Predicting the spatial distribution of soil organic carbon stock in Swedish forests using a group of covariates and site-specific data

The status of the soil organic carbon (SOC) stock at any position in the landscape is subject to a complex interplay of soil state factors operating at different scales and regulating multiple processes resulting either in soils acting as a net sink or net source of carbon. Forest landscapes are characterized by high spatial variability, and key drivers of SOC stock might be specific for sub-areas compared to those influencing the whole landscape. Consequently, separately calibrating models for sub-areas (local models) that collectively cover a target area can result in different prediction accuracy and SOC stock drivers compared to a single model (global model) that covers the whole area. The goal of this study was therefore to (1) assess how global and local models differ in predicting the humus layer, mineral soil, and total SOC stock in Swedish forests and (2) identify the key factors for SOC stock prediction and their scale of influence. We used the Swedish National Forest Soil Inventory (NFSI) database and a digital soil mapping approach to evaluate the prediction performance using random forest models calibrated locally for the northern, central, and southern Sweden (local models) and for the whole of Sweden (global model). Models were built by considering (1) only site characteristics which are recorded on the plot during the NFSI, (2) the group of covariates (remote sensing, historical land use data, etc.) and (3) both site characteristics and group of covariates consisting mostly of remote sensing data. Local models were generally more effective for predicting SOC stock after testing on independent validation data. Using the group of covariates together with NFSI data indicated that such covariates have limited predictive strength but that site-specific covariates from the NFSI showed better explanatory strength for SOC stocks. The most important covariates that influence the humus layer, mineral soil (0–50 cm), and total SOC stock were related to the site-characteristic covariates and include the soil moisture class, vegetation type, soil type, and soil texture. This study showed that local calibration has the potential to improve prediction accuracy, which will vary depending on the type of available covariates.

Pore structure of the Cretaceous lacustrine shales and shale-oil potential assessment in the Songliao Basin, Northeast China

Aiming to study the pore structure and its impact on shale oil enrichment, a total of nine lacustrine shales (including one immature shale and eight mature shales) from the Qingshankou Formation in the Songliao Basin were subjected to low-pressure gas sorption (LPGS) of CO2 and N2 and mercury intrusion capillary pressure (MICP) measurements. The combination of the LPGS and MICP methods demonstrates that the pore volumes of these shales are mainly associated with mesopores, whereas the micropores and macropores are relatively undeveloped. The correlation between the shale compositions and pore volumes of LPGS suggests that the micropores and mesopores are mainly contributed by illite/smectite mixed layer mineral. On the contrary, we have found that the oil/bitumen and carbonates could occupy the micropores and mesopores, respectively, and reduce these pore volumes significantly. The oil saturation index (OSI) was found to display a positive correlation with the maturity Ro value in the range of 0.37%–1.24%, and this may suggest that the shale-oil content is controlled by hydrocarbon generation. However, the pore structure also exerts a great influence on the shale oil enrichment. We suggested that the porosity of MICP could be considered as an index for appraising the shale-oil potential of a given shale player because there is a good positive correlation between the porosity of MICP and the OSI value. Furthermore, a negative correlation between the micropore volume and the OSI value may imply that the shale oil could be adsorbed in micropores, whereas a good positive correlation between the OSI value and the Hg-retained ratio suggests that shale oil is a kind of residual hydrocarbon, which is closely related with the mesopore volume of these shales.

Predicting the spatial distribution of soil organic carbon stock in Swedish forests using remotely sensed and site-specific variables

The status of the SOC stock at any position in the landscape is subject to a complex interplay of soil-state factors operating at different scales and regulating multiple processes resulting either in soils acting as a net sink or net source of carbon. Forest landscapes are characterized by high spatial variability and key drivers of SOC stock might be specific for subareas compared to those influencing the whole landscape. Consequently, separately calibrating models for subareas (local models) that collectively cover a target area can result in different prediction accuracy and SOC stock drivers compared to a single model (global model) that covers the whole area. The goal of this study was therefore to (1) assess how global and local models differ in predicting the humus layer, mineral soil and total SOC stock in Swedish forests, (2) identify the key factors for SOC stock prediction and their scale of influence. We use the Swedish National Forest Soil Inventory (NFSI) database and a digital soil mapping approach to evaluate the prediction performance using Random Forest modelling calibrated locally for the northern, central and southern Sweden (local models) and for the whole Sweden (global model). Models were built by considering (1) only site characteristics which are recorded on the plot during NFSI, (2) remotely sensed variables and (3) both site characteristics and remotely sensed variables. Local models are generally more effective for predicting SOC stock after testing on independent validation data. Using remotely sensed variables together with NFSI data indicates that such covariates have limited predictive strength but that site specific variables from the NFSI covariates show better explanatory strength for SOC stocks. The most important covariates that influence the humus layer, mineral soil and total SOC stock were related to the site characteristic covariates and include the soil moisture class, vegetation type, soil type and soil texture. Future studies could focus in mapping these influential site covariates which have potential for future SOC stock prediction models.

Models transport Saharan dust too low in the atmosphere compared to observations

We investigate the dust forecasts from two operational global atmospheric models in comparison with in-situ and remote sensing measurements obtained during the AERosol properties – Dust (AER-D) field campaign. Airborne elastic backscatter lidar measurements were performed on-board the Facility for Airborne Atmospheric Measurements during August 2015 over the Eastern Atlantic, and they permitted to characterize the dust vertical distribution in detail, offering insights on transport from the Sahara. They were complemented with airborne in-situ measurements of dust size-distribution and optical properties, and datasets from the Cloud-Aerosol Transport System spaceborne lidar (CATS) and the Moderate Resolution Imaging Spectroradiometer (MODIS). We compare the airborne and spaceborne datasets to operational predictions obtained from the Met Office Unified Model (MetUM) and the Copernicus Atmosphere Monitoring Service (CAMS). The dust aerosol optical depth predictions from the models are generally in agreement with the observations, but display a low bias. However, the predicted vertical distribution places the dust lower in the atmosphere than highlighted in our observations. This is particularly noticeable for the MetUM, which does not transport coarse dust high enough in the atmosphere, nor far enough away from source. We also found that both model forecasts underpredict coarse mode dust, and at times overpredict fine mode dust. An analysis of the processes driving dust uplift in the models suggests that errors in the large scale wind and dust size distribution at source could be the cause of differences between model predictions and observations of the Saharan Air Layer. Mineral dust is an important component of the climate system, therefore it is important to assess how models reproduce its properties and transport mechanisms.

Evidence of an in vitro Coupled Diffusion Mechanism of Lesion Formation within Microcosm Dental Plaque

The purpose of this study was to determine whether or not the dual constant-depth film fermenter (dCDFF) is able to produce caries-like enamel lesions and to ascertain further information regarding the performance of this fully functional biological caries model. Conditions were defined by the continuation (CF) or cessation (FF) of a saliva-type growth medium supply during 50-mM sucrose exposures (8 times daily). Hydroxyapatite (n = 3) and bovine enamel (n = 3) substrata were included within each condition and samples extracted after 2, 4, 8, and 16 days. Community profiles were generated for fastidious anaerobes, Lactobacillus spp., Streptococcus spp., mutans streptococci (MS), and Veillonella spp. using selective culture techniques and enamel demineralisation assessed by transverse microradiography. Results demonstrated that the dCDFF model is able to produce caries-like enamel lesions with a high degree of sensitivity where reduced ionic strength within the FF condition increased surface layer mineral deposition. Between conditions, biofilm communities did not differ significantly, although MS in the biofilms extracted from the FF condition rose to a higher proportion (by 1.5 log10 units), and Veillonella spp. were initially greater within the CF condition (by 2.5 log10 units), indicating an enhanced ability for the clearance of low-pKa acids following exposures to sucrose. However, both conditions retained the ability for caries-like lesion formation.

Microstructural and geometric influences in the protective scales of Atractosteus spatula

Atractosteus spatula has been described as a living fossil (having existed for 100 Myr), retaining morphological characteristics of early ancestors such as the ability to breathe air and survive above water for hours. Its highly effective armour consists of ganoid scales. We analyse the protective function of the scales and identify key features which lead to their resistance to failure. Microstructural features include: a twisted cross-plied mineral arrangement that inhibits crack propagation in the external ganoine layer, mineral crystals that deflect cracks in the bony region in order to activate the strength of mineralized collagen fibrils, and saw-tooth ridges along the interface between the two scale layers which direct cracks away from the intrinsically weak interface. The macroscale geometry is additionally evaluated and it is shown that the scales retain full coverage in spite of minimal overlap between adjacent scales while conforming to physiologically required strain and maintaining flexibility via a process in which adjacent rows of scales slide and concurrently reorient.

Occurrence of tosudite in the Guezouman, Tarat and Tchirezrine 2 formations, hosts of uranium deposits in Niger (Tim Mersoï basin)

Tosudite, a regularly interstratified chlorite-smectite, crystallizes as an alteration mineral of several preexisting Al-bearing silicates (feldspars, kaolin minerals, chlorites) present in arkosic sandstones hosted in uranium deposits in Niger. X-ray diffraction patterns show a sharp superstructure at 29–29.6 Å for an air-dried state and a peak at 30.8–31.6 Å following ethylene glycol solvation. The 060 reflection at 1.507–1.509 Å indicates an overall dioctahedral character, and the very low coefficient of variation of the d00l reflections for the solvated mineral (0.03–0.13) permits validation of the regular interstratification justifying its identification as tosudite. Microprobe analysis allowed specification of the component layers of this mixed-layer mineral. The chlorite is a di-trioctahedral type analogous to sudoite (Si3Al4Mg2(OH)8), and the smectite component is a low-charge montmorillonite type Tosudite is characterized by large Al2O3 and MgO contents and small Fe content; its composition corresponds approximately to the formula where octahedral occupancy is ∼7. Scanning electron microscope (SEM) observations show that tosudite is closely associated with some uranium minerals: tosudite crystallization occurred during a late alteration event which post-dates burial diagenesis and during which uranium was remobilized by Mg-rich oxidizing fluids.

Chlorite and chloritization processes through mixed-layer mineral series in low-temperature geological systems – a review

This present study provides an overview of the clay-mineral reactions involved in the chloritization process in a mixed-layer mineral series, and focuses on the properties of the resulting lowtemperature chlorites (formed at <220°C) in diagenetic and hydrothermal systems. According to the literature, most chlorite species occurring in low-temperature geological systems are derived fromspecific clay precursors except for direct precipitates from solution in veins. In addition, three main types of clay-mineral series have been associated with these chloritization processes: saponite-to-chlorite, berthierineto- chlorite and kaolinite-to-sudoite reactions. The conversion of saponite to chlorite results in the most common sequence of trioctahedral clay minerals related to the occurrence of Mg-Fe trioctahedral chlorite in a wide variety of hydrothermal and diagenetic to very low-grade metamorphism environments. Two models were proposed in the literature to describe the saponite-to-chlorite conversion through corrensite. The first model is a continuous transition model based on solid-state transformation (SST) mechanisms and is valid in rock-dominated systems (closed micro-systems with very low fluid-rock ratios). The second model is a stepwise transition model based on dissolution-crystallization mechanisms (DC) and is efficient in fluid-dominated systems (open systems with high fluid-rock ratio). The berthierine to Fechlorite transition results in a sequence of trioctahedral phases which are related to chloritization processes in iron-rich and reducing environments. This transformation is a cell-preserved phase transition dominated by a SST mechanismthat operates simultaneously in different domains of the parental mineral and may be considered as a polymorphic mineral reaction. Finally, the conversion of kaolinite to sudoite (Al-Mg ditrioctahedral chlorite) has not been documented like the other two aforementioned conversion series. Despite the scarcity of detailed investigations, the conversion of kaolinite to sudoite through tosudite is considered a stepwise mineral reaction that is dominated by a DC mechanism. From a compilation of literature data, it appears that several parameters of hydrothermal and diagenetic chlorites differ, including the minimal temperature, the textural and structural characteristics and the extents of compositional fields. In hydrothermal systems, discrete chlorite occurs at a minimal temperature near 200°C, regardless of its chemical composition. In diagenetic systems, discrete chlorite occurs at minimal temperatures that vary according to its crystal chemistry (100–120°C for Mg-chlorite as opposed to 40–120°C for Fe chlorite). The strong discrepancy between the lowest temperature at which Mg- and Fe-chlorite form in buried sediments and in geothermal systems should result from drastically different heating rates, heat-flow conditions and tectonism between basins at passivemargins and geothermal systems at active margins. The morphology, structure and compositional fields of the diagenetic Fe-rich chlorite may have been inherited from those of the berthierine precursor. All of the chlorite species formed through theDC mechanism have good geothermometry potential. However, the SST mechanism in which berthierine is transformed into chlorite could have unexplored consequences regarding the use of the chemistry (including stable isotope composition) of diagenetic Fe-chlorite for reconstructing the burial history of sediments. Further investigations regarding the formationmechanisms of mixed-layerminerals are required to provide us with insight to understand the chloritization process in low-temperature geological systems.

Environmental pollution impact on radiation properties of atmosphere, snow and ice cover: Study from Barentsburg (Spitsbergen Archipelago)

The value of the albedo of snow and ice surface is associated with the texture and structure of the surface layer of snow or ice (sea ice, glaciers), the peculiarities of the vertical redistribution of contaminations in this layer (mineral or organic particles of various concentrations, the size and shape), temperature regime of the surface layer of the atmosphere. Identifying links with the albedo characteristics of natural and artificial contamination is very important. For example, the results of mathematic modeling the evolution of ice sheets, sea ice and snow cover demonstrate the high sensitivity of the model to this parameter. Original results in the framework of this problem were obtained by researches from AARI and St. Petersburg State University during the 2010-2012 years on Svalbard in the vicinity of the Russian mining settlement Barentsburg. We present original results showing the relationship of "albedo-contaminations" and the influence of anthropogenic factors. The estimation of solar radiation that penetrates deep into the snow, and the impact of contamination on its redistribution in the snow thickness were obtained.