| 1. |
- Grelle, Achim, et al.
(author)
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Affordable relaxed eddy accumulation system to measure fluxes of H2O, CO2, CH4 and N2O from ecosystems
- 2021
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In: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 307
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Journal article (peer-reviewed)abstract
- The relaxed eddy accumulation (REA) technique is frequently applied to measure fluxes of a large variety of atmospheric tracers above ecosystems. It is often the method of choice since the eddy covariance (EC) technique is limited to a few tracers due to the lack of fast response analysers, high financial costs and in some cases high power consumption. REA avoids the need for a fast response analyser by collecting air from up-drafts and down-drafts into separate reservoirs. After collecting the air over a predefined time period, trace gas concentrations in the reservoirs are analysed by a slow response analyser and the average fluxes can be calculated.We developed and tested a REA system that is capable of measuring CO2, CH4, N2O and H2O fluxes simultaneously with only one gas analyser (Picarro G2805). This system is compatible with virtually any gas analyser and thus supports the flux analysis of a wide range of other air constituents such as isotopes, aerosols and volatile organic compounds. Furthermore, the modular design and rugged casing makes the sampling system robust and portable, and with its 12 V DC operation it is suitable for a wide range of field campaigns. The performance of the REA system was tested during the growing seasons of 2018 and 2020 on a grassland on organic soil in central Sweden.The system has worked reliably during several months in the Nordic climate, covering ambient temperatures between -20°C and +30°C. Measured fluxes of CO2 and H2O agree well with fluxes measured independently by an EC system. The similarity in the technology and the determined detection limits made us confident that the REA system even captures fluxes of CH4 and N2O well.
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| 3. |
- Keck, Hannes
(author)
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Greenhouse gas fluxes from drained peatland : Measurement techniques and management impacts
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Agricultural use of drained peatlands has significant implications for national greenhouse gas (GHG) emission inventories. Once drained, peatlands emit large amounts of carbon dioxide (CO2), may become small methane (CH4) sinks and, with nitrogen fertilisation, may emit large quantities of nitrous oxide (N2O). Studies on the influence of set-aside cropland in reducing GHG emissions from peatlands are rare, measurement techniques for continuous long-term observations are costly and detection of small fluxes is critical. This thesis investigated management effects on GHG fluxes from a cropland (CL) and an adjacent set-aside (SA) grassland on peat. An affordable relaxed eddy accumulation (REA) system for measuring continuous fluxes of CO2, N2O, CH4, and water vapour (H2O) was designed and tested. A convenient method for optimising chamber flux measurement duration and number of concentrations was developed and tested against experimental data. The SA site showed higher annual CO2 emissions than the CL site (0.41 and 0.16 kg CO2 m-2 yr1 , respectively). Nitrous oxide and CH4 emissions had a minor influence on the climate effect at both sides. The REA system reliably measured GHG fluxes over complete growing seasons, based on a comparison of CO2 and H2O fluxes with an eddy covariance system. The chamber optimisation method yielded similar results to experimental data, and can be valuable in the planning phase of measurement campaigns. In conclusion, this thesis found no evidence that setting-aside agricultural land on peat reduced GHG emissions and emphasises the importance of affordable and reliable measuring equipment.
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| 4. |
- Keck, Hannes
(author)
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Particle size distribution in soils and marine sediments by laser diffraction using Malvern Mastersizer 2000-method uncertainty including the effect of hydrogen peroxide pretreatment
- 2018
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In: Journal of Soils and Sediments. - : Springer Science and Business Media LLC. - 1439-0108 .- 1614-7480. ; 18, s. 2500-2510
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Journal article (peer-reviewed)abstract
- Methods for particle size distribution (PSD) determination by laser diffraction are not standardized and differ between disciplines and sectors. The effect of H2O2 pretreatment before a sonication treatment in laser diffraction analysis of soils and marine sediments was examined on soils with less than 1% C and some marine sediments.The method uncertainty for particle size analysis by the laser diffraction method using or not using H2O2 pretreatment followed by 2 min ultrasound and 1-mm sieving was determined for two soil samples and two aquatic sediments by analyzing ten replicates on a Malvern M2000 instrument. The carbon content was in the normal range for upland soils 0.1-0.9% C, but one of the aquatic sediment samples had a high carbon content (16.3% C) for which the H2O2 pretreatment was not feasible.The effect of H2O2 pretreatment on the PSD was small and not significant. The standard deviation (std) in particle size fractions increased with particle size. PSDs and std for some samples were presented for future reference. Similar to other studies, the content of clay and silt (by sieving/hydrometer, SHM) was lower by the laser diffraction method (LDM) than by the hydrometer method. To avoid confusion, LDM results for the < 2-mu m fraction should not be reported as a clay fraction to be used in texture classification. The absolute standard deviation of within-bin class was well below 1% in the colloidal fractions (using 2, 6, 8, and 20 mu m bin delimitations) and below 0.2-3% in the sand fractions.The LDM method requires new calibrated transfer functions for classification of soil textural class due to deviating results for colloidal fractions. It can be used without H2O2 pretreatment on soils containing less than about 1% C, but results should be corrected for 1-2-mm coarse sand content if higher than, e.g., 5%. If the analysis is not referring to a particular volume of sample, the correction for 1-2-mm material can be omitted.
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| 5. |
- Keck, Hannes, et al.
(author)
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Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil
- 2017
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In: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 3, s. 177-189
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Journal article (peer-reviewed)abstract
- Several studies have shown that the distribution of cation adsorption sites (CASs) is patchy at a millimetre to centimetre scale. Often, larger concentrations of CASs in biopores or aggregate coatings have been reported in the literature. This heterogeneity has implications on the accessibility of CASs and may influence the performance of soil system models that assume a spatially homogeneous distribution of CASs. In this study, we present a new method to quantify the abundance and 3-D distribution of CASs in undisturbed soil that allows for investigating CAS densities with distance to the soil macropores. We used X-ray imaging with Ba2+ as a contrast agent. Ba2+ has a high adsorption affinity to CASs and is widely used as an index cation to measure the cation exchange capacity (CEC). Eight soil cores (approx. 10 cm3) were sampled from three locations with contrasting texture and organic matter contents. The CASs of our samples were saturated with Ba2+ in the laboratory using BaCl2 (0.3 mol L−1). Afterwards, KCl (0.1 mol L−1) was used to rinse out Ba2+ ions that were not bound to CASs. Before and after this process the samples were scanned using an industrial X-ray scanner. Ba2+ bound to CASs was then visualized in 3-D by the difference image technique. The resulting difference images were interpreted as depicting the Ba2+ bound to CASs only. The X-ray image-derived CEC correlated significantly with results of the commonly used ammonium acetate method to determine CEC in well-mixed samples. The CEC of organic-matter-rich samples seemed to be systematically overestimated and in the case of the clay-rich samples with less organic matter the CEC seemed to be systematically underestimated. The results showed that the distribution of the CASs varied spatially within most of our samples down to a millimetre scale. There was no systematic relation between the location of CASs and the soil macropore structure. We are convinced that the approach proposed here will strongly aid the development of more realistic soil system models.
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| 6. |
- Keck, Hannes, et al.
(author)
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Setting-aside cropland did not reduce greenhouse gas emissions from a drained peat soil in Sweden
- 2024
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In: Frontiers in Environmental Science. - 2296-665X. ; 12
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Journal article (peer-reviewed)abstract
- In the process of their formation, northern peatlands were accumulating vast amounts of carbon (C). When drained for agricultural use, a large proportion of that C is oxidized and emitted as carbon dioxide (CO2), turning those peatlands to strong CO2 emitters. As a mitigation option, setting-aside farmland on drained peat is being incentivized by policies, but recent evidence casts doubt on these policies' efficiency for greenhouse gas (GHG) emission mitigation. To investigate the effects of setting-aside farmland on GHG fluxes from a Swedish peatland, we measured CO2, nitrous oxide (N2O), and methane (CH4) fluxes on two adjacent sites under contrasting management. The cultivated (CL) site was used for cereal production (wheat or barley) and the set-aside (SA) site was under permanent grassland. Carbon dioxide fluxes were measured from 2013 to 2019 using the eddy covariance (EC) method. Additionally, CO2, N2O, and CH4 fluxes were measured during the growing seasons of 2018-2020, using transparent and opaque chambers on vegetated plots and on bare peat. The cumulative CO2 fluxes measured by EC over the measurement period were 0.97 (+/- 0.05) and 2.09 (+/- 0.17) kg m-2 with annual average losses of 0.16 and 0.41 kg CO2 m-2 yr-1 for the CL and SA site, respectively. Thus, the SA site acted as a stronger CO2 source than the CL site. Both sites' contribution to global warming, calculated on basis of the chamber measurements, was dominated by CO2. The contribution of the SA site was higher than that of the CL site. Nitrous oxide emissions were low at both sites with higher emissions from the CL site for transparent measurements and measurements on bare peat. Whereas, CH4 uptake was highest on the SA grassland. Thus, on the basis of our study, we found no evidence that setting-aside farmland on shallow drained peat soils will reduce GHG emissions or even turn the peatland into a C sink.
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| 7. |
- Keck, Hannes, et al.
(author)
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Setting-aside cropland did not reduce greenhouse gas emissions from a drained peat soil in Sweden
- 2024
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In: Frontiers in Environmental Science. - : Frontiers Media S.A.. - 2296-665X. ; 12
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Journal article (peer-reviewed)abstract
- In the process of their formation, northern peatlands were accumulating vast amounts of carbon (C). When drained for agricultural use, a large proportion of that C is oxidized and emitted as carbon dioxide (CO2), turning those peatlands to strong CO2 emitters. As a mitigation option, setting-aside farmland on drained peat is being incentivized by policies, but recent evidence casts doubt on these policies' efficiency for greenhouse gas (GHG) emission mitigation. To investigate the effects of setting-aside farmland on GHG fluxes from a Swedish peatland, we measured CO2, nitrous oxide (N2O), and methane (CH4) fluxes on two adjacent sites under contrasting management. The cultivated (CL) site was used for cereal production (wheat or barley) and the set-aside (SA) site was under permanent grassland. Carbon dioxide fluxes were measured from 2013 to 2019 using the eddy covariance (EC) method. Additionally, CO2, N2O, and CH4 fluxes were measured during the growing seasons of 2018-2020, using transparent and opaque chambers on vegetated plots and on bare peat. The cumulative CO2 fluxes measured by EC over the measurement period were 0.97 (+/- 0.05) and 2.09 (+/- 0.17) kg m-2 with annual average losses of 0.16 and 0.41 kg CO2 m-2 yr-1 for the CL and SA site, respectively. Thus, the SA site acted as a stronger CO2 source than the CL site. Both sites' contribution to global warming, calculated on basis of the chamber measurements, was dominated by CO2. The contribution of the SA site was higher than that of the CL site. Nitrous oxide emissions were low at both sites with higher emissions from the CL site for transparent measurements and measurements on bare peat. Whereas, CH4 uptake was highest on the SA grassland. Thus, on the basis of our study, we found no evidence that setting-aside farmland on shallow drained peat soils will reduce GHG emissions or even turn the peatland into a C sink.
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