| 1. |
- Bölscher, Tobias, et al.
(författare)
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Changes in pore networks and readily dispersible soil following structure liming of clay soils
- 2021
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 390
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Tidskriftsartikel (refereegranskat)abstract
- Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (ø ≥ 0.3 mm) in soil columns and mesopores (ø ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (ε>1.0 mm) and medium sized macropores (ε0.3–1.0 mm) towards smaller macropores (ε0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space.
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| 2. |
- Chakrawal, Arjun, et al.
(författare)
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Dynamic upscaling of decomposition kinetics for carbon cycling models
- 2020
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 13:3, s. 1399-1429
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of organic substrates and microorganisms in soils is spatially heterogeneous at the microscale. Most soil carbon cycling models do not account for this microscale heterogeneity, which may affect predictions of carbon (C) fluxes and stocks. In this study, we hypothesize that the mean respiration rate (R) over bar at the soil core scale (i) is affected by the microscale spatial heterogeneity of substrate and microorganisms and (ii) depends upon the degree of this heterogeneity. To theoretically assess the effect of spatial heterogeneities on (R) over bar, we contrast heterogeneous conditions with isolated patches of substrate and microorganisms versus spatially homogeneous conditions equivalent to those assumed in most soil C models. Moreover, we distinguish between biophysical heterogeneity, defined as the nonuniform spatial distribution of substrate and microorganisms, and full heterogeneity, defined as the nonuniform spatial distribution of substrate quality (or accessibility) in addition to biophysical heterogeneity. Four common formulations for decomposition kinetics (linear, multiplicative, Michaelis-Menten, and inverse Michaelis-Menten) are considered in a coupled substrate-microbial biomass model valid at the microscale. We start with a 2-D domain characterized by a heterogeneous substrate distribution and numerically simulate organic matter dynamics in each cell in the domain. To interpret the mean behavior of this spatially explicit system, we propose an analytical scale transition approach in which microscale heterogeneities affect (R) over bar through the second-order spatial moments (spatial variances and covariances). The model assuming homogeneous conditions was not able to capture the mean behavior of the heterogeneous system because the second-order moments cause (R) over bar to be higher or lower than in the homogeneous system, depending on the sign of these moments. This effect of spatial heterogeneities appears in the upscaled nonlinear decomposition formulations, whereas the upscaled linear decomposition model deviates from homogeneous conditions only when substrate quality is heterogeneous. Thus, this study highlights the inadequacy of applying at the macroscale the same decomposition formulations valid at the microscale and proposes a scale transition approach as a way forward to capture microscale dynamics in core-scale models.
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| 3. |
- Hansson, Linnea, et al.
(författare)
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Impacts of off-road traffic on soil physical properties of forest clear-cuts: X-ray and laboratory analysis
- 2018
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 33:2, s. 166-177
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Informa UK Limited, trading as Taylor & Francis Group Due to the great year-round demand for forest products, off-road forestry traffic occurs even when the ground is susceptible to soil compaction and rutting. We investigated the impacts of repeated passes with a laden forwarder (34Mg) on the soil physical properties of two clear-cuts on stony till soils in northern Sweden. Core samples (n=71) were collected from the top 5cm of mineral soil in and beside wheel tracks, after six passes with the forwarder. Soil physical properties were quantified using classical soil physical analyses and X-ray tomography. The hydraulic conductivity was 70% lower in the wheel tracks than in the soil beside. The X-ray image analysis indicated that this was due to the smaller total volume and lower connectivity of structural pores (φ > 60µm). Total porosity was 24% and 12% lower in the tracks at the two sites respectively, and mean bulk density was 1.39gcm −3 in the tracks, compared to 1.13gcm −3 beside them. To conclude, traffic changed the soil physical properties in a way that may lead to longer periods of high water content in the wheel tracks, increased risk of surface runoff and insufficient aeration for optimal seedling growth.
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| 4. |
- Lehoux, Alizée, et al.
(författare)
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Extreme gas production in anthropogenic fibrous sediments : An overlooked biogenic source of greenhouse gas emissions
- 2021
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 781
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Tidskriftsartikel (refereegranskat)abstract
- Fibrous sediments that originated from old pulp and paper industry emissions are recognized as a potential threat to the aquatic environment because they are highly contaminated. In addition, biogenic degradation of the organic material from so-called "fiberbanks" has a high potential to produce greenhouse gases (GHG). In this study, X-ray tomography, optical sensors and gas analyzers were used to identify and quantify the gas produced and released from samples of two different fiberbanks. We show that a finer fibrous structure allows the formation of larger gas bubbles and higher gas production rates compared to coarser material composed of wood pieces. High contents of methane (average 56% to 65%) and carbon dioxide (average 18% to 20%) were measured in the gas emitted from both types of fiberbank. Measured methane production rates from the fiberbanks samples are one to three orders of magnitude higher than previously reported rates from sediments within the studied temperature range (between 0.03 and 0.51 mu m CH4/h/g dw over 4.7 to 20 degrees C). The potential for methane and carbon dioxide production in the fiberbank volume likely present in Sweden is estimated to correspond to 7% of Sweden's total known GHG emissions for 2019. These findings show that fiberbanks have the potential to be a significant emitter of GHG.
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