plots (0.45 × 0.45 m) to partition the net forest-floor exchange (NE_FF) into its contributing components, i.e., gross primary production (GPP_FF) and respiration (ER_FF). ER_FF was further separated into plant autotrophic and soil heterotrophic respiration (Ra_FF and Rh_FF). Plot-level biometric measurements were conducted to determine the net primary production of trees and forest floor vegetation (NPP_T and NPP_FF) as well as heterotrophic dead wood respiration (decomposition, Rh_DW). Finally, NEP was calculated as NEP = NPP_T + NPP_FF – Rh_FF – Rh_DW.

Our results showed that NPP_T consistently increased with forest ageing, while an opposite pattern was observed for NPP_FF. In general, spruce stands showed lower NPP_T compared to spruce stands at each given age class. In contrast, pine stands showed consistently higher NE_FF, GPP_FF, ER_FF, Rh_FF, Ra_FF, and NPP_FF compared to spruce stands. The forest floor was a net CO₂ source, which increased with stand age due to the progressive decrease in GPP_FF, while the ER_FF remained similar among all the age classes. In addition, an analogous age-related pattern was observed in Rh_FF. Our findings also depicted an increasing NEP with forest age from about ≈ 54±67 g C m^-2 yr^-1 during the initial stages of development (i.e., 5-30 years-old) to a maximum of ≈ 170±68 g C m^-2 yr^-1 in middle-aged stands (i.e., 60-100 years-old). Higher NEP was generally observed for pine compared to spruce stands. Interestingly, we found that the old-growth forests steadily continue to accumulate C, which is contrary to the common view that they become C neutral or sources.

Overall, this comprehensive study improves our understanding of the spatial variability of the C balance over the heterogeneous regional forest landscape in northern Sweden, identifying tree species, forest floor vegetation and forest ageing as key drivers.

How to cite: Martínez García, E., Nilson, M. B., Laudon, H., Wallerman, J., Fransson, J. E. S., Lundmark, T., and Peichl, M.: Spatial variability of the net ecosystem production and its component fluxes across a managed boreal forest landscape in Sweden: A biometric and chamber data-based analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22260, https://doi.org/10.5194/egusphere-egu2020-22260, 2020.