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1.	Arrazola Vasquez, Elsa, et al. (författare) Earthworm burrowing modes and rates depend on earthworm species and soil mechanical resistance 2022 Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 178 Tidskriftsartikel (refereegranskat)abstract Earthworms drive multiple soil processes, but their specific impact on soil functions differs between earthworm species and ecological categories. A key challenge in modern agriculture is soil compaction due to heavy ma-chinery, but we have limited quantitative knowledge about how the burrowing activity of different earthworm species is affected by compaction. Here, we address this question in a laboratory experiment with 2-D terraria, where we used Aporrectodea caliginosa (Savigny, 1826) and Aporrectodea longa (Ude, 1885) as representatives of two different ecological categories. We exposed both species to four different soil mechanical resistance levels and monitored their burrowing activity for three days. We quantified burrowing rates and cast production, assessed the burrowing mode, and estimated energy requirements as a function of soil mechanical resistance. The results showed that the burrowing rates of both earthworm species significantly decreased with increasing soil mechanical resistance, but that the impact was species-dependent and lower for A. longa. Earthworms changed their burrowing mode towards ingestion when soil mechanical resistance increased, and this shift was more prominent for A. caliginosa that primarily burrowed via cavity expansion (i.e. by pushing soil aside) at low soil mechanical resistance. We further show that energy requirement and cast produced per unit burrow length increased with soil mechanical resistance. Our study revealed significant and species-dependent adverse effects of soil mechanical resistance on earthworm burrowing, which in turn has consequences for many soil processes mediated by earthworms, such as water infiltration, soil aeration, nutrient cycling and soil organic matter turnover.
2.	Arrazola Vasquez, Elsa Maria, et al. (författare) Estimating energy costs of earthworm burrowing using calorimetry 2024 Ingår i: European Journal of Soil Biology. - 1164-5563 .- 1778-3615. ; 121 Tidskriftsartikel (refereegranskat)abstract Earthworm burrowing is essential for soil functioning in temperate climates. It is known that soil compaction hampers earthworm burrowing, but there is a lack of knowledge on how it affects the energy costs of earthworms. In the present study, we used respirometry and isothermal calorimetry to quantify earthworm respiration rates and heat dissipation in two endogeic species, Aporrectodea caliginosa and Aporrectodea tuberculata , in compacted and non -compacted soils. We put the measured respiration rates and heat dissipation in relation to the burrow volume and cast volume produced by the earthworms. We found that at higher compaction levels, respiration rates and dissipated heat increased for both studied species. The energy costs associated with burrowing were a significant fraction of the total energy costs. Our results indicate that energy costs per burrow volume increase due to compaction, and that the specific energy costs for burrowing (i.e., per gram earthworm) were lower for A. tuberculata than for A. caliginosa . Further studies are needed to confirm our results. We discuss the potential and current limitations of isothermal calorimetry as a method for direct quantification of energy costs of earthworms. There is a need for further studies that quantify how energy costs of burrowing are affected by various soil conditions, to better predict the implications of land use and soil management on soil processes and functions mediated by earthworm burrowing.
3.	Blombäck, Karin, et al. (författare) Applicability of Models to Predict Phosphorus Losses in Drained Fields: A Review 2015 Ingår i: Journal of Environmental Quality. - : Wiley. - 0047-2425 .- 1537-2537. ; 44, s. 614-628 Tidskriftsartikel (refereegranskat)abstract Most phosphorus (P) modeling studies of water quality have focused on surface runoff loses. However, a growing number of experimental studies have shown that P losses can occur in drainage water from artificially drained fields. In this review, we assess the applicability of nine models to predict this type of P loss. A model of P movement in artificially drained systems will likely need to account for the partitioning of water and P into runoff, macropore flow, and matrix flow. Within the soil profile, sorption and desorption of dissolved P and filtering of particulate P will be important. Eight models are reviewed (ADAPT, APEX, DRAINMOD, HSPF, HYDRUS, ICECREAMDB, PLEASE, and SWAT) along with P Indexes. Few of the models are designed to address P loss in drainage waters. Although the SWAT model has been used extensively for modeling P loss in runoff and includes tile drain flow, P losses are not simulated in tile drain flow. ADAPT, HSPF, and most P Indexes do not simulate flow to tiles or drains. DRAINMOD simulates drains but does not simulate P. The ICECREAMDB model from Sweden is an exception in that it is designed specifically for P losses in drainage water. This model seems to be a promising, parsimonious approach in simulating critical processes, but it needs to be tested. Field experiments using a nested, paired research design are needed to improve P models for artificially drained fields. Regardless of the model used, it is imperative that uncertainty in model predictions be assessed.
4.	Bölscher, Tobias, et al. (författare) Changes in pore networks and readily dispersible soil following structure liming of clay soils 2021 Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 390 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.
5.	Bösch, Yvonne, et al. (författare) Minimizing tillage modifies fungal denitrifier communities, increases denitrification rates and enhances the genetic potential for fungal, relative to bacterial, denitrification 2022 Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 170 Tidskriftsartikel (refereegranskat)abstract Nitrous oxide (N2O) emissions from arable soils are predominantly caused by denitrifying microbes, of which fungal denitrifiers are of particular interest, as fungi, in contrast to bacteria, terminate denitrification with N2O. Reduced tillage has been shown to increase gaseous nitrogen losses from soil, but knowledge of how varying tillage regimes and associated soil physical and chemical alterations affect fungal denitrifiers is limited. Based on results from a long-term (>40 years) tillage experiment, we show that non-inversion tillage resulted in increased potential denitrification activity in the upper soil layers, compared to annual or occasional (every 4-5 years) conventional inversion tillage. Using sequence-corrected abundance of the fungal nirK gene, we further identified an increased genetic potential for fungal denitrification, compared to that caused by bacteria, with decreasing tillage intensity. Differences in the composition and diversity of the fungal nirK community imply that different tillage regimes select for distinct fungal denitrifiers with differing functional capabilities and lifestyles, predominantly by altering carbon and nitrogen related niches. Our findings suggest that the creation of organic hotspots through stratification by non-inversion tillage increases the diversity and abundance of fungal denitrifier communities and modifies their composition, and thus their overall relevance for N2O production by denitrification, in arable soils.
6.	Casali, Emilien, et al. (författare) Macropore flow in relation to the geometry and topology of soil macropore networks: Re-visiting the kinematic wave equation 2024 Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 630 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.
7.	Colombi, Tino, et al. (författare) A time-lapse imaging platform for quantification of soil crack development due to simulated root water uptake 2021 Ingår i: Soil and Tillage Research. - : Elsevier BV. - 0167-1987 .- 1879-3444. ; 205 Tidskriftsartikel (refereegranskat)abstract Plants are major drivers of soil structure dynamics. Root growth creates new macropores and provides essential carbon to soil, while root water uptake may induce crack formation around roots. Cracks can facilitate root growth as they provide pathways of least resistance and improve water infiltration and soil aeration. Due to the lack of suitable quantification methods, knowledge on the effects of root water uptake on soil crack formation remains limited. In the current study, we developed a time-lapse imaging platform that allows i) simulating root water uptake through localized soil drying and ii) quantifying the development of two-dimensional crack networks. Customized soil boxes that were 50 mm wide, 55 mm high and 5 mm deep were designed. Artificial roots made of dialysis tubes were inserted into the soil boxes and polyethylene glycol solution was circulated through the tubes. This induced a gradient in osmotic potential at the contact area (150 mm(2)) between the soil and the dialysis tubes, resulting in controlled soil drying. Drying intensity was varied by using different polyethylene glycol concentrations. Experiments were conducted with three soils that were subjected to three drying intensities for 6.5 days. We developed a time-lapse imaging system to record soil crack formation at two-minute intervals in twelve samples simultaneously. Resulting crack networks were quantified with an automated image analysis pipeline. Across soils and drying intensities, crack network development slowed down after 24-48 h of soil drying. The extent and complexity of crack networks increased with drying intensity and crack networks were larger and more complex in the clay and clay loam soil than in the silt loam soil. Smaller and less complex crack networks were better connected than larger and more complex networks. These results demonstrate that the platform developed in this study is suitable to quantify crack network development in soil due to simulated root water uptake at high temporal resolution and high throughput. Thereby, it can provide information needed to improve our understanding on how plants modify soil structure.
8.	Cornelis, Geert, et al. (författare) Solubility and transport of Cr(III) in a historically contaminated soil – Evidence of a rapidly reacting dimeric Cr(III) organic matter complex 2017 Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 189, s. 709-716 Tidskriftsartikel (refereegranskat)abstract Chromium is a common soil contaminant and, although it has been studied widely, questions about its speciation and dissolutions kinetics remain unanswered. We combined information from an irrigation experiment performed with intact soil columns with data from batch experiments to evaluate solubility and mobilization mechanisms of Cr(III) in a historically contaminated soil (>65 years). Particulate and colloidal Cr(III) forms dominated transport in this soil, but their concentrations were independent of irrigation intensity (2-20 mm h(-1)). Extended X-ray absorption fine structure (EXAFS) measurements indicated that Cr(III) associated with colloids and particles, and with the solid phase, mainly existed as dimeric hydrolyzed Cr(III) bound to natural organic matter. Dissolution kinetics of this species were fast (<= 1 day) at low pH (<3) and slightly slower (<= 5 days) at neutral pH. Furthermore, it proved possible to describe the solubility of the dimeric Cr(III) organic matter complex with a geochemical equilibrium model using only generic binding parameters, opening the way for use of geochemical models in risk assessments of Cr(III)-contaminated sites. (C) 2017 The Authors. Published by Elsevier Ltd.
9.	Etana, Ararso, et al. (författare) Effect of subsoil compaction on hydraulic parameters 2010 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
10.	Etana, Ararso, et al. (författare) Persistent subsoil compaction and its effects on preferential flow patterns in a loamy till soil 2013 Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 192, s. 430-436 Tidskriftsartikel (refereegranskat)abstract Persistence of subsoil compaction was investigated in a field experiment in southern Sweden. The investigation compared two treatments (control and compaction by four passes track-by-track), 14 years after the experimental traffic. The compaction experiment was carried out in 1995 with a 6-row sugar beet harvester with a wheel load of c. 10.4 Mg. Investigations included penetration resistance, bulk density, water retention, saturated hydraulic conductivity, in situ near-saturated hydraulic conductivity, and dye tracing experiments. The measurements of penetration resistance and bulk density clearly showed the persistence of subsoil compaction. In addition, both macroporosity and saturated and near-saturated hydraulic conductivity were smaller in the compacted plots, although these differences were not statistically significant. Dye tracing allowed us to visualize flow patterns in the soil and to quantitatively distinguish compacted and non-compacted subsoil profiles. Despite significant soil textural heterogeneity across the experimental field, the dye tracing data showed that persistent compaction may enhance preferential flow. (C) 2012 Elsevier B.V. All rights reserved.
11.	Etana, Ararso, et al. (författare) Visualization of subsoil compaction 2010 Ingår i: DJF Report. ; , s. 87-90 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
12.	Fukumasu, Jumpei, et al. (författare) Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter? 2024 Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 449 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.
13.	Fukumasu, Jumpei, et al. (författare) Oxalate-extractable aluminum alongside carbon inputs may be a major determinant for organic carbon content in agricultural topsoils in humid continental climate 2021 Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 402 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.
14.	Fukumasu, Jumpei, et al. (författare) Relations between soil organic carbon content and the pore size distribution for an arable topsoil with large variations in soil properties 2022 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.
15.	Ghafoor, Abdul, et al. (författare) Soil properties and susceptibility to preferential solute transport in tilled topsoil at the catchment scale 2013 Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 492, s. 190-199 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.
16.	Hellner, Qarin, et al. (författare) Effects of tillage and liming on macropore networks derived from X-ray tomography images of a silty clay soil 2018 Ingår i: Soil Use and Management. - : Wiley. - 0266-0032 .- 1475-2743. ; 34, s. 197-205 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.
17.	Hosseinpour Ashenaabad, Reza, et al. (författare) Dual-platform micromechanical characterization of soils: Oscillation shear rheometry and spherical indentation 2022 Ingår i: Soil and Tillage Research. - : Elsevier BV. - 0167-1987 .- 1879-3444. ; 223 Tidskriftsartikel (refereegranskat)abstract The dynamics of soil structure is caused by biotic and abiotic processes, with the onset and magnitude of deformation controlled by soil rheological and mechanical properties. Quantification of such properties is challenging because soil behaviour changes with soil moisture, but common rheological tests are not applicable over all consistency ranges. Here, we combine oscillation shear rheometry with spherical indentation mechanical measurements of soil to obtain greater characterization over a broader range of water contents. The elastic modulus could be measured with either approach, with good agreement found for measured silt and clay textured remoulded agricultural soils. For shear rheometry, plastic viscosity, complex modulus and shear yield stress were also obtained. The spherical indentation provided measurements of hardness and yield stress. Although yield stress was correlated between approaches, the values were orders of magnitude greater for the indenter (0.54 +/- 0.33 kPa vs. 34.4 +/- 31.2 kPa), presumably because of different loading and failure conditions. At drier water contents, yield stress varied more between the two tests on the clay soil, which corresponded with brittle fracture creating artefacts in shear rheometry measurements. Spherical indentation has not been widely applied to the testing of soils, but the good agreement over a wide water content range between elastic modulus obtained from spherical indentation measurements (0.66 +/- 0.27 MPa in wetter zone to 4.45 +/- 2.53 MPa in drier zone) and shear rheometry (0.47 +/- 0.11 MPa in wetter zone to 2.02 +/- 0.98 MPa in drier zone) is promising. Moreover, spherical indentation can be applied to materials varying from brittle to viscous and allows testing on structurally intact soil aggregates. The geometry of a spherical indenter may more closely mimic contacting soil aggregates, so scope exists to extend the approach to explore the slumping of aggregated seedbeds produced by tillage.
18.	Jarvis, Nicholas, et al. (författare) Connectivity and percolation of structural pore networks in a cultivated silt loam soil quantified by X-ray tomography 2017 Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 287, s. 71-79 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/).
19.	Jarvis, Nicholas, et al. (författare) Improved descriptions of soil hydrology in crop models: The elephant in the room? 2022 Ingår i: Agricultural Systems. - : Elsevier BV. - 0308-521X .- 1873-2267. ; 202 Tidskriftsartikel (refereegranskat)abstract Soil-crop simulation models are widely used to assess the impacts of soil management and climate change on soil water balance, solute transport and crop production. In this context, it is important that hydrological processes in the soil-crop system are accurately modelled. We suggest here that empirical treatments of soil water flow, water uptake by plant mots and transpiration limit the applicability of crop models and increase prediction errors. We further argue that this empiricism is to a large extent unnecessary, as parsimonious physics-based descriptions of these water flow processes in the soil-crop system are now available. Recent reviews and opinion articles, whilst strongly advocating the need for improvements to crop models, fail to mention the significant role played by accurate treatments of soil hydrology. It seems to us that empirical models of soil water flow have become the elephant in the room.
20.	Jarvis, Nicholas, et al. (författare) Interactions between soil structure dynamics, hydrological processes, and organic matter cycling: A new soil-crop model 2024 Ingår i: European Journal of Soil Science. - 1351-0754 .- 1365-2389. ; 75 Tidskriftsartikel (refereegranskat)abstract The structure of soil is critical for the ecosystem services it provides since it regulates many key soil processes, including water, air and solute movement, root growth and the activity of soil biota. Soil structure is dynamic, driven by external factors such as land management and climate and mediated by a wide range of biological agents and physical processes operating at strongly contrasting time-scales, from seconds (e.g., tillage) to many decades (e.g., faunal activity and soil aggregation). In this respect, positive feedbacks in the soil-plant system may lead in the longer term to soil physical degradation or to the recovery of structurally poor soils. As far as we are aware, no existing soil-crop model can account for such processes. In this paper, we describe a new soil-crop model (USSF, Uppsala model of Soil Structure and Function) that accounts for the effects of soil structure dynamics on water and organic matter cycling at the soil profile scale. Soil structure dynamics are expressed as time-varying physical (bulk density, porosity) and hydraulic properties (water retention, hydraulic conductivity) responding to the activity of biological agents (i.e., earthworms, plant roots) and physical processes (i.e., tillage, soil swell-shrink) at seasonal to decadal time-scales. In this first application of the model, we present the results of 30-year scenario simulations that illustrate the potential role and importance of soil structure dynamics for the soil water balance, carbon storage in soil, root growth, and winter wheat yields on two soils (loam and clay) in the climate of central Sweden. A sensitivity analysis was also performed for these two scenarios using the Morris method of elementary effects, which revealed that the most sensitive parameters controlling soil structure dynamics in the USSF model are those determining aggregation induced by organic matter turnover and swell/shrink. We suggest that the USSF model is a promising new tool to investigate a wide range of processes and phenomena triggered by land use and climate change. Results from this study show that feedback in the soil-crop system mediated by the dynamics of soil physical and hydraulic properties are potentially of central importance for long-term predictions of soil water balance, crop production, and carbon sequestration under global change.
21.	Jarvis, Nicholas, et al. (författare) Long-term effects of grass-clover leys on the structure of a silt loam soil in a cold climate 2017 Ingår i: Agriculture, Ecosystems and Environment. - : Elsevier BV. - 0167-8809 .- 1873-2305. ; 247, s. 319-328 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.
22.	Jarvis, Nicholas, et al. (författare) MACRO (v5.2): Model Use, Calibration, and Validation 2012 Ingår i: Transactions of the Asabe. - : American Society of Agricultural and Biological Engineers (ASABE). - 2151-0032 .- 2151-0040. ; 55, s. 1413-1423 Tidskriftsartikel (refereegranskat)abstract MACRO is a one-dimensional dual-permeability model of variably saturated water flow and reactive solute transport in soil that has been used since the early 1990s as a research tool to investigate the effects of macropore flow on soil hydrology and contaminant transport under transient field conditions. It is also widely used in the form of bespoke versions in pesticide exposure and risk assessments for groundwater and surface waters, e.g., in registration procedures in the European Union (EU). Macropore flow is a highly episodic, fast, non-equilibrium process that can dominate the leaching of reactive solutes in structured soils. This has important consequences for model calibration and validation procedures. Firstly, it means that in addition to water contents and resident solute concentrations, water flows and flux concentrations measured at high time resolution are required. Secondly, it implies that more weight must be placed on flux data obtained during these important but short-lived episodic flow events if parameters controlling macropore flow are to be reliably estimated. Although the choice of approach will vary with the purpose, automatic or hybrid automatic/manual calibration procedures are generally recommended for MACRO, especially global methods that account for uncertainty within a multi-objective framework. Despite the complexity of the processes it attempts to represent, MICRO is a parsimonious model, requiring only five additional parameters to simulate water flow and reactive solute transport, compared to the use of the Richards equation and the advection-dispers ion equation. Nevertheless, for practical reasons, the size of the parameter space that can be explored by calibration is often quite limited. This emphasizes the importance of measuring those parameters that can be measured and the role of sensitivity analyses in supporting the choice of parameters to calibrate. This will vary between applications, but at least for structured soils, all five parameters regulating the generation and strength of non-equilibrium flow and transport are usually rather influential.
23.	Jarvis, Nicholas, et al. (författare) Modelling the effects of bioturbation on the re-distribution of 137Cs in an undisturbed grassland soil 2010 Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 61, s. 24-34 Tidskriftsartikel (refereegranskat)abstract Summary Under favourable conditions, soil ingestion by earthworm populations can be equivalent to approximately 5–10% of the topsoil mass per year. This suggests that for contaminants that are strongly bound to soil, earthworm ‘bioturbation’ may be a more important transport mechanism than water-borne advection dispersion. It is therefore quite surprising that few modelling studies to date have explicitly considered the effects of biological processes on contaminant transport in soil. In this study, we present a general model that incorporates the effects of both ‘local’ and ‘non-local’ biological mixing into the framework of the standard physical (advective-dispersive) transport model. The model is tested against measurements of the redistribution of caesium-137 (137Cs) derived from the Chernobyl accident, in a grassland soil during 21 years after fallout. Three model parameters related to biological transport were calibrated within ranges defined by measured data and literature information on earthworm biomasses and feeding rates. Other parameters such as decay half-life and sorption constant were set to known or measured values. A physical advective-dispersive transport model based on measured sorption strongly underestimated the downward displacement of 137Cs. A dye-tracing experiment suggested the occurrence of physical non-equilibrium transport in soil macropores, but this was inadequate to explain the extent of the deep penetration of 137Cs observed at the site. A simple bio-diffusion model representing ‘local’ mixing worked reasonably well, but failed to reproduce the deep penetration of Cs as well as a dilution observed close to the soil surface. A comprehensive model including physical advectivedispersive transport, and both ‘local’ and ‘non-local’ mixing caused by the activities of both endogeic and anecic earthworms, gave an excellent match to the measured depth profiles of 137Cs, with predictions mostly lying within confidence intervals for the means of measured data and model efficiencies exceeding 0.9 on all sampling occasions but the first
24.	Jarvis, Nicholas, et al. (författare) Reply to ‘Comment on “Understanding preferential flow in the vadose zone: Recent advances and future prospects” by N. Jarvis et al.’ 2017 Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 16 Tidskriftsartikel (refereegranskat)
25.	Jarvis, Nicholas, et al. (författare) Soil and crop management practices and the water regulation functions of soils: a qualitative synthesis of meta-analyses relevant to European agriculture 2023 Ingår i: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 9, s. 1-20 Forskningsöversikt (refereegranskat)abstract Adopting soil and crop management practices that conserve or enhance soil structure is critical for supporting the sustainable adaptation of agriculture to climate change, as it should help maintain agricultural production in the face of increasing drought or water excess without impairing environmental quality. In this paper, we evaluate the evidence for this assertion by synthesizing the results of 34 published meta-analyses of the effects of such practices on soil physical and hydraulic properties relevant for climate change adaptation in European agriculture. We also review an additional 127 meta-analyses that investigated synergies and trade-offs or help to explain the effects of soil and crop management in terms of the underlying processes and mechanisms. Finally, we identify how responses to alternative soil–crop management systems vary under contrasting agro-environmental conditions across Europe. This information may help practitioners and policymakers to draw context-specific conclusions concerning the efficacy of management practices as climate adaptation tools.Our synthesis demonstrates that organic soil amendments and the adoption of practices that maintain “continuous living cover” result in significant benefits for the water regulation function of soils, mostly arising from the additional carbon inputs to soil and the stimulation of biological processes. These effects are clearly related to improved soil aggregation and enhanced bio-porosity, both of which reduce surface runoff and increase infiltration. One potentially negative consequence of these systems is a reduction in soil water storage and groundwater recharge, which may be problematic in dry climates. Some important synergies are reductions in nitrate leaching to groundwater and greenhouse gas emissions for nonleguminous cover crop systems. The benefits of reducing tillage intensity appear much less clear-cut. Increases in soil bulk density due to traffic compaction are commonly reported. However, biological activity is enhanced under reduced tillage intensity, which should improve soil structure and infiltration capacity and reduce surface runoff and the losses of agro-chemicals to surface water. However, the evidence for these beneficial effects is inconclusive, while significant trade-offs include yield penalties and increases in greenhouse gas emissions and the risks of leaching of pesticides and nitrate.Our synthesis also highlights important knowledge gaps on the effects of management practices on root growth and transpiration. Thus, conclusions related to the impacts of management on the crop water supply and other water regulation functions are necessarily based on inferences derived from proxy variables. Based on these knowledge gaps, we outlined several key avenues for future research on this topic.
26.	Jarvis, Nicholas, et al. (författare) Soil compaction and preferential solute transport 2012 Ingår i: NJF Report. - 1653-2015. ; 8, s. 47- Konferensbidrag (övrigt vetenskapligt/konstnärligt)
27.	Jarvis, Nicholas, et al. (författare) Understanding Preferential Flow in the Vadose Zone: Recent Advances and Future Prospects 2016 Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 15 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.
28.	Keller, Thomas, et al. (författare) Risk assessment and effects of soil compaction: research chains at work 2012 Ingår i: NJF Report. - 1653-2015. ; 8, s. 13-16 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
29.	Keller, Thomas, et al. (författare) Subsoil pore characteristics and functions are negatively affected 14 years after compaction in a Swedish sandy clay loam 2011 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
30.	Klaminder, Jonatan, 1976-, et al. (författare) 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.
31.	Klöffel, Tobias, et al. (författare) Freeze-thaw effects on pore space and hydraulic properties of compacted soil and potential consequences with climate change 2024 Ingår i: Soil and Tillage Research. - 0167-1987 .- 1879-3444. ; 239 Tidskriftsartikel (refereegranskat)abstract Freezing and thawing affect the pore -space structure in agricultural soils with implications for soil hydraulic properties and water flow. Previous studies have focused on the upper few centimeters of the tilled topsoil, where most freeze -thaw (FT) cycles occur, even though deeper soil layers are also subject to freezing and thawing in cold climates. Thus, little is known about how freezing and thawing affect untilled soil layers, which often show high bulk densities that restrict vertical water movement. Furthermore, it remains unclear how shifts in FT patterns with climate change may change the pore -space structure and water flow through these soil layers. Here we investigated the effects of freezing and thawing on X-ray imaged pore -space characteristics, water retention and near -saturated hydraulic conductivity (K) in untilled soil directly below plough depth. Intact cores were sampled at two sites in central Sweden under the same long-term reduced tillage management. The two soils, a silt loam and a silty clay loam, were subjected to three FT scenarios in a laboratory environment intended to represent FT patterns that are considered likely under current and future winter conditions for this region. The latter scenario was characterised by more FT cycles and a lower freezing temperature. Freezing and thawing increased K in the near -saturated range in both soils, which we attribute to observed small (<0.01 mm(3 )mm( -3)) increases in the volume of pores of diameters close to the X-ray resolution limit. Concomitant increases in pore network connectivity and critical pore diameter, especially in the denser silty clay loam soil, probably contributed to this increase in K. The water retention data suggested that changes in pore -space characteristics below X-ray resolution also occurred in both soils. Furthermore, our results indicate that both soils may show higher drainage rates due to shifts in FT patterns in the future, although longer -term changes in pore -space structure with an increasing number of FT cycles would mostly be limited to soils with relatively high clay contents. These soils are often more compacted below plough depth and, thus, benefits from improvements in soil structure such as improved root growth and plant water supply are also expected to be larger.
32.	Koestel, Johannes, et al. (författare) Approaches to delineate aggregates in intact soil using X-ray imaging 2021 Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 402 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.
33.	Koestel, Johannes, et al. (författare) Imaging and quantification of preferential solute transport in soil macropores 2014 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.
34.	Koestel, Johannes, et al. (författare) Potential of combined neutron and X-ray imaging to quantify local carbon contents in soil 2022 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.
35.	Koestel, Johannes, et al. (författare) Scale and REV analyses for porosity and pore connectivity measures in undisturbed soil 2020 Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 366 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.
36.	Larsbo, Mats, et al. (författare) A Dual-Permeability Approach for Modeling Soil Water Flow and Heat Transport during Freezing and Thawing 2019 Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 18 Tidskriftsartikel (refereegranskat)abstract Preferential flow may become significant in partially frozen soils because infiltration can occur through large, initially air-filled pores surrounded by a soil matrix with limited infiltration capacity. The objectives of this study were to develop and evaluate a dual-permeability approach for simulating water flow and heat transport in macroporous soils undergoing freezing and thawing. This was achieved by introducing physically based equations for soil freezing and thawing into the dual-permeability model MACRO. Richards' equation and the heat flow equation were loosely coupled using the generalized Clapeyron equation for the soil micropore domain. Freezing and thawing of macropore water is governed by a first-order equation for energy transfer between the micropore and macropore domains. We assumed that macropore water was unaffected by capillary forces, so that water in macropores freezes at 0 degrees C. The performance of the model was evaluated for four test cases: (i) redistribution of water in the micropore domain during freezing, (ii) a comparison between the first-order energy transfer approach and the heat conduction equation, (iii) infiltration and water flow in frozen soil with an initially air-filled macropore domain, and (iv) thawing from the soil surface during constant-rate rainfall. Results show that the model behaves in accordance with the current understanding of water flow and heat transport in frozen macroporous soil. To improve modeling of water and heat flow in frozen soils, attention should now be focused on providing experimental data suitable for evaluating models that account for macropore flow.
37.	Larsbo, Mats (författare) An Episodic Transit Time Model for Quantification of Preferential Solute Transport 2011 Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 10, s. 378-385 Tidskriftsartikel (refereegranskat)abstract Variations in the concentrations of naturally occurring isotopes in rainfall provide a "continuous" signal that has the potential to generate more information on how weather conditions control solute transport than traditional field tracer experiments. An isotopically distinct rainfall event can be rapidly transferred through the system when preferential flow occurs. The objective of this study was to develop and test an approach for analyzing how rainfall and soil moisture control preferential transport to tile drains. An episodic solute transit time distributions model that accounts for these effects was developed. The model was tested on artificial data (daily values of tile drain discharge and (18)O concentrations in the drainage water) generated by the MACRO model for soils with different potentials for preferential flow. The results showed that the transit time model gave an excellent fit to the artificial data for the soil with a high potential for preferential flow. The dynamics of the preferential flow events were well captured also for the soil with medium potential for preferential flow but the magnitude was sometimes poorly simulated. Once the model parameter values have been determined, the model can be used to calculate the amount and distribution with time of preferential flow to tile drains for all daily rainfall data. Model calculations integrate the soil's potential for preferential flow and the effects of weather conditions and are, therefore, highly relevant as site-specific indicators for the risk of preferential leaching of agrochemicals. The approach needs to be evaluated against real field data, however, before its usefulness can be established.
38.	Larsbo, Mats, et al. (författare) Effects of surfactant use and peat amendment on leaching of fungicides and nitrate from golf greens 2009 Ingår i: Biologia. - : Springer Science and Business Media LLC. - 0006-3088 .- 1336-9563. ; 64, s. 419-423 Tidskriftsartikel (refereegranskat)abstract Soil water repellency in golf putting greens may induce preferential "finger flow", leading to enhanced leaching of surface applied agrochemicals such as fungicides and nitrate. We examined the effects of root zone composition and the use of the non-ionic surfactant Revolution on soil water repellency, soil water content distributions, infiltration rates, turf quality, and fungicide and nitrate leaching from April 2007 to April 2008. The study was made on 4-year-old experimental green seeded with creeping bentgrass (Agrostis stolonifera L.) 'Penn A-4' at Landvik in southeast Norway. Eight lysimeters with two different root zone materials: (i) straight sand (1% gravel, 96% sand, 3% silt and clay, and 4 g kg(-1) organic matter) (SS) and (ii) straight sand mixed with Sphagnum peat to an organic matter content of 25 g kg(-1) (SP) were used in this study. Surfactant treatment reduced the spatial variability of water contents, increased infiltration rates and reduced water drop penetration times (WDPTs) by on average 99% in and just below the thatch layer. These effects were most evident for SS lysimeters. Surfactant treatment resulted on average in an 80% reduction of total fungicide leaching, presumably due to reduced preferential finger flow facilitated by decreased soil water repellency. Peat amendment reduced fungicide leaching by 90%, probably due to increased sorption of the fungicides to organic matter. Nitrate leaching was also smaller from surfactant-treated straight-sand root zones, but this effect was not significant.
39.	Larsbo, Mats, et al. (författare) Herbicide sorption, degradation, and leaching in three Swedish soils under long-term conventional and reduced tillage 2009 Ingår i: Soil and Tillage Research. - : Elsevier BV. - 0167-1987 .- 1879-3444. ; 105, s. 200-208 Tidskriftsartikel (refereegranskat)abstract Soil tillage has the potential to influence water flow and solute transport through the soil by cutting continuous macropores which connect the soil surface to the subsoil. Tillage also affects soil organic carbon sequestration which may lead to different sorption and degradation properties depending on the long-term tillage practices. The objective of this study was to quantify the differences in sorption, degradation and leaching of the herbicides bentazone and isoproturon between conventional tillage (CT) and reduced tillage (RT) under Swedish conditions. Three sites, Ultuna (silty clay), Saby (loam), and Lonnstorp (sandy loam moraine till), where replicate plots had been under either CT or RT for at least 9 years, were included in the study. A higher organic carbon content had developed in the top 5 cm of RT plots compared to the 10-20 cm depth and CT plots since the establishment of the experimental treatments. Adsorption and degradation were studied in laboratory experiments and solute transport was studied in undisturbed column experiments using non-reactive tracers and herbicides. The results from the column experiments were not significantly different between tillage treatments for Saby and Lonnstorp. For Ultuna, RT resulted in a more pronounced preferential tracer transport pattern and isoproturon leaching was twelve times larger compared to CT columns. This indicates that the tillage treatment had affected the macropore connectivity only at Ultuna. Freundlich adsorption coefficients for both bentazone and isoproturon were larger (though not always significantly) in the top 5 cm of RT soil compared to the 10-20 cm depth and to CT, reflecting the higher organic carbon content. The degradation rate was also generally larger (though not always significantly) in the top 5 cm of RT soil. These results show that RT has the potential to reduce pesticide leaching. However, any such reduction may be counter-balanced by enhanced preferential flow for soils where RT results in improved macropore connectivity. (C) 2009 Elsevier B.V. All rights reserved.
40.	Larsbo, Mats, et al. (författare) Leaching of Five Pesticides of Contrasting Mobility through Frozen and Unfrozen Soil 2019 Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 18 Tidskriftsartikel (refereegranskat)abstract Field and laboratory studies show increased leaching of pesticides through macropores in frozen soil. Fast macropore flow has been shown to reduce the influence of pesticide properties on leaching, but data on these processes are scarce. The objective of this study was to investigate the effect of soil freezing and thawing on transport of pesticides with a range of soil sorption coefficients (K-f ). To do this we conducted a soil column study to quantify the transport of bromide and five pesticides (2-methyl-4-chlorophenoxyacetic acid, clomazone, boscalid, propiconazole, and diflufenican). Intact topsoil and subsoil columns from two agricultural soils (silt and loam) in southeastern Norway were used in this experiment, and pesticides were applied to the soil surface in all columns. Half the columns were then frozen (-3 degrees C), and the other half were left unfrozen (4 degrees C). Columns were subjected to repeated irrigation events where 25 mm of rainwater was applied during 5 h at each event. Irrigations were followed by 14-d periods of freezing or refrigeration. Percolate was collected and analyzed for pesticides and bromide. Pesticide leaching was up to five orders of magnitude larger from frozen than unfrozen columns. Early breakthrough (<<1 pore volume) of high concentrations was observed for pesticides in frozen columns, indicating that leaching was dominated by preferential flow. The rank order in pesticide leaching observed in this study corresponded to the rank order of mean K-f values for the pesticides, and the results suggest that sorption plays a role in determining leaching losses even in frozen soil.
41.	Larsbo, Mats, et al. (författare) Pesticide leaching from two Swedish topsoils of contrasting texture amended with biochar 2013 Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 147, s. 73-81 Tidskriftsartikel (refereegranskat)
42.	Larsbo, Mats (författare) Pesticide regulatory risk assessment, monitoring, and fate studies in the northern zone: recommendations from a Nordic-Baltic workshop 2016 Ingår i: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 23, s. 15779-15788 Tidskriftsartikel (refereegranskat)
43.	Larsbo, Mats, et al. (författare) Preferential Transport in Macropores is Reduced by Soil Organic Carbon 2016 Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 15 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.
44.	Larsbo, Mats, et al. (författare) Quantifying earthworm soil ingestion from changes in vertical bulk density profiles 2024 Ingår i: European journal of soil biology. - : Elsevier. - 1164-5563 .- 1778-3615. ; 120 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.
45.	Larsbo, Mats (författare) Quantifying the impact of a succession of freezing-thawing cycles on the pore network of a silty clay loam and a loamy sand topsoil using X-ray tomography 2017 Ingår i: CATENA. - : Elsevier BV. - 0341-8162. ; 156, s. 365-374 Tidskriftsartikel (refereegranskat)abstract In the Nordic countries, changes in pore structure during winter can affect e.g. water transport capacity in soils after winter. A reduction in pore space can cause an increase in runoff volume due to snowmelt and rain, resulting in flooding and soil erosion. This study quantified the effect of freezing-thawing cycles (FTCs) on the macropore structure of a silt and a sandy soil. Six consecutive FTCs were applied to intact soil samples, which were scanned after 0, 1, 2, 4 and 6 FTCs with an industrial X-ray scanner. Using state-of-the-art image processing and analysis techniques, changes in soil macropore network characteristics were quantified. The results showed that freezing-thawing affected the looser sandy soil more than the silt with its more cohesive structure. However, in both soils freezing-thawing had a negative effect on properties of macropore networks (e.g. reduction in macroporosity, thickness and specific surface area of macropores). These findings can help improve understanding of how undisturbed soils react to different winter conditions, which can be beneficial in the development of models for predicting flooding and soil erosion.
46.	Larsbo, Mats, et al. (författare) Relations between macropore network characteristics and the degree of preferential solute transport 2014 Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 18, s. 5255-5269 Tidskriftsartikel (refereegranskat)abstract The characteristics of the soil macropore network determine the potential for fast transport of agrochemicals and contaminants through the soil. The objective of this study was to examine the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport. Experiments were carried out under near-saturated conditions on undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-D X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h-1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disc infiltrometer placed on top of the columns. Results showed that many of the macropore network characteristics were inter-correlated. For example, large macroporosities were associated with larger specific macropore surface areas and better local connectivity of the macropore network. Generally, an increased flow rate resulted in earlier solute breakthrough and a shifting of the arrival of peak concentration towards smaller drained volumes. Columns with smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities exhibited a greater degree of preferential transport. This can be explained by the fact that, with only two exceptions, global (i.e. sample scale) continuity of the macropore network was still preserved at low macroporosities. Thus, for any given flow rate, pores of larger diameter were actively conducting solute in soils of smaller near-saturated hydraulic conductivity. This was associated with larger local transport velocities and, hence, less time for equilibration between the macropores and the surrounding matrix which made the transport more preferential. Conversely, the large specific macropore surface area and well-connected macropore networks associated with columns with large macroporosities limit the degree of preferential transport because they increase the diffusive flux between macropores and the soil matrix and they increase the near-saturated hydraulic conductivity. The normalised 5% arrival times were most strongly correlated with the estimated hydraulic state variables (e.g. with the degree of saturation in the macropores R2 = 0.589), since these combine into one measure the effects of irrigation rate and the near-saturated hydraulic conductivity function, which in turn implicitly depends on the volume, size distribution, global continuity, local connectivity and tortuosity of the macropore network.
47.	Larsbo, Mats (författare) Simulation of Pharmaceutical and Personal Care Product Transport to Tile Drains after Biosolids Application 2009 Ingår i: Journal of Environmental Quality. - : Wiley. - 0047-2425 .- 1537-2537. ; 38, s. 1274-1285 Tidskriftsartikel (refereegranskat)abstract pharmaceuticals and personal care products (PPCPs) carried in biosolids may reach surface waters or ground water when these materials are applied as fertilizer to agricultural land. During preferential flow conditions created by land application of liquid Municipal biosolids (LMB), the residence time Of Solutes in the macropores may be too short for sorption equilibration. The physically based dual-permeability model MACRO is used in environmental risk assessments for pesticides and may have potential as an environmental risk assessment tool for PPCPs. The objective of this study was to evaluate MACRO and an updated version of MACRO that included non-equilibrium sorption in macropores using data from experiments conducted in eastern Ontario, Canada on the transport of three PPCPs (atenolol, carbamazepine, and triclosan), the nicotine metabolite cotinine, and the strongly sorbing dye rhodamine WT applied in LMB. Results showed that the MACRO model could not reproduce the measured rhodamine WT concentrations (Nash-Sutcliffe coefficient [NS] for the best simulation = -0.057) in drain discharge. The updated version resulted in better fits to measured data for PPCP (average NS = 0.97) and rhodamine WT (NS = 0.84) concentrations. However, it was not possible to simulate all compounds using the same set of hydraulic parameters, which indicates that the model does not fully account for all relevant processes. The results presented herein show that non-equilibrium sorption in macropores has a large impact on simulated solute transport for reactive compounds contained in LMB. This process should be considered in solute transport models that are used for environmental risk assessments for such compounds.
48.	Larsbo, Mats, et al. (författare) Surface Runoff of Pesticides from a Clay Loam Field in Sweden 2016 Ingår i: Journal of Environmental Quality. - : Wiley. - 0047-2425 .- 1537-2537. ; 45, s. 1367-1374 Tidskriftsartikel (refereegranskat)abstract Pesticides stored at or close to the soil surface after field application can be mobilized and transported off the field when surface runoff occurs. The objective of our study was to quantify the potential pesticide losses in surface runoff from a conventionally managed agricultural field in a Swedish climate. This was achieved by measuring surface runoff volumes and concentrations in runoff of six spring-applied pesticides and autumn-applied glyphosate and its metabolite aminomethylphosphonic acid (AMPA). Measurements were performed for 3 yr both during the growing seasons and during intervening winter snowmelt periods on a clay loam field close to Uppsala. During growing seasons, surface runoff was generated on only five occasions during one 25-d period in 2012 when the infiltration capacity of the soil may have been reduced by structural degradation due to large cumulative rainfall amounts after harrowing. Concentrations in surface runoff exceeded Swedish water quality standards in all samples during this growing season for diflufenican and pirimicarb. Surface runoff was generated during three snowmelt periods during the winter of 2012-2013. All of the applied pesticides were found in snowmelt samples despite incorporation of residues by autumn plowing, degradation, and leaching into the soil profile during the period between spraying and sampling. Concentrations of glyphosate ranged from 0.12 to 7.4 mg L-1, and concentrations of AMPA ranged from 0 to 2.7 mg L-1. Our results indicate that temporal changes in hydraulic properties during the growing season and when the soil freezes during winter affect pesticide losses through surface runoff.
49.	Larsbo, Mats, et al. (författare) The effect of freezing and thawing on water flow and MCPA leaching in partially frozen soil 2018 Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 219, s. 72-85 Tidskriftsartikel (refereegranskat)abstract Limited knowledge and experimental data exist on pesticide leaching through partially frozen soil. The objective of this study was to better understand the complex processes of freezing and thawing and the effects these processes have on water flow and pesticide transport through soil. To achieve this we conducted a soil column irrigation experiment to quantify the transport of a non-reactive tracer and the herbicide MCPA in partially frozen soil. In total 40 intact topsoil and subsoil columns from two agricultural fields with contrasting soil types (silt and loam) in South-East Norway were used in this experiment. MCPA and bromide were applied on top of all columns. Half the columns were then frozen at -3 degrees C while the other half of the columns were stored at +4 degrees C. Columns were then subjected to repeated irrigation events at a rate of 5 mm artificial rainwater for 5 h at each event. Each irrigation was followed by 14-day periods of freezing or refrigeration. Percolate was collected and analysed for MCPA and bromide. The results show that nearly 100% more MCPA leached from frozen than unfrozen topsoil columns of Hov silt and Kroer loam soils. Leaching patterns of bromide and MCPA were very similar in frozen columns with high concentrations and clear peaks early in the irrigation process, and with lower concentrations leaching at later stages. Hardly any MCPA leached from unfrozen topsoil columns (0.4-0.5% of applied amount) and concentrations were very low. Bromide showed a different flow pattern indicating a more uniform advective-dispersive transport process in the unfrozen columns with higher concentrations leaching but without clear concentration peaks. This study documents that pesticides can be preferentially transported through soil macropores at relatively high concentrations in partially frozen soil. These findings indicate, that monitoring programs should include sampling during snow melt or early spring in areas were soil frost is common as this period could imply exposure peaks in groundwater or surface water.
50.	Löv, Åsa, et al. (författare) Evaluating the ability of standardised leaching tests to predict metal(loid) leaching from intact soil columns using size-based elemental fractionation 2019 Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 222, s. 453-460 Tidskriftsartikel (refereegranskat)abstract Laboratory-based leaching tests are frequently used for in situ risk assessments of contaminant leaching to groundwater and surface waters. This study evaluated the ability of three standardised leaching tests to assess leaching of lead (Pb), zinc (Zn), arsenic (As) and antimony (Sb) from four intact soil profiles, by considering particulate (0.45-8 mu m; percolation test), colloidal (10 kDa-0.45 mu m) and truly dissolved (<10 kDa) fractions of these elements. Deionised water was used as the percolation test leachant, while either deionised water or 1 mM CaCl2 was used in batch tests. Data from an irrigation experiment were used as reference. The results indicated that in percolation tests, leachate should be collected at a liquid:solid ratio (L/S) range of 2-10, instead of 0-0.5 or 0.5-2. Even at L/S = 2-10, the percolation test overestimated total Pb concentration, mainly because of greater mobilisation of particle-bound Pb, but appeared suitable for categorising soils into high/low risk with respect to mobilisation of particulate and colloidal contaminants. The batch test performed better with CaCl2 than with deionised water when standard membrane filtration (0.45 gm) was used, as the high Ca2+ concentration reduced colloidal mobilisation, avoiding overestimation of concentrations of elements such as Pb. However, the higher Ca2+ concentration and lower pH could result in overestimated concentrations of weakly sorbed elements, e.g. Zn. (C) 2019 The Authors. Published by Elsevier Ltd.

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