High arsenic, chromium and nickel in soils can pose a hazard to the ecosystem and/or human health. Large areas can be affected by elevated potentially toxic elements (PTE) background contents, ...entailing a significant effort for managing the potential risk. Assessing the environmental hazard associated to PTE-contaminated soils requires the determination of soil PTE environmental bioavailability, which reflects the capacity of these elements to be transferred to living organisms. Here we assess the environmental bioavailability of As, Cr and Ni in topsoils from the Liège basin and Belgian Lorraine, two areas in Wallonia, Belgium, affected by elevated As, Cr and Ni background contents. The source of soil As, Cr and Ni differs in Liège and Lorraine: anthropogenic in the former location and geogenic in the latter. The environ- mental bioavailability of PTE was determined using two complementary approaches: (1) by chemical fractionation with the Community Bureau of Reference (BCR) three- step sequential extraction protocol and (2) by estimating the phytoavailability using a plant-based biotest (Lolium multiflorum as plant model). The results show that total As (6-130 mg·kg
), Cr (15-268 mg·kg
), and Ni (8-140 mg·kg
) contents in the Liège and Lorraine soils frequently exceed the soil clean-up standards. However, no positive correlation was found between the total contents and BCR extraction results or rye- grass contents, except for As in Liège soils. Total As, Cr or Ni contents surpassing soil standards do not necessarily result in elevated mobile, potentially mobilizable and phytoavailable contents. In general, environmental bioavailability of As, Cr and Ni is higher in soils from Liège basin compared to those sampled in Belgian Lorraine. The mobile and potentially mobilizable fractions of As, Cr and Ni account for <30 % of their total contents following the BCR extractions. Our study provides valuable information for sustainable management at the regional scale of soils containing high PTE contents.
•Sentinel-2 composites for large scale mapping of soil organic carbon in croplands.•Identification of pure soil pixels and quantification of uncertainty.•Normalized Burn Ratio < 0.05 removes crop ...residues and soil moisture.•Soil property mapping improves when more than 6 scenes per pixel are used in composite.•Uncertainty of soil organic carbon mapping reaches 5.5 g C kg–1.
Soil organic carbon (SOC) prediction from remote sensing is often hindered by disturbing factors at the soil surface, such as photosynthetic active and non–photosynthetic active vegetation, variation in soil moisture or surface roughness. With the increasing amount of freely available satellite data, recent studies have focused on stabilizing the soil reflectance by building reflectance composites using time series of images. Although composite imagery has demonstrated its potential in SOC prediction, it is still not well established if the resulting composite spectra mirror the reflectance fingerprint of the optimal conditions to predict topsoil properties (i.e. a smooth, dry and bare soil).
We have collected 303 photos of soil surfaces in the Belgian loam belt where five main classes of surface conditions were distinguished: smooth seeded soils, soil crusts, partial cover by a growing crop, moist soils and crop residue cover. Reflectance spectra were then extracted from the Sentinel–2 images coinciding with the date of the photos. After the growing crop was removed by an NDVI < 0.25, the Normalized Burn Ratio (NBR2) was calculated to characterize the soil surface, and a threshold of NBR2 < 0.05 was found to be able to separate dry bare soils from soils in unfavorable conditions i.e. wet soils and soils covered by crop residues. Additionally, we found that normalizing the spectra (i.e. dividing the reflectance of each band by the mean reflectance of all spectral bands) allows for cancelling the albedo shift between soil crusts and smooth soils in seed–bed conditions. We then built the exposed soil composite from Sentinel–2 imagery for southern Belgium and part of Noord-Holland and Flevoland in the Netherlands (covering the spring periods of 2016–2021). We used the mean spectra per pixel to predict SOC content by means of a Partial Least Squares Regression Model (PLSR) with 10–fold cross–validation. The uncertainty of the models was assessed via the prediction interval ratio (PIR). The cross validation of the model gave satisfactory results (mean of 100 bootstraps: model efficiency coefficient (MEC) = 0.48 ± 0.07, RMSE = 3.5 ± 0.3 g C kg–1, RPD = 1.4 ±0.1 and RPIQ = 1.9 ± 0.3). The resulting SOC prediction maps show that the uncertainty of prediction decreases when the number of scenes per pixel increases, and reaches a minimum when at least six scenes per pixel are used (mean PIR of all pixels is 12.4 g C kg–1, while mean SOC predicted is 14.1 g C kg–1). The results of a validation against an independent data set showed a median difference of 0.5 g C kg–1 ± 2.8 g C kg–1 SOC between the measured (average SOC content 13.5 g C kg–1) and predicted SOC contents at field scale. Overall, this compositing method shows both realistic within field and regional SOC patterns.
Elucidating when Neanderthal populations disappeared from Eurasia is a key question in paleoanthropology, and Belgium is one of the key regions for studying the Middle to Upper Paleolithic ...transition. Previous radiocarbon dating placed the Spy Neanderthals among the latest surviving Neanderthals in Northwest Europe with reported dates as young as 23,880 ± 240 B.P. (OxA-8912). Questions were raised, however, regarding the reliability of these dates. Soil contamination and carbon-based conservation products are known to cause problems during the radiocarbon dating of bulk collagen samples. Employing a compound-specific approach that is today the most efficient in removing contamination and ancient genomic analysis, we demonstrate here that previous dates produced on Neanderthal specimens from Spy were inaccurately young by up to 10,000 y due to the presence of unremoved contamination. Our compound-specific radiocarbon dates on the Neanderthals from Spy and those from Engis and Fonds-de-Forêt demonstrate that they disappeared from Northwest Europe at 44,200 to 40,600 cal B.P. (at 95.4% probability), much earlier than previously suggested. Our data contribute significantly to refining models for Neanderthal disappearance in Europe and, more broadly, show that chronometric models regarding the appearance or disappearance of animal or hominin groups should be based only on radiocarbon dates obtained using robust pretreatment methods.
Agricultural watersheds tend to be places of intensive farming activities that permanently modify their microtopography. The surface characteristics of the soil vary depending on the crops that are ...cultivated in these areas. Agricultural soil microtopography plays an important role in the quantification of runoff and sediment transport because the presence of crops, crop residues, furrows and ridges may impact the direction of water flow. To better assess such phenomena, 3-D reconstructions of high-resolution agricultural watershed topography are essential. Fine-resolution topographic data collection technologies can be used to discern highly detailed elevation variability in these areas. Knowledge of the strengths and weaknesses of existing technologies used for data collection on agricultural watersheds may be helpful in choosing an appropriate technology. This study assesses the suitability of terrestrial laser scanning (TLS) and unmanned aerial system (UAS) photogrammetry for collecting the fine-resolution topographic data required to generate accurate, high-resolution digital elevation models (DEMs) in a small watershed area (12ha). Because of farming activity, 14 TLS scans (≈25pointsm−2) were collected without using high-definition surveying (HDS) targets, which are generally used to mesh adjacent scans. To evaluate the accuracy of the DEMs created from the TLS scan data, 1098 ground control points (GCPs) were surveyed using a real time kinematic global positioning system (RTK-GPS). Linear regressions were then applied to each DEM to remove vertical errors from the TLS point elevations, errors caused by the non-perpendicularity of the scanner's vertical axis to the local horizontal plane, and errors correlated with the distance to the scanner's position. The scans were then meshed to generate a DEMTLS with a 1×1m spatial resolution. The Agisoft PhotoScan and MicMac software packages were used to process the aerial photographs and generate a DEMPSC (Agisoft PhotoScan) and DEMMCM (MicMac), respectively, with spatial resolutions of 1×1m. Comparing the DEMs with the 1098 GCPs showed that the DEMTLS was the most accurate data product, with a root mean square error (RMSE) of 4.5cm, followed by the DEMMCM and the DEMPSC, which had RMSE values of 9.0 and 13.9cm, respectively. The DEMPSC had absolute errors along the border of the study area that ranged from 15.0 to 52.0cm, indicating the presence of systematic errors. Although the derived DEMMCM was accurate, an error analysis along a transect showed that the errors in the DEMMCM data tended to increase in areas of lower elevation. Compared with TLS, UAS is a promising tool for data collection because of its flexibility and low operational cost. However, improvements are needed in the photogrammetric processing of the aerial photographs to remove non-linear distortions.
•We assess the suitability of TLS and UAS-based data for agricultural DEM generation.•TLS data have to be statistically processed to remove systematic errors.•We compare DEMs generated from TLS and UAS photogrammetry.•DEMs from TLS and UAS have RMSE less than 10cm.
Soil aggregate stability (AS) reflects a soil's resistance to external erosive forces and is an indicator that varies with changing elementary soil properties across space and time. However, the ...quantification of AS via conventional wet-sieving is too resource-demanding a task to be carried out at large scales. We explored the possibility of using laboratory Visible-Near infrared (Vis-NIR) spectroscopy to predict aggregate mean weight diameter (MWD), and three aggregate size fractions (i.e. clay + silt, microaggregate (63–250 μm) and macroaggregate (>250 μm)) resulting from wet-sieving. Two spectra-based approaches, one (SPF approach) that built direct linkage between soil spectra and four AS indexes via partial least squares regression and the other (SPF + PTF approach) that established pedotransfer functions based on spectroscopically predicted elementary soil properties, were developed on a total of 83 topsoil samples collected in the Belgian Loam Belt. These two approaches were later compared to a third approach (PTF approach) that built pedotransfer functions using measured elementary soil properties. Results show that, with the PTF approach consistently giving the best performance, all three approaches produced good prediction models (R2: 0.62–0.85; RPD: 1.59–2.46) for MWD, microaggregate and macroaggregate fractions, while no correct model was developed for the clay + silt fraction using the two spectra-based approaches, due to the rather homogenous soil texture in the study area. Soil organic carbon was a major factor that controlled the variations in AS, and a critical threshold of 2% SOC content was found to be the level that separated the “stable” and “unstable” AS classes. This study demonstrated that Vis-NIR spectroscopy is a promising technique that enables large-scale assessment of AS and aggregate size fractions, especially considering that future space-borne hyperspectral imagers will provide high-resolution Vis-NIR spectral data at unprecedented scales.
•Vis-NIR spectroscopy was found to be an efficient method to estimate aggregate stability.•Two spectral-based methods both gave satisfactory prediction models for MWD.•Microaggregate and macroaggregate fractions could also be predicted well.•Correlation between MWD and soil chromophore led to successful model development.
The combination of revegetation and application of stabilizing soil amendments on heavy metal-contaminated soils is generally considered to be a promising alternative to expensive classical ...remediation techniques. Here, we simultaneously investigated the effects of six cost-effective amendments (CaCO3, iron grit, fly ash, manure, bentonite and bone meal) on Cd, Zn and Pb leaching and phytoavailability (assessed using white lupin, Lupinus albus L.). The Cd and Zn leaching was reduced by all amendments mainly due to alkalinity increase. The Pb leaching was strongly affected by the dissolved organic carbon (DOC) release. Therefore, bone meal and manure treatments, which highly increased DOC concentrations in leachates, increased the flow-weighted mean Pb concentrations by 2.3 and 16 times, respectively. Surprisingly, while iron grit induced strong Cd and Pb leaching reductions, this amendment doubled Cd and Pb concentrations in shoots of white lupin. Conversely, the addition of bone meal reduced Pb concentrations in shoots by 74%, probably because organo-Pb complexes (predicted using Visual MINTEQ) were largely dominant in solution. Overall, the addition of CaCO3 offered the best compromise as it successfully reduced both the leaching and the phytoavailability of the three considered metals. Our results demonstrate the efficacy of several amendments while stressing the need to measure simultaneously the leaching and the phytoavailability of metals induced by each amendment.
► We study the effects of amendments on Cd, Zn and Pb leaching and phytoavailability. ► pH controls Cd and Zn leaching while DOC controls Pb leaching. ► Iron grit highly lowers metal leaching but doubles Cd and Pb phytoavailability. ► Bone meal and manure lower metal phytoavailability but strongly increase Pb leaching. ► CaCO3 appears to be the most effective amendment.
This study reports mineralogical and physical property changes linked to geo-chemical alterations processes during three ultra-long-term tri-axial tests on outcrop-chalk from Liège (Belgium). The ...test core plugs were flooded with MgCl2-brines for approximately one and a half, two and three years, mimicking effective reservoir stresses (9.5–12.5 MPa) and temperature (130 °C) of important hydrocarbon deposits at the Norwegian Continental Shelf. The flooded cores were studied using electron microscopy, whole-rock and stable isotope geochemical analyses, and ion chromatography of the effluent water.
All tests show altered textures and mineralogy at the flow-inlet side of the approximately 7 cm long cores. With longer duration of flooding, these alterations moved further into the cores, and for the three-year-test, the entire core was altered. When studied at nano-scale, the newly formed crystals were found to be magnesite containing minor calcium impurities, together with clay-minerals. On the outlet side of the alteration-fronts in the two shorter tests, the mineralogy still mainly consists of calcite and primary clay-minerals, together with newly formed magnesite and secondary clay-minerals. Dolomite or low- and high-Mg-calcite are not observed. The textures of larger micro-fossils are often preserved, but the mineralogy of their shells is altered.
A sharp, only 4 mm narrow transition zone at the border of the alteration front towards the less altered area for the two shorter tests, shows the highest porosity in the cores. This pattern resembles what is observed in single-crystal experiments, where the alterations are driven by phase dissolution and subsequent precipitation, the progression of high porosity zones and the state of equilibrium at the boundary between the primary and new mineral phase. This is also in line with observations in nature and models for transport driven mineral replacement in porous media, where differences in dissolution and precipitation rates may cause high porosity transitions zones.
During the experiments, all cores underwent severe overall compaction between 10.1% and 18.2%. However, in the two- and three-year long test-cores, the permeability, and calculated porosity, started to increase after a primary phase of reduction. As magnesite precipitates at the expense of calcite, the density increase, but the solid volume decrease. As the bulk volume is constant, porosity and permeability are increased. The changes in ion-concentration of effluents, monitored throughout the experiments, balance the changes in mineralogy, compaction and permeability within the cores. Compositional variations of the injection fluid effectively control the amount of chemical reaction in chalk. This allows for control and predicting changes in geo-mechanical parameters induced by mineralogical replacement, which has significant impact on reservoir conditions.
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•Conservation agricultural practices promote aggregation and phytolith preservation.•Soil microaggregates contribute over 60% to the pool of phytoliths in bulk soil.•Soil aggregation ...protects phytoliths from rapid dissolution.•Phytoliths control bioavailable silicon.
Phytoliths are fine silt-sized amorphous silica particles that form in living plant tissues. Once deposited in soils through plant debris, they may dissolve and increase the fluxes of silicon (Si) towards the biosphere and hydrosphere, thus enhancing positive Si impacts on e.g., plant health and carbon fixation by marine diatoms. Here we analyzed the role of soil aggregates in phytolith protection against dissolution. We investigated the distribution of phytoliths in the size fractions of a sandy loam topsoil subjected to two long-term treatments: conventional (CT) and no tillage (NT). The topsoil size fractions were separated through wet sieving and named, respectively: macroaggregates (250–2000 µm), free microaggregates (50–250 µm), and silt + clay (<50 µm). Protected microaggregates held within macroaggregates were extracted using a constant and continuous water flow process. We assessed the pool of phytoliths through heavy liquid separation and alkaline dissolution (Na2CO3), and we assessed the bioavailability of Si using CaCl2 extraction. As expected, NT generates larger amounts of aggregates than CT. Concentrations and stocks of phytoliths determined by heavy liquid separation are ten times higher than those measured by Na2CO3 in bulk soil and size fractions. Soil microaggregates contribute for over 60% to the pool of phytoliths, which control bioavailable Si. The release of bioavailable Si from microaggregates is slower than that from the silt + clay fraction, suggesting that soil microaggregates can trap phytoliths and protect them from rapid dissolution. No-tillage and associated conservation agricultural practices may thus promote the stabilization of phytoliths in soils and decrease their dissolution rate. We propose that the entrapment of phytoliths in soil aggregates may be one of the processes favoring the persistence of phytoliths in soils and sediments. We expect that this persistence should be enhanced in strongly aggregated soils.
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