| 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. |
- Jarvis, Nicholas, et al.
(författare)
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Long-term effects of grass-clover leys on the structure of a silt loam soil in a cold climate
- 2017
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Ingår i: Agriculture, Ecosystems and Environment. - : Elsevier BV. - 0167-8809 .- 1873-2305. ; 247, s. 319-328
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Tidskriftsartikel (refereegranskat)abstract
- Grass/legume leys are commonly included in the crop rotation in mixed farming systems in cold or humid regions in order to sustain the supply of nutrients and maintain soil fertility. Leys are also known to sequester soil organic carbon and also improve the structural stability and mechanical properties of soil. However, few studies have investigated the long-term effects of ley rotations on the architectural properties of the structural pore space in soil. We investigated the effects of grass/clover leys on soil structure in the topsoil and upper subsoil of a silt loam in a long-term field trial established in 1956 at Offer in northern Sweden. This experiment includes four treatments with varying proportions of ley (1, 2, 3 or 5 years) in 6-year rotations. We used X-ray tomography to quantify topsoil structural pore space at a resolution of 65 mu m in the first year of arable cropping following the ley break, a few weeks after sowing in spring. Earthworm populations were quantified by both hand-sorting and chemical extraction, while near-saturated infiltration was measured as a proxy for soil structure in the upper subsoil. In the topsoil, the treatments with a greater proportion of ley had larger organic carbon contents, smaller bulk densities and larger porosities. However, effects of crop rotation on the pore space were limited to pores smaller than 65 pm, as no treatment effects were found for the volume, size distribution, connectivity or complexity of the X-ray imaged pore space, even though the grass-clover leys promoted larger numbers and biomass of topsoil-dwelling earthworm species. Furthermore, no positive effects of grass/clover leys on organic carbon content and soil structure were found in the subsoil. The macropore infiltration capacity in upper subsoil was generally very small (overall median value of 3 mm h(-1)) indicating a lack of functional macroporosity below plough depth. Consistent with these results, no individuals of deep-burrowing earthworm species were found at the site, while previous observations showed only shallow rooting, both of which are attributed to the cold climate and poor subsoil drainage.
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| 5. |
- 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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| 6. |
- Bacher, Matthias, et al.
(författare)
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Three-Dimensional Printing of Macropore Networks of an Undisturbed Soil Sample
- 2015
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 14, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Macropore systems predominantly determine rapid water flow and solute transport in undisturbed soils. Repeated experiments are needed to investigate the relationship between the nature of the macropore network and the resulting water and solute transport under different hydraulic initial and boundary conditions. However, the large heterogeneity in soil macropore network structures renders each soil sample unique and multiple identical samples impossible. In addition, the fragile nature of soil strongly limits the possible number of repeated experiments on one individual sample. Micromodels that mimic the precise shape and location of the macropores in undisturbed soil are therefore necessary to allow repeated experiments. In this study we investigated whether such micromodels can be obtained using contemporary three-dimensional (3-D) printing techniques and materials. We used X-ray computed tomography to digitize the 3-D macropore structure of an undisturbed soil sample. We printed a subsection of this macropore system in five different materials. Four out of the five investigated materials had essential parts of their macropore system clogged with residual printing or printing-aid material. Only one reprint, namely the prime-gray sample that was printed using stereo lithography, exhibited no pore clogging and had the largest hydraulic conductivity of all investigated reprints. Prime gray showed subcritical water repellency with a medium contact angle of approximately 65 degrees, which is similar to contact angles found in natural soil. We conclude that the 3-D printing of undisturbed soil macropore systems is in principle possible with contemporary 3-D printing systems.
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| 7. |
- Casali, Emilien, et al.
(författare)
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Macropore flow in relation to the geometry and topology of soil macropore networks: Re-visiting the kinematic wave equation
- 2024
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Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 630
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Tidskriftsartikel (refereegranskat)abstract
- The rapid flow of water through soil macropores significantly affects the partitioning of precipitation between surface runoff and infiltration and also the rate of solute transport in soil, both of which have an impact on the risk of contamination of surface water and groundwater. The kinematic wave equation is often employed as a model of gravity-driven water flow through soil macropores. The exponent in this simple model influences the pore water velocity attained in the macropores at any given input rate and is usually estimated by inverse modelling against measured flow rates or water contents. In theory, the exponent in the kinematic wave equation should depend on the geometry and topology of the conducting macropore networks, although these relationships have not so far been investigated. In this study, we related metrics of soil structure derived from X-ray images to values of the kinematic exponent estimated from drainage experiments on twenty-two columns sampled at three different field sites under two contrasting land uses and at three different depths. We found that smaller values of the exponent in the kinematic wave equation, which would equate to more rapid flow of water through soil macropores, were found in plough pan and subsoil columns of smaller macroporosity, for which biopores comprised a significant fraction. The macroporosity in these columns was more vertically oriented and poorly inter-connected, though still continuous across the sample. In contrast, topsoil columns from both arable land and grassland had better connected, denser and more isotropically-distributed macropore networks and larger values of the kinematic exponent. Our results suggest that for predictive modelling at large scales, it may be feasible to estimate the kinematic exponent using class pedotransfer functions based on pedological information such as land use and horizon type.
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| 8. |
- Fukumasu, Jumpei, et al.
(författare)
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Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter?
- 2024
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 449
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Tidskriftsartikel (refereegranskat)abstract
- An improved understanding of preferential solute transport in soil macropores would enable more reliable predictions of the fate of agrochemicals and the protection of water quality in agricultural landscapes. The objective of this study was to investigate how soil organic carbon (SOC) and soil texture shape soil pore structure and thereby determine the susceptibility to preferential transport under steady-state near-saturated flow conditions. To do so, we took intact topsoil samples from an arable field that has large variations in SOC content (1.1-2.7%) and clay content (8-42%). Soil pore structure was quantified by X-ray tomography and soil water retention measurements. Non-reactive solute transport experiments under steady-state near-saturated conditions were carried out at irrigation rates of 2 and 5 mm h- 1 to quantify the degree of preferential transport. Near- saturated hydraulic conductivities at pressure heads of-1.3 and-6 cm were also measured using a tension disc infiltrometer. The results showed that larger abundances of small macropores (240-720 mu m diameter) and mesopores (5-100 mu m diameter) resulted in weaker preferential transport, due to larger hydraulic conductivities in the soil matrix that prevented the activation of water flow and solute transport in large macropores. In particular, the degree of preferential transport was most strongly and negatively correlated with the mesoporosity in the 30-100 mu m diameter class. In contrast, the degree of preferential transport was not correlated with connectivity measures (e.g. the percolating fraction and critical pore diameter for the macropore network), probably because i.) the pore space of almost all samples was highly connected, being dominated by one percolating cluster, and ii.) only a part of this percolating macroporosity was active under the near-saturated conditions of the experiment. We also found that the degree of preferential transport was strongly and negatively correlated with clay content, whilst the effects of SOC were not significant. Nevertheless, macroporosity in the 240-720 mu m diameter class and mesoporosity were positively correlated with SOC content in our soils and in some previous studies. Therefore, SOC sequestration in arable soils may potentially reduce the risk of preferential transport under near-saturated flow conditions through better developed networks of small macropores and mesopores.
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| 9. |
- Fukumasu, Jumpei, et al.
(författare)
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Oxalate-extractable aluminum alongside carbon inputs may be a major determinant for organic carbon content in agricultural topsoils in humid continental climate
- 2021
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 402
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Tidskriftsartikel (refereegranskat)abstract
- The relative importance of various soil mineral constituents (e.g. clay-sized particles, aluminum- and iron-bearing mineral reactive phases) in protecting soil organic carbon (SOC) from decomposition is not yet fully understood in arable soils formed from quaternary deposits in humid continental climates. In this study, we investigated the relationships between soil physico-chemical properties (i.e. contents of oxalate-extractable aluminum (Alox) and iron (Feox) and clay size particle < 2 mu m), grain yield (as a proxy for carbon input) and total SOC as well as SOC in different soil fractions for samples taken from the topsoil of an arable field at Bjertorp in south-west Sweden. We found a positive correlation between Alox and total SOC content, where Alox explained ca. 48% of the spatial variation in SOC. We also found that ca. 80% of SOC was stored in silt- and claysized (SC) fractions, where Al-bearing reactive mineral phases (estimated by Alox) may be important for organicmineral associations and clay aggregation. Our results were supported by data collated from the literature for arable topsoil in similar climates, which also showed positive correlations between SOC and Alox contents (R-2 = 23.1 - 74.5%). Multiple linear regression showed that including spatially-variable crop yields as a proxy for carbon inputs improved the prediction of SOC variation across the Bjertorp field. Other unquantified soil properties such as exchangeable calcium may account for the remaining unexplained variation in topsoil SOC. We conclude that Al-bearing reactive mineral phases are more important than clay content and Fe-bearing reactive mineral phases for SOC stabilization in arable topsoil in humid continental climates.
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| 10. |
- Fukumasu, Jumpei, et al.
(författare)
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Relations between soil organic carbon content and the pore size distribution for an arable topsoil with large variations in soil properties
- 2022
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 73
-
Tidskriftsartikel (refereegranskat)abstract
- Soil organic carbon (SOC) in arable topsoil is known to have beneficial effects on soil physical properties that are important for soil fertility. The effects of SOC content on soil aggregate stability have been well documented; however, few studies have investigated its relationship with the soil pore structure, which has a strong influence on water dynamics and biogeochemical cycling. In the present study, we examined the relationships between SOC and clay contents and pore size distributions (PSDs) across an arable field with large spatial variations in topsoil SOC and clay contents by combining X-ray tomography and measurements of soil water retention. Additionally, we investigated the relationships between fractionated SOC, reactive Fe and Al oxide contents and soil pore structure. We found that porosities in the 0.2-720 mu m diameter class were positively correlated with SOC content. A unit increase of SOC content was associated with a relatively large increase in porosity in the 0.2-5 and 480-720 mu m diameter classes, which indicates that enhanced SOC content would increase plant available water content and unsaturated hydraulic conductivity. On the other hand, macroporosities (1200-3120 mu m diameter classes) and bioporosity were positively correlated with clay content but not with SOC content. Due to strong correlations between soil texture, carbon-to-nitrogen ratios and reactive iron contents, we could not separate the relative importance of these soil properties for PSDs. Reactive aluminium and particulate organic carbon contents were poorer predictors for PSDs compared with clay and SOC contents. This study provides new insights on the relations between SOC and soil pore structure in an arable soil and may lead to improved estimations of the effects of enhanced SOC sequestration on soil water dynamics and soil water supply to crops. Highlights Relations between soil organic carbon (SOC) and pore size distribution (PSD) in an arable soil were explored. We used X-ray tomography and soil water retention to quantify a wide range of PSD. There were positive correlations between SOC and porosities in 0.2-720 mu m diameter classes. Porosities in 0.2-5 and 480-720 mu m diameter classes were more strongly correlated with SOC than clay. Our results have implications for improved estimates of effects of SOC sequestration on soil water dynamics.
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| 11. |
- Ghafoor, Abdul, et al.
(författare)
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Soil properties and susceptibility to preferential solute transport in tilled topsoil at the catchment scale
- 2013
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 492, s. 190-199
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Tidskriftsartikel (refereegranskat)abstract
- Preferential water flow and solute transport can have dramatic effects on the leaching of contaminants to groundwater and surface waters (via subsurface drainage) and is therefore of major concern to policy and decision-makers in the realm of water resources management. Unfortunately, we cannot measure these processes at the landscape scales that are relevant for management (farms, catchments, regions), which implies that an approach based on pedotransfer functions is needed to support model predictions. However, the extent to which susceptibility to preferential solute transport can be predicted from proxy site and soil attributes that can be observed and mapped at the landscape scale is still largely unknown. We therefore carried out non-reactive solute breakthrough experiments on 45 topsoil columns sampled from the contrasting soil types found in a 13 km(2) agricultural catchment in Sweden. Non-parametric indicators of preferential solute transport were derived from the shapes of the solute breakthrough curves and related to soil physical and hydraulic properties measured in the same columns. The results showed that preferential transport was weakly (and negatively) correlated with the saturated macropore hydraulic conductivity. In contrast, it was much more strongly controlled by the size of the largest water-filled pore, which in turn was significantly correlated to the saturated hydraulic conductivity of the soil matrix and soil textural classes. Preferential transport was also weakly expressed in three fine-textured soils of large organic carbon content. We conclude that the spatial pattern of preferential transport across the studied catchment should show a clear deterministic component since it depended on soil properties (e.g. clay content) that are expressed relatively uniformly across larger areas of land. (C) 2013 Elsevier B.V. All rights reserved.
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| 12. |
- Heinze, Wiebke Mareile, et al.
(författare)
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Nanoplastic Transport in Soil via Bioturbation by Lumbricus terrestris
- 2021
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55, s. 16423-16433
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Tidskriftsartikel (refereegranskat)abstract
- Plastic pollution is increasingly perceived as an emerging threat to terrestrial environments, but the spatial and temporal dimension of plastic exposure in soils is poorly understood. Bioturbation displaces microplastics (>1 mu m) in soils and likely also nanoplastics (<1 mu m), but empirical evidence is lacking. We used a combination of methods that allowed us to not only quantify but to also understand the mechanisms of biologically driven transport of nanoplastics in microcosms with the deep-burrowing earthworm Lumbricus terrestris. We hypothesized that ingestion and subsurface excretion drives deep vertical transport of nanoplastics that subsequently accumulate in the drilosphere, i.e., burrow walls. Significant vertical transport of palladium-doped polystyrene nanoplastics (diameter 256 nm), traceable using elemental analysis, was observed and increased over 4 weeks. Nanoplastics were detected in depurated earthworms confirming their uptake without any detectable negative impact. Nanoplastics were indeed enriched in the drilosphere where cast material was visibly incorporated, and the reuse of initial burrows could be monitored via X-ray computed tomography. Moreover, the speed of nanoplastics transport to the deeper soil profile could not be explained with a local mixing model. Earthworms thus repeatedly ingested and excreted nanoplastics in the drilosphere calling for a more explicit inclusion of bioturbation in nanoplastic fate modeling under consideration of the dominant mechanism. Further investigation is required to quantify nanoplastic re-entrainment, such as during events of preferential flow in burrows.
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| 13. |
- Hellner, Qarin, et al.
(författare)
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Effects of tillage and liming on macropore networks derived from X-ray tomography images of a silty clay soil
- 2018
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Ingår i: Soil Use and Management. - : Wiley. - 0266-0032 .- 1475-2743. ; 34, s. 197-205
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Tidskriftsartikel (refereegranskat)abstract
- Soil structure influences water infiltration, aeration and root growth and, thereby, also the conditions for sustainable crop production. Our objective was to quantify the effects of different soil management methods and land uses on the topsoil structure of a silty clay soil. We sampled 32 intact soil columns (18 cm high, 12.7 cm diameter) from an experimental silty clay field with four treatments: conventional tillage (CT), conventional tillage followed by liming (CTL), reduced tillage (RT) and unfertilized fallow (UF). The columns were analysed using 3-D X-ray tomography. The samples were taken in autumn after harvest, 7 yr after quick lime was applied to the CTL plots. Despite a relatively large number of replicates per treatment (8, 8, 8 and 6 (two UF samples were excluded), respectively), there were no significant differences between any of the investigated macropore network properties related to tilled treatments. The UF treatment, in contrast, exhibited more vertically oriented macropores, which were also better connected compared to the other treatments. This confirms previous findings that tillage may disrupt the vertical continuity of macropore clusters. The impact of liming on soil pore network properties may have been limited to pores smaller than the resolution in our X-ray images. It is also possible that the effects of lime on soil structure were limited to a few years which means that any effect would have diminished by the time of this study. These matters should be further investigated in follow-up studies to understand better the potential of lime amendments to clay soil.
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| 14. |
- Jarvis, Nicholas, et al.
(författare)
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Connectivity and percolation of structural pore networks in a cultivated silt loam soil quantified by X-ray tomography
- 2017
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 287, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- The connectivity of macropore networks is thought to exert an important control on preferential flow in soil, although little progress has been made towards incorporating an understanding of these effects into management oriented flow and transport models. In principle, concepts from percolation theory should be well suited to quantify the connectivity of preferred flow pathways, but so far its relevance for natural soils in the field has not been tested. To investigate this question, X-ray tomography was used to measure soil pore space architecture at an image resolution of 65 pm for 64 samples taken in two consecutive years in the harrowed and ploughed layers of a silt loam soil a few weeks after spring cultivation. The results showed that the pore networks displayed key features predicted by classical percolation theory: a strong relationship was found between the percolating fraction and the imaged porosity, with a percolation threshold of ca. 0.04 to 0.06 m(3) m(-3) in the harrowed layer. A percolation threshold was less clearly identifiable in topsoil that had not been recently tilled, although this may probably be attributed to finite size sampling effects in this layer, which showed a more heterogeneous and structured distribution of the pore space. Although further work on more strongly structured soil horizons, especially subsoils, would be desirable, it is tentatively suggested that percolation concepts could prove useful to estimate the conducting macroporosity in management models of preferential flow and transport. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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| 15. |
- Jarvis, Nicholas, et al.
(författare)
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Impacts of soil management and climate on saturated and near-saturated hydraulic conductivity: analyses of the Open Tension-disk Infiltrometer Meta-database (OTIM)
- 2023
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Ingår i: Hydrology and Earth System Sciences. - 1027-5606 .- 1607-7938. ; 27, s. 2703-2724
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Tidskriftsartikel (refereegranskat)abstract
- Saturated and near-saturated soil hydraulic conductivities K-h (mmh(-1)) determine the partitioning of precipitation into surface runoff and infiltration and are fundamental to soils' susceptibility to preferential flow. Recent studies found indications that climate factors influence K-h, which is highly relevant in the face of climate change. In this study, we investigated relationships between pedoclimatic factors and K-h and also evaluated effects of land use and soil management. To this end, we collated the Open Tension-disk Infiltrometer Meta-database (OTIM), which contains 1297 individual data entries from 172 different publication sources. We analysed a spectrum of saturated and near-saturated hydraulic conductivities at matric potentials between 0 and 100 mm. We found that methodological details like the direction of the wetting sequence or the choice of method for calculating infiltration rates to hydraulic conductivities had a large impact on the results. We therefore restricted ourselves to a subset of 466 of the 1297 data entries with similar methodological approaches. Correlations between K-s and K-h at higher supply tensions decreased especially close to saturation, indicating a different flow mechanism at and very close to saturation than towards the dry end of the investigated tension range. Climate factors were better correlated with topsoil near-saturated hydraulic conductivities at supply tensions >= 30mm than soil texture, bulk density and organic carbon content. We find it most likely that the climate variables are proxies for soil macropore networks created by the respective biological activity, pedogenesis and climate-specific land use and management choices. Due to incomplete documentation in the source publications of OTIM, we were able to investigate only a few land use types and agricultural management practices. Land use, tillage system and soil compaction significantly influenced K-h, with effect sizes appearing comparable to the ones of soil texture and soil organic carbon. The data in OTIM show that experimental bias is present, introduced by the choice of measurement time relative to soil tillage, experimental design or data evaluation procedures. The establishment of best-practice rules for tension-disk infiltrometer measurements would therefore be helpful. Future studies are needed to investigate how climate shapes soil macropore networks and how land use and management can be adapted to improve soil hydraulic properties. Both tasks require large numbers of new measurement data with improved documentation on soil biology and land use and management history.
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| 16. |
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| 17. |
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| 18. |
- Jarvis, Nicholas, et al.
(författare)
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Understanding Preferential Flow in the Vadose Zone: Recent Advances and Future Prospects
- 2016
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- In this update, we review some of the more significant advances that have been made in the last decade in the study of preferential flow through the vadose zone as well as suggest some research needs in the coming years. We focus mostly on work that aims to improve understanding of the processes themselves and less on more applied aspects concerning the various consequences of preferential flow (e.g., for surface water and groundwater quality). In recent years, the research emphasis has shifted somewhat toward the two extremes of the scale continuum, the pore scale and the scale of management ( field, catchments, and landscapes). This trend has been facilitated by significant advances in both measurement technologies (e.g., noninvasive imaging techniques and high frequency-high spatial resolution monitoring of soil moisture at field and catchment scales) and application of novel methods of analysis to large datasets (e.g., machine learning). This work has led to a better understanding of how pore network properties control preferential flow at the pore to core scales as well as some new insights into the influence of site attributes (climate, land uses, soil types) at field to landscape scales. We conclude that models do not at present fully reflect the current state of process understanding and empirical knowledge of preferential flow. However, we expect that significant advances in computational techniques, computer hardware, and measurement technologies will lead to increasingly reliable model predictions of the impacts of preferential flow, even at the larger scales relevant for management.
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| 19. |
- Jordá Guerra, Helena, et al.
(författare)
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Using boosted regression trees to explore key factors controlling saturated and near-saturated hydraulic conductivity
- 2015
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 66, s. 744-756
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Tidskriftsartikel (refereegranskat)abstract
- Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near-saturated hydraulic conductivities in undisturbed soils with a global meta-database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta-databases may strongly over-estimate prediction performance unless they are validated against each individual data source separately. For such a source-wise cross-validation, we estimated the hydraulic conductivity at a tension of 10 cm (K-10) and the saturated hydraulic conductivity (K-s) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K-10 were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in-depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K-10, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension-sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for K-s. The direction of the tension-sequence and the soil texture class were also important, with both coarse and fine-textured soils generally having larger K-s values than medium-textured soils.
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| 20. |
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| 21. |
- Keck, Hannes, et al.
(författare)
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Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil
- 2017
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Ingår i: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 3, s. 177-189
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Tidskriftsartikel (refereegranskat)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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| 22. |
- Keller, Thomas, et al.
(författare)
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Soil structure recovery following compaction: Short-term evolution of soil physical properties in a loamy soil
- 2021
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Ingår i: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 85, s. 1002-1020
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Tidskriftsartikel (refereegranskat)abstract
- Soil compaction by farm machinery may persist for decades, hampering soil productivity and functioning. Assessing compaction costs and guiding recovery strategies are hindered by paucity of data on soil structure recovery rates. A long-term Soil Structure Observatory was established on a loamy soil in Switzerland to monitor soil structure recovery after prescribed compaction, and to better assess the roles of natural processes (vegetation, macrofauna, and shrink-swell cycles) on recovery patterns. The aim of this study was to quantify short-term soil structure recovery under natural conditions in the presence and absence of plant cover (ley and bare soil). We measured soil porosity and gas and water transport capabilities at 0.1 and 0.3 m depth. Two years after the compaction event, soil physical properties have not recovered to precompaction levels, even within the topsoil. Surprisingly, no differences were observed in the recovery patterns of ley and bare soil treatments. Measurements show that recovery rates differ among soil properties with the most severely affected properties by compaction (permeability) exhibiting highest recovery rates. Total soil porosity shows no recovery trend, suggesting lack of soil decompaction. Improved soil functions and decompaction are distinct aspects of soil structure recovery, with the latter requiring net upward transport of soil mass. We suggest that soil structure recovery proceeds at two fronts: from the soil surface downward, and expanding around local biologically-active pockets (marked by biopores) into the compacted soil volumes. This concept could be tested with additional data of longer time series at our site as well as in other soils and climates.
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| 23. |
- Klaminder, Jonatan, 1976-, et al.
(författare)
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Holes in the tundra : Invasive earthworms alter soil structure and moisture in tundra soils
- 2023
-
Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 859
-
Tidskriftsartikel (refereegranskat)abstract
- Human introductions have resulted in earthworms establishing in the Arctic, species known to cause cascading ecosystem change. However, few quantitative outdoor experiments have been performed that describe how these soil modifying earthworms are reshaping structures in tundra soils. In this study, we used three-dimensional (3-D) X-ray images of soil cores (approximately 10 cm diameter, 20 cm height, N = 48) to assess how earthworms (Aporrectodea sp. and Lumbricus sp.) affect soil structure and macropore networks in an outdoor mesocosm experiment that lasted four summers. Effects were assessed in both shrub-dominated (heath) and herb-dominated (meadow) tundra. Earthworms almost doubled the macroporosity in meadow soils and tripled macroporosity in heath. Interestingly, the fractal dimension of macropores decreased in response to earthworm burrowing in both systems, indicating that the presence of earthworms reduced the geometric complexity in comparison to other pore-generating processes active in the tundra. Observed effects on soil structure occurred along with a dramatically reduced soil moisture content, which was observed the first winter after earthworm introduction in the meadow. Our findings suggest that predictions of future changes in vegetation and soil carbon pools in the Arctic should include major impacts on soil properties that earthworms induce.
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| 24. |
- Koestel, Johannes, et al.
(författare)
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Approaches to delineate aggregates in intact soil using X-ray imaging
- 2021
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 402
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Tidskriftsartikel (refereegranskat)abstract
- Soil structure refers to the spatial arrangement of primary soil particles and pores, and is known to influence a variety of soil functions including carbon sequestration and water holding capacity. At present, research in this field is often divided, focusing either on pores where pore networks are investigated in undisturbed soil or on solids where isolated soil aggregates are commonly studied. The choice of approach depends on the needs and traditions in different disciplines of soil science. While there is much debate regarding how well these viewpoints relate to each other, there have been only marginal research efforts undertaken to compare them quantitatively. In this study, we presented and evaluated methods to identify 3-D subunits in X-ray images of eight undisturbed soil samples that we interpreted as macroaggregates, and compared these to to results from drop-shatter tests. Here, we exploited the cohesive forces of water that induces shrinkage cracks under drying. Despite promising trends, comparisons between image and drop-shatter test derived aggregate properties remained inconclusive. Nevertheless, our results encourage further investigations on larger sample sets and different observation scales. The here presented and discussed aggregate delineation methods illustrate an approach to harmonize soil structure characterization in terms of both pore-networks and soil aggregation. For example, respective extended approaches may be developed to evaluate the locations of microaggregates within macroaggregates.
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| 25. |
- Koestel, Johannes, et al.
(författare)
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Evaluation of Nonparametric Shape Measures for Solute Breakthrough Curves
- 2011
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 10, s. 1261-1275
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Tidskriftsartikel (refereegranskat)abstract
- A better understanding of the relationships among preferential solute transport, hydrologic boundary conditions, and site properties will help to improve predictions of the fate of contaminants in the vadose zone. The diversity of mechanisms underlying preferential transport, together with problems of nonuniqueness in fitting models to experimental data, suggests that model-independent (nonparametric) indicators of solute transport may help to establish such relationships. We therefore investigated 17 distinct nonparametric measures of solute breakthrough curve (BTC) shape using a data set of 115 tracer BTCs sampled from the literature. We tested the shape measures for sensitivity to deconvolution approaches based on Gaussian, lognormal, and gamma probability density functions and the mobile-immobile model. Furthermore, we evaluated collinearities among the 17 shape measures. Most deconvolution approaches gave very good fits to the data, with coefficients of determination larger than 0.98. Dual-domain transfer functions were superior to single-domain ones, even after accounting for measures of parsimony. The least sensitive shape measures were the normalized first temporal moment, the mean transport velocity, the apparent dispersion coefficient, and the relative arrival time of the first 5 and 85% of the tracer mass. In contrast, the skewness and kurtosis were most sensitive to the choice of deconvolution approach, even for BTC experiments with very long data series of more than eight water-filled pore volumes. The relative arrival time of the first 5% of the tracer mass was identified as the most robust shape parameter that could serve as an indicator of preferential flow and transport.
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| 26. |
- Koestel, Johannes
(författare)
-
Exploring the relationship between soil structure and soil functions via pore-scale imaging
- 2020
-
Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 370
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Tidskriftsartikel (refereegranskat)abstract
- Biogeochemical and structural heterogeneities at the pore-scale govern processes in soil in many ways. They are therefore of key importance for understanding soil functioning. Prominent examples are the stabilization of soil organic matter due to reduced bioavailability in aggregated soil structure, preferential transport of nutrients and contaminants along macropores, highly localized greenhouse gas emission around a few hotspots of microbial activity like particulate organic matter and the formation of the rhizosphere as a complex system composed of plant roots, soil and associated microorganisms.All of these processes have in common that the underlying relevant mechanisms are fairly well understood in artificial systems with reduced degrees of heterogeneity, like soil suspensions, glass beads, micromodels with known structure and so on. However, the far more complex pore architecture of undisturbed soils leads to emergent system behavior which needs to be addressed when studying these structure-mediated processes. The opaque nature of soils predestines the use of non-invasive imaging techniques for exploring how biogeochemical and structural heterogeneities are shaping soil functions. Such imaging techniques and subsequent image analyses are now widely used to study soils. While previously many properties were defined only by averaged bulk parameters, pore-scale imaging reveals details at smaller scales and provides spatial information, in two, three or even more dimensions including time or multispectral data.This virtual special issue presents fourteen contributions that employ pore scale imaging in order to highlight the role of soil structure on soil functions or reversely the effect of soil processes on soil structure or report methodological advancements in pore scale imaging. In this editorial we briefly outline the different conceptions of soil structure, demonstrate the relevance of soil structure for various soil functions with a specific example and review the different avenues along which recent advances in pore scale imaging of soil have been made, before we briefly categorize and summarize the contributions to this virtual special issue.
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| 27. |
- Koestel, Johannes
(författare)
-
Hydro-pedotransfer functions: a roadmap for future development
- 2024
-
Ingår i: Hydrology and Earth System Sciences. - 1027-5606 .- 1607-7938. ; 28, s. 3391-3433
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Forskningsöversikt (refereegranskat)abstract
- Hydro-pedotransfer functions (PTFs) relate easy-to-measure and readily available soil information to soil hydraulic properties (SHPs) for applications in a wide range of process-based and empirical models, thereby enabling the assessment of soil hydraulic effects on hydrological, biogeochemical, and ecological processes. At least more than 4 decades of research have been invested to derive such relationships. However, while models, methods, data storage capacity, and computational efficiency have advanced, there are fundamental concerns related to the scope and adequacy of current PTFs, particularly when applied to parameterise models used at the field scale and beyond. Most of the PTF development process has focused on refining and advancing the regression methods, while fundamental aspects have remained largely unconsidered. Most soil systems are not represented in PTFs, which have been built mostly for agricultural soils in temperate climates. Thus, existing PTFs largely ignore how parent material, vegetation, land use, and climate affect processes that shape SHPs. The PTFs used to parameterise the Richards-Richardson equation are mostly limited to predicting parameters of the van Genuchten-Mualem soil hydraulic functions, despite sufficient evidence demonstrating their shortcomings. Another fundamental issue relates to the diverging scales of derivation and application, whereby PTFs are derived based on laboratory measurements while often being applied at the field to regional scales. Scaling, modulation, and constraining strategies exist to alleviate some of these shortcomings in the mismatch between scales. These aspects are addressed here in a joint effort by the members of the International Soil Modelling Consortium (ISMC) Pedotransfer Functions Working Group with the aim of systematising PTF research and providing a roadmap guiding both PTF development and use. We close with a 10-point catalogue for funders and researchers to guide review processes and research.
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| 28. |
- Koestel, Johannes, et al.
(författare)
-
Imaging and quantification of preferential solute transport in soil macropores
- 2014
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Ingår i: Water Resources Research. - 0043-1397 .- 1944-7973. ; 50, s. 4357-4378
-
Tidskriftsartikel (refereegranskat)abstract
- Despite significant advances during the last decades, there are still many processes related to nonequilibrium flow and transport in macroporous soil that are far from completely understood. The use of X-ray for imaging time-lapse 3-D solute transport has a large potential to help advance the knowledge in this field. We visualized the transport of potassium iodide (20 g iodide l21 H2O) front through a small undisturbed soil column (height 3.8 cm, diameter 6.8 cm) under steady state hydraulic conditions using an industrial X-ray scanner. In addition, the electrical conductivity was measured in the effluent solution during the experiment. We attained a series of seventeen 3-D difference images which we related to iodide concentrations using a linear calibration relationship. The solute transport through the soil mainly took place in two cylindrical macropores, by-passing more than 90% of the bulk soil volume during the entire experiment. From these macropores the solute diffused into the surrounding soil matrix. We illustrated the properties of the investigated solute transport by comparing it to a 1-D convective-dispersive transport and by calculating the temporal evolution of the dilution index. We furthermore showed that the tracer diffusion from one of the macropores into the surrounding soil matrix could not be exactly fitted with the cylindrical diffusion equation. We believe that similar studies will help establish links between soil structure and solute transport processes and lead to improvements in models for solute transport through undisturbed soil.
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| 29. |
- Koestel, Johannes, et al.
(författare)
-
Influence of soil, land use and climatic factors on the hydraulic conductivity of soil
- 2013
-
Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 17, s. 5185-5195
-
Tidskriftsartikel (refereegranskat)abstract
- Due to inadequate data support, existing algorithms used to estimate soil hydraulic conductivity, K, in (eco)hydrological models ignore the effects of key site factors such as land use and climate and underplay the significant effects of soil structure on water flow at and near saturation. These limitations may introduce serious bias and error into predictions of terrestrial water balances and soil moisture status, and thus plant growth and rates of biogeochemical processes. To resolve these issues, we collated a new global database of hydraulic conductivity measured by tension infiltrometer under field conditions. The results of our analyses on this data set contrast markedly with those of existing algorithms used to estimate K. For example, saturated hydraulic conductivity, K-s, in the topsoil (<0.3m depth) was found to be only weakly related to texture. Instead, the data suggests that K-s depends more strongly on bulk density, organic carbon content and land use. In this respect, organic carbon was negatively correlated with K-s, presumably due to water repellency, while K-s at arable sites was, on average, ca. 2-3 times smaller than under natural vegetation, forests and perennial agriculture. The data also clearly demonstrates that clay soils have smaller K in the soil matrix and thus a larger contribution of soil macropores to K at and near saturation.
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| 30. |
- Koestel, Johannes, et al.
(författare)
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Links between soil properties and steady-state solute transport through cultivated topsoil at the field scale
- 2013
-
Ingår i: Water Resources Research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49, s. 790-807
-
Tidskriftsartikel (refereegranskat)abstract
- It is known that solute transport through soil is heterogeneous at all spatial scales. However, little data are available to allow quantification of these heterogeneities at the field scale or larger. In this study, we investigated the spatial patterns of soil properties, hydrologic state variables, and tracer breakthrough curves (BTCs) at the field scale for the inert solute transport under a steady-state irrigation rate which produced near-saturated conditions. Sixty-five undisturbed soil columns approximately 20 cm in height and diameter were sampled from the loamy topsoil of an agricultural field site in Silstrup (Denmark) at a sampling distance of approximately 15 m (with a few exceptions), covering an area of approximately 1 ha (60 m x 165 m). For 64 of the 65 investigated soil columns, we observed BTC shapes indicating a strong preferential transport. The strength of preferential transport was positively correlated with the bulk density and the degree of water saturation. The latter suggests that preferential macropore transport was the dominating transport process. Increased bulk densities were presumably related with a decrease in near-saturated hydraulic conductivities and as a consequence to larger water saturation and the activation of larger macropores. Our study provides further evidence that it should be possible to estimate solute transport properties from soil properties such as soil texture or bulk density. We also demonstrated that estimation approaches established for the column scale have to be upscaled when applied to the field scale or larger. Citation: Koestel, J. K., T. Norgaard, N. M. Luong, A. L. Vendelboe, P. Moldrup, N. J. Jarvis, M. Lamande, B. V. Iversen, and L. Wollesen de Jonge (2013), Links between soil properties and steady-state solute transport through cultivated topsoil at the field scale, Water Resour. Res., 49, doi: 10.1002/wrcr.20079.
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| 31. |
- Koestel, Johannes, et al.
(författare)
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Meta-analysis of the effects of soil properties, site factors and experimental conditions on solute transport
- 2012
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 16, s. 1647-1665
-
Tidskriftsartikel (refereegranskat)abstract
- Preferential flow is a widespread phenomenon that is known to strongly affect solute transport in soil, but our understanding and knowledge is still poor of the site factors and soil properties that promote it. To investigate these relationships, we assembled a database from the peer-reviewed literature containing information on 733 breakthrough curve experiments under steady-state flow conditions. Most of the collected experiments (585 of the 733 datasets) had been conducted on undisturbed soil columns, although some experiments on repacked soil, clean sands, and glass beads were also included. In addition to the apparent dispersivity, we focused our attention on three indicators of preferential solute transport: namely the 5%-arrival time, the holdback factor, and the ratio of piston-flow and average transport velocities. Our results suggest that, in contrast to the 5%-arrival time and the holdback factor, the piston-flow to transport velocity ratio is not related to preferential macropore transport but rather to the exclusion or retardation of the applied tracer. Confirming that the apparent longitudinal dispersivity is positively correlated with the travel distance of the tracer, our results also illustrate that this relationship is refined if the normalized 5%-tracer arrival time is also taken into account. In particular, we found that the degree of preferential solute transport increases with apparent dispersivity and decreases with travel distance. A similar but weaker relationship was observed between apparent dispersivity, 5%-tracer arrival time, and lateral observation scale, such that the degree of preferential transport increases with lateral observation scale. However, we also found that the travel distance and the lateral observation scale in the investigated dataset are correlated, which makes it difficult to distinguish their influence on these transport characteristics. We also found that the strength of preferential transport increased at larger flow rates and water saturations, which suggests that macropore flow was a more important flow mechanism than heterogeneous flow in the soil matrix. Nevertheless, our data show that heterogeneous flow in the soil matrix also occasionally leads to strong preferential transport. Furthermore, we show that preferential solute transport under steady-state flow depends on soil texture in a threshold-like manner: moderate to strong preferential transport was found to occur only for undisturbed soils that contain more than 8% clay. Preferential flow characteristics were also absent for columns filled with glass beads, clean sands, or sieved soil. No clear effect of land use on the pattern of solute transport could be discerned, probably because the available dataset was too small and too strongly affected by cross-correlations with experimental conditions. Our results suggest that, in developing pedotransfer functions for solute transport properties of soils, it is critically important to account for travel distance, lateral observation scale, and water flow rate and saturation.
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| 32. |
- Koestel, Johannes
(författare)
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Microbial spatial footprint as a driver of soil carbon stabilization
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Increasing the potential of soil to store carbon (C) is an acknowledged and emphasized strategy for capturing atmospheric CO2. Well-recognized approaches for soil C accretion include reducing soil disturbance, increasing plant biomass inputs, and enhancing plant diversity. Yet experimental evidence often fails to support anticipated C gains, suggesting that our integrated understanding of soil C accretion remains insufficient. Here we use a unique combination of X-ray micro-tomography and micro-scale enzyme mapping to demonstrate for the first time that plant-stimulated soil pore formation appears to be a major, hitherto unrecognized, determinant of whether new C inputs are stored or lost to the atmosphere. Unlike monocultures, diverse plant communities favor the development of 30-150 mu m pores. Such pores are the micro-environments associated with higher enzyme activities, and greater abundance of such pores translates into a greater spatial footprint that microorganisms make on the soil and consequently soil C storage capacity.
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| 33. |
- Koestel, Johannes
(författare)
-
Occurrence of power law tailings in inert tracer breakthrough curves through undisturbed soil
- 2013
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Breakthrough curves from inert solute transport experiments in soils often exhibit power law tailings. Understanding how onset, duration and inclination of log-log linear slopes in breakthrough curve recessions are related to flow field properties and boundary conditions will improve predictions of contaminant displacement in the subsurface. The study of Willmann et al. (2008) [1] investigates exactly this for aquifers. However, flow field properties are difficult to measure, at least at large scales for which predictions of contaminant displacement are needed. It is therefore of interest to examine if soil properties and site factors can be used as proxy variables to directly infer to the occurrence and characteristics of log-log linear slopes in breakthrough curve tailings. In this study I investigated 82 breakthrough curves from inert tracer experiments conducted on undisturbed soil columns under steady state irrigation. The breakthrough curves were collated from the peer-reviewed literature. A preliminary evaluation of the dataset yielded that half of the investigated breakthrough curves exhibited log-log linear slopes. The inclination of the slopes ranged from -1.3 to -5. As also reported by Willmann et al. (2008), I found that the inclination of the log-log linear slope was correlated with breakthrough curve connectivity indicators like small relative 5%-arrival times (p0.05, Figure 1; see [2] and [3]). Note that p0.05 is the inverse of what is denoted as CT1 in Knudby and Carrera (2005) [2]. Figure 1: The duration and inclination of log-log linear slopes in breakthrough curve tailings are shown together with the corresponding relative 5%-arrival time, p0.05. Reduced inclinations of log-log linear slopes were promoted by initially dry conditions, near saturated conditions as well as efforts to reduce air entrapment. The use of anionic tracers was related with steeper log-log linear slopes. The onset of the log-log linear slopes was not correlated with any soil property or experimental condition. The duration of the log-log linear slope was decreased for soil samples with a large bulk density and for experiments with a seepage face at the bottom of the column. For the future, I plan to increase the number of experiments in the database and to deepen the statistical evaluation. [1] Willmann, M., Carrera, J. and Sanchez-Vila, X., Transport up-scaling in heterogeneous aquifers: What physical parameters control memory functions?, Water Resources Research, Dec. 44(12), - (2008). [2] Knudby C. and Carrera J., On the relationship between indicators of geostatistical, flow and transport connectivity, Advances in Water Resources, 28(4), 405-421 (2005). [3] Koestel J., Moeys J. and Jarvis N., Meta-analysis of the effects of soil properties, site factors and experimental conditions on solute transport, Hydrol Earth Syst Sci., 16(6), 1647-1665 (2012).
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| 34. |
- Koestel, Johannes
(författare)
-
Pedotransfer Functions in Earth System Science: Challenges and Perspectives
- 2017
-
Ingår i: Reviews of Geophysics. - 8755-1209 .- 1944-9208. ; 55, s. 1199-1256
-
Forskningsöversikt (refereegranskat)abstract
- Soil, through its various functions, plays a vital role in the Earth's ecosystems and provides multiple ecosystem services to humanity. Pedotransfer functions (PTFs) are simple to complex knowledge rules that relate available soil information to soil properties and variables that are needed to parameterize soil processes. In this paper, we review the existing PTFs and document the new generation of PTFs developed in the different disciplines of Earth system science. To meet the methodological challenges for a successful application in Earth system modeling, we emphasize that PTF development has to go hand in hand with suitable extrapolation and upscaling techniques such that the PTFs correctly represent the spatial heterogeneity of soils. PTFs should encompass the variability of the estimated soil property or process, in such a way that the estimation of parameters allows for validation and can also confidently provide for extrapolation and upscaling purposes capturing the spatial variation in soils. Most actively pursued recent developments are related to parameterizations of solute transport, heat exchange, soil respiration, and organic carbon content, root density, and vegetation water uptake. Further challenges are to be addressed in parameterization of soil erosivity and land use change impacts at multiple scales. We argue that a comprehensive set of PTFs can be applied throughout a wide range of disciplines of Earth system science, with emphasis on land surface models. Novel sensing techniques provide a true breakthrough for this, yet further improvements are necessary for methods to deal with uncertainty and to validate applications at global scale.Plain Language Summary For the application of pedotransfer functions in current Earth system models, and specifically for the different fluxes of water, solutes, and gas between soil and atmosphere, subject of the land surface models, recent developments of knowledge are entered in a new generation of pedotransfer functions. Methods for development and evaluation of pedotransfer functions are described in this comprehensive review, and perspectives for future developments in different Earth system science disciplines are presented. Challenges are still present for the application in some extreme environments of the Earth. We argue that a comprehensive set of pedotransfer functions can be applied throughout a wide range of disciplines of Earth system science, with emphasis on land surface models. Even though methodological challenges are still present for extrapolation and scaling, as outlined, integration and validation in global-scale models is an achievable goal.
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| 35. |
- Koestel, Johannes
(författare)
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Percolation theory applied to soil tomography
- 2020
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 357
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Tidskriftsartikel (refereegranskat)abstract
- This study provides insights on the significance of network features of soil macropores on the transport of solutes and colloids, and in the filtrating capacity of the soil. We applied percolation theory and network analysis to the pore network extracted from X-ray computed tomography (imaged porosity) in intact columns sampled from topsoils with different tillage treatments. Moreover, we developed a procedure to extract the backbone, which is the part of the percolation cluster that controls the direct flow between two boundaries in near saturated conditions, using the ImageJ open source imaging software. We also calculated the percolation threshold of each soil, the probability at which the soil starts to percolate (for the resolution considered).Some backbone characteristics (pore volume, wall surface, circularity, fractal dimension, number of loops and tortuosity) showed significant differences between the treatments. Tilled conventional and organic with high earthworm activity exhibited more complex backbones than no-till soil. Backbone volume, surface, fractal dimension and number of loops are correlated with the surface area of pore walls stained by fluorescent microspheres (MS) used as a colloidal tracer. We also found significant correlations between the tortuosity and the number of end-points of the backbone and the transport model parameters for the microspheres and bromide. These findings reinforce the phenomenology between transport in porous media and percolation theory. Moreover, the properties based on percolation theory allow a complete characterization of the complex soil structure and the development of more accurate transport models.
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| 36. |
- Koestel, Johannes, et al.
(författare)
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Perspectives on the misconception of levitating soil aggregates
- 2024
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Ingår i: Soil. - 2199-3971 .- 2199-398X. ; 10, s. 23-31
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Tidskriftsartikel (refereegranskat)abstract
- Soil aggregation is an important process in nearly all soils across the globe. Aggregates develop over time through a series of abiotic and biotic processes and interactions, including plant growth and decay, microbial activity, plant and microbial exudation, bioturbation, and physicochemical stabilization processes, and are greatly influenced by soil management practices. Together, and through feedback with organic matter and primary soil particles, these processes form dynamic soil aggregates and pore spaces, which jointly constitute a soil's structure and contribute to overall soil functioning. Nevertheless, the concept of soil aggregates is hotly debated, leading to confusion about their function or relevancy to soil processes. We argue here that the opposition to the concept of soil aggregation likely stems from the fact that the methods for the characterization of soil aggregates have largely been developed in the context of arable soils, where tillage promotes the formation of distinct soil aggregates that are easily visible in the topsoil. We propose that the widespread use of conceptual figures showing detached and isolated aggregates can be misleading and has contributed to the skepticism towards soil aggregates. However, the fact that we do not always see discrete aggregates within soils in situ does not mean that aggregates do not exist or are not relevant to the study of soil processes. Given that, by definition, soil aggregates consist of any group of soil particles that cohere more strongly to each other than neighboring particles, aggregates may, but do not necessarily need to be, bordered by pore space. Here, we illustrate how aggregates can form and dissipate within the context of undisturbed, intact soils, highlighting the point that aggregates do not necessarily need to have a discrete physical boundary and can exist seamlessly embedded in the soil. We hope that our contribution helps the debate on soil aggregates and supports the foundation of a shared understanding on the characterization and function of soil structure.
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| 37. |
- Koestel, Johannes, et al.
(författare)
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Potential of combined neutron and X-ray imaging to quantify local carbon contents in soil
- 2022
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 73
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigated the potential and limitations of using joint X-ray and time-of-flight (TOF) neutron imaging for mapping the 3-dimensional organic carbon distribution in soil. This approach is viable because neutron and X-ray beams have complementary attenuation properties. Soil minerals consist to a large part of silicon and aluminium, and elements that are relatively translucent to neutrons but attenuate X-rays. In contrast, attenuation of neutrons is strong for hydrogen, which is abundant in soil organic matter (SOM), while hydrogen barely attenuates X-rays. In theory, TOF neutron imaging does further more allow the imaging of Bragg edges, which correspond to d-spacings in minerals. This could help to distinguish between SOM and clay minerals, the mineral group in soil that is most strongly associated with hydrogen atoms. We collected TOF neutron image data at the IMAT beamline at the ISIS facility and synchrotron X-ray image data at the I12 beamline at the Diamond Light source, both located within the Rutherford Appleton Laboratory, Harwell, UK. The white beam (the full energy spectrum) neutron image clearly showed variations in neutron attenuation within soil aggregates at approximately constant X-ray attenuations. This indicates a constant bulk density with varying organic matter and/or clay content. Unfortunately, the combination of TOF neutron and X-ray imaging was not suited to allow for a distinction between SOM and clay minerals at the voxel scale. While such a distinction is possible in theory, it is prevented by technical limitations. One of the main reasons is that the neutron frequencies available at modern neutron sources are too large to capture the main d-spacings of clay minerals. As a result, inference to voxel scale SOM concentrations is presently not feasible. Future improved neutron sources and advanced detector designs will eventually overcome the technical problems encountered here. On the positive side, combined X-ray and TOF neutron imaging demonstrated abilities to identify quartz grains and to distinguish between plastics and plant seeds. Highlights Full understanding of biogeochemical processes requires three-dimensional (3-D) maps of organic matter in soil (SOM). This study investigates a novel method to map voxel-scale SOM contents with 3-D resolution. The method is based a combination of X-ray and time-of-flight neutron tomography. At present, technical limitations prevent distinguishing between SOM and clay mineral contents. More advanced neutron sources are required to overcome the encountered technical obstacles.
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| 38. |
- Koestel, Johannes
(författare)
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Potential of natural language processing for metadata extraction fromenvironmental scientific publications
- 2023
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Ingår i: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 9, s. 155-168
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Tidskriftsartikel (refereegranskat)abstract
- Summarizing information from large bodies of scientific literature is anessential but work-intensive task. This is especially true in environmentalstudies where multiple factors (e.g., soil, climate, vegetation) cancontribute to the effects observed. Meta-analyses, studies thatquantitatively summarize findings of a large body of literature, rely onmanually curated databases built upon primary publications. However, giventhe increasing amount of literature, this manual work is likely to requiremore and more effort in the future. Natural language processing (NLP)facilitates this task, but it is not clear yet to which extent theextraction process is reliable or complete. In this work, we explore threeNLP techniques that can help support this task: topic modeling, tailoredregular expressions and the shortest dependency path method. We apply thesetechniques in a practical and reproducible workflow on two corpora ofdocuments: the Open Tension-diskInfiltrometer Meta-database (OTIM) and the Meta corpus. The OTIM corpus contains the sourcepublications of the entries of the OTIM database of near-saturated hydraulicconductivity from tension-disk infiltrometer measurements(https://github.com/climasoma/otim-db, last access: 1 March 2023). The Meta corpus is constituted ofall primary studies from 36 selected meta-analyses on the impact ofagricultural practices on sustainable water management in Europe. As a firststep of our practical workflow, we identified different topics from theindividual source publications of the Meta corpus using topic modeling.This enabled us to distinguish well-researched topics (e.g., conventionaltillage, cover crops), where meta-analysis would be useful, from neglectedtopics (e.g., effect of irrigation on soil properties), showing potentialknowledge gaps. Then, we used tailored regular expressions to extractcoordinates, soil texture, soil type, rainfall, disk diameter and tensionsfrom the OTIM corpus to build a quantitative database. We were able toretrieve the respective information with 56 % up to 100 % of allrelevant information (recall) and with a precision between 83 % and100 %. Finally, we extracted relationships between a set of driverscorresponding to different soil management practices or amendments (e.g.,"biochar", "zero tillage") and target variables (e.g., "soilaggregate", "hydraulic conductivity", "crop yield") from thesource publications' abstracts of the Meta corpus using the shortestdependency path between them. These relationships were further classifiedaccording to positive, negative or absent correlations between the driverand the target variable. This quickly provided an overview of the differentdriver-variable relationships and their abundance for an entire body ofliterature. Overall, we found that all three tested NLP techniques were ableto support evidence synthesis tasks. While human supervision remainsessential, NLP methods have the potential to support automated evidencesynthesis which can be continuously updated as new publications becomeavailable.
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| 39. |
- Koestel, Johannes
(författare)
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Quantification of the structure evolution in a garden soil over the course of two years
- 2019
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 338, s. 597-609
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Tidskriftsartikel (refereegranskat)abstract
- In this proof-of-concept, we demonstrate the potential of quantifying the structural evolution in an individual soil sample with the help of X-ray imaging. The soil sample was acquired in summer 2013 after a manual seedbed preparation and scanned with X-ray CT on six occasions during the following two years. After each imaging session, the soil sample was re-installed into the field. We focused on analyzing the evolution of soil morphologic measures that are thought to be fundamental to air and water flow in soil. We also quantified deformation of the soil matrix during the experiment. Our results illustrate the effects of several biotic and abiotic processes on the evolution of soil structure. A well-connected inter-aggregate pore network after seedbed preparation was replaced by a sparser network of larger biopores. Macro-faunal burrowing activity generally increased morphological measures associated with larger air and hydraulic conductivity as well as a better aeration. Soil settling and the growth of a dandelion tap-root acted in the opposite direction. Soil settling and compaction continued during the entire experimental period, but was restricted to soil depths below 20 mm. Other noteworthy observations that appear worth investigating in follow-up experiments were i.) the strong variation in the critical pore diameter, which could explain the commonly noted large temporal variability of saturated hydraulic conductivity, ii) the much greater extent of lateral compaction due to tap root growth than macro-faunal burrowing, and iii.) the short life-span of large biopores. We conclude that the approach presented here shows great potential for quantifying soil structural dynamics pertaining to individual structure-forming and degrading processes under field conditions. This kind of data could also prove very useful for constructing and testing 'next-generation' models that link a dynamic description of soil structure to various processes and functions in the soil-plant system.
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| 40. |
- Koestel, Johannes
(författare)
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Quantifying Physical Properties of Three Sphagnum-Based Growing Media as Affected by Drying-Wetting Cycles
- 2019
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- The suitability of organic materials as growing media in plant production is largely dependent on their physical properties. However, the properties and impacts of different stress factors on Sphagnum-based materials are not fully understood. This study aimed to quantify differences in water retention, aeration, and pore structure characteristics of three different low- or non-humified Sphagnum-based growing media using three-dimensional (3D) X-ray imaging and conventional physical measurements. In addition, we assessed the impacts of intense drying-wetting cycles on their pore structure. The imaged porosities of the materials differed significantly with decomposition degree. Drying curve observations showed that drying of the materials occurred in three phases with (i) large changes in the air-filled porosity in the matric potential range 0.2 to 3.2 kPa, (ii) clearly smaller changes at 3.2 to 312 kPa, and (iii) large changes at 312 to 1585 kPa, comparable to the change in the wet end of the drying curves (0.2-3.2 kPa). The aeration of the materials was sufficient for plant growth in the second and third phases, where the amount of easily available water was low. This challenges the suitability of the materials under conditions without regular irrigation. The 3D imaging also revealed how pore-size distributions shifted toward smaller pore-size classes with increasing decomposition degree and stress impact of the drying-wetting cycles. However, unexpectedly most of the imaged porosity (>= 97%) and height (96-98%) of the samples was recovered during rewetting. Overall, the results demonstrate how the water retention, aeration, and shrinkage properties of growing media are inherently interlinked.
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| 41. |
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| 42. |
- Koestel, Johannes, et al.
(författare)
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Scale and REV analyses for porosity and pore connectivity measures in undisturbed soil
- 2020
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 366
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Tidskriftsartikel (refereegranskat)abstract
- Soil samples with a volume of approximately 100 mL are commonly used for measuring soil properties needed to parameterize continuum models of transport processes in soils. The necessary assumption that the sampled soil volume corresponds to a representative elementary volume (REV) has only been occasionally tested. Furthermore, the few studies so far have focused on bulk properties such as porosity and bulk density and have not investigated the scale-dependence of pore-space connectivity, which is fundamental for transport properties such as the permeability of soil. In this study, we investigated the scale-dependence of morphologic properties of the soil pore-space in 25 undisturbed soil columns sampled from five different depths (8, 23, 33, 53 and 73 cm) from a field site in southern Norway (Skuterud). We conducted the analyses of scale-dependence on regions of interests of 40 x 40 x 40 mm(3) from binarized X-ray images with a resolution of 40 mu m. We focused our evaluation on imaged porosity and three measures of pore-space connectivity (the connection probability, the Euler-Poincare number and the critical pore diameter). As pore network connectivity is scale-dependent and because the connectivity of large pores has a very strong impact on the soil permeability, we conducted our analyses considering three contrasting minimum pore diameters, namely 80, 250 and 500 mu m.We found that the pore connectivity improved with scale, predominantly due to the presence of pores with diameters of less than 0.25 mm. This stresses the importance of image resolution in scale analyses. We moreover observed that both the mean and the standard deviation of the critical pore diameter increased with scale, which may explain why the mean and standard deviation of the saturated hydraulic conductivity are often found to increase with scale. We detected an REV range for the macroporosity between approximately 15 and 65 mm. This range decreased with an increase in the minimum pore diameter considered. However, we also found evidence contradicting the existence of the detected REV range for the macroporosity due to a lack of statistical homogeneity. No REV range could be found for the three investigated connectivity measures, probably because the evaluated scales were too small. Based on our results we conclude that larger soil samples should be used to measure soil properties and investigate processes that depend on the pore network connectivity, such as permeability or water flow and long-range solute transport. We recommend that future studies should investigate REVs for connectivity measures and investigate which REV criteria are most meaningful in a continuum modelling context. Such studies are needed to evaluate whether REVs for transport properties are common in soils. If not, flow and transport models that explicitly account for heterogeneity are necessary.
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| 43. |
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| 44. |
- Koestel, Johannes
(författare)
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SoilJ: An ImageJ Plugin for the Semiautomatic Processing of Three-Dimensional X-ray Images of Soils
- 2018
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- Noninvasive three- and four-dimensional X-ray imaging approaches have proved to be valuable analysis tools for vadose zone research. One of the main bottlenecks for applying X-ray imaging to data sets with a large number of soil samples is the relatively large amount of time and expertise needed to extract quantitative data from the respective images. SoilJ is a plugin for the free and open imaging software ImageJ that aims at automating the corresponding processing steps for cylindrical soil columns. It includes modules for automatic column outline recognition, correction of image intensity bias, image segmentation, extraction of particulate organic matter and roots, soil surface topography detection, as well as morphology and percolation analyses. In this study, the functionality and precision of some key SoilJ features were demonstrated on five different image data sets of soils. SoilJ has proved to be useful for strongly decreasing the amount of time required for image processing of large image data sets. At the same time, it allows researchers with little experience in image processing to make use of X-ray imaging methods. The SoilJ source code is freely available and may be modified and extended at will by its users. It is intended to stimulate further community-driven development of this software.
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| 45. |
- Koestel, Johannes
(författare)
-
Spatial patterns of extracellular enzymes: Combining X-ray computed micro-tomography and 2D zymography
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 135, s. 411-419
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Tidskriftsartikel (refereegranskat)abstract
- Linking the distribution of enzyme activity to the size and properties of soil pores is a necessary prerequisite for mechanistic understanding of soil biochemical processes. In this study we used soil 2D zymography and X-ray computed tomography (mu CT) to assess the relationship between enzymes and pores. The objectives of the study were (i) to assess spatial distribution patterns in the activity of six enzymes contributing to C, N and P cycles, namely, cellobiohydrolase, beta-glucosidase, xylanase acid phosphatase, leucine aminopeptidase, and N-acetylglucosaminidase, in soils from five long-term land use and management practices, (ii) to study the correlation between enzyme activities and mu CT information, i.e., pore characteristics and image grayscale values, and (iii) to explore the potential use of soil 2D zymography in predicting enzyme activities within 3D soil cores. 3D pore-size distributions were obtained from mu CT images of 13 intact soil cores and then 8-15 2D zymography maps were taken from each core. Spatial distributions in the activities of all studied enzymes were auto-correlated; the spatial correlation ranges were equal to similar to 7-8 mm. The relative activity of all enzymes was positively associated within 60-180 mu m empty set pores. Combining 3D mu CT information with 2D zymography maps visualized the overall patterns of enzyme activity distributions with respect to soil pores and particulate organic matter locations. Based on the findings we propose a conceptual scheme relating localization of microorganisms, enzymes and substrates to pores of different size ranges. Specifically, we suggest that pores in the tens of microns size range represent optimal microbial habitats, and as such are associated with greater microbial abundance, leading to high enzyme production and activity.
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| 46. |
- Koestel, Johannes
(författare)
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The Impact of Capillary Trapping of Air on Satiated Hydraulic Conductivity of Sands Interpreted by X-ray Microtomography
- 2020
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between entrapped air content and the corresponding hydraulic conductivity was investigated experimentally for two coarse sands. Two packed samples of 5 cm height were prepared for each sand. Air entrapment was created by repeated infiltration and drainage cycles. The value of K was determined using repetitive falling-head infiltration experiments, which were evaluated using Darcy's law. The entrapped air content was determined gravimetrically after each infiltration run. The amount and distribution of air bubbles were quantified by micro-computed X-ray tomography (CT) for selected runs. The obtained relationship between entrapped air content and satiated hydraulic conductivity agreed well with Faybishenko's (1995) formula. CT imaging revealed that entrapped air contents and bubbles sizes were increasing with the height of the sample. It was found that the size of the air bubbles and clusters increased with each experimental cycle. The relationship between initial and residual gas saturation was successfully fitted with a linear model. The combination of X-ray computed tomography and infiltration experiments has a large potential to explore the effects of entrapped air on water flow.
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| 47. |
- Koestel, Johannes, et al.
(författare)
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What determines the strength of preferential transport in undisturbed soil under steady-state flow?
- 2014
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 217, s. 144-160
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Tidskriftsartikel (refereegranskat)abstract
- Preferential flow and transport has to be taken into account to successfully predict solute transport through the vadose zone. The relative 5%-arrival time of inert tracer can serve as a measure for the strength of preferential transport. As direct measurements of solute transport are not practical at large scales, soil susceptibility to preferential flow and transport has to be estimated using proxy variables. In this study we investigated how well the relative 5%-arrival time of inert tracer could be inferred from soil properties, site factors, scale and hydrologic conditions for 442 breakthrough curve experiments on undisturbed soil columns under steady state irrigation. Using a random forest as a global regression tool, we found a coefficient of determination of 0.561 in a ten-fold cross-validation. When predicting relative 5%-arrival times on a completely independent benchmark dataset of 149 experiments we obtained a still reasonable coefficient of determination of 0336. When the soil columns had not been sampled from the same site and soil horizon, the random forest was able to rank the experiments correctly according to their relative 5%-arrival time, apart from one exception. Our study demonstrates that soil susceptibility to preferential flow and transport occurring under steady state initial and boundary conditions is to a large part predictable from proxy variables. We furthermore found evidence that the prediction performance should be considerably increased if information on the water saturation state during the experiment could be included into the random forest. An investigation of the importance of the predictors for estimating the relative 5%-arrival time yielded that the clay content was fundamental. Next important were the ratio between clay content and organic carbon, the lateral observation scale and whether the column had been slowly saturated from the bottom prior to the experiment or not. Flow rate, soil management and bulk density were found useful to further refine the predictions. A caveat has to be given that the investigated dataset includes few experiments on large columns and no experiments under natural transient hydrologic boundary conditions, since such experiments are scarce. Availability of such experiments is crucial to account for additional important preferential flow transport mechanisms caused by hydrophobicity, instabilities at infiltration fronts or funneling at soil horizon boundaries. (C) 2013 Elsevier B.V. All rights reserved.
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| 48. |
- Koestel, Johannes
(författare)
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X-ray computed tomography to predict soil N2O production via bacterial denitrification and N2O emission in contrasting bioenergy cropping systems
- 2018
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Ingår i: GCB Bioenergy. - : Wiley. - 1757-1693 .- 1757-1707. ; 10, s. 894-909
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Tidskriftsartikel (refereegranskat)abstract
- While renewable biofuels can reduce negative effects of fossil fuel energy consumption, the magnitude of their benefits depends on the magnitude of N2O emissions. High variability of N2O emissions overpowers efforts to curb uncertainties in estimating N2O fluxes from biofuel systems. In this study, we explored (a) N2O production via bacterial denitrification and (b) N2O emissions from soils under several contrasting bioenergy cropping systems, with specific focus on explaining N2O variations by accounting for soil pore characteristics. Intact soil samples were collected after 9years of implementing five biofuel systems: continuous corn with and without winter cover crop, monoculture switchgrass, poplars, and early-successional vegetation. After incubation, N2O emissions were measured and bacterial denitrification was determined based on the site-preference method. Soil pore characteristics were quantified using X-ray computed microtomography. Three bioenergy systems with low plant diversity, that is, corn and switchgrass systems, had low porosities, low organic carbon contents, and large volumes of poorly aerated soil. In these systems, greater volumes of poorly aerated soil were associated with greater bacterial denitrification, which in turn was associated with greater N2O emissions (R-2=0.52, p<0.05). However, the two systems with high plant diversity, that is, poplars and early-successional vegetation, over the 9years of implementation had developed higher porosities and organic carbon contents. In these systems, volumes of poorly aerated soil were positively associated with N2O emissions without a concomitant increase in bacterial denitrification. Our results suggest that changes in soil pore architecture generated by long-term implementation of contrasting bioenergy systems may affect the pathways of N2O production, thus, change associations between N2O emissions and other soil properties. Plant diversity appears as one of the factors determining which microscale soil characteristics will influence the amounts of N2O emitted into the atmosphere and, thus, which can be used as effective empirical predictors.
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| 49. |
- Larsbo, Mats, et al.
(författare)
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Preferential Transport in Macropores is Reduced by Soil Organic Carbon
- 2016
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that some management practices and farming systems that promote C sequestration may exacerbate the risk of groundwater pollution due to fast preferential transport in soil macropores. However, soil organic C (SOC) may also impact the soil pore structure at scales smaller than the macropore scale, where complexes of SOC and clay form micro-aggregates that may increase pore volumes in the micrometer size range. These effects of SOC per se on pore network architecture, water flow, and solute transport have hardly been investigated. Therefore, to investigate this question, we measured tracer transport through soil cores sampled along a transect on a field under grass-clover ley with a natural gradient in SOC content. The strength of preferential transport was characterized at two flow rates (2 and 5 mm h-1) and related to the volume, size distribution, heterogeneity, and connectivity of pore networks quantified by X-ray tomography. The results showed that soils with a larger SOC content had larger volumes of pores in the smallest imaged size range (200-600 mm) that were also more uniformly distributed. These effects of SOC on the imaged pore networks were only apparent up to a threshold value of the ratio between clay and SOC of 10: 1, which is assumed to correspond with the amount of SOC needed for C saturation of the clay fraction. The increased flow capacity of these smaller macropores in soil columns with larger SOC contents prevented flow from being activated in larger pores, which significantly reduced the strength of preferential transport.
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| 50. |
- Larsbo, Mats, et al.
(författare)
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Quantifying earthworm soil ingestion from changes in vertical bulk density profiles
- 2024
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Ingår i: European journal of soil biology. - : Elsevier. - 1164-5563 .- 1778-3615. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- Soil mixing by earthworms can have a large impact on the fate of nutrients and pollutants and on the soil's ability to sequester carbon. Nevertheless, methods to quantify earthworm ingestion and egestion under field conditions are largely lacking. Soils of the Fennoscandian tundra offer a special possibility for such quantifications, as these soils commonly lack burrowing macrofauna and exhibit a well-defined O horizon with low bulk density on top of a mineral soil with higher density. Since ingestion-egestion mixes the two soil layers, the temporal changes in the bulk density profile of such soils may be useful for estimating field ingestion rates. In this study, we applied a model for earthworm burrowing through soil ingestion to observed changes in soil densities occurring in a mesocosm experiment carried out in the arctic during four summers with intact soil. The earthworms present in the mesocosms were Aporrectodea trapezoides, Aporrectodea tuberculata, Aporrectodea rosea, Lumbricus rubellus and Lumbricus Terrestris (fourth season only). We show that changes in soil density profiles can indeed be used to infer earthworm ingestion rates that are realistic in comparison to literature values. Although uncertainties in parameter values were sometimes large, the results from this study suggest that soil turnover rates and endogeic earthworm soil ingestion rates in tundra heath and meadow soils may be as high as those reported for temperate conditions. Such large ingestion rates can explain observed large morphological changes in arctic soils where dispersing earthworms have resulted in complete inmixing of the organic layer into the mineral soil. Our approach is applicable to soil profiles with marked vertical differences in bulk density such as the soils of the Fennoscandian tundra where earthworms are currently dispersing into new areas and to layered repacked soil samples that are incubated in the field.
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