Carbon Redistribution Research Articles

The importance of a surface organic layer in simulating permafrost thermal and carbon dynamics

Abstract. Permafrost-affected soils contain twice as much carbon as currently exists in the atmosphere. Studies show that warming of the perennially frozen ground could initiate significant release of the frozen soil carbon into the atmosphere. Initializing the frozen permafrost carbon with the observed soil carbon distribution from the Northern Circumpolar Soil Carbon Database reduces the uncertainty associated with the modeling of the permafrost carbon feedback. To improve permafrost thermal and carbon dynamics we implemented a dynamic surface organic layer with vertical carbon redistribution, and introduced dynamic root growth controlled by active layer thickness, which improved soil carbon exchange between frozen and thawed pools. These changes increased the initial amount of simulated frozen carbon from 313 to 560 Gt C, consistent with observed frozen carbon stocks, and increased the spatial correlation of the simulated and observed distribution of frozen carbon from 0.12 to 0.63.

Effect of annealing on mechanical properties of nickel electrodeposited using supercritical CO2 emulsion evaluated by micro-compression test

Nanocrystalline nickel film was electrodeposited with supercritical CO2 emulsion. The effects of annealing on nanocrystalline nickel were evaluated with scanning electron microscopy. The deposited films had a grain size of 16nm with 2at.% of interstitial carbon. A slight grain growth to 30nm grain size was observed after low temperature (<200°С) annealing. Higher temperature (>300°С) annealing caused Ni3C precipitation at grain boundaries and prominent grain growth above 300nm grain size. Micro-compression samples of each annealed films and as-deposited film were fabricated to investigate the mechanical properties. Low temperature annealed nickel was fractured by cracking with higher yield strength compared to the as-deposited nickel while high temperature annealed nickel simply had a decrease in strength. The brittle fracture after annealing is suggested to be related to the redistribution of carbon and relaxation of grain boundaries. High yield strength of 1GPa after 400°С annealing is achieved thanks to the fine precipitates of Ni3C.

Understanding the role of soil erosion on co2-c loss using 13c isotopic signatures in abandoned Mediterranean agricultural land

Understanding soil water erosion processes is essential to evaluate the redistribution of soil organic carbon (SOC) within a landscape and is fundamental to assess the role of soil erosion in the global carbon (C) budget. The main aim of this study was to estimate the C redistribution and losses using 13C natural abundance. Carbon losses in soil sediment, dissolved organic carbon (DOC) and CO2 emission were determined. Four bounded parallel plots were installed on a 10% slope. In the upper part of the plots, C3soil was replaced with C4soil. The SOC and δ13C were measured after 145.2mm rainfall in the upper (2m far from C4strip), middle (4m far from C4strip) lower (6m far from C4strip) trams of the plot and in the sediments collected in the Gerlach collector at the lower part of the plot. A laboratory incubation experiment was performed to evaluate the CO2 emission rate of soils in each area. OC was mainly lost in the sediments as 2.08g−2 of C was lost after 145.2mm rainfall. DOC losses were only 5.61% of off-site OC loss. Three months after the beginning of the experiment, 15.90% of SOC in the upper tram of the plot had a C4 origin. The C4-SOC content decreased along the 6m length of the plot, and in the sediments collected by the Gerlach collector. CO2 emission rate was high in the upper plot tram due to the high SOC content. The discrimination of CO2 in C3 and C4 portion permitted to increase our level of understanding on the stability of SOC and its resilience to decomposition. The transport of sediments along the plot increased SOC mineralization by 43%. Our study underlined the impact of rainfall in C losses in soil and water in abandoned Mediterranean agriculture fields and the consequent implications on the C balance.

Tomato response traits to pathogenic Pseudomonas species: Does nitrogen limitation matter?

Induced chemical defence is a cost-efficient protective strategy, whereby plants induce the biosynthesis of defence-related compounds only in the case of pest attack. Plant responses that are pathogen specific lower the cost of defence, compared to constitutive defence. As nitrogen availability (N) in the root zone is one of the levers mediating the concentration of defence-related compounds in plants, we investigated its influence on response traits of tomato to two pathogenic bacteria, growing plants hydroponically at low or high N supply. Using two sets of plants for each level of N supply, we inoculated one leaf of one set of plants with Pseudomonas syringae, and inoculated the stem of other set of plants with Pseudomonas corrugata. Tomato response traits (growth, metabolites) were investigated one and twelve days after inoculation. In infected areas, P. syringae decreased carbohydrate concentrations whereas they were increased by P. corrugata. P. syringae mediated a redistribution of carbon within the phenylpropanoid pathway, regardless of N supply: phenolamides, especially caffeoylputrescine, were stimulated, impairing defence-related compounds such as chlorogenic acid. Inoculation of P. syringae produced strong and sustainable systemic responses. By contrast, inoculation of P. corrugata induced local and transient responses. The effects of pathogens on plant growth and leaf gas exchanges appeared to be independant of N supply. This work shows that the same genus of plant pathogens with different infection strategies can mediate contrasted plant responses.

Potential Vegetation and Carbon Redistribution in Northern North America from Climate Change

There are strong relationships between climate and ecosystems. With the prospect of anthropogenic forcing accelerating climate change, there is a need to understand how terrestrial vegetation responds to this change as it influences the carbon balance. Previous studies have primarily addressed this question using empirically based models relating the observed pattern of vegetation and climate, together with scenarios of potential future climate change, to predict how vegetation may redistribute. Unlike previous studies, here we use an advanced mechanistic, individually based, ecosystem model to predict the terrestrial vegetation response from future climate change. The use of such a model opens up opportunities to test with remote sensing data, and the possibility of simulating the transient response to climate change over large domains. The model was first run with a current climatology at half-degree resolution and compared to remote sensing data on dominant plant functional types for northern North America for validation. Future climate data were then used as inputs to predict the equilibrium response of vegetation in terms of dominant plant functional type and carbon redistribution. At the domain scale, total forest cover changed by ~2% and total carbon storage increased by ~8% in response to climate change. These domain level changes were the result of much larger gross changes within the domain. Evergreen forest cover decreased 48% and deciduous forest cover increased 77%. The dominant plant functional type changed on 58% of the sites, while total carbon in deciduous vegetation increased 107% and evergreen vegetation decreased 31%. The percent of terrestrial carbon from deciduous and evergreen plant functional types changed from 27%/73% under current climate conditions, to 54%/46% under future climate conditions. These large predicted changes in vegetation and carbon in response to future climate change are comparable to previous empirically based estimates, and motivate the need for future development with this mechanistic model to estimate the transient response to future climate changes.

Влияние структурных и фазовых изменений при термической обработке трубных сталей на скорость общей коррозии

Corrosion is one of key factors limiting the service life of oil and gas pipelines. To increase corrosion resistance steels are alloyed with elements permitting to obtain an oxide film protecting the metal from dissolution. But one may expect that corrosion rate of conventional carbon and low-alloy steels can be partially controlled through changing the structure by means of heat treatment. This research is devoted to studying the role of this factor for pipeline steels 20A and 20FA taken as examples. The steels were subjected to 18 different heat treatment regimes including normalizing at various temperatures, full quench hardening followed with high-temperature tempering, and quenching from intercritical temperature range followed with high-temperature tempering. Mechanical properties of heat treated steels were evaluated, as well as uniform (general) corrosion rate in a model medium containing hydrogen sulphide, with the aim to reveal possible effect of structural changes on steels’ resistance to corrosion. The worst corrosion resistance was provided by regimes including intercritical quench hardening, apparently because redistribution of carbon and alloying elements between a and g phases during holding in the Ac 1 ... Ac 3 range intensifies corrosion. But in general corrosion resistance of steels oscillated irregularly, with no appreciable correlation with grain size, type of structure, tempering temperature and level of impact toughness. It is therefore clearly demonstrated that resistance of pipeline steels to corrosion in hydrogen sulphide media is mainly determined not by heat treatment regimes and structural characteristics, but by the chemistry of metal dissolution process (e.g., formation of protective films) and, possibly, by non-metallic inclusions.

Exploring bainite formation kinetics distinguishing grain-boundary and autocatalytic nucleation in high and low-Si steels

Bainite formation in steels begins with nucleation of bainitic ferrite at austenite grain boundaries (γ/γ interfaces). This leads to creation of bainitic ferrite/austenite interfaces (α/γ interfaces). Bainite formation continues through autocatalysis with nucleation of bainitic ferrite at these newly created α/γ interfaces. The displacive theory of bainite formation suggests that the formation of bainitic ferrite is accompanied by carbon enrichment of surrounding austenite. This carbon enrichment generally leads to carbide precipitation unless such a reaction is thermodynamically or kinetically unfavourable. Each bainitic ferrite nucleation event is governed by an activation energy. Depending upon the interface at which nucleation occurs, a specific activation energy would be related to a specific nucleation mechanism. On the basis of this concept, a model has been developed to understand the kinetics of bainite formation during isothermal treatments. This model is derived under the assumptions of displacive mechanism of bainite formation. The fitting parameters used in this model are physical entities related to nucleation and microstructural dimensions. The model is designed in such a way that the carbon redistribution during bainite formation is accounted for, leading to prediction of transformation kinetics both with and without of carbide precipitation during bainite formation. Furthermore, the model is validated using two different sets of kinetic data published in the literature.

Quenched and Partitioned CMnSi Steels Containing 0.3 wt.% and 0.4 wt.% Carbon

The effect of partitioning parameters on mechanical properties and carbon partitioning in quenching and partitioning (Q&P)-treated C-1.5Mn-1.5Si steels was studied using 0.3 wt.% and 0.4 wt.% carbon compositions. Fully austenitized specimens were quenched to a fixed quenching temperature followed by partitioning at 400°C and 450°C for varying times. In most cases, increasing the partitioning temperature decreased UTS and increased TE, and both UTS and TE decreased with increasing partitioning times. Similar ultimate tensile strength levels were obtained for the 0.3C alloy partitioned at 400°C and the 0.4C alloy partitioned at 450°C. Increasing alloy carbon content increased retained austenite fractions. Mossbauer effect spectroscopy results were used to investigate carbon redistribution after Q&P processing in the 0.4C alloy.

3.46 Ga Apex chert ‘microfossils’ reinterpreted as mineral artefacts produced during phyllosilicate exfoliation

Filamentous microstructures from the 3.46billionyear (Ga)-old Apex chert of Western Australia have been interpreted as remnants of Earth's oldest cellular life, but their purported biological nature has been robustly questioned on numerous occasions. Despite recent claims to the contrary, the controversy surrounding these famous microstructures remains unresolved.Here we interrogate new material from the original ‘microfossil site’ using high spatial resolution electron microscopy to decode the detailed morphology and chemistry of the Apex filaments. Light microscopy shows that our newly discovered filaments are identical to the previously described ‘microfossil’ holotypes and paratypes. Scanning and transmission electron microscopy data show that the filaments comprise chains of potassium- and barium-rich phyllosilicates, interleaved with carbon, minor quartz and iron oxides. Morphological features previously cited as evidence for cell compartments and dividing cells are shown to be carbon-coated stacks of phyllosilicate crystals. Three-dimensional filament reconstructions reveal non-rounded cross sections and examples of branching incompatible with a filamentous prokaryotic origin for these structures.When examined at the nano-scale, the Apex filaments exhibit no biological morphology nor bear any resemblance to younger bona fide carbonaceous microfossils. Instead, available evidence indicates that the microstructures formed during fluid-flow events that facilitated the hydration, heating and exfoliation of potassium mica flakes, plus the redistribution and adsorption of barium, iron and carbon within an active hydrothermal system.

Elucidating the role of copper in CHO cell energy metabolism using (13)C metabolic flux analysis.

(13)C-metabolic flux analysis was used to understand copper deficiency-related restructuring of energy metabolism, which leads to excessive lactate production in recombinant protein-producing CHO cells. Stationary-phase labeling experiments with U-(13)C glucose were conducted on CHO cells grown under high and limiting copper in 3 L fed-batch bioreactors. The resultant labeling patterns of soluble metabolites were measured by GC-MS and used to estimate metabolic fluxes in the central carbon metabolism pathways using OpenFlux. Fluxes were evaluated 300 times from stoichiometrically feasible random guess values and their confidence intervals calculated by Monte Carlo simulations. Results from metabolic flux analysis exhibited significant carbon redistribution throughout the metabolic network in cells under Cu deficiency. Specifically, glycolytic fluxes increased (25%-79% relative to glucose uptake) whereas fluxes through the TCA and pentose phosphate pathway (PPP) were lower (15%-23% and 74%, respectively) compared with the Cu-containing condition. Furthermore, under Cu deficiency, 33% of the flux entering TCA via the pyruvate node was redirected to lactate and malate production. Based on these results, we hypothesize that Cu deficiency disrupts the electron transport chain causing ATP deficiency, redox imbalance, and oxidative stress, which in turn drive copper-deficient CHO cells to produce energy via aerobic glycolysis, which is associated with excessive lactate production, rather than the more efficient route of oxidative phosphorylation.

A model for the microstructure behaviour and strength evolution in lath martensite

A new model describing the microstructure and strength of lath martensite is introduced. The packet and block size were found to linearly depend on the prior-austenite grain size when introducing relevant crystallographic and geometric relationships of their hierarchical arrangements. A mechanism for the lath boundary arrangement within a block is postulated to ensure complete carbon redistribution to the lath boundaries. Accordingly, the dislocation density is obtained by considering the lattice distortion energy within a lath being equal to the strain energy of the dislocation density at the lath boundaries. Tempering effects are introduced by estimating the extent of carbon diffusing away from the lath boundaries; this mechanism relaxes the Cottrell atmospheres of lath dislocations and coarsens the boundaries. The yield stress as well as the microstructure evolution during tempering are successfully predicted by combining these results. The model is further extended to describe the yield stress in dual-phase steel microstructures by employing the iso-work principle. The model predictions are validated against experimental data in seven martensitic and five dual-phase steels, where the prior-austenite grain size, carbon content, tempering conditions and martensite volume fraction are employed as input. These results cover wide composition, initial microstructure and tempering conditions.

Atomically resolved cementite dissolution governed by the strain state in pearlite steel wires

Atom probe tomography was performed to study cementite dissolution as a function of the strain state of pearlite colonies with respect to the applied external strain in severely drawn pearlite steels. We prove that the migration of carbon from cementite into ferrite in the colonies increases under iso-stress conditions relative to that under iso-strain conditions at strains above 1.26. Our findings indicate that the strain state is an important microstructural component that controls the carbon redistribution in steel wires. We propose that the carbon–dislocation interaction is likely to be more prevalent under iso-stress conditions than in the iso-strain state.

Spatial variability of epibenthic communities on the Alaska Beaufort Shelf

Arctic marine epibenthos contribute significantly to the regional biomass, remineralization and redistribution of organic carbon, and are key elements of local food webs. The main purpose of this study was to describe the epibenthic invertebrate community on the Alaska Beaufort Shelf and identify links between community patterns and environmental drivers. Using a plumb-staff beam trawl, 71 stations were sampled between 13 and 220 m and from 145.09°W to 155.25°W along the shelf, in August/September of 2011. At each station, epibenthic taxonomic composition, abundance and biomass data were collected together with environmental data. Significant spatial variability in community composition and standing stock of the dominant taxa were observed along changes in depth and along-shelf position. The significant interaction between along-shelf position and depth helped define six geographic domains (two regions with three depth groups each). Shallow stations (<25 m) were dominated by mobile crustaceans and had the lowest values in diversity indices and total number of taxa. Mid-depth stations (26–100 m) had the highest values in diversity indices and were dominated by mollusks, crustaceans and echinoderms. Deep stations (101–220 m) were mostly represented by echinoderms and crustaceans with intermediate diversity values but high abundance and biomass values. However, at constant depth ranges, there were very few similar representative taxa in the eastern and western regions. Also, a clear reduction in abundance and biomass along the shelf break was observed from west to east. The six most influential environmental drivers (sediment phaeopigments, bottom water salinity, bottom water temperature, sediment organic matter, bottom water pH and percent sand) explained up to 50 % of the variance in epibenthic community structure. Through this study, we learned that the epibenthic community on the Alaska Beaufort Shelf is diverse, spatially heterogeneous and can have high biomass and density. Also we show how these community assemblages and total epibenthic biomass are linked to spatial changes in the environment through changes in bottom water temperature, salinity, sediment grain size and proxies for food quantity and quality.

The effect of subduction on the sulphur, carbon and redox budget of lithospheric mantle

AbstractSubduction of hydrated lithospheric mantle introduces HO, ferric iron, oxidized carbon and sulphur to the subduction zone system. The fate of these components is poorly known, but is intimately linked to the global geochemical cycles of iron, carbon and sulphur, the genesis of arc‐related ore deposits, the temporal evolution of mantle redox state and subduction‐related earthquakes and magmatism. thermocalc is used to provide first‐order constraints on the effect of subduction zone metamorphism on metamorphic redistribution of iron, carbon, sulphur and water in ultramafic rocks via construction of P−T and T‐X(O) pseudosections with open system calculation of the effect of fluid loss. The calculations replicate observed mineral assemblages in high‐P to low‐T ultramafic rocks at P−T conditions consistent with those suggested by other workers. The results are consistent with open system fluid loss without significant fluid infiltration. Water loss is complete by 850 C, the corresponding depth of fluid loss being consistent with that inferred for earthquakes in subducting slabs. Losses of carbon and sulphur are relatively minor, at around &lt;5% and &lt;1%, respectively, so it is envisaged that most carbon and sulphur subducted in ultramafic lithologies is transported to &gt;5 GPa, below the depths of the source zone for arc volcanoes. Oxygen activity for rocks in closed systems that evolve with a fixed redox budget is calculated to change from ΔFMQ −1 at 350 C to over ΔFMQ +3 at 850 C. This result emphasizes the need to consider redox budget as well as oxygen activity when the results of experiments performed at fixed oxygen activity relative to some buffer are interpreted in the context of natural systems. In open systems, devolatilization is calculated to increase the redox budget and oxygen activity of the residue via loss of methane and HS at the brucite‐out and serpentine‐out reactions respectively. No fluid‐induced mechanism for oxidation of sub‐arc mantle by transfer of redox budget from hydrated ultramafic lithologies to the overlying sub‐arc mantle was identified, although further thermodynamic data on fluid species such as S are required to confirm this.

Effects of different amendments for the reclamation of coastal saline soil on soil nutrient dynamics and electrical conductivity responses

High salinity and macronutrient deficiencies are two important limitations of coastal saline soils. The present study focused on the changes in electrical conductivity (EC), and the redistribution of water soluble carbon (C), total nitrogen (N), and absorbable phosphorus (P) during the reclamation of coastal saline soil using different amendments. Eight soil treatments were tested: cotton straw powder (J), domestic sewage sludge (W), sewage sludge+cotton residue (J+W), beach sand (S), cotton straw powder+beach sand (J+S), domestic sewage sludge+beach sand (W+S), domestic sewage sludge+cotton residue+beach sand (J+W+S), and a control treatment (CK). Triplicate soil samples for each treatment were initially treated once with underground saltwater (with or without bacterial manure). After the first month of incubation, irrigation was conducted weekly. EC measurements in different soil layers showed that sewage sludge was the best amendment for reducing soil EC, while cotton straw powder had no significant effect. Concentrations of N and C increased with soil depth, while the highest P concentration was observed in the uppermost soil. Soil amended with organic matter showed the highest P concentrations, and P availability increased with the application of all amendments except sand, which had no significant effect. The compound treatments had more positive impacts on N availability than did single amendments; however, their effects on P concentration were minimal. The results indicated that sewage sludge was the most effective amendment for reclaiming coastal saline soil and improving the availability of macronutrients.

Erosion-induced carbon redistribution, burial and mineralisation — Is the episodic nature of erosion processes important?

There is still an ongoing scientific discussion regarding the importance of erosion-induced lateral soil organic carbon (SOC) redistribution for the burial and/or mineralisation of carbon and the resulting long-term C balance at the catchment scale. Especially the effects of the event driven nature of water erosion and the potentially associated enrichment of SOC in sediment delivery are still unclear. In general, two processes lead to enrichment of SOC: (i) enrichment due to selective interrill erosion at erosion sites, and (ii) enrichment due to selective depletion at deposition sites. In this study, the conceptual soil erosion and SOC turnover model SPEROS-C was adapted to integrate these processes and applied in a small arable catchment (4.2ha) in Germany for a 57-year period. A total number of 901 model runs were performed with different realisations of frequency and magnitude of water erosion as well as realisations of enrichment and depletion ratios taken from literature and compared to a reference model run representing mean annual erosion without enrichment processes. In general, our modelling study indicates that ignoring temporal variability and enrichment processes may lead to a substantial misinterpretation of erosion-induced C fluxes. Especially the vertical C flux (difference between C inputs from plant assimilates and organic fertilizer and SOC mineralisation) at deposition sites strongly depends on the model parameterisation ranging from a maximum C source of −336gCm−2 to a maximum C sink of 44gCm−2. In combination with a substantially higher C export due to enrichment processes, the overall C balance of the catchment potentially turns into a maximum C source of −44gCm−2 at the end of the simulation period compared to a C source of −1gCm−2 for the reference run.

Microstructural heterogeneity and its relationship to the strength of martensite

The complex microstructure of ferrous martensite is reflected in its complex mechanical response. In an attempt to highlight how carbon redistribution during quenching and/or low temperature tempering can affect mechanical response, a set of controlled experiments were performed. By rapidly quenching samples it was possible to limit autotempering allowing the evolution of mechanical response and microstructure to be followed with low temperature tempering. This was compared to a situation where the material was more slowly quenched, leading to a highly autotempered state. The gradual transition from elastic to plastic deformation is interpreted based on possible sources of microstructural heterogeneity. Lath-to-lath variations of dislocation density are discussed as a contributor to the development of microstructural heterogeneity during tempering. These results shed light on the possible origins of the continuous-composite like mechanical response of lath martensite proposed in recent work.

Facile Synthesis and Electrocatalytic Activity of Sulfur Doped Carbon for Oxygen Reduction

Fuel cells and metal-air batteries have attracted much attention over the past few years due to their high energy density and the potential to reduce the negative impact of climate change [1,2]. However, the sluggish oxygen reduction reaction (ORR) at the cathode, which requires highly efficient and low cost electrocatalysts, is one of the important factors that restrict the wide application of fuel cells [3-5]. Exploring low-cost and sustainable electrocatalysts with high efficiency to alternate the platinum-based noble electrocatalysts for the ORR is critical for the development of fuel cells and metal-air batteries [6-8]. Heteroatom-doped carbon materials have emerged as promising alternative electrocatalyts for the ORR due to its low price, high catalytic activity and environmental friendliness [6-13]. The heteroatom doped in carbon is usually N, S, B, F and P et al., which can modify the electronic structure (like charge and/or spin density redistribution) of carbon and create the active sites favorable for the adsorption of O2 molecule and facilitate the ORR process [9-13]. Considerable efforts have been devoted to the study of N-doped carbon catalysts for the ORR[14-17]. Sulfur doping is also convinced to be a valid method in promoting the catalytic activity of carbon towards ORR. Sulfur has an electronegativity of 2.58, which is similar to carbon’s (2.55) [12]. In contrast, the electronegativity of N(3.04) is higher than that of carbon. Therefore the modification of structure and the catalytic activity of carbon resulting from N doping and S doping is different. S-doped graphene has been reported to show improved electrocatalytic activity for ORR [11,18]. Nevertheless, there have been few reports about the ORR activity of S-doped porous carbon. It’s known that porous carbon can provide effective triple phase (solid-liquid-gas) region for the mass transfer of reactants and products during the ORR. To better understand the effect of S-doping on the structure and ORR activity of carbon, we developed a facile method to synthesize the S-doped porous carbon via a hydrothermal method with sucrose and benzyl disulfide (BDS) as the carbon and sulfur sources, respectively. The influence of S doping on the electrocatalytic activity of the carbon for the ORR in alkaline media was investigated. The pyrolysis temperature has a significant impact on the structure and texture of the S-doped carbon, which further affects the ORR activity and durability of S-doped carbon as shown in Figure 1. Acknowledgements This work is supported by National Natural Science Foundation of China (Nos.51272167 and 21206101 ).

Redistribution of black carbon in aerosol particles undergoing liquid‐liquid phase separation

AbstractAtmospheric black carbon (BC) is a major anthropogenic greenhouse agent, yet substantial uncertainties obstruct understanding its radiative forcing. Particularly debated is the extent of the absorption enhancement by internally compared to externally mixed BC, which critically depends on the interior morphology of the BC‐containing particles. Here we suggest that a currently unaccounted morphology, optically very different from the customary core‐shell and volume‐mixing assumptions, likely occurs in aerosol particles undergoing liquid‐liquid phase separation (LLPS). Using Raman spectroscopy on micrometer‐sized droplets, we show that LLPS of an organic/inorganic model system drives redistribution of BC into the outer (organic) phase of the host particle. This results in an inverted core‐shell structure, in which a transparent aqueous core is surrounded by a BC‐containing absorbing shell. Based on Mie theory calculations, we estimate that such a redistribution can increase the absorption efficiency of internally mixed BC aerosols by up to 25% compared to the core‐shell approximation.

Effectiveness of carbon isotopic signature for estimating soil erosion and deposition rates in Sicilian vineyards

Traditional methods for measurement of soil erosion provide information on erosion rates and mechanisms but fail to determine the spatial distribution of sediment redistribution. Recent studies have used carbon (C) stable isotopes to trace sediment and to monitor soil organic carbon (SOC) redistribution. The difference in δ13C values in a slope-transect or in a watershed provides information about the source of suspended organic matter and sediment removal and deposition, but miss enough information to quantify sediment loss. The objective of this research was to develop a method to estimate soil erosion using the natural discrimination of δ13C-SOC with soil depth, comparing δ13C variation in different profiles sampled along a slope. The method was developed in a Sicilian vineyard, where soil losses were previously measured by means of Gerlach collectors and by pole methods. δ13C was measured in different soil profiles in the top, middle and bottom of the slope. The variation of δ13C with soil depth in the profiles along the slope was compared to the δ13C values of the near flat area, in order to reconstruct the original topography of slope transect. δ13C increased with depth and decreased from the top to the bottom of the slope in all pedons. The soil δ13C signature ranged from −26.7‰ to −25.7‰, from −26.2‰ to −25.3‰, and from −27.0‰ to −24.8‰ in the profiles at the top, middle, and bottom of the slope, respectively. The rates of δ13C enrichment along the slope could be explained as different rates of detachment and deposition. The erosion value estimated with δ13C method was 77Mgha−1y−1. The comparison of different methods (102Mgha−1y−1 with the pole method and 89.6Mgha−1y−1 with the Gerlach method) indicate that carbon isotopic signature is a reliable indicator of short- and long-term soil erosion processes.