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Influence of production variables and starting material on charcoal stable isotopic and molecular characteristics
Abstract
We present a systematic study on the effect of starting species, gas composition, temperature, particle size and duration of heating upon the molecular and stable isotope composition of high density (mangrove) and low density (pine) wood. In both pine and mangrove, charcoal was depleted in δ13C relative to the starting wood by up to 1.6‰ and 0.8‰, respectively. This is attributed predominantly to the progressive loss of isotopically heavier polysaccharides, and kinetic effects of aromatization during heating. However, the pattern of δ13C change was dependant upon both starting species and atmosphere, with different structural changes associated with charcoal production from each wood type elucidated by Solid-State 13C Nuclear Magnetic Resonance Spectroscopy. These are particularly evident at lower temperatures, where variation in the oxygen content of the production atmosphere results in differences in the thermal degradation of cellulose and lignin. It is concluded that production of charcoal from separate species in identical conditions, or from a single sample exposed to different production variables, can result in significantly different δ13C of the resulting material, relative to the initial wood. These results have implications for the use of charcoal isotope composition to infer past environmental change.
... Carbonization induces the preferential degradation of 13 C-enriched wood compounds (i.e., proteins, amino acids, holocellulose), resulting in a decrease of δ 13 C close to the signature of the 13 C-depleted lignin [32,33]. The changes in δ 13 C have been attributed mainly to kinetic effects related to temperature and the physiochemistry of the main wood components [34][35][36]. However, in contrast to the evolution of δ 13 C during charring, the behaviour of δ 18 Ο remains poorly documented. ...
... The increase in pyrolysis temperature mainly results in two distinct Table S1; [23,36,37]). In addition, the decrease of intensity in carbonyl groups bands observed in FTIR spectra at 1735 cm − 1 ( Fig. 3 and Table 1) is consistent with the thermal decomposition of hemicellulose initiated between 200 • C and 300 • C as described by Cheng et al. [50] and Yang et al. [30]. ...
... The intensity of carbonization depends both on temperature and oxygen availability since at a given temperature, the carbonization and pyrolysis do not produce the same results. In addition, other characteristics of the wood such as its moisture content, chemical composition (including its mineral content), density, and porosity as well as the size and shape of the wood particles may affect the evolution of the isotopic composition under heat treatment [23,26,34,36]. ...
The carbonization process induces significant physical, elemental, and structural transformations of wood. In this study, the modification of δ18O in wood during the carbonization process was investigated in conjunction with elemental analysis, infrared spectroscopy (FTIR), and Rock-Eval thermal analysis, to explore the connection between the chemical composition of the materials and the alterations in δ18O. Quercus petraea wood samples were experimentally burned at temperatures ranging from 200 °C to 1000 °C under inert (pyrolysis) and oxidative atmospheres. The results reveal that the modification of δ18O values in charred wood can be described as a sequential two-step process. The initial step, occurring below 300 °C, involves the volatilization and preferential degradation of thermolabile compounds, leading to an increase of +1.6‰ in δ18O. The subsequent step, below 700 °C, results in a decrease in δ18O values of –21.6‰, primarily driven by the thermal degradation of cellulose and lignin, as well as the increase of aromaticity and reorganization. The components and the δ18O of wood undergo distinct changes in combustion mode, due to different carbonization kinetics as evidenced by FTIR and elemental analysis. To assess the intensity of the carbonization process, influenced by temperature, oxygen availability, and wood characteristics, the H/C atomic ratio, a good indicator of aromaticity, is used. A non-linear regression model was established, relating δ18O to the H/C atomic ratio, thereby demonstrating that δ18O values undergo changes as wood aromatization progresses, independent of the carbonization conditions. The second order model has a mean confidence interval of 1.9‰ and a prediction interval of 8.1‰. This work provides a fundamental understanding of the connection between the chemical composition of woody materials, alterations in δ18O, and the carbonization process, offering valuable insights for further studies and applications related to oxygen-related information that may be preserved in charcoals.
... However, available field and laboratory experiment data are inadequate to fully explain the isotope effects during fireinduced thermal degradation of plant-derived OM. For instance, changes in the isotope values associated with the burning of plant biomass have been attributed mainly to the kinetic isotope effect and source-induced isotopic fractionation (Krull et al., 2003;Turney et al., 2006;Ascough et al., 2008;Jambrina-Enríquez et al., 2018). In general, the magnitude of the kinetic isotope effect depends on the burning conditions associated with the availability of oxygen and temperature and is therefore not influenced by the biochemical composition of the plant materials (Jones and Chaloner, 1991;Ballentine et al., 1998;Ferrio et al., 2006;Wang et al., 2017). ...
... In general, the magnitude of the kinetic isotope effect depends on the burning conditions associated with the availability of oxygen and temperature and is therefore not influenced by the biochemical composition of the plant materials (Jones and Chaloner, 1991;Ballentine et al., 1998;Ferrio et al., 2006;Wang et al., 2017). While the source-induced isotopic fractionation is a function of plant biochemistry and the extent of changes in isotope values are highly dependent on the photosynthetic pathways and growth forms of the plant (Bird and Grö cke, 1997;Turekian et al., 1998;Krull et al., 2003;Ascough et al., 2008). Although several attempts have been made to identify and quantify the burning-induced isotope effects in anoxic conditions (Czimczik et al., 2002;Poole et al., 2002;Jambrina-Enríquez et al., 2018;Connolly et al., 2021), there are limited studies on the burning of plant OM in the presence of oxygen Das et al., 2010;Knicker et al., 2013). ...
... This affects our ability to postulate a generalized model to elucidate changes in the stable isotope values of plant biomass during burning since natural vegetation fires are characterized by both oxic and anoxic microenvironments (Burrows, 2001;Grootemaat et al., 2015). In addition, burning experiments under ambient oxygen (oxic) have only investigated combustion-induced changes in the total organic carbon (TOC) content (Krull et al., 2003;Ascough et al., 2008), the d 13 C OM values (Das et al., 2010), and the distribution pattern in lipid components (n-alkanes and n-alkanoic acids; Ballentine et al., 1998;Knicker et al., 2013). To the best of our knowledge, studies on fire-induced thermal alterations in d 13 C n-alk and d 2 H n-alk values under oxic conditions are yet to be available. ...
In fire-dominated biomes, interpretation of stable isotope-enabled paleoecological proxies could be associated with uncertainties since the plant biomolecules can be thermally modified during vegetation fires and the extent of alterations are yet to be well constrained. Towards this, we performed a series of controlled experiments where leaf samples from C3 (tree and shrub) and C4 (grass) plants were burned under ambient O2 at temperatures between 200 °C and 500 °C (at intervals of 50 °C). The experiments showed that the total organic carbon (TOC) content in burned plant leaves was 79 to 96% lower than in the unburned samples. Upon burning, leaf samples showed a significant decrease in the concentration of n-alkanes (up to 91%) and n-alkanoic acid (FAs; up to 100%). We also observed a decline in the abundance of long-chain (from 99 to 39%) and an increase in the mid (from 1 to 28%) and short-chain (from 0 to 33%) homologues due to the burning of plant leaves. In burned plant leaves, the typical odd-over-even predominance in long-chain n-alkanes or even-over-odd in FAs were lost, leading to a decrease in the carbon preference index by up to 9 units. The burning-induced thermal degradation also influenced the isotopic composition of the plant leaves. Burning of leaf samples from C3 plants (tree and shrub) increased the bulk carbon isotopic composition (13COM) by 1.0 to 1.4‰, while in C4 grasses, it was 0.4 to 1.6‰ lower than their unburned counterparts. The carbon isotopic composition of n-alkanes (13Cn-alk) mostly decreased (by ~4.6‰) during the burning of C3 and C4 plant leaf samples. In contrast, the hydrogen isotopic compositions of n-alkanes (2Hn-alk) in the burned samples were up to 86‰ higher than their initial values. In summary, our results show that changes in the chemical properties and isotopic composition of organic matter strongly depend on the plant type and the burning temperature. Findings from this work would have implications for paleoproductivity, paleovegetation, paleoclimate and soil organic carbon studies that are largely dependent on TOC content, lipid biomarker indices, 13COM, 13Cn-alk and 2Hn-alk values. Therefore, we recommend careful consideration and identification of vegetation fire history before using stable isotope-enabled organic proxies for generating paleoecological records.
... 13 C fractionation can be explained by the kinetic isotope effect and source-induced isotopic fractionations. In the specific case of wood carbonisation, it has been demonstrated that 13 C fractionation was mainly driven by the thermal degradation of isotopically distinct biomolecules presenting distinct thermostabilities [16][17][18] . Several investigations have demonstrated that Δ 13 C modifications are directly related to the 13 C isotope composition of thermolabile organic moieties degraded in the course of carbonisation [16][17][18] . ...
... In the specific case of wood carbonisation, it has been demonstrated that 13 C fractionation was mainly driven by the thermal degradation of isotopically distinct biomolecules presenting distinct thermostabilities [16][17][18] . Several investigations have demonstrated that Δ 13 C modifications are directly related to the 13 C isotope composition of thermolabile organic moieties degraded in the course of carbonisation [16][17][18] . Between ca. ...
... 180 °C and ca. 450 °C, the thermal degradation of 13 C-enriched hemicelluloses and cellulose and the subsequent relative enrichment in 13 C-depleted lignin have been shown to yield a reduction in bulk δ 13 C values close to the value determined on lignin 13,[16][17][18] . In oak and pine woods, taxa commonly identified in European archaeological sites, carbonisation can therefore yield Δ 13 www.nature.com/scientificreports/ ...
Ancient charcoal fragments, produced by the use of wood as fuel in archaeological contexts or during natural or anthropic forest fires, persist in soil and sediments over centuries to millennia. They thus offer a unique window to reconstruct past climate, especially palaeo-precipitation regimes thanks to their stable carbon isotope composition. However, the initial δ 13 C of wood is slightly modified as a function of the carbonisation temperature. Carbonisation-induced 13 C fractionation is classically investigated through a transfer function between experimental carbonisation temperatures and the carbon content. This approach assumes that the carbon content is conservative through time in ancient charcoals and neglects the potential impact of post-depositional oxidation occurring in soils and sediments. In the present study, we first show that post-depositional oxidation can lead to a large underestimation of past carbonisation temperatures, thereby minimising the estimation of carbonisation-induced 13 C fractionations and possibly biasing δ 13 C-based climate reconstructions. Secondly, by combining carbon content, Fourier-transform infrared and Raman spectroscopy, we propose a new framework to assess the carbonisation temperatures registered in ancient charcoals. This new framework paves the way to reassessing δ 13 C-based climate reconstruction. The stable carbon isotope composition (δ 13 C) of woods is a function of the 13 C/ 12 C ratio of the initial wood, which depends on environmental conditions such as hydric stress, temperature, the isotope composition of CO 2 and of the photosynthetic carbon fixation pathway 1-7. The δ 13 C of woods (δ 13 C wood) is therefore widely used to infer past environmental changes 8-11. In contrast to wood remnants, charred woods, e.g. charcoals, persist in soils and sediments over centuries and millennia owing to their chemical structure dominated by aromatic units, which limits their biological and abiotic degradation with time 12. Produced by the use of wood as fuel in archaeological contexts or during natural or anthropic forest fires, charcoals are commonly found in soils and sediments. The δ 13 C values of charcoals (δ 13 C char) have therefore been proposed as a useful proxy to assess changes in past environmental conditions-especially paleo-precipitation regimes-provided carbonisation-induced 13 C fractionation is non-significant or is corrected 13-15. Expressed as Δ 13 C (Δ 13 C = δ 13 C char-δ 13 C wood), this 13 C fractionation depends on the carbonisation temperatures undergone by the woods. 13 C fractionation can be explained by the kinetic isotope effect and source-induced isotopic fractionations. In the specific case of wood carbonisation, it has been demonstrated that 13 C fractiona-tion was mainly driven by the thermal degradation of isotopically distinct biomolecules presenting distinct thermostabilities 16-18. Several investigations have demonstrated that Δ 13 C modifications are directly related to the 13 C isotope composition of thermolabile organic moieties degraded in the course of carbonisation 16-18. Between ca. 180 °C and ca. 450 °C, the thermal degradation of 13 C-enriched hemicelluloses and cellulose and the subsequent relative enrichment in 13 C-depleted lignin have been shown to yield a reduction in bulk δ 13 C values close to the value determined on lignin 13,16-18. In oak and pine woods, taxa commonly identified in Euro-pean archaeological sites, carbonisation can therefore yield Δ 13 C reaching − 1.4 (600 °C) and − 2.0 ‰ (800 °C), OPEN
... 13 C fractionation can be explained by the kinetic isotope effect and source-induced isotopic fractionations. In the specific case of wood carbonisation, it has been demonstrated that 13 C fractionation was mainly driven by the thermal degradation of isotopically distinct biomolecules presenting distinct thermostabilities [16][17][18] . Several investigations have demonstrated that Δ 13 C modifications are directly related to the 13 C isotope composition of thermolabile organic moieties degraded in the course of carbonisation [16][17][18] . ...
... In the specific case of wood carbonisation, it has been demonstrated that 13 C fractionation was mainly driven by the thermal degradation of isotopically distinct biomolecules presenting distinct thermostabilities [16][17][18] . Several investigations have demonstrated that Δ 13 C modifications are directly related to the 13 C isotope composition of thermolabile organic moieties degraded in the course of carbonisation [16][17][18] . Between ca. ...
... 180 °C and ca. 450 °C, the thermal degradation of 13 C-enriched hemicelluloses and cellulose and the subsequent relative enrichment in 13 C-depleted lignin have been shown to yield a reduction in bulk δ 13 C values close to the value determined on lignin 13,[16][17][18] . In oak and pine woods, taxa commonly identified in European archaeological sites, carbonisation can therefore yield Δ 13 www.nature.com/scientificreports/ ...
Ancient charcoal fragments, produced by the use of wood as fuel in archaeological contexts or during natural or anthropic forest fires, persist in soil and sediments over centuries to millennia. They thus offer a unique window to reconstruct past climate, especially palaeo-precipitation regimes thanks to their stable carbon isotope composition. However, the initial δ ¹³ C of wood is slightly modified as a function of the carbonisation temperature. Carbonisation-induced ¹³ C fractionation is classically investigated through a transfer function between experimental carbonisation temperatures and the carbon content. This approach assumes that the carbon content is conservative through time in ancient charcoals and neglects the potential impact of post-depositional oxidation occurring in soils and sediments. In the present study, we first show that post-depositional oxidation can lead to a large underestimation of past carbonisation temperatures, thereby minimising the estimation of carbonisation-induced ¹³ C fractionations and possibly biasing δ ¹³ C-based climate reconstructions. Secondly, by combining carbon content, Fourier-transform infrared and Raman spectroscopy, we propose a new framework to assess the carbonisation temperatures registered in ancient charcoals. This new framework paves the way to reassessing δ ¹³ C-based climate reconstruction.
... Once the woods have been transformed into charcoal by fast heating, the main process that take place between 200 and 340 • C is depolymerization by band scission with a release of water and volatiles (mainly CO, CO 2 and some hydrocarbons [69,70]). The presence in this stage of hydrogen-rich functional groups (i.e., aliphatic compounds) is probably the cause of the high fluorescence [71] that characterizes Raman spectra at temperature below ca 325 • (Rc% lower than 0.78%, Figure 5 and Table 1). Concurrently, the D band position downshifts and the decrease of the G band width up to temperatures of about 500 • C ( Figures 5 and 7) reflects an increase of the size of the aromatic clusters that pass, in this stage, from simple mono-aromatic units up to larger compounds [71][72][73]. ...
... The presence in this stage of hydrogen-rich functional groups (i.e., aliphatic compounds) is probably the cause of the high fluorescence [71] that characterizes Raman spectra at temperature below ca 325 • (Rc% lower than 0.78%, Figure 5 and Table 1). Concurrently, the D band position downshifts and the decrease of the G band width up to temperatures of about 500 • C ( Figures 5 and 7) reflects an increase of the size of the aromatic clusters that pass, in this stage, from simple mono-aromatic units up to larger compounds [71][72][73]. This is confirmed by [72], which measured the content of aromatic carbon in charcoals, showing an increase with temperature from less than the half (14% at 200 • C and 19% at 250 • C) to about 88% at 350 • C and more than 90% above 400 • C. ...
... The third stage, for temperatures from 600 • up to a maximum of 1000 • C, is out of our ranges. Nevertheless, it is worth noting that the Raman evolution at this higher stage is related to a further increase degree of aromatic condensation of the turbostratically aligned polyaromatic [22,[71][72][73] and has been described by [42], consisting mainly of a relative D band area and intensity increase with respect to the G band. ...
The study of the structural order of charcoals embedded in pyroclastic density currents provides information on their emplacement temperature during volcanic eruptions. In the present work, a set of charcoals from three distinct pyroclastic density currents deposits whose temperatures have been previously estimated by charcoal reflectance analyses to lie between 250 °C and 550 °C, was studied by means of Raman spectroscopy. The analyses reveal a very disordered structural ordering of the charcoals, similar to kerogen matured under diagenetic conditions. Changes in Raman spectra at increasing temperatures reflect depolymerization and an increase of aromaticity and can be expressed by parameters derived from a simplified fitting method. Based on this approach, a second order polynomial regression with a high degree of correlation and a minimum error was derived to predict paleotemperatures of pyroclastic deposits. Our results show that Raman spectroscopy can provide a reliable and powerful tool for volcanological studies and volcanic hazard assessment given its advantage of minimum samples preparation, rapid acquisition processes and high precision.
... However, available field and laboratory experiment data are inadequate to fully explain the isotope effects during fireinduced thermal degradation of plant-derived OM. For instance, changes in the isotope values associated with the burning of plant biomass have been attributed mainly to the kinetic isotope effect and source-induced isotopic fractionation (Krull et al., 2003;Turney et al., 2006;Ascough et al., 2008;Jambrina-Enríquez et al., 2018). In general, the magnitude of the kinetic isotope effect depends on the burning conditions associated with the availability of oxygen and temperature and is therefore not influenced by the biochemical composition of the plant materials (Jones and Chaloner, 1991;Ballentine et al., 1998;Ferrio et al., 2006;Wang et al., 2017). ...
... In general, the magnitude of the kinetic isotope effect depends on the burning conditions associated with the availability of oxygen and temperature and is therefore not influenced by the biochemical composition of the plant materials (Jones and Chaloner, 1991;Ballentine et al., 1998;Ferrio et al., 2006;Wang et al., 2017). While the source-induced isotopic fractionation is a function of plant biochemistry and the extent of changes in isotope values are highly dependent on the photosynthetic pathways and growth forms of the plant (Bird and Grö cke, 1997;Turekian et al., 1998;Krull et al., 2003;Ascough et al., 2008). Although several attempts have been made to identify and quantify the burning-induced isotope effects in anoxic conditions (Czimczik et al., 2002;Poole et al., 2002;Jambrina-Enríquez et al., 2018;Connolly et al., 2021), there are limited studies on the burning of plant OM in the presence of oxygen Das et al., 2010;Knicker et al., 2013). ...
... This affects our ability to postulate a generalized model to elucidate changes in the stable isotope values of plant biomass during burning since natural vegetation fires are characterized by both oxic and anoxic microenvironments (Burrows, 2001;Grootemaat et al., 2015). In addition, burning experiments under ambient oxygen (oxic) have only investigated combustion-induced changes in the total organic carbon (TOC) content (Krull et al., 2003;Ascough et al., 2008), the d 13 C OM values (Das et al., 2010), and the distribution pattern in lipid components (n-alkanes and n-alkanoic acids; Ballentine et al., 1998;Knicker et al., 2013). To the best of our knowledge, studies on fire-induced thermal alterations in d 13 C n-alk and d 2 H n-alk values under oxic conditions are yet to be available. ...
In fire-prone biomes, the interpretation of paleoecological proxies is subjected to uncertainties since the plant biomarkers/molecules are thermally modified during vegetation fires, and the extent of alterations is yet to be well-constrained, particularly for oxic conditions. Towards this, we performed a series of controlled experiments where leaf samples from C3 (tree and shrub) and C4 (grass) plants were burned under ambient oxygen at temperatures between 200 °C and 500 °C. A topsoil sample was also heated to understand the effect of thermal degradation on organic matter (OM) already present in the soil. Our results show a reduction in the total organic carbon content and leaf wax concentrations which is consistent with the previous studies. We also observed a shift from predominantly long-chain homologues (with odd-over-even in n-alkanes or even-over-odd predominance in n-alkanoic acids; FAs) to balanced distributions with increased mid and short-chain homologues. We observed that the short, mid, and long-chain n-alkanes were mainly formed at the expense of FAs (with losses up to 100%), possibly due to oxygen-rich burning conditions. Burning of plant leaves also affected their stable isotopic compositions. In burned C3 plant leaves (tree and shrub), the bulk carbon isotope values (δ¹³COM) increased by 1.0 to 1.4‰, while in C4 grasses, it was 0.4 to 1.6‰ lower than their unburned counterparts. The changes in the δ¹³COM values are suggested to be a cumulative product of the kinetic isotope effect and source-driven isotopic fractionation. The carbon isotope values in long-chain n-alkanes (δ¹³Cn-alk) mostly decreased (up to 4.6‰) in burned C3 and C4 plant leaves due to the isotopic modifications associated with the generation of secondary n-alkanes from FAs. In contrast, the hydrogen isotope values in n-alkanes (δ²Hn-alk) in the burned samples were up to 86‰ higher than their initial values, mainly due to the kinetic isotope effect. Therefore, in biomes susceptible to frequent canopy and litter layer fires, unusually high δ²Hn-alk values coupled with a disproportionate change between δ¹³Cn-alk and δ²Hn-alk values might indicate pyrogenic OM presence within soil. We also observed that changes in the n-alkane characteristics due to heating of soil samples were substantially lower than those in plant leaves due to the protected lipid component within organomineral complexes. In summary, we recommend using isotopic compositions of long-chain FAs for paleoecological studies in fire-prone biomes, as they would represent OM derived from unburned plants.
... The environmental persistence of PyC is predominantly attributed to a chemical structure containing abundant carbon aromatic rings, which require high energy input to break down, compared to non-polyaromatic structures such as cellulose. These ring structures grow in size with increasing production temperature and/or pyrolysis duration (Ascough et al., 2008). The importance of PyC is also increasingly apparent to the modern global carbon cycle, both in terms of its size as a global carbon stock, and its environmental dynamics Santín et al., 2015). ...
... In the above concept, the time period over which PyC remained "intact" in any given context would be dictated firstly by production conditions, predominantly temperature. As production temperature increases, so does aromaticity, shifting the initial structure of the PyC to a "SPAC-dominant" state (Ascough et al., 2008;McBeath et al., 2015). In identical environments therefore, the PyC produced at higher temperature would be preserved over a longer period than material produced at lower temperatures. ...
... Hydropyrolysis (HyPy) was used to assess the content of polycyclic aromatic carbon structures of ≥7 rings (also known as Black Carbon as defined by HyPy: BC HyPy ) in the samples on a secure chemical basis (Ascough et al., 2009;Meredith et al., 2012). Immediately after formation, the proportion of these (resistant) chemical structures is a function of production temperature (Ascough et al., 2008). The process separates the larger polycyclic aromatic domains from labile chemical structures in the sample, and therefore provides a quantitative assessment of the proportion of the sample that exists in either the polycyclic aromatic or non-aromatic (or small aromatic structural) chemical forms. ...
Pyrogenic Carbon (PyC) is ubiquitous in global environments, and is now known to form a significant, and dynamic component of the global carbon cycle, with at least some forms of PyC persisting in their depositional environment for many millennia. Despite this, the factors that determine the turnover of PyC remain poorly understood, as do the physical and chemical changes that this material undergoes when exposed to the environment over tens of thousands of years. Here, we present the results of an investigation to address these knowledge gaps through chemical and physical analysis of a suite of wood PyC samples exposed to the environment for varying time periods, to a maximum of >90,000 years. This includes an assessment of the quantity of resistant carbon, known as Stable Polyaromatic Carbon (SPAC) vs. more chemically labile carbon in the samples. We find that, although production temperature is likely to determine the initial “degradation potential” of PyC, an extended exposure to environmental conditions does not necessarily mean that remaining PyC always progresses to a “SPAC-dominant” state. Instead, some ancient PyC can be composed largely of chemical components typically thought of as environmentally labile, and it is likely that the depositional environment drives the trajectory of preservation vs. loss of PyC over time. This has important implications for the size of global PyC stocks, which may have been underestimated, and also for the potential loss of previously stored PyC, when its depositional environment alters through environmental or climatic changes.
... According to some studies, there are no significant changes in the δ 13 C values of wood or plant parts in general due to charring (Leavitt et al. 1982;DeNiro and Hastorf 1985;Hastorf and DeNiro 1985;Marino and DeNiro 1987;Turekian et al. 1998). In other cases, δ 13 C decreases with higher carbonization temperature (Ascough et al. 2008), while there is a significant increase in C% (Ferrio et al. 2006). However, carbonizing grass epidermis samples resulted in a 13 C-enrichment of 1.0±1.6‰ ...
... (Beuning and Scott 2002). An overview of different studies with examples of 13 C-enrichment and -depletion is provided by Ascough et al. (2008). It has also been reported that the climatic signal recorded by δ 13 C in wood is unaffected by carbonization (Vignola et al. 2018) and that in cases with significant δ 13 C shifts, a correction using the measured C% can be applied (Ferrio et al. 2006). ...
... As we find this δ 13 C-enrichment due to charring fairly consistently for different species and throughout time, this could indicate a general mechanism-in contrast to the literature, where both enrichment, depletion and unchanged δ 13 C values are reported (see the Introduction and e.g. Ascough et al. 2008 for an overview). The nutshells of both species, hazel and oak, have intermediate δ 13 C values between wood and charcoal (see Supplementary Figure 1). ...
The aim of this study is to investigate the range, the degree of variability, and a possible time or species dependence of wood and charcoal δ ¹³ C values within one small study area. To achieve this, we used δ ¹³ C and ¹⁴ C determinations of more than 400 archaeological samples from a ca. 300 ha area in Denmark, spanning 5000 years and covering several different species. The δ ¹³ C values of the wood and charcoal range from −32.8‰ to −21.2‰. We found no time-dependence of wood and charcoal δ ¹³ C values, neither in general nor within one species. The mean δ ¹³ C of all wood samples is −28.5‰, while the means of individual species range from −30.6‰ to −26.3‰. The mean of all charcoal samples is −25.7‰, with the means of individual species ranging from −28.1‰ to −24.3‰. The wood δ ¹³ C values can be used to infer the possible range of plant δ ¹³ C values, which otherwise are not available. They imply that a high degree of variability can be expected at the base of the food chain. This is relevant for palaeodietary studies that rely on the measurement of baseline isotope values.
... General trends of carbon isotopic changes in B/P products obtained in experiments agree with results published earlier by different authors. In general, it is agreed that the isotopic composition of charcoal differs from wood by up to 2‰ (Ferrio et al., 2006;Turney et al., 2006;Ascough et al., 2008;Das et al., 2010 andBird andAscough, 2012). It is also agreed that it is temperature dependent. ...
... Significant differences between δ 13 C of charcoal produced by pyrolysis and incomplete combustion reported in published studies were explained by the acceleration of cellulose decomposition by pyrolysis in comparison to decomposition in the presence of O 2 (Turney et al., 2006;Ascough et al., 2008;Das et al., 2010 andBird andAscough, 2012). The experiments with pine wood (Fig. 3) do not show differences in the carbon isotopic composition of "charcoal" and "bio-oils" in pyrolysis (in N 2 ) and heating in the presence of O 2 (burning in artificial CO 2 -free air). ...
... Published B/P experimental results for δ 13 C values of charcoal suggested no time dependence of the carbon isotopic composition (Turney et al., 2006;Ascough et al., 2008;Das et al., 2010 andBird andAscough, 2012). The B/P experiment with oak at 300°C showed significant changes in isotopic composition of incomplete burning products with time (Table 3 and Fig. 6). ...
A series of laboratory experiments was performed to determine the carbon stable isotopic composition of different combustion/pyrolysis (B/P) products. Variation in the δ ¹³ C values of the products was observed, up to 4‰. The differences in the carbon isotopic compositions of the B/P products were dependent on temperature, time and wood type. Comparison of the results for fresh and fossil oak wood suggested that the δ ¹³ C differences were the effect of selective decomposition of some wood components during the fossilization process. The temperature dependence of the carbon isotopic composition was linked to variation in the carbon isotopic composition of the main wood components, which each had different levels of thermal stability. Isotopes exchange reactions in between different products can be also considered as possible source of variation of δ ¹³ C on temperature. Both these hypotheses were supported by molecular simulations of cellulose and lignin B/P. The results confirm that B/P should be treated as a continuous process, where the results depend on the degree of process development. Natural burning processes are dynamic and burning conditions change rapidly and it is necessary to take care when using combustion products as a paleoenvironmental proxy or as an isotopic characteristic for the identification of source material.
... L'ensemble de ces travaux a néanmoins été effectué en utilisant des méthodes de carbonisation assez éloignées des conditions régnant dans les foyers domestiques d'où sont issus les charbons archéologiques étudiés. En effet, les études portant sur la modification des rapports isotopiques du bois due à sa carbonisation ont été généralement menées dans des fours, principalement sous atmosphère inerte, et, en utilisant des échantillons de taille réduite, voire de la poudre de bois (Ascough et al., 2008;Beuning and Scott, 2002;Czimczik et al., 2002;Jones and Chaloner, 1991;Pyle et al., 2015;Turney et al., 2006). De ce fait, non seulement la variabilité de la carbonisation dans un foyer n'est pas prise en compte, ni la présence d'oxygène, mais, de surcroît, les variations du 13 C entre les cernes n'ont pas été étudiées à l'aune des effets de la carbonisation. ...
... Ces ruptures concernent de prime abord les liaisons les plus faibles, c'est à dire celles impliquant les atomes d'hydrogène, d'oxygène et d'azote qui sont alors évacués dans les gaz chauds issus de la carbonisation (Bird and Ascough, 2012). Lors de la carbonisation, on assiste à la formation progressive de cycles aromatiques dans la matière organique résiduelle (Knicker, 2007) et cette aromaticité augmente avec la température de carbonisation (Ascough et al., 2008;Wiedemeier et al., Page | 59 2015). Les cycles aromatiques formés s'ordonnent progressivement en feuillets qui s'agrandissent et se superposent (Rouzaud et al., 2015). ...
... principalement dus à des conditions expérimentales variées (Bird and Ascough, 2012). En effet, les températures utilisées, le régime de carbonisation (pyrolyse ou combustion), l'espèce et le climat ainsi que la forme des échantillons étudiés sont autant de facteurs pouvant influencer l'impact de la carbonisation sur le 13 C des plantes (Ascough et al., 2008;Bird and Ascough, 2012). ...
Les charbons de bois trouvés en contexte archéologique permettent de reconstituer les couverts forestiers passés et les pratiques sylvicoles associées. Le δ13C de ces charbons a été utilisé pour des reconstructions paléoclimatiques, cependant ses variations peuvent aussi être dues à la carbonisation. Afin de mieux contraindre, à l’échelle du cerne, les variations du δ13C du bois dues à la carbonisation, des carbonisations ont été faites avec des échantillons de chêne cadicufoliés en conditions proches des foyers domestiques. Une diminution du δ13C après la carbonisation a été observée. Cet effet est très variable, notamment en fonction du compartiment du bois considéré (aubier, duramen, bois initial, bois final). Ces mesures de δ13C ont été complétées par celles du taux de carbone montrant qu’il ne varie pas parallèlement au δ13C. De ce fait l’utilisation, prônée par certains travaux, du taux de carbone pour évaluer les variations de d13C suite à la carbonisation n’est pas pertinente. Cependant, les variations cerne à cerne et intracerne du δ13C ne sont pas significativement affectées par la carbonisation, et des reconstructions climatiques à partir du δ13C de bois carbonisés paraissent donc envisageables. Afin de tester cette approche cerne à cerne, plusieurs charbons archéologiques issus du site Néolithique de Chalain, dont les paléoclimats étaient bien documentés, ont été échantillonnés. Cette approche a été couplée à des mesures dendro-anthracologiques (largeurs des cernes, proportion du bois final, rayon de courbure et proportion de vaisseaux avec des thylles) afin de mieux comprendre les variations de δ13C mesurées, et de tenter de les coupler aux pratiques sylvicoles. Les valeurs de δ13C sont en accord avec les paléoclimats déjà inférés et les variations intra-cerne, ou saisonnières, de δ13C révèlent que la période froide était caractérisée par des saisons plus contrastées. Les mesures dendro-anthracologiques ont permis, entre autres, de préciser les variations de δ13C entre les différents compartiments du bois et de proposer une interprétation concernant les variations des pratiques sylvicoles en lien avec le climat. En conclusion, la carbonisation oxygénée provoque un abaissement des valeurs de δ13C du bois mais n’empêche pas les reconstructions paléo-climatiques à partir de leurs variations, notamment saisonnières, mesurées sur des charbons archéologiques.
... The effects of charcoalification on the isotope composition of wood are not well documented in domestic open fireplaces. However, muffle furnace experimentations suggested that carbonization either (i) leads to no significant isotope effect, at least at moderate temperatures (i.e. up to 300e400 C; DeNiro and Hastorf, 1985;Turekian et al., 1998;Czimczik et al., 2002;Ascough et al., 2008) or (ii) tends to shift whole wood d 13 C values down to that of lignin, especially at temperatures higher than 500 C (Czimczik et al., 2002;Turney et al., 2006;Ferrio et al., 2006;Ascough et al., 2008). Above 500 C, carbonization thus eventually gives access to an isotope signal close to that of a single plant component (i.e. ...
... The effects of charcoalification on the isotope composition of wood are not well documented in domestic open fireplaces. However, muffle furnace experimentations suggested that carbonization either (i) leads to no significant isotope effect, at least at moderate temperatures (i.e. up to 300e400 C; DeNiro and Hastorf, 1985;Turekian et al., 1998;Czimczik et al., 2002;Ascough et al., 2008) or (ii) tends to shift whole wood d 13 C values down to that of lignin, especially at temperatures higher than 500 C (Czimczik et al., 2002;Turney et al., 2006;Ferrio et al., 2006;Ascough et al., 2008). Above 500 C, carbonization thus eventually gives access to an isotope signal close to that of a single plant component (i.e. ...
... Layers Ascough et al., 2008). The H D /H G ratio gives an estimation of the highest combustion temperature undergone by charcoals, as established for pine and poplar woods carbonized at various temperatures in a muffle furnace (Deldicque et al., 2016). ...
Charcoal fragments from the Neolithic settlements of Lake Chalain (Jura Mountains, France) were characterized by dendro-anthracology (charcoal-pith distance, tree-ring width, earlywood/latewood proportion) and ring-scale isotope geochemistry (¹³C) to assess the relevance of this combined approach for paleoclimate reconstructions. Two differing climatic periods were investigated: (i) a climatic deterioration period characterized by cool and moist conditions and (ii) a climatic improvement period characterized by slightly less precipitation and warmer temperature. Latewood proportion in charcoal tree-rings was similar for the two studied climatic periods. However, the charcoal tree-rings exhibited width and ¹³C-content significantly different between the two studied periods, in agreement with previously inferred climatic difference. Monitoring ring-to-ring ¹³C variation within each charcoal fragment revealed no noticeable climatic trend, for none of the studied periods. However, calculation of the difference in ¹³C-content between earlywood and latewood of a given tree-ring suggested that the cool and moist climatic period also corresponded to higher seasonal contrast than the dryer climatic period. Although this exploratory study needs further confirmation, it opens promising developments for paleoclimatic reconstructions based on the stable carbon isotope composition of archeological charcoals: the potential for recording subtle paleoclimatic variations and seasonal contrasts.
... Sin embargo, investigaciones previas advirtieron que las relaciones isotópicas en materiales vegetales de sitios arqueológicos sufren un fraccionamiento y desplazamiento producto de procesos de combustión y degradación [1][2]. En el caso de los carbones, estudios experimentales mostraron fraccionamientos debido al proceso de combustión, de magnitud variable dependiendo de la temperatura alcanzada y/o del oxigeno disponible en la combustión, entre las variables más relevantes [3][4][5][6][7][8]. Por su parte, los materiales vegetales sin combustionar se ven sometidos a procesos de degradación de los distintos componentes con composición isotópica diferente -por ejemplo: lignina, lípidos o celulosa -que afectan la composición isotópica de la muestra [2]. ...
... Por otra parte, el planteo del trabajo implica desprender expectativas de las tendencias de los fraccionamientos obtenidos en trabajos experimentales. Estos se realizaron a partir de la combustión de diversas partes de las plantas y el control de variables de relevancia como temperatura, combustión oxidante o reductora, tiempo de exposición, vía fotosintética, etc [3][4][5][6][7][8]. Los resultados de estos experimentos fueron variables y se compilaron en la Tabla 1, destacando la media, los rangos y la vía fotosintética de la planta. ...
... En primer lugar, la tendencia a un enriquecimiento en la comparación a escala regional y la inexistencia de diferencias en la muestra sin discriminar por regiones no condice con la mayoría de los trabajos experimentales. Estos, en su mayoría, tienden a un empobrecimiento de las señales isotópicas después del proceso de combustión [3][4][5][6][7][8]. No obstante, hay dos trabajos experimentales en la vía fotosintética C 3 que tienen un fraccionamiento en el que se enriquecen las relaciones isotópicas del carbono en las muestras combustionadas [3,5]. ...
El objetivo de este trabajo es evaluar la pertinencia de la utilización de las señales isotópicas del δ13C de materiales vegetales provenientes de sitios arqueológicos en reconstrucciones paleodietarias y paleoclimatológicas, estén éstos carbonizados o no. En el caso de los primeros, estudios experimentales mostraron fraccionamientos debido al proceso de combustión, de magnitud variable dependiendo de la temperatura alcanzada y oxígeno disponible en la combustión, entre las variables más relevantes. Por su parte, los materiales vegetales sin carbonizar sufren procesos de degradación de los distintos componentes que afectan su composición isotópica. El abordaje metodológico del problema se realiza a partir del cotejo de valores δ13C de plantas modernas y arqueológicas pertenecientes a distintas regiones de la Argentina. A partir de esta comparación, y considerando los fraccionamientos de los distintos tejidos de las plantas, se evaluarán las diferencias entre los valores δ13C de estos dos contextos y su comportamiento en relación a las expectativas de los estudios experimentales. Esta discusión tiene implicancias para la disciplina debido a la disponibilidad de valores δ13C de fechados radiocarbónicos realizados sobre vegetales, mayormente carbones, y permitirá evaluar hasta qué punto es posible utilizar esta información y cuáles son los recaudos necesarios al momento de utilizarlos en reconstrucciones paloeodietarias y paleoclimatológicas.
... Discrepancies in natural vs. experimental fire thermometry may also be perpetuated by variable environmental conditions, and the inter-and intraheterogeneity of fuels (Ishimaru et al., 2007a;Guedes et al., 2010). Furthermore, in the context of palaeowildfires, the nature of archaeological and geological records with regards to charcoal suggest considerable potential for alteration of wildfire evidence, through diagenetic processes such as humification and oxidation (Cohen-Ofri et al., 2006;Braadbaart et al., 2009;Ascough et al., 2008;Ascough et al., 2010;Ascough et al., 2011a;Ascough et al., 2018;Ascough et al., 2020;de Sousa et al., 2020;Smidt et al., 2020), and taphonomic bias (Scott and Damblon, 2010 and references therein). Such natural variability, particularly with regards to the influence of energy flux may bring into question the validity of historic assessments of palaeowildfire temperature. ...
... For charcoals held or deposited terrestrially, high aromaticity due to high temperatures of formation (e.g., Ascough et al., 2008), contributes not only toward microstructural maturation but subsequent increases in charcoal stability and resistance to oxidative degradation (Ascough et al., 2018;, growing increasingly susceptible with time and exposure (Ascough et al., 2011a;Ascough et al., 2020;Smidt et al., 2020), particularly in alkaline environments (Braadbaart et al., 2009;Ascough et al., 2011b). This suggests that low-temperature charcoals are in turn more susceptible to alteration, degradation, and preferential loss from the palaeofire record, including as a result of sample acquisition and analysis . ...
Charcoal geothermometry continues to offer considerable potential in the study of palaeowildfires over decadal, centennial, millennial, and deep time scales—with substantial implications for the understanding of modern wildfire intensification. Recent developments in the application of Raman spectroscopy to carbonaceous organic material have indicated its capability to potentially reconstruct the palaeocharcoal formation temperature, and equivalent palaeowildfire pyrolysis intensity. Charcoal reflectance geothermometry (which also relies upon microstructural change with thermal maturation) has also been the subject of extensive modern evaluation, with multiple studies highlighting the key influence of energy flux on the resultant charcoal microstructure. The ability to accurately quantify modern wildfire temperatures based upon novel Raman-charcoal analyses has not yet been attempted. Using Raman band width-ratios (i.e., FWHMRa) and accompanying geothermometric trends to natural wildfire charcoals, our results identify differences between microstructurally-derived fire temperatures compared to those recorded during the fire event itself. Subsequent assessments of wildfire energy flux over time indicate no dominant influence for the observed differences, due to the inherent complexity of natural fire systems. Further analysis within this study, regarding the influence of reference pyrolysis methodology on microstructural change, also highlights the difficulty of creating accurate post-fire temperature reconstructions. The application of Raman spectroscopy, however, to the quantification of relative changes in fire temperature continues to prove effective and insightful.
... Nilsson et al., 2001;Blaauw and Christen, 2005). The abundance of charcoal in the geologic record, coupled with its resistance to environmental degradation, has made it invaluable for dating terrestrial samples across Earth science and archaeological disciplines (Ascough et al., 2008(Ascough et al., , 2010. ...
... Charcoal is the residue from the incomplete combustion of plant material under reducing conditions (Ascough et al., 2008;Bird and Ascough, 2012), and is broadly considered chemically stable (e.g. Schmidt and Noack, 2000;Tomiyama et al., 2016). ...
Pyrogenic carbon (charcoal, black carbon, elemental carbon) is one of the most common materials used for radiocarbon dating of terrestrial samples. However, exogenous carbon contamination can compromise the accuracy of radiocarbon ages. This study presents the results of two chemical pretreatments prior to hydrogen pyrolysis (hypy) as improved protocols for the isolation and decontamination of pyrogenic carbon, i) a simple acid-oxidation step (A-Ox/hypy) and ii) acid-base-acid (ABA/hypy). The A-Ox/hypy protocol uses HNO3 and H2O2, while ABA/hypy uses HCl and NaOH. Both pretreatments remove labile and inorganic carbon before hypy, decreasing the potential for in situ production of pyrogenic carbon during the hypy reaction. The effectiveness of each protocol was directly measured on charcoal artificially produced at 350 °C, 450 °C and 550 °C from radiocarbon-free wood, and exposed to environmental contamination for 1–3 yrs. The results show a >94% reduction in carbon contamination for the 450 °C and 550 °C charcoal samples occurred using A-Ox/hypy, but this treatment was less effective for the 350 °C charcoal. A >99% reduction in carbon contamination in all charcoal samples examined occurred using ABA/hypy. The A-Ox/hypy protocol was further tested on cave guano sediments, which had previously reported erroneous dates following simple organic solvent extraction followed by ABA pretreatment. Effective decontamination was achieved using A-Ox/hypy on the guano, which corrected a radiocarbon age reversal. Overall, ABA/hypy effectively decontaminated the charcoals and was a more efficient pretreatment for charcoal than A-Ox/hypy, however resulting in larger sample mass loss. Therefore, ABA/hypy is the recommended protocol for older (>30,000 14C yr BP) charcoal or sediment samples, or where date accuracy is imperative, while A-Ox/hypy represents an improved protocol for the quick and cost-effective measurement of younger samples (<30,000 14C yr BP) when sample size is of concern
... Charcoals are a key component of the continuum of products that comprise the fire-derived organic matter pool, known as pyrogenic carbon (PyC) (Bird et al., 2015;Santín et al., 2016). The properties of charcoals relate not only to the nature of the fuel from which they are formed, but also to the characteristics of the fire that generated them (Ascough et al., 2008;McBeath et al., 2013;Michelotti and Miesel, 2015;Belcher and Hudspith, 2016;Hudspith et al., 2017b). These properties should also determine how different charcoals are then subsequently modified chemically and physically in the post fire environment (Harvey et al., 2012;Santín et al., 2017). ...
... This is achieved by embedding charcoal in resin, polishing the sample and studying the charcoal under oil in reflected light with a photometric measurement taken of the fraction of incident light radiation reflected from the samples surface (e.g., Belcher and Hudspith, 2016;Hudspith et al., 2017a). More highly reflecting chars ( Figure 1A) are thought to contain more stable, well organized graphite-like domains while lower reflecting chars ( Figure 1B) are characterized by a more complex disorganized phase containing a greater proportion of less stable aliphatic phases (Cohen-Ofri et al., 2006;Ascough et al., 2008). ...
Here, we explore how charcoal formation under different heating regimes and circumstances leads to chars of different physical properties. In order to do this, we have undertaken (1) carefully controlled laboratory experiments that replicate the different heating regimes that might be experienced during a wildfire and (2) two experimental wildfires where heat variations were monitored across the burn from which resulting charcoal has been studied. The charcoal properties were assessed using charcoal reflectance that measures the light reflected back from the charcoals structure and which links to changes in its structural properties. We find that increased total heat released during combustion positively correlates with increased charcoal reflectance and that this is evidenced from both our laboratory experiments and experimental wildfires. Charcoals that related to lower total heat release were found to have more lignin remaining than those subjected to greater heating indicating that charcoals formed in lower energy regimes are likely to be more susceptible to post-fire degradation. We conclude that charcoal reflectance may make a useful metric with which to determine the distribution of energy delivery across a burned area and that this may be utilized to inform both variations in fire severity and enable the prediction of long-term C budgeting for different types of wildfire.
... For Nothofagus spp. wood, S. officinarum bagasse, and BEST biochar before environmental exposure, %C, concentrations clearly increased and %O and %H concentrations decreased as production temperature increased (Table 1), consistent with previous work (e.g., Ascough et al., 2008). C. vagabunda algae is different; although O is progressively lost at higher production temperatures, C and H show little change with production temperature after 300 • C. ...
... Production temperature is known to dictate the aromaticity of biochar/PyC, and determine the extent to which non-aromatic material (including oxygen and hydrogen) is removed from the sample (e.g., Ascough et al., 2008;Krull et al., 2009). A finding from this research, however, is that lignocellulosic and non-lignocellulosic biomasses have very different trajectories of chemical change during pyrolysis. ...
Pyrogenic carbon (PyC) is a polyaromatic residue of the incomplete combustion of biomass or fossil fuels. There is a growing recognition that PyC forms an important part of carbon budgets, due to production rates of 116–385 Tg C yr, and the size and ubiquity of PyC stocks in global carbon reservoirs. At least a proportion of PyC exists in a highly recalcitrant chemical form, raising the prospect of long-term carbon sequestration through soil amendment with “biochar,” which is generally produced with the aim of making a particularly recalcitrant form of PyC. However, there is growing evidence that some PyC, including biochar, can be both physically and chemically altered and degraded upon exposure to the environment over annual timescales, yet there is a lack of information concerning the mechanisms and determining factors of degradation. Here, we investigate three main factors; production temperature, feedstock composition, and the characteristics of the environment to which the material is exposed (e.g., pH, organic matter composition, oxygen availability) by analysis of biochar samples in a litterbag experiment before and after a year-long field study in the tropical rainforests of northeast Australia. We find that non-lignocellulosic feedstock has lower aromaticity, plus lower O/C and H/C ratios for a given temperature, and consequently lower carbon sequestration potential. The rate at which samples are altered is production temperature-dependant; however even in the highest temperature samples loss of the semi-labile aromatic carbon component is observed over 1 year. The results of ¹³C-MAS-NMR measurements suggest that direct oxygenation of aromatic structures may be even more important than carboxylation in environmental alteration of biochar (as a subset of PyC). There is a clear effect of depositional environment on biochar alteration even after the relatively short timescale of this study, as changes are most extensive in the most oxygenated material that was exposed on the soil surface. This is most likely the result of mineral ingress and colonization by soil microbiota. Consequently, oxygen availability and physical or chemical protection from sunlight and/or rainwater is vital in determining the alteration trajectory of this material.
... The oldest sample (2,355 ysf) has the highest proportion of aryl C (71%) and aromaticity (0.79). The CP spectra underestimate aromatic C without attached hydrogens; this effect is more important for samples high in O and di-Oalkyl C including carbohydrate but becomes less important as the proportion of aromatic C increases (Baldock and Smernik, 2002;Czimczik et al., 2002;Ascough et al., 2008;McBeath et al., 2011;Preston, 2014;Preston et al., 2014a,b). Our spectra indicate a trend to higher aromaticity with increasing ysf (not shown), but obviously, the low sample size, especially at higher ysf and the qualitative aspect of the NMR areas does not allow us to establish statistical inference. ...
... NMR Similar to C and N values determined on a larger sample set, the nine NMR spectra obtained show a wide variation in appearance and intensity distribution for the younger samples, whereas the oldest samples generally have higher aromaticity and simpler features, with greater dominance of the aryl C signal around 130 ppm. These structural variations are consistent with observations of increasing aromaticity with temperature in laboratory charring studies (Baldock and Smernik, 2002;Czimczik et al., 2002;Ascough et al., 2008;Soucémarianadin et al., 2013;Hart and Luckai, 2014). Organic horizon/biomass char produced in field settings (wildfire or prescribed fire) also shows a range of intensity distributions depending on fire severity, from little alteration to high aromaticity (Nocentini et al., 2010;Miesel et al., 2015;Soucémarianadin et al., 2015b). ...
Wildfires are a major driver of carbon stocks and ecosystem development in Canadian boreal forests, but there is little information on amounts and properties of the charcoal produced. Using data and samples available from a previous study, we determined amounts, depth distribution and chemical properties of visually-determined charcoal (>2 mm) in a boreal chronosequence in the Abitibi region of Quebec, Canada. Sites ranged from 24 to 2,355 years since fire (ysf) and originated from low- and high-severity soil burns (>5 or <5 cm organic horizon unburned, respectively). Two or three pits were sampled at 1-cm depth intervals from 20 jack pine (Pinus banksiana) sites (one low severity and 19 high severity) and 31 black spruce (Picea mariana) sites (12 low severity and 19 high severity). Site-level charcoal stocks ranged from 50 to 5,527 kg ha⁻¹ with high within-site variability and lower stocks for the oldest sites. Depth distributions typically peaked around the organic-mineral interface, but some low-severity sites also had charcoal layers within the organic horizon. Means from 30 charcoal samples were 569 mg g⁻¹ total C, 4.1 mg g⁻¹ total N and 140 C/N (molar), with total C and C/N showing a trend of decline with time since fire, and total N showing an increase. Solid-state ¹³C CPMAS NMR spectra of nine samples showed high variability among the younger samples, but a trend to higher aromaticity for the older ones. A literature survey focusing on boreal forests similarly showed highly variable stocks and chemical properties of charcoal in organic horizon and upper mineral soil, with reduction of variance and lower stocks after several hundred years. This initial variation was also consistent with reports of highly variable temperatures and duration of charring in wildfires. Adding reports available for char production, and considering that most studies of char stocks and production are limited to the organic horizon (forest floor), suggests that initial production of charred material from boreal wildfires might be around 5–10 tons ha⁻¹.
... Evidence of changes in pollen assemblages following these fire events indicates that they indeed represent burning within the pollen and charcoal source areas of Silver Lake ( Figure S6). The only distinct change in biogeochemical proxies after these fires was an initial decrease in δ 13 C (Figure 6), which may simply reflect the influx of charcoal itself, given that partial combustion can deplete wood δ 13 C by up to 1.6‰ (Ascough et al., 2008). ...
Wildfires strongly influence forest ecosystem processes, including carbon and nutrient cycling, and vegetation dynamics. As fire activity increases under changing climate conditions, the ecological and biogeochemical resilience of many forest ecosystems remains unknown.
To investigate the resilience of forest ecosystems to changing climate and wildfire activity over decades to millennia, we developed a 4800‐year high‐resolution lake‐sediment record from Silver Lake, Montana, USA (47.360° N, 115.566° W). Charcoal particles, pollen grains, element concentrations and stable isotopes of C and N serve as proxies of past changes in fire, vegetation and ecosystem processes such as nitrogen cycling and soil erosion, within a small subalpine forest watershed. A published lake‐level history from Silver Lake provides a local record of palaeohydrology.
A trend towards increased effective moisture over the late Holocene coincided with a distinct shift in the pollen assemblage c. 1900 yr BP, resulting from increased subalpine conifer abundance. Fire activity, inferred from peaks in macroscopic charcoal, decreased significantly after 1900 yr BP, from one fire event every 126 yr (83–184 yr, 95% CI) from 4800 to 1900 yr BP, to one event every 223 yr (175–280 yr) from 1900 yr BP to present.
Across the record, individual fire events were followed by two distinct decadal‐scale biogeochemical responses, reflecting differences in ecosystem impacts of fires on watershed processes. These distinct biogeochemical responses were interpreted as reflecting fire severity, highlighting (i) erosion, likely from large or high‐severity fires, and (ii) nutrient transfers and enhanced within‐lake productivity, likely from lower severity or patchier fires. Biogeochemical and vegetation proxies returned to pre‐fire values within decades regardless of the nature of fire effects.
Synthesis. Palaeorecords of fire and ecosystem responses provide a novel view revealing past variability in fire effects, analogous to spatial variability in fire severity observed within contemporary wildfires. Overall, the palaeorecord highlights ecosystem resilience to fire across long‐term variability in climate and fire activity. Higher fire frequencies in past millennia relative to the 20th and 21st century suggest that northern Rocky Mountain subalpine ecosystems could remain resilient to future increases in fire activity, provided continued ecosystem recovery within decades.
... For grains, the magnitude of the isotopic difference between charred and uncharred grains depends on the stable isotope compositions of the original biochemical components (e.g. lipids, carbohydrates and proteins) and on how the length and level of heating affects such components (Ascough et al., 2008(Ascough et al., , 2010Czimczik et al., 2002). For example, lipids and other volatiles such as water are lost at moderately low temperatures (<150 • C) (Czimczik et al., 2002). ...
... The literature data in these figures include CO (Kato et al., 1999), CO 2 Umezawa et al., 2011), CH 4 (Chanton et al., 2000;Snover et al., 2000;Stevens and Engelkemeir, 1988;Umezawa et al., 2011;Yamada et al., 2006), OC Cachier et al., 1985;Czimczik et al., 2002;Garbaras et al., 2015;Turekian et al., 1998), EC (Das et al., 2010;G. Liu et al., 2014), and char (Ascough et al., 2008;Bird and Gröcke, 1997;Czimczik et al., 2002;Das et al., 2010;Jones and Chaloner, 1991;Leavitt et al., 1982;G. Liu et al., 2014;Poole et al., 2002;Purakayastha et al., 2016;Turekian et al., 1998). ...
Landscape fires are a significant contributor to atmospheric burdens of greenhouse gases and aerosols. Although many studies have looked at biomass burning products and their fate in the atmosphere, estimating and tracing atmospheric pollution from landscape fires based on atmospheric measurements are challenging due to the large variability in fuel composition and burning conditions. Stable carbon isotopes in biomass burning (BB) emissions can be used to trace the contribution of C3 plants (e.g. trees or shrubs) and C4 plants (e.g. savanna grasses) to various combustion products. However, there are still many uncertainties regarding changes in isotopic composition (also known as fractionation) of the emitted carbon compared to the burnt fuel during the pyrolysis and combustion processes. To study BB isotope fractionation, we performed a series of laboratory fire experiments in which we burned pure C3 and C4 plants as well as mixtures of the two. Using isotope ratio mass spectrometry (IRMS), we measured stable carbon isotope signatures in the pre-fire fuels and post-fire residual char, as well as in the CO2, CO, CH4, organic carbon (OC), and elemental carbon (EC) emissions, which together constitute over 98 % of the post-fire carbon. Our laboratory tests indicated substantial isotopic fractionation in combustion products compared to the fuel, which varied between the measured fire products. CO2, EC, and residual char were the most reliable tracers of the fuel 13C signature. CO in particular showed a distinct dependence on burning conditions; flaming emissions were enriched in 13C compared to smouldering combustion emissions. For CH4 and OC, the fractionation was the other way round for C3 emissions (13C-enriched) and C4 emissions (13C-depleted). This indicates that while it is possible to distinguish between fires that were dominated by either C3 or C4 fuels using these tracers, it is more complicated to quantify their relative contribution to a mixed-fuel fire based on the δ13C signature of emissions. Besides laboratory experiments, we sampled gases and carbonaceous aerosols from prescribed fires in the Niassa Special Reserve (NSR) in Mozambique, using an unmanned aerial system (UAS)-mounted sampling set-up. We also provided a range of C3:C4 contributions to the fuel and measured the fuel isotopic signatures. While both OC and EC were useful tracers of the C3-to-C4 fuel ratio in mixed fires in the lab, we found particularly OC to be depleted compared to the calculated fuel signal in the field experiments. This suggests that either our fuel measurements were incomprehensive and underestimated the C3:C4 ratio in the field or other processes caused this depletion. Although additional field measurements are needed, our results indicate that C3-vs.-C4 source ratio estimation is possible with most BB products, albeit with varying uncertainty ranges.
... This raises the question of the cellulose preservation during fire and the classical protocol adaptation in this specific context. Cellulose decomposition is observed from 280 °C up to the complete destruction at 400 °C [13][14][15] . What will be the state of cellulose in the cathedral's woods when temperatures higher than 500 °C, or even 1300 °C were reached during the fire [16] , even if a temperature gradient has to be expected in wood? ...
Notre-Dame de Paris, the so famous Catholic cathedral standing on Ile de la Cité in Paris, was partially destroyed by fire on April 15 of 2019. This unfortunate destruction miraculously spared a part of the frame and made these woods accessible to the scientific community. As scientists particularly interested in the isotopic composition of wood as memory of past climate and as a clock to the past, we will take advantage of this tragedy and give new life to the Notre Dame woods. In the context of a programmatic action, the δ¹³C and δ¹⁸O chronologies will open a window on the climate of the Middle Ages. They will allow rekindling the debate on the geographical extension of the MWP and, therefore, on its origin. The ¹⁴C record, at a yearly resolution, is expected to be implemented in the next ¹⁴C calibration curve and to be used to document past changes in ¹⁴C production resulting either from changes in solar activity or supernovae.
... Once the combustion ends, charcoal pieces conserve plant anatomy, and they are considered as chemically inert and therefore resistant to decay (Scott and Jones 1991;Nichols et al. 2000;Scott and Glasspool 2007). However, charcoal is not a pure form of carbon, and it might be affected by diagenetic alterations (Smernik et al. 2000;Antal and Gronli 2003;Cohen-Ofri et al. 2006;Ascough et al. 2008). The final product of combustion is a mix of charcoal pieces, fragments, microfragments, and particles, but also of ash and soot. ...
The recovery of archaeological wood charcoals from combustion features provides insights into the exploitation and use of wood fuel resources and past landscapes. The quality of our interpretation based on wood charcoals, however, depends on reliable information about the charcoal assemblages resulting from taphonomy. Charcoal is very fragile in comparison to other combustion residues such as burnt bones. In archaeological contexts, charcoal can easily be fragmented into small pieces (<0.25 mm) due to their fragile property. The investigation of small fragments and particles is particularly important for the interpretation of combustion residues when large pieces of charcoal are rare or apparently absent in archaeological sites, which is mainly true for many European Palaeolithic sites. Here, archaeologists get incomplete information when only the largest pieces and fragments are considered. In this chapter, we present a method for extracting and quantifying charcoal pieces, fragments, and particles. This approach can be considered as a strategy to minimize the impact of sample incompleteness and biases related to combustion residues in archaeological contexts. We further provide (1) a definition of what the charcoal signal means in an archaeological context; (2) an overview of taphonomy that causes charcoal fragmentation; (3) a review of charcoal sampling, extraction, observation and quantification protocols; (4) a manual (pictures and descriptions) for the observation of charcoal, from large pieces to the smallest particles; and (5) a discussion about why the charcoal signal is useful for archaeologists. By taking into account the consequences of taphonomy, the microscopic charcoal analysis in archaeological contexts provides a reliable assessment of firewood and fuel management practices and the related resilience of societies through time. The microscopic charcoal analysis can further offer additional information about the intensity of taphonomical processes and dating.
... Samples of wood of Eucalyptus spp., Quercus robur and Pinus radiata were subjected to the charring temperature range 200-800°C (ref.31). Similarly, pine and mangrove wood were also subjected to the temperature range 300-600°C during charring32 . To examine the effect of time bound shift in isotopic composition at different charring temperatures irrespective of the different protocols used for conducting charring process involving different plant parts, we introduced a normalization scheme where deviation from the original composition at a particular temperature was estimated and defined as Δ 13 C (difference between the original and final δ 13 C value). ...
Rice cultivation over Asia has several thousand years
of history. Adequate water availability is a prime factor
for the cultivation of rice in this region. The
remains of rice at the archaeological sites, therefore,
provide an indirect clue on rainfall in this region. The
stable isotopic compositions in remains of rice grains
allow estimation of rainfall condition during rice cultivation.
Often, such remains found at the archaeological
sites suffer from the process of charring, which is
likely to modify the original isotopic signature. Here,
we performed charring experiments on rice grains at
two different temperatures, i.e. 230°C and 250°C and
documented the changes in the morphology and carbon
isotopic composition (δ13C). A noticeable morphological
shift was registered in the samples with
progressive duration and temperature of charring.
Further, cellulose was extracted and analysed for
δ13C. Our results showed that the shift in δ13C
observed for charred rice was relatively lower as
compared to that observed in other cereals.
... One early focus of biochar studies was on the anthropic soil of the Amazon forest known as "Indian Black Earth," which is found in open-air archaeological sites with human occupation dating between 800 and 2000 years before the present (BP) [9][10][11][12]. Despite the numerous studies on biochar, its stability and dynamics in the environment have yet to be fully elucidated, and this question has been examined and discussed for decades [13][14][15][16][17]. Previous researchers clarified that a higher burning temperature produces biochar with higher polyaromatic structures and larger crystallite size. ...
The presence of biochar with high carbon accumulation capacity and nutrient adsorption is causally associated with archeological soils. Although this type of soil organic matter has been known for a long time, the knowledge of its structure and environmental behavior is still limited. This work used Raman spectroscopy to obtain structural information and identify alterations in biochar particles. To this end, we studied biochar particles found in an archaeological site with a temporal window lasting 12451 to 11080 yr cal BP. The molecular, structural and sp2/sp3 characteristics of the charcoal particles were determined at the time of burning and associated with the temperature, time and characteristics of the burnt material. We propose that the process of oxidation of the biochar occurs during the first 2000 years after its genesis. The oxidation process is a reflection of decreases in the number of defects related to sp2 bonds on amorphous carbons and increases in the number of defects associated with ionic impurities, which clearly indicate the interaction between biochar particles and the soil matrix. The data confirm the hypothesis that the persistence of biochar in the environment is due to its graphite structure and suggest that over a 12000 year timeframe, biochar particles undergo several changes that occur in the disordered phase and are rapidly oxidized.
... The influence of heating regimes and plant species on structural and compositional changes of biosourced materials are now well studied (Ascough et al., 2008;Michelotti and Miesel, 2015;Belcher et al., 2018;Hudspith and Belcher, 2017;Santín et al., 2017). Chars with vitreous structure are identified to have suffered plastic deformation with clear signs of melting and development of macropores caused by emission of large quantities of volatiles under high heating-rate (Fisher et al., 2012;Kurosaki et al., 2003;Lester et al., 2018;Trubetskaya et al., 2015). ...
Anthracological research has not yet elucidated wood vitrification ranging from partial fusion of the cell structure to a dense vesicular glass which has been so far not experimentally reproduced. We have proposed previously that vitrification would trace wood flash-pyrolysis induced by aeroplasma and lightning due to the production of ionized aerosols in the atmosphere and their accumulation in the tissues during the tree growth.
Here we further explore the factors involved in vitrification by flash-pyrolysis, in terms of firing processes, heating rates and wood composition. Our study promotes the challenging potential of vitreous chars and related by-products in archaeological firing assemblages to explore the link between atmospheric conditions, fuel properties and heating processes which has never been so far debated.
Our study is based on the comparison of firing-assemblages from diverse archaeological contexts and the ones from solar reactor experiments as well as present-day firing situations. We focus on the characteristics of charcoals showing different stages of vitrification and on the tightly associated polymeric compounds. Their in situ structure characterization and composition are performed at meso to nanoscale with the SEM-EDS in backscattered mode and completed by TEM, Raman spectrometry and XRD analyses.
Biomass thermochemical conversion for gas production provides a solid knowledge to understand that the extreme vitrification of wood fuel can only be induced by flash-pyrolysis. This process is shown to involve depolymerisation of wood tissues and reformation of diverse carbonaceous solid phases, along to degassing of the most volatile compounds. Wood vitrification due to flash-pyrolysis can thus be traced by a continuum of pyrolytic residues formed of lamellar to vesicular charcoals, black carbon aggregates, polymerised plant fragments, polymer films and filaments and densely recrystallized ash.
We establish the key influence of non-condensable gas with metal and mineral impurities of high electrical conductivity that were incorporated within the plant tissues on the characteristics of the solid residues formed by flash-pyrolysis and on their properties. The pyrolytic debris share in common a nanostructuration, an imbrication at nanoscale of mineral and carbonaceous phases and nanostructured metal films.
Using the record of present-day lightning-strikes, we describe the assemblage of pyrolytic debris and their characteristics to trace primary flash-pyrolysis that is instantaneously produced by the sudden release of incondensable gases and segregation of impurities. We show the difference of pyrolytic debris formed by a secondary flash-pyrolysis that can be locally achieved in long-maintained high temperature heating due to enhanced concentrations of non-condensable gases in confined pores.
The characteristics of the strongly vitrified chars with the associated pyrolytic debris of the archaeological firing assemblages match the ones of primary flash-pyrolysis, but not the ones of lightning-strikes. Instead, we propose that they would have formed under periods marked by enhanced atmospheric electrification and production of electrically charged aerosols.
Our observations emphasize the key-role of graphitized nanocarbons with their bound catalytic metals from possible volcanic sources on the initiation of flash-pyrolysis in air or at the ground and on the long-term protection of the produced pyrolytic residues.
... However, the enrichment of PyC in sediments from the higher burn severity sites may also be due to differences in overall PyC production and interrelated differences in erosion properties in sites experiencing different burn severities. Other research has demonstrated that temperature exhibits a significant control on the properties of PyC, including hydrophobicity, specific surface area, C and N concentration, hydrophobicity, and density, among other properties (Ascough et al., 2008;Mimmo et al., 2014;Santín et al., 2017). These properties likely led to the enhanced erosion of PyC in the high burn severity sites, and depressed erosion of PyC in the moderate burn severity sites. ...
Pyrogenic carbon (PyC) is an incomplete combustion by‐product with longer soil residence times compared with nonpyrogenic components of the soil carbon (C) pool and can be preferentially eroded in fire‐affected landscapes. To investigate geomorphic and fire‐related controls on PyC erosion, sediment fences were established in three combinations of slope (high 13.9–37.3%; moderate 0–6.7%) and burn severity (high; moderate) plots within the perimeter of the Rim Fire in 2013, Yosemite National Park, California, USA. After each major precipitation event following the fire, we determined transport rates of total sediment, fine and coarse sediment fractions, and C and nitrogen (N). We measured stable isotope (δ¹³C and δ¹⁵N) compositions and ¹³C‐nuclear magnetic resonance spectra of soils and eroded sediments. The highest total and fine (<2 mm) sediment transport in high severity burned areas correlated with initial discharge peaks from an adjacent stream, while moderate burn severity sites had considerably more of the >2 mm fraction transported than high burn severity sites. The δ¹³C and δ¹⁵N values and ¹³C‐nuclear magnetic resonance analyses indicated that sediment eroded from moderate severity burn areas included fresh organic matter that was not as significantly affected by the fire, whereas sediments from high severity burn areas were preferentially enriched in PyC. Our results indicate that along a single hillslope after the Rim Fire, burn severity acted as a primary control on PyC transport postfire, with slope angle likely playing a secondary role. The preferential erosion of PyC has major implications for the long‐term persistence of PyC within the soil system.
... One series was high-temperature degassing in which samples were degassed at 350°C for 3 h. This temperature usually is the volatile loss of carbon [28]. The other series was water washing. ...
The specific surface area (SSA) of fly ash has a significant effect on its pozzolanic reactivity and on the performance of fly ash-blended concrete. Because fly ash contains a considerable amount of irregularly shaped particles and unburned carbon, determination of an accurate SSA is analytically troublesome by conventional methods. Various methods for determining the SSA of fly ash are evaluated and compared in this study, including Blaine air permeability, nitrogen absorption testing, laser diffraction testing and image analysis. The experimental results show that Blaine air permeability and laser diffraction testing tend to underestimate the SSA of fly ash because they involve the assumption of perfectly spherical particle geometry. The SSA determined by nitrogen absorption testing is found to be associated with a significant overestimation induced by unburned carbon. Image analysis coupled with BSE appears to give consistent results and appears to be the most promising method of determining an accurate value for absolute SSA.
... While the stable carbon isotopic compositions of n-C 21 -n-C 25 odd n-alkanes in fresh leaves was enriched in 13 C (average -32.0‰), those from branches and twigs were depleted (average bark -33.6‰ and -34.4‰ respectively; average xylem: -32.7‰ and -30.9‰) ( Table 2 and Fig. 3). Since leaves and wood differ in their chemical composition (e.g., lipids, lignin, cellulose, hemicellulose, sucrose) d 13 C bulk values of these parts can differ by 2-3‰ (Ascough et al., 2008). The 13 C depletion of bulk wood compared to leaves can mainly be explained by its higher lignin content (depleted in 13 C) and lower cellulose content (enriched in 13 C) (Ehleringer et al., 2000). ...
Leaf waxes have been assumed to be the dominant source of wax delivered to sediment. However, wooden branches and twigs have not been widely considered in this context and could be a potential source of wax lipids in fire places or combustion structures. Black sedimentary layers are the main material of open-air archaeological combustion structures and represent either carbonized fuel (wood) or the charred ground beneath the fire (mainly leaves) and it is difficult to discern between the two sources. To identify different plant parts as components of combustion residues, fresh and charred leaves, branches and twigs (bark and xylem) of the Celtis australis tree were analyzed for aliphatic and aromatic hydrocarbons and fatty acid concentrations, as well as the carbon isotopic composition of n-alkanes (δ13Calkane). Charred biomass was produced under limited oxygen conditions at 150, 250 (3 and 5 h), 350 and 450 °C for 1 h. The n-alkyl profiles in different parts of C. australis are sufficiently distinct to allow their identification as components of combustion structures under low combustion temperature conditions. Average chain lengths and carbon preference index ratios decrease with increasing temperature and vary among plant parts. The δ13Calkane values remained slightly unaltered up to 350 °C and changed by 3–4‰ at 450 °C. Our results provide new information on the molecular and isotopic changes that occur upon burning different plant parts, which in turn show potential for good preservation of organic matter in archaeological black layers and for positive identification of burned leaf and wood residues in them.
... Although initial wood composition controls the dynamics of PyOM formation (Ascough et al. 2008;McBeath et al. 2014;Soucémarianadin et al. 2013), how these dynamics differ between gymnosperm and angiosperm species remains unclear. This work focuses on jack pine (JP; Pinus banksania) and red maple (RM; Acer rubrum) as representative gymnosperm and angiosperm tree species. ...
Few studies have quantitatively assessed the interacting controls of taxa-specific properties and PyOM production temperature on native soil C (NSC) stabilization/de-stabilization dynamics (i.e. priming effects - PE) because of difficulty in distinctly assessing NSC reactivity apart from added PyOM-C. To quantify PyOM-induced PE, we incubated ¹³C-enriched jack pine (JP) or red maple (RM) wood and associated ¹³C-PyOM produced at 200 (PyOM200), 300 (PyOM300), 450 (PyOM450) and 600 (PyOM600) °C in soil from a northern temperate forest (Michigan, U.S.A.) for 10 months. We found that (1) net PE was negative with addition of both wood and PyOM from both taxa, with a 3–40% suppression in mineralization across treatments, (2) RM200, RM450, and RM600 exhibited initial positive PE in the first week of incubation, (3) PyOM300 of both taxa, the temperature associated with initial aromatization and carbohydrate conversion, induced the most negative PE and exhibited the largest increase in soil oxidative enzyme activity in JP300, (4) addition of sucrose to the incubations as labile C, offset negative PE in JP treatments but not in RM treatments and, (5) mean residence times of the fast cycling C pool of NSC were lower (1.4–1.6 d) for RM than for JP (2.9–8.3 d) additions. These results suggest that future changes in tree taxa dominance in fire prone systems could alter soil C stability though introduction of PyOM of distinct, taxa-specific, chemical properties that may be largely controlled by taxa specific temperature thresholds in thermochemical conversion of woody tissues to PyOM.
... Depending on the concentrations, PyC potentially can be analyzed for isotopes of carbon ( 13 C/ 12 C or 14 C), oxygen ( . Stable carbon ( 13 C/ 12 C) isotopic analysis have been used to either trace shifts of vegetation with measurements of 13 C concentrations because certain plants differ in their photosynthetic pathways (C3, C4, CAM) or to study the interaction and degradation of PyC in the environment (Ascough et al. 2008) with artificially enriched (labeled) 13 C concentrations (Zhou et al. 2017, Singh et al. 2014. The stable isotopes of oxygen ( 18 O/ 16 O) and hydrogen ( 2 H/ 1 H) allow the reconstruction of past climate factors at the time of formation as well as they may help to assess dynamics of PyC degradation . ...
Fire is a combustion process and as such has been an integral driver of the natural biogeochemical cycles on our planet Earth since its first occurrence about four hundred million years ago. Humans have interacted with fire for thousands of years, yet industrialization and with it the accompanied utilization of fossil fuels marked the beginning of a new epoch, the Anthropocene. Combustion processes are incomplete and cause the formation of pyrogenic carbon (PyC). The term describes a continuum of condensed aromatic structures originating from biomass burning and fossil fuel combustion. They are ubiquitous in the environment.
The scope of this thesis was to reconstruct combustion history from environmental archives foremost aquatic sediments of the northeastern United States (U.S.) from the preindustrial era and throughout industrialization until the early 2000s. A sedimentary sequence in high temporal resolution facilitated the development and the comparison of quantitative PyC records in high temporal resolution. The results showed that sediments chronicle different modes of PyC production: condensation products and residuals of pyrolysis and their temporal trends are clearly decoupled. To decipher the origins of combustion products, isotopic records
of radiocarbon (14C) measurements facilitated source apportionment to either biomass burning or fossil fuel combustion. A comprehensive error analysis was carried out for the specific markers of combustion residues, benzene polycarboxylic acids (BPCAs), aiming at yielding robust molecular 14C data. Triplicate measurements of BPCAs 14C on four standard reference materials provided new benchmark 14C values on these environmental samples. Temporal 14C records for BPCAs and the precursors of combustion condensates, polycyclic aromatic
hydrocarbons (PAHs), allowed for unravelling the origins and the transport trajectory of sedimentary PyC from a sub-urban and a remote catchment in the U.S. The majority of PyC stems from local sources and is supplied to ‘ultimate’ sites of burial on different time scales: decadal and millennial. Whereas a small portion stems from contemporary sources, the majority of PyC entails a time lag because it was retained in catchment soils and underwent temporary storage before deposition. Additionally, BPCAs (soot) and PAHs (precursors of soot) trace
fossil fuel-derived PyC and both coincide with historical records on the consumption of fossil fuels in U.S. yet never account for more than 19 % of total PyC.
In this thesis it could be shown that sedimentary profiles chronicle combustion history on local and regional scale and it is necessary to use complementary approaches coupled with qualitative measures such as 14C to unambiguously allocate sources of PyC in the Anthropocene. With the onset of industrialization, long-range atmospheric transport and deposition started to supply fossil fuel-derived PyC to sub-urban and remote (pristine) locations. The temporal resolution of sedimentary sequences thus facilitate the reconstruction of past combustion practices to elucidate the human impact on natural biogeochemical cycles in the modern environment.
... While some authors have reported that δ 13 C values do not change from the original biomass values [11], others have reported a moderate decrease [12,13] or increase [15,16]. The wide variability of results indicates the complexity of the process, since many factors (carbonization temperature and time, aerobic or anaerobic conditions, pH, and initial biomass composition, etc.) can influence the δ 13 C preservation potential [17]. Understanding the stable carbon isotope systematics is important during thermal treatment of biomass, especially when HCs are applied for soil amendment. ...
This work studied the changes of stable isotope compositions (C and N) of diverse biomass feedstocks (loblolly pine, cow manure, and sewage biosolids) as a result of hydrothermal carbonization (HTC), and provides insight into degradation pathways based on these changes. HTC was conducted at different times (5 and 30 min) and temperatures (180, 220, and 260 °C) and produced hydrochars were characterized in terms of ultimate, proximate, stable carbon isotope (δ¹³C), and stable nitrogen isotope (δ¹⁵N) compositions. In addition to reaction conditions, results showed that the differences in feedstock composition, closely related to reactivity, determined in large part isotope behavior. In general, the carbon densification associated with HTC corresponded to a small but consistent decrease of δ¹³C values. In contrast, there were significant increases of δ¹⁵N values during HTC, with larger shifts associated with increased HTC reaction severity. These trends in isotopic compositions, related to changes of characteristic elemental indices (O/C, H/C, O/N, H/N), allowed for the identification of particular reaction pathways for individual feedstocks.
... It seems that, in the present experiment, the above-mentioned change happened at 200°C/4 h and also at 400°C/2 h (though, as noted, the specimens from Kragujevac likely lost some of the moisture through drying prior to charring). Another process recognised for wood, but when experimentally heated to high temperature (>300°C), is the loss of cellulosea component isotopically heavy relative to the total contentwhich leads to overall 13 C depletion [56,57], see also [58,59]. Here, the more negative δ 13 C values in specimens heated at 400°C/4 h perhaps reflect a similar process (i.e. ...
The carbon stable isotope content of Cornelian cherry stones collected from wild tree stands in Serbia, SE Europe, was measured using elemental analyser-isotope ratio mass spectrometry, with the aim of recording natural carbon isotope composition of the fruit stones and its possible variation. The results show a significant variation in the carbon isotope values; we identified several environmental factors that, along with a number of other possible determinants, likely contributed to this variation. The obtained data are compared with the measurement of carbon isotope content of an archaeological specimen of Cornelian cherry stone discovered at the Neolithic site of Vinča (ca. 5600–4500 BC) in Serbia. Notwithstanding the limitedness of the data and the complexity surrounding carbon fractionation and the isotopic variation, it is suggested that the differences/similarities in carbon isotope ratios between modern and archaeological Cornelian cherry stones, when measured for much larger assemblages, could potentially offer a glimpse into growing conditions of Cornelian cherry trees in the past.
*** https://www.tandfonline.com/eprint/4IwXA8Yk6iWKX7TEGRXU/full ***
... A high pyrolysis temperature (550°C) destroys aliphatic alkyl and ester carbon groups (Fig. S2). It is noteworthy that increasing pyrolysis temperature of pine sawdust biomass increased the aromaticity of BC550 to a higher extend than BC300 (Ascough et al., 2008;Baldock and Smernik, 2002;Krull et al., 2009;McBeath et al., 2011;Nguyen et al., 2010). Increasing BC pyrolysis temperature led to a decrease in oxygenated and unsaturated alkyl functional groups and increase the aromatic structures (Czimczik et al., 2002;David et al., 2008;McBeath et al., 2014). ...
To date, no investigation has been carried out to explore the effects of biochars produced at different pyrolysis temperatures on the dynamics of redox potential (EH) and pH in a contaminated floodplain soil. Thus, we aimed to quantify the dynamics of EH and pH in contaminated flooded soils treated with 70 t ha-1 of pine sawdust biomass (S&BM) and biochars pyrolyzed at 300 ºC (S&BC300) and 550 ºC (S&BC550) and pre-incubated for 105 days in an automated biogeochemical microcosm system. Microbial community composition was also determined via phospholipid fatty acid (PLFA).We found that BC300 and BC550 treatments substantially decreased (3–6.5%) and BM increased (~ 37%) the mean of soil EH compared to the untreated contaminated soil (CS).The largest EH decline in S&BC550 was at the rate of -80 mV h-1 at 10 hours while it was observed at 25 hours in S&BC300 and 20–25 hours in S&BM or CS, respectively. At high EH, a higher total PLFA biomass and microbial groups in the CS (71– 87%) were found in comparison to treated soils. Higher aromaticity and ash content in BC550 than BC300 and BM led to the greater PLFA biomass and microbial groups which contributed to higher capacity of accepting and donating electrons in soil slurry and were probably one reason for the largest decrease in EH. Pine sawdust biomass and BCs have a noticeable influence in soil biogeochemical processes relevant to fluctuating redox conditions.
... The existence of old, biochar-abundant Terra Preta in the Amazon (Glaser et al., 2001) and similar biochar-rich soils elsewhere in the world (Downie et al., 2011) further provides examples of the long-term C sequestration potential of biochar in soils. However, MRTs of decadal to century time scales have also been observed for laboratory-produced and natural biochar in soils (Ascough et al., 2008;Cheng et al., 2008;Hilscher and Knicker, 2011). ...
Assessing biochar's ability to resist oxidation is fundamental to understanding its potential to sequester carbon. Chemical oxidation exhibits good performance in estimating the oxidation resistance of biochar. Herein, oxidation resistance of 14 types of biochars produced from four feedstocks at different pyrolysis conditions (hydrothermal versus thermal carbonization) was investigated via hydrogen peroxide oxidation with varying concentrations. The oxidation resistance of organic carbon (C) of hydrochars was relatively higher than that of 250°C pyrochars (P250) but was comparable to that of 450°C pyrochars (P450). Both hydrochars and P450 from ash-rich feedstocks contained at least three different C pools (5.9-18.3% labile, 43.2-56.5% semi-labile and 26.9-45.9% stable C). Part (<33%) of aromatic C within 600°C pyrochars (P600) was easily oxidizable, which consisted of amorphous C. The influence of pyrolysis temperature upon oxidation resistance of biochars depended on the feedstock. For ash-rich feedstock (rice straw, swine manure and poultry litter), the oxidation resistance of biochars was determined by both aromaticity and mineral components, and mineral protection was regulated by pyrolysis conditions. The amorphous silicon within hydrochars and P450 could interact with C, preventing C from being oxidized, to some extent. Nevertheless, this type of protection did not occur for P250 and P600.
... Wildfire charring led to higher N% than slow pyrolysis (Fig. 1f), which could be partially due to a substantial inorganic N fraction in the natural PyC materials 43 . For the δ 13 C signature, no trends were observed with increasing HTT, as the values were very similar along the range of wildfire charring/pyrolysis conditions studied, all slightly more negative than the unburnt feedstocks (Table 1), which can be explained by the loss of isotopically heavy cellulose 44 . ...
Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, δ¹³C and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charring- and slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biochar’s environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa.
... Within this continuum, charcoal comprises coarse particles (mm-cm) that retain the physical and chemical properties allowing to identify its biomass source (Bird and Ascough, 2012;Knicker et al., 2008;Scott, 2010). The aromatic structure gives charcoal an inherent increased resistance to biotic and abiotic degradation (Eckmeier et al., 2007;Wiechmann et al., 2015), which is further increased once the charcoal is buried in soil, due to enhanced physical protection, to an extent that charcoal is a common source of paleoenvironmetal and archaeological proxy data (Ascough et al., 2008). ...
Charcoal is a heterogeneous material exhibiting a diverse range of properties. This variability represents a serious challenge in studies that use the properties of natural charcoal for reconstructing wildfires history in terrestrial ecosystems. In this study, we tested the hypothesis that particle size is a sufficiently robust indicator for separating forest wildfire combustion products into fractions with distinct properties. For this purpose, we examined two different forest environments affected by contrasting wildfires in terms of severity: an eucalypt forest in Australia, which experienced an extremely severe wildfire, and a Mediterranean pine forest in Italy, which burned to moderate severity. We fractionated the ash/charcoal layers collected on the ground into four size fractions (>2, 2-1, 1-0.5, <0.5mm) and analysed them for mineral ash content, elemental composition, chemical structure (by IR spectroscopy), fuel source and charcoal reflectance (by reflected-light microscopy), and chemical/thermal recalcitrance (by chemical and thermal oxidation). At both sites, the finest fraction (<0.5mm) had, by far, the greatest mass. The C concentration and C/N ratio decreased with decreasing size fraction, while pH and the mineral ash content followed the opposite trend. The coarser fractions showed higher contribution of amorphous carbon and stronger recalcitrance. We also observed that certain fuel types were preferentially represented by particular size fractions. We conclude that the differences between ash/charcoal size fractions were most likely primarily imposed by fuel source and secondarily by burning conditions. Size fractionation can therefore serve as a valuable tool to characterise the forest wildfire combustion products, as each fraction displays a narrower range of properties than the whole sample. We propose the mineral ash content of the fractions as criterion for selecting the appropriate number of fractions to analyse.
... 16 Here, spectroscopy is an invaluable tool to track the removal of contaminants, with 13 C-solid state nuclear magnetic resonance ( 13 C SS-NMR) particularly useful in this regard. Pyrogenic carbon gives a distinctive peak in 13 C SS-NMR spectra, centred on 130 ppm, 17 so it is possible to track the removal of contaminants such as cellulose, with its characteristic peaks between ca 20-105 ppm, see, for example, Figure 2. ...
In summary, important questions remain surrounding the role of pyrogenic carbon in the global carbon cycle, and we are only just starting to address some of these questions. It seems as though the fate of pyrogenic carbon in the environment depends strongly upon, not only the specific chemistry of the material itself, but also the depositonal environment in which it is emplaced. Spectroscopy is central to answering these questions, predominantly in the form of KC-SS-NMR and FT-IR, although it is the ntegraticn of several methodolo- ges that cffe's the most fruitful approach to understanding this missing link in the carbon cycle.
... The basic chemical structure of carbonized biomass consists of the polycondensed aromatic units. The aromaticity and degree of aromatic condensation, the key parameters for its characterization, are governed mainly by the highest heat treatment temperature-HTT (Keiluweit et al. 2010;Zimmerman 2010;McBeath et al. 2011), although other pyrolysis parameters, such as: residence time (Knicker et al. 2005;Melligan et al. 2012;Rutherford et al. 2012); O 2 availability (Ascough et al. 2008); and pressure (Melligan et al. 2011), as well as the precursor biomass (Wiedemeier et al. 2015), can also significantly affect these fundamental chemical properties of biochar. These properties can be assessed by several analytical methods, described and evaluated in reference (Wiedemeier et al. 2015). ...
Nuclear magnetic resonance spectroscopy has been one of the most important analytical techniques to analyze biomass materials and their transformation products. 1H, 13C, 15N, and 31P NMR techniques have been used to analyze carbohydrates, proteins, lipids, and polycondensed compounds in raw and processed biomass, from plants, animals, fungi, algae, and other living beings. NMR has been used in qualitative and quantitative analyses of biomass materials, determination of the chemical composition, and structure and dynamics of monomers, oligomers, and polymeric materials. One of the major NMR advantages is its nondestructive nature that maintains sample integrity and the analyzed samples can be analyzed by other methods. This chapter provides basic information about NMR measurements and spectroscopic parameters, analysis in solid state, liquid state and in heterogeneous samples.
... While a lot of work has been done on the effect of heat on organic materials, particularly on wood (e.g. Ascough et al., 2008;Braadbaart and Poole, 2008;Cohen-Ofri et al., 2006;Scott, 2010), the understanding of another common bioorganic fire residue, heated bone, is far more fragmentary. The presence of a high amount of inorganic compounds in bone makes it distinct from wood and other organic plant and/or animal tissues. ...
Charcoal is commonly preserved in both natural and artificial sediments, and is intensively used in paleontological, paleoenvironmental, and archaeological studies due to the abundant bio-information it contains. The biochemical properties of charcoal are also used for paleoclimatic reconstruction; however, the reliability of this approach has been challenged due to a lack of clarity on how physicochemical properties change during the charring process, as well as the temperatures required for charcoalification. To address this lack, in this study, Qinghai spruce and Chinese pine wood samples from the northeastern Tibetan Plateau were heated at different temperatures and for different lengths of time under restricted oxygen conditions. The reflectance; carbon, nitrogen, and oxygen content; and tracheid morphology were quantified before and after heating to assess changes related to the charring process. Archaeological charcoal remains were then evaluated to determine the charcoalification temperatures by comparing with the experimental results. The minimum temperature required for wood charcoalification was ∼300℃, while temperatures of 400–500℃ were recorded for archaeological charcoal. During the charring experiments, the tracheid cell walls gradually homogenized, and tracheid cell wall thickness and lumen area decreased by ∼20%. On average, 50% mass losses were observed; the carbon and oxygen content (% wt.) approximately changed from 47% to 60% and 48% to 35% respectively, while the nitrogen content (% wt.) fluctuated around 0.2%. The reflectance increased slightly from 0% to 0.5%. We propose that the charcoalification of wood tissue refers to charring (in restricted air) and carbonization (in the almost absence of air) when the wood is exposed to a heat source, which then finally transforms into a black, inert solid. This quantitative study provided valuable data and a thorough assessment of the process of wood charcoalification, as well as accurately estimated the feasibility of using charcoal physicochemical properties in paleoclimatic research.
Due to rapid growth in urbanization and industrialization, a large volume of wastewater is generated which adversely affects overall water quality. Oxyanions commonly referred to as the oxygen (O)-containing anions of elements (A) with general formula AxOyz − are abundant in the wastewater and are responsible for degrading the water quality. There is a pressing need for the development of sustainable low-cost wastewater treatment for oxyanions that can reduce negative environmental impacts. Biochar can be a potential solution for retaining these oxyanions; however, biochar faces several challenges for this purpose due to limited anion exchange sites, cost, and often needs surface modification strategies. The purpose of this chapter is to summarize the available literature regarding biochar physicochemical properties, feedstock and pyrolysis conditions, and different modification strategies, and to provide directions for the improvement of wastewater management and the development of effective oxyanions’ (arsenate, nitrate, and phosphate) control strategies in wastewater.
Methodologies based on ¹³ C‐enrichment ( E ), ¹³ C‐depletion ( D ) and ¹³ C‐natural abundance ( NA ) to estimate the stability of biochar in soil were critically examined. The stability of ¹³ C‐enriched biochar can be estimated by the quantitative recovery of excess ¹³ C, either in the soil or in evolved CO 2 . Both approaches have advantages and disadvantages. Recovery in the soil is a measure of both residual biochar ¹³ C + ¹³ C immobilised in soil organic matter during biochar decomposition. Variable proportions of organic‐ and inorganic‐C are present in alkaline biochars, and few data exist on the uniformity of labelling, which is a basic requirement of the respired ¹³ CO 2 and E methodology. The E technique has had limited application due to the cost and difficulty of obtaining a uniformly‐enriched feedstock through continuous labelling of plants with ¹³ CO 2 at a constant ¹³ C enrichment. In contrast, the NA technique has been widely applied. The NA and D techniques are in situ methods that involve the addition of C 4 ‐derived biochar to a C 3 ‐soil or vice versa. Stability is estimated by a two‐end‐member mixing model that allows the proportion of evolved CO 2 derived from the biochar (Cdfb) to be estimated. The mixing model has recently been misused to estimate the Cdfb of ¹³ C‐enriched biochar, with ¹³ C‐abundance expressed as erroneously large δ values. ¹³ C‐based methods provide a yardstick against which rapid stability tests should be evaluated. While numerous laboratory incubation comparisons have been conducted, very few field‐based data have been published.
Highlights
¹³ C methods for estimating biochar stability are based on uniform isotopic labelling.
Organic and inorganic constituents of biochar may not be uniformly labelled.
Expression of ¹³ C enriched biochar as large δ values (>500 units) rather than atom fraction excess led to larger errors in stability estimation.
Few ¹³ C field‐based estimates of biochar stability exist.
This chapter focuses on the synthesis and application of agro-waste-based biochar with a perspective of circular bioeconomy. Numerous methods are known for the synthesis of biochar; however, pyrolysis of agro-waste is the highly acclaimed method for biochar production from agro-waste. Biochar production is influenced by multiple factors including nature and source of feedstock, pyrolysis conditions, and the system/device used for thermal treatment. The biochar properties enable it to be applied in several fields including wastewater treatment, soil improvement, reduction of greenhouse gas emissions, carbon sequestration, sludge improvement, etc. The commissioning and erection of production facilities nearby agro-waste production sites, can reduce the supply chain and transport, and also improve the sustainability and development of circular bioeconomy. The application of biochar in water treatment can reduce the burden on market for the production and application of expensive adsorbents and hence, the agro-waste-based green adsorbent (biochar) can enhance bio-sustainability and subsequently circular bioeconomy
Résumé
La datation par l’isotope radioactif du carbone est fiable si l’origine du carbone daté est vérifiée à l’issu d’un traitement de décontamination. Les procédés chimiques de décontamination sont adaptés à l’élimination des acides humiques et des carbonates qui sont les principaux contaminants dans les sédiments des sites de plein air. Il n’en est pas de même pour l’élimination des composés issus de la dégradation de substances bactériennes ou animales que l’on rencontre dans les grottes. Il est alors indispensable de vérifier l’origine du carbone daté. Comme les carbones contaminants proviennent de structures chimiques souvent voisines de celles du charbon de bois, leur identification et leur séparation sont difficiles et quelquefois impossibles à réaliser par voie chimique. Il n’existe actuellement, à notre avis, qu’un seul moyen pour identifier l’origine du carbone : la mesure de la concentration en isotope stable 13 du carbone. Nous l’avions déjà indiqué (Jouve, 2013) et, à la lumière de nouvelles mesures, nous précisons certains points importants et examinons les datations d’échantillons provenant du Mur des gravures (Muro de los Grabados) dans la grotte de Candamo en Espagne.
This work studies carbon (C) and hydrogen (H) isotope composition of plant biomass and soil organic matter (SOM) in an attempt to assess both, changes exerted by fire and possible inputs of charred materials to the soil after a wildfire. Isotope composition of bulk soil, soil particle size fractions and biomass of the dominant standing vegetation in the area (Quercus suber) from Doñana National Park (SW-Spain) were studied by isotope ratio mass spectrometry (IRMS). SOM C isotope composition indicates the occurrence of two SOM pools with different degree of alteration. Coarse soil fractions (>0.5 mm) were found ¹³C depleted with δ¹³C values close to those in leaf biomass, pointing to a predominance of poorly transformed SOM. Conversely, fine fractions (<0.1 mm) were found enriched in ¹³C as corresponds to a more humified SOM. The fire produced no changes in this trend, although a consistent ¹³C enrichment (c. 1‰) was observed in all soil fractions with decreasing size. Concerning H isotopes, the coarse fractions (>0.5 mm) displayed significant lower δ²H values than the intermediate and fine ones (<0.5 mm), again similar to those in leaf biomass (c. -80‰), whereas the fine fractions were found deuterium (²H)-enriched with significant higher δ²H values (c. 50‰), suggesting physical speciation of H depending on soil particle size. The fire produced a significant ²H depletion (Δ²H c. -10‰) in the finer fractions (<0.1 mm). The study of stable isotope analysis added new information and complements the results obtained by other proxies to better understand the effect of fire on SOM.
Material composition changes of coal and gas under igneous intrusion have been one of the hot research fields in global geology. In this study, through in-depth discussion of a case from Huainan coalfield, North China, some important characteristics of thermal altered coal (TAC) are expounded by using the methods of element geochemistry and vitrinite reflectance (Rmax, Ro, and Rmin) calculation. The results show that the profile of coal reflectance/thermal metamorphic temperature (TMT) vs. distance from the intrusion indicates that the thermal aureole range reveals by the thickness of 2.4 m intrusion is approximately 3.24 m. Close to intrusion, the carbon (Cdaf) of coal increases significantly, while hydrogen (Hdaf) and oxygen (Odaf) decreases significantly, and the nitrogen (Ndaf) change is very irregular. After acid treatment, the volatile matter (VMacid) and ash yield (Ashacid) losses of coal have reached 5× and 4× of the ambient zone. The atomic ratios O/C and H/C are parallel to the changes of VMacid. Based on Rmax-Rmin diagram, the pressure effect of TAC is analyzed. In the actual geological model, the coal is mainly subjected to the bearing stress perpendicular to the contact surface instead of the vertical gravity of the magma body, and the applicable conditions of the theoretical model are proposed. Summing up the previous calculation methods of TMT, the exponential function method can be used when the Rmax is <1.0. On the contrary, the previous method can be used. The empirical formula for calculating the carbon isotope (δ¹³ CCH4) of gas by using Rmax of TAC shows a negative result. The δ¹³ CCH4 of the gas near the contact is relatively positive, which proves to some extent that ¹³ C of the thermal residual coal and ¹² CH4 of the gas are subjected to carbon isotope fractionation. Here, the regression model between the Rmax of TAC and δ¹³ CCH4of gas in the case can be expressed as δ¹³ CCH4 = 16.777Ln(Rmax)-49.859.
The use of biochar to improve soil properties and decrease the leaching of nutrients has received attention, yet very little research has focused on its effects on Calcaric Cambisols. We evaluated the effect of rice (Oryza sativa L.) husk biochar at the highest pyrolysis temperatures of 450°C and 650°C (RH450 and RH650) on nutrient leaching, nutrient availability, and microbial properties of Calcaric Cambisols in the karst region of southwestern China. In a soil column leaching experiment, rice husk biochars produced under two temperatures were added at 1%, 2%, and 5% (weight/weight) to Calcaric Cambisols following application of fertilizer (ammonium nitrate [NH 4 NO 3 ] and monopotassium phosphate [KH 2 PO 4 ]) and incubated for 28 weeks. A control treatment (without rice husk biochar) was also included. After a 28-week incubation, both temperature rice husk biochars significantly reduced the cumulative amounts of ammonium (NH 4⁺ ) in leachate from Calcaric Cambisols, while they increased cumulative amounts of leachate phosphate (PO 43– ) and potassium (K ⁺ ). Addition of 2% and 5% RH650 significantly reduced cumulative amounts of leachate nitrate (NO 3– ), while RH450 amendment had no significant influence on NO 3– -N leaching.Addition of 5% RH450 significantly increased soil available nitrogen (N) content simultaneously accompanied by a significant increase in microbial biomass N, suggesting net N mineralization was enhanced and soil microorganisms utilized a portion of mineral N for their own cell building. Both temperature rice husk biochar additions caused a significant increase in soil available phosphorus (P) and K.The highest P availability was observed in RH450-treated soil samples at 5% rate. Compared with RH450 treatment, higher K availability was found in RH650-treated soils. Both rice husk biochar additions significantly increased soil microbial biomass carbon
Fires are likely to have been central to the formation of certain inertinite macerals in South African coals. To investigate this hypothesis, a Permian, medium rank C bituminous Witbank coal (No. 4 Seam Upper) was density fractionated to yield an inertinite-rich and a vitrinite-rich sample, and assessed using stable nitrogen and carbon (δ¹⁵N and δ¹³C) isotopes in conjunction with nitrogen functionalities. The parent coal comprises of 41.6 vol% vitrinite and 48.5 vol% inertinite. The vitrinite-rich sample is dominated by collotelinite and collodetrinite (81 vol% vitrinite), and the inertinite-rich sample by fusinite, semifusinite, and inertodetrinite (63 vol% inertinite). The δ¹⁵N and δ¹³C values and nitrogen functionalities were used to constrain early coal formation pathways for the dominant macerals in the density fractionated samples. The vitrinite-rich sample has a lower δ¹³C relative to the inertinite-rich counterpart. However, the inertinite-rich sample has the lower δ¹⁵N value, along with a lower concentration of N-quaternary and higher N-pyrrolic compounds. Because these samples are of the same coal maturity, and the major macerals were derived from similar precursors, differences in δ¹⁵N and δ¹³C and nitrogen functionalities reflect differences in coal formation pathways. Degradation of ¹³C-rich cellulose in wood through either charring or bacterial activity leads to lower δ¹³C values. The lower ¹⁴N content for the vitrinite-rich sample along with higher N-quaternary and N-pyridinic suggests cellulose degradation driven by bacterial activity. In contrast, the higher ¹⁴N coupled with higher N-pyrrolic and N-oxide complexes for the inertinite-rich sample, suggests fusinite and semifusinite were formed through charring. Inertodetrinite is attributed to the disintegration of the charred matter.
Biochar application to soils is being considered as a means to sequester carbon (C) while concurrently improving soil functions. The main focus of this report is providing a critical scientific review of the current state of knowledge regarding the effects of biochar application to soils on soil properties and functions. Wider issues, including atmospheric emissions and occupational health and safety associated to biochar production and handling, are put into context. The aim of this review is to provide a sound scientific basis for policy development, to identify gaps in current knowledge, and to recommend further research relating to biochar application to soils. See Table 1 for an overview of the key findings from this report. Biochar research is in its relative infancy and as such substantially more data are required before robust predictions can be made regarding the effects of biochar application to soils, across a range of soil, climatic and land management factors.
Annual oak (Quercus robur L.) latewood delta13C values are presented for the period 1895-1994 from two sites with different hydrological characteristics. Both ring width and delta13C indices record high-frequency common forcing better than lower-frequency forcing. At both sites the high-frequency variance in the delta13C indices of latewood cellulose is highly correlated with combined July and August environmental variables. The association between the high-frequency variance in annual ring width indices and climate is not as strong. Higher correlations with environmental variables were found for the high-frequency delta13C indices at the dry site (Sandringham) than at the wet site (Babingley), but the differences are not statistically significant. These results illustrate the need for routine signal quantification in isotope records and hence a requirement for between-tree replication of isotope series in future studies. High-frequency (year-to-year) interseries correlation is shown to be relatively strong, indicating that only small numbers of replicate series are needed to represent interannual isotope variability accurately. However, common signal variance is diminished at lower (decadal and longer period) frequencies. This implies a need for increased sample replication in order to achieve chronology confidence equivalent to that routinely produced for simple ring width data. This work demonstrates that significant high-frequency climate signals are contained in isotopic measurements of trees whose ring widths contain little or no such information.
Soils in the Barreirinhas region, Maranhao State, were sampled for 613 C analysis and buried charcoal fragments in the soils were radiocarbon dated. Three soil profiles collected in forested areas around the Lagoa do Caqö and one in a woody savanna (mixture of non-arboreal and arboreal species) located approximately 10 km southeast of the Lagoa were studied. A high-resolution pollen record was obtained from lake sediments, showing that forest vegetation was predominant in the area in the early Holocene. From approximately 10 000 14C yr BP the pollen spectrum gradually changed, suggesting the dominance of open savanna communities, these were transformed to a more forested landscape (woody savanna) from approximately 7500 yr BP. The lake sediments also record evidence of fire (indicated by buried charcoal particles at several soil depths) during the Holocene. The 613 C analysis of soil organic matter (SOM) indicates that from between approximately IO0000 yr BP and 9000 yr BP to -4000 yr BP, a woody savanna prevailed at two sites around the lake, probably reflecting a drier climate. From -4000-3000 yr BP to the present, the results indicate a moderate and progressive increase in arboreal vegetation around the lake as a result of the return to more humid climate conditions probably similar to the present-day. The carbon isotope results from the site located 10 km from the lake indicate the presence of an open vegetation from the early Holocene. In general, there is agreernent between the palaeovegetation patterns inferred from the pollen and carbon isotope data. However, a much less uniform landscape, with a mosaic of different ecosystems at any given time, is inferred from the carbon isotope record.
Three southern Appalachian stands with sparse and unproductive pine-hardwood overstories and dense Kalmia latifolia L. understories were treated to restore productivity and diversity on steep slopes. An adaptation of the fell and burn practice was applied in summer and fall 1990. About one-half of the woody fuels were consumed at each site. A range of fire intensities was observed. Flame temperatures approached 800-degrees-C, but the heat pulse into the forest floor only reached 60-degrees-C at 5 cm. Humus and chaffed leaf litter remained on most of the surface after burning. Evidence of soil erosion was spotty and related to points of local soil disturbance. No soil left the sites. At the end of the first growing season, 23% of the burned surfaces were covered by growing plants and 62% by residual forest floor and woody debris. Felling and burning reduced evapotranspiration so that soil in the treated areas remained moister than under adjacent uncut stands. Opening the sites increased soil temperatures 2 to 5-degrees-C at 10 cm during the first 16 months after treatment.
To determine how grassland, woodland, and bordering forests respond to increased aridity, we used paleoecological methods to examine past responses along a transect of three sites at the eastern boundary of the Northern Plains of North America. Our study region corresponds to the confluence of three air streams that control central North American climates and, hence, should be sensitive to climate change. Sediment cores were analyzed for evidence of Holocene vegetation and fire from tall-grass prairie in eastern North Dakota (Moon Lake), from mixed forest near the prairie border in northwestern Minnesota (Deming Lake), and from mixed forest more remote from prairie in western Wisconsin (Dark Lake). Together with pollen and charcoal analysis, we present a new method for determining 13 C of terrestrial (charred) organic matter and, thus, the relative importance of C 3 and C 4 photosynthetic pathways in past vegetation. Paleorecords were supplemented with surface charcoal accumulation and 13 C from 21 North American lakes that span boreal, deciduous, pine, and mixed forest to tall-and mixed-grass prairie. Surface charcoal and 13 C follow vegetation and climate gradients, with high charcoal accumulation and 13 C (20‰) in the Plains (Dakotas, Nebraska, and southwest Minnesota) and decreases to the east, west, and north. The 13 C pattern is consistent with observed patterns of C 3 :C 4 dominance across the region. Sediment, pollen, charcoal, and terrestrial 13 C show that vegetation response to climate change varied substantially among tall-grass prairie, bordering woodland, and forest. During maximum aridity (8000–4000 yr BP) prairie vegetation in eastern North Dakota showed a demise of woody vegetation followed by a fluctuating dominance of grasses (40% C 4) and forbs. Meanwhile, prairie expanded eastward into northwestern Minnesota, where it produced a shifting dominance between mostly C 4 grasses and woody vegetation until more humid conditions and mixed forest developed after 4000 yr BP. Mixed forest in southwestern Wisconsin showed little response to mid-Holocene aridity. Elevated 13 C values from 5000 to 3000 yr BP suggest that composition of grasses changed (to increased C 4), although pollen data indicate that the total abundance of grasses remained constant. The increase in C 4 grasses at this time is consistent with previous studies suggesting a delayed dry interval in eastern Iowa. Reduced aridity of the last 2000 yr brought increased fire to tall-grass prairie as higher primary productivity led to increased fuel load. Meanwhile, forest expanded in northwestern Minnesota, leading to decreased ignition and fine fuels, in turn resulting in decreased fire at the woodland margin. Key words: C 4 ; carbon isotopes; charcoal analysis; climate change; 13 C determination meth-odology; fire; Holocene climate change and vegetation effects; Northern Great Plains (USA); paleo-ecological data; pollen analysis; prairie; woodland.
Carbon isotope discrimination (Δ13C) in charred grains from archaeological sites provides reliable information about water availability of ancient crops. However,
as cereals are cultivated plants, they may reflect not only climatic fluctuations, but also the effect on water status of
certain agronomic practices, such as sowing in naturally wet soils or irrigation. In this work, we propose a methodological
approach to combine Δ13C data from different plant species, in order to discriminate between climate-derived and anthropogenic effects on ancient
crops. We updated previous models for estimating water inputs from Δ13C of cereal grains of Hordeum vulgare and Triticum aestivum/durum, and we applied them to published data from several archaeological sites, including samples from the Neolithic to the present
day in northeast and southeast Spain, as well as from the Neolithic site of Tell Halula (northwest Syria). We found an important
decrease in water availability from the Neolithic to the present time in the three areas of study, especially clear for the
two driest areas (southeast Spain and northwest Syria). Potential differences in water management practices between wheat
and barley, as well as between cereal and legume crops (Vicia faba and Lens culinaris), are also discussed on the basis of the comparison of Δ13C values across several archaeological sites.
We report measurements of the susceptibility of a variety of elemental and organic carbon samples to oxidative degradation using both acid dichromate and basic peroxide reagents. Organic carbon is rapidly oxidized using either reagent, or both reagents sequentially. Elemental carbon exhibits a wide range of susceptibilities to oxidation related both to the degree to which the precursor plant material was carbonized during pyrolysis and to the surface area available for oxidation. Despite a range of susceptibilities, a component of oxidation-resistant elemental carbon has been identified which can be reproducibly separated from organic contaminants.The carbon isotope composition (δ13C value) of the precursor plant materials underwent a 0–1.6‰ decrease during the production of the elemental carbon by pyrolysis, while the subsequent oxidative degradation of the samples resulted in only small (generally < 0.5%o) changes in the δ13C value of the remaining elemental carbon.The results suggest that the technique can be used to obtain records of elemental carbon abundance in marine sediment cores, and thus a record of the intensity of biomass burning on adjacent continental land masses in the geologic past. In addition, the δ13C value of the elemental carbon can provide an indication of the type of vegetation being burnt.
Charred organic remains are ubiquitous in the archaeological and fossil record and are often used to interpret past environments and climate. This study focuses on the physical and chemical alteration that takes place during heating (i.e. charring). Modifications to the internal and external morphology were noted alongside the change in molecular and stable carbon isotope signature. Molecular analyses were undertaken using direct temperature resolved mass spectrometry and the stable carbon isotopes determined using isotope ratio mass spectrometry. The results of this study document a general enrichment in 13C/12C composition of charred material which could reflect the changes observed in both the molecular composition and the relative proportions of the molecules formed. These results indicate that spurious results might be inferred when comparing the stable carbon isotope signature of charred/charcoalified material with uncharred organic matter
Biomass burning, one of the most important global sources of particulate matter, produces both airborne particles that may influence global and regional climate, and particles incorporated into sediments that provide records of past local, regional, and global impacts of biomass burning. Determining the mass concentrations, chemical compositions, and physical properties of these particles is a prerequisite for assessing the environmental effects of biomass burning. In this Chapter we describe methods for chemical and physical characterization of airborne and sedimentary particles used in biomass burning studies, with particular emphasis on the carbonaceous material. For each method we review the principles, problems and uncertainties and, when possible, discuss analytical features presently or potentially applicable to characterizing both airborne and sediment particles.
Results of thermogravimetric studies of cellulose pyrolysis in flowing nitrogen at elevated pressures are presented. Unique aspects of the thermobalance design include the flow of gas through a packed bed of a relatively large sample of pyrolyzate, and direct contact of the thermocouple with the solid sample during pyrolysis. In most studies of cellulose pyrolysis using TGA, the charcoal yield is low (typically below 10%) and is not greatly influenced by the experimental conditions. In this work the charcoal yield varies from 6% to 41% and is strongly influenced by process conditions. Decreasing the velocity of purge gas passing through the sample increases the charcoal yield from about 6% to more than 21% at 0.1 MPa. Increasing the pressure from 0.1 MPa to 1.0 MPa (with a constant purge gas velocity) further increases the charcoal yield to a value of 41%. Increasing pressure with constant purge gas mass flow also increases the charcoal yield. Kinetic studies of the weight loss data are largely inconclusive because the trends reflect extremely complex phenomena which cannot be universally described by simple models.
CP/MAS 13C NMR spectra were obtained at various contact times on ten solid organic compounds containing a variety of simple functional groups. The spectra show that signal intensities that agree with atomic ratios can be obtained with a contact time of 2.25 ms and often with a contact time as short as about 1 ms. Computer analysis of signal intensities obtained at a minimum of ten different contact times provides TCH data that are consistent with these experimental results. The experimental results are also consistent with the previously reported lack of significant variation in the spectra of complex organic solids obtained with contact times of about 1-3 ms. In general, nonprotonated carbon atoms polarize more slowly than protonated carbon atoms. The compounds exhibit a wide range of proton spin lattice relaxation times. Some compounds exhibit more resonances than are found in the 13C{1H} spectra of the compounds in solution because the crystalline environment removes the nominal spatial equivalence found for carbon atoms related to each other by unimolecular symmetry elements.
Solid-state 13C CPMAS NMR offers many options for characterizing carbon in soil organic matter (SOM). Its effectiveness, however, is often limited by a poor understanding of the techniques, and lack of hands-on access and training opportunities for students. Of nearly 250 modern NMR systems in Canada, approximately one is genuinely available for SOM studies, and there is poor communication between NMR operators and SOM users. While quantitative reliability can be addressed to some extent by multiple contact-time experiments or single-pulse (Bloch decay) spectra, it is also important to consider the effects of spectrometer background, spinning sidebands (especially with higher magnetic fields) and processing operations such as line-broadening, phasing and baseline correction. In many studies, more consideration needs to be given to instrument specifications, the type of information needed, and whether sample fractionation or pretreatment should be used. Structural information can be greatly enhanced by dipolar-dephasing and sideband suppression sequences. Sequences based on relaxation differences can reveal pools of carbon with different structures. Data analysis can be enhanced by principal component analysis, spectrum deconvolution and difference spectra. Studies of xenobiotics and C metabolism can be greatly aided by 13C-labeling. However, a key limitation to SOM applications remains the gap in culture and expectations of the users.
Thermal modification of wood produces a wood material with many interesting properties, such as enhanced dimensional stability, lower equilibrium moisture content and increased biological durability. Changes in the chemical structure of pine (Pinus sylvestris) caused by thermal treatment were investigated by studying various components of wood using C-13 CPMAS NMR spectroscopy. Electron spin resonance (ESR) spectroscopy on the same set of samples was used to study the formation and stability of free radicals formed during the treatment. The most remarkable changes revealed by solid state NMR were the increase in relative crystallinity of cellulose and destruction and deacetylation of hemicelfuloses. Changes in the lignin fraction were mostly registered as diminishment in the methoxyl content, although the intensity of the aromatic region increased relative to the carbohydrate fraction during the treatment. Increase in the intensities of the ESR signals from thermally treated wood samples proves the formation of stable free radicals. In addition, radical formation is believed to take part in condensation reactions leading to crosslinks within the lignin and possibly between lignin and other wood components. Both of the methods used indicate that the changes are most remarkable when the treatment temperature is over 200 degreesC.
The research area, wood and wood products, is an extremely large field and it can be approached in a variety of ways. The diversity of NMR spectroscopy together with the increased knowledge and the development of the hardware and software possibilities during recent years provide many opportunities for characterising wood products. High resolution liquid state NMR as well as the NMR imaging are not reviewed in this context. One main topic under consideration deals with the solid-state NMR methods and the latest results from one-dimensional and two-dimensional solid-state spectroscopy applied to the structures of wood and pulp components. Water has been used as a probe molecule inside a wood, paper or fibre matrix. The response of water molecules studied by NMR gives information of solid material that is difficult to obtain with other methods. The results dealing with this field were considered as a second main topic in this review. The results obtained in the field have provided valuable information to wood product technology. The versatile application possibilities of NMR spectroscopy will ensure continued active research in this field in the coming years.
Soils in the Barreirinhas region, Maranhao State, were sampled for delta(13)C analysis and buried charcoal fragments in the soils were radiocarbon dated. Three soil profiles collected in forested areas around the Lagoa do Caco and one in a woody savanna (mixture of non-arboreal and arboreal species) located approximately 10 km southeast of the Lagoa were studied. A high-resolution pollen record was obtained from lake sediments, showing that forest vegetation was predominant in the area in the early Holocene. From approximately 10 000 C-14 yr BP the pollen spectrum gradually changed, suggesting the dominance of open savanna communities, these were transformed to a more forested landscape ( woody savanna) from approximately 7500 yr BP. The lake sediments also record evidence of fire ( indicated by buried charcoal particles at several soil depths) during the Holocene. The delta(13)C analysis of soil organic matter (SOM) indicates that from between approximately 10 000 yr BP and 9000 yr BP to similar to 4000 yr BP, a woody savanna prevailed at two sites around the lake, probably reflecting a drier climate. From similar to 4000 - 3000 yr BP to the present, the results indicate a moderate and progressive increase in arboreal vegetation around the lake as a result of the return to more humid climate conditions probably similar to the present-day. The carbon isotope results from the site located 10 km from the lake indicate the presence of an open vegetation from the early Holocene. In general, there is agreement between the palaeovegetation patterns inferred from the pollen and carbon isotope data. However, a much less uniform landscape, with a mosaic of different ecosystems at any given time, is inferred from the carbon isotope record.
The objectives of this synthesis are (1) to review the factors that influence the ecological, geographical, and palaeoecological
distributions of plants possessing C4 photosynthesis and (2) to propose a hypothesis/model to explain both the distribution of C4 plants with respect to temperature and CO2 and why C4 photosynthesis is relatively uncommon in dicotyledonous plants (hereafter dicots), especially in comparison with its widespread
distribution in monocotyledonous species (hereafter monocots). Our goal is to stimulate discussion of the factors controlling
distributions of C4 plants today, historically, and under future elevated CO2 environments. Understanding the distributions of C3/C4 plants impacts not only primary productivity, but also the distribution, evolution, and migration of both invertebrates and
vertebrates that graze on these plants. Sixteen separate studies all indicate that the current distributions of C4 monocots are tightly correlated with temperature: elevated temperatures during the growing season favor C4 monocots. In contrast, the seven studies on C4 dicot distributions suggest that a different environmental parameter, such as aridity (combination of temperature and evaporative
potential), more closely describes their distributions. Differences in the temperature dependence of the quantum yield for
CO2 uptake (light-use efficiency) of C3 and C4 species relate well to observed plant distributions and light-use efficiency is the only mechanism that has been proposed
to explain distributional differences in C3/C4 monocots. Modeling of C3 and C4 light-use efficiencies under different combinations of atmospheric CO2 and temperature predicts that C4-dominated ecosystems should not have expanded until atmospheric CO2 concentrations reached the lower levels that are thought to have existed beginning near the end of the Miocene. At that time,
palaeocarbonate and fossil data indicate a simultaneous, global expansion of C4-dominated grasslands. The C4 monocots generally have a higher quantum yield than C4 dicots and it is proposed that leaf venation patterns play a role in increasing the light-use efficiency of most C4 monocots. The reduced quantum yield of most C4 dicots is consistent with their rarity, and it is suggested that C4 dicots may not have been selected until CO2 concentrations reached their lowest levels during glacial maxima in the Quaternary. Given the intrinsic light-use efficiency
advantage of C4 monocots, C4 dicots may have been limited in their distributions to the warmest ecosystems, saline ecosystems, and/or to highly disturbed
ecosystems. All C4 plants have a significant advantage over C3 plants under low atmospheric CO2 conditions and are predicted to have expanded significantly on a global scale during full-glacial periods, especially in
tropical regions. Bog and lake sediment cores as well as pedogenic carbonates support the hypothesis that C4 ecosystems were more extensive during the last glacial maximum and then decreased in abundance following deglaciation as
atmospheric CO2 levels increased.
The condensation of amino acids and sugars (Maillard reaction) is one possible diagenetic pathway for the formation of humic materials in sediments. In this study, aqueous solutions of alanine and glucose were heated (100°C) for up to 40 days. The δ13C- and δ13N-values of reactants and products were monitored. With increased heating time, the stable carbon and nitrogen isotope compositions of the unreacted alanine in solution were enriched by up to 8.8‰ and 2.7‰, respectively, relative to their initial compositions. In contrast, the insoluble melanoidin product and alanine recovered by acid hydrolysis of the melanoidin were both depleted in13C and15N relative to the starting materials. The magnitude of this isotopic fractionation varied as a function of the relatieve concetration of alanine to glucose in the starting solution. The CO2 that evolved during the reaction is depleted in13C relative to the initial δ13C composition of alanine and its car☐yl group, suggesting that13C-depleted amino acids initially condense with glucose to form insoluble melanoidins. Subsequent to melanoidin formation, a second isotope fractionation takes place whereby13C-depleted car☐yl groups are preferentially cleaved from the melanoidin. Assuming that humic substances may form in natural environments via condensation reactions like the Maillard reaction, it is hypothesized that the stable isotope fractionation that occurs during the transformation of organic matter to humic materials and kerogen might be at least partially explained by kinetic effects during condensation reactions rather than decar☐ylation of the primary amino acids.
Changes in cellulose crystallinity during kraft pulping were investigated by analysing a series of kraft pulps with yields between 96 and 47% using X-ray diffraction and infrared (IR) spectroscopy. The results were compared with those obtained for the same set of samples using solid state C-13 nuclear magnetic resonance (NMR) spectroscopy. All three methods indicated that the degree of crystallinity of the cellulose increased as kraft pulping proceeded due to preferential removal of the less ordered carbohydrates. Both X-ray and IR analyses indicated that the amount of crystalline cellulose remaining in the fibre stayed nearly constant as pulping proceeded. NMR spectroscopy, on the other hand, showed some increase in the amount of crystal interior cellulose in the early stages of pulping and evidence for damaged cellulose at yields below 57%. The differences between the results obtained using the three methods are discussed.
Hackschnitzel von Fichtenholz (Picea abies) wurden nach einem normalen Kraftprozeß zu Zellstoffen mit verschiedenen Ausbeuten gekocht. Die ausgelösten Lignine wurden isoliert, acetyliert und mittels 13C-NMR Spektroskopie charakterisiert. Die erhaltenen Spektren wurden durch Vergleich der chemischen Verschiebungen der verschiedenen Resonanz-Signale mit den Signal Verschiebungen in 13C-NMRSpektren entsprechender acetylierter Ligninmodellsubstanzen gedeutet.
Charcoal results from incomplete combustion of plant material. It is produced naturally by wildfire, and being relatively tough and unbiodegradable it may be transported and incorporated into a variety of sedimentary environments. Wildfire requires adequate atmospheric oxygen for the combustion of plant fuel (wood, leaf litter). Fossil charcoal from the Devonian onwards suggests that the oxygen level in the atmosphere has not fallen below 13% in this interval. Further, the extreme flammability of even wet plant fuel at oxygen levels above 35% makes this the highest figure compatible with the occurrence of terrestrial vegetation. -Author
Structural changes in lignocellulosic biomass heated under conditions comparable to those encountered in several types of natural or planned burnings have been studied by solid-state 13C- and 15N-CPMAS NMR spectroscopy of 15N-enriched ryegrass (Lolium rigidum) after being subjected to progressive thermal treatment. The solid-state 15N-NMR spectra of biomass subjected to severe heating revealed amide-N in forms which are resistant to the thermal treatment. Progressive burning was found to occur in two well-defined stages: In the early stage the free amino acid and some NH2 groups were removed, but no substantial disruption of the peptide structure was observed. In the final stage of burning the amide-N was converted to heterocyclic structures such as pyrroles, imidazoles and indoles. Some evidence for the presence of pyridines and phenazines was also found at this stage. These findings suggest that a major portion of the N is in forms that may survive most natural fires and that their stability towards further microbial degradation is increased by the heating. The solid-state 13C-NMR spectra revealed that the carbohydrate fraction is converted into condensed dehydrated material producing intense signals in the aromatic region.
The nature of organic carbon in the < 2, 2–20, 20–53, 53–200, and 200–2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS). Analyses were repeated after high energy ultraviolet photo-oxidation was performed on the three finest fractions. All four soils, studied contained appreciable amounts of physically protected carbon while three of the soils contained even higher amounts of charcoal. It was not possible to measure the charcoal content of soils directly, however, after photo-oxidation, charcoal remained and was identified by its wood-like morphology revealed by scanning electron microscopy (SEM) together with a highly aromatic chemistry determined by solid state 13C n.m.r. Charcoal appears to be the major contributor to the 130 ppm band seen in the n.m.r. spectra of many Australian soils. By using the aromatic region in the n.m.r. spectra, an approximate assessment of the charcoal distribution through the size fractions demonstrated that more than 88% of the charcoal present in two of the soils occurred in the < 53 µm fractions. These soils contained up to 0.8 g C as charcoal per 100 g of soil and up to 30% of the soil carbon as charcoal. Humic acid extractions performed on soil fractions before and after photo-oxidation suggest that charcoal or charcoal-derived material may also contribute significantly to the aromatic signals found in the n.m.r. spectra of humic acids. Finely divided charcoal appears to be a major constituent of many Australian soils and probably contributes significantly to the inert or passive organic carbon pool recognised in carbon turnover models.
The behaviour of wood polymers during heat treatment carried out under inert atmosphere at 240°C has been reinvestigated to understand the important decrease of the O/C ratio observed in a previous study using X-ray photoelectron spectroscopy (XPS). Heat treatment was performed not only on beech sawdust but also on its lignin and holocellulose fractions obtained after acidic hydrolysis of polysaccharides or delignification with sodium chlorite. CP/MAS 13C NMR spectra indicate as previously reported an important degradation of hemicelluloses after thermal treatment. However, assignments of the signals appearing in the range of 125–135ppm and 35ppm attributed up to now to thermal crosslinking of lignin and formation of methylene bridges should be reconsidered. Indeed, heat treatment of the holocellulose fraction indicates quite similar signals showing that these latter are not due to lignin modification. According to the literature, these new signals have been attributed to the beginning of char formation. Determination of Klason lignin and HPLC analysis of the sugars contained in the hydrolysate support the hypothesis of formation of carbonaceous materials within the wood structure during heat treatment by mild pyrolysis.
Treatment of dewaxed maize stems, rye straw, and rice straw with 1 M NaOH at 30 °C for 18 h resulted in a dissolution of 78.0, 68.8, and 82.1% of the original lignin, and 72.1, 72.6, and 84.6% of the original hemicelluloses, respectively. The three alkali lignin fractions and three hemicellulosic preparations and the corresponding residues (mainly cellulose) were characterized by both degraded methods, such as alkaline nitrobenzene oxidation and acid hydrolysis, and non-destructive techniques, e.g. ultraviolet (UV), Fourier transform infrared (FT-IR), carbon-13 nuclear magnetic resonance spectroscopies (13C-NMR), and gas permeation chromatography (GPC). It was found that the three lignin preparations contained substantial amounts of non-condensed guaiacyl and syringyl units with fewer p-hydroxyphenyl units, and had weight-average molecular weights between 3280 and 3890 g mol−1. The two hemicellulosic preparations, obtained from maize stems and rye straw, were dominant in glucuronoarabinoxylans. While the hemicelluloses present in rice straw were mainly composed of α-glucan and k-arabino-(4-O-methyl-d-glucurono)-d-xylan. The thermal analysis of the polymers showed that hemicelluloses degraded in first place, while lignin showed less degradation, and therefore, its structure was more stable. Cellulose, on the other hand, showed an important degradation process, mainly between 250 and 330 °C, and its thermal stability is lower than that of lignin, but higher than that of hemicelluloses.
Time has shown wood as a very important material in several areas related to civil construction. Because of its organic origin, wood presents different physical and mechanical properties for different species. In consequence of these variations, there is the necessity to study chemical composition and molecular dynamic to better understand its property that will promote the use in civil construction. The focus of this work is to evaluate the Angelin Pedra wood in relation to the main chemical components, the domain type and the chemical components that constitute these domains. Solid state nuclear magnetic resonance (NMR) will be used for that, since the main advantage of NMR comparing to other techniques specially for the sample in question, is the potential of this spectroscopy to provide analysis of all functional group without pre-treatment of the sample. Some solid state NMR techniques were used and it was observed that the wood in investigation presents different packing, cells arrangements and chains ordination along the fibers in the different parts of the wood, because of the different distribution of the main wood components along the fibers.
The thermal degradation and charring of both larch lignin and manchurian ash lignin in the condensed phase were comparatively investigated by using TGA, FTIR and XPS. TGA experimental results showed that larch lignin produced more char residue than manchurian ash lignin under pure nitrogen at high temperature. This demonstrated that the carbon backbone of larch lignin was more stable than that of manchurian ash lignin. This is attributed to more carbon-carbon bonds existing in larch lignin than in manchurian ash lignin. Under air condition, the lignin completely was decomposed to form volatiles at high temperature. There was no char residue in either larch lignin or manchurian ash lignin. This was because oxygen catalyzed the oxidative reactions of C–C and C–H bonds, which is supported by FTIR. FTIR and XPS data indicated that the cleavage of aliphatic ester bonds took place mainly under pure nitrogen, and more aromatic rings remained in the condensed phase. Manchurian ash lignin showed a high crosslinking rate based upon the relative intensity of C1s and C1s (C–C) and an obvious increase of the ratio of carbon to oxygen. Different thermal degradation of both larch lignin and manchurian ash lignin under pure nitrogen and air has been proved by TGA, FTIR and XPS.
The intrinsic oxidation reactivity in air of an activated carbon char derived from bituminous coal was investigated using a new thermogravimetric analysis (TGA) method. Applying the new method, values of the Arrhenius activation energy E and pre-exponential factor A were estimated from TGA data obtained via heating samples at different constant rates. A novel statistical criterion was subsequently used to determine the heating rate at which optimum values of E and A were obtained. This is a valuable development, for in conventional non-isothermal TGA, while it is accepted that Arrhenius parameters vary with heating rate, there is no formal method for selecting one rate (and hence one set of values of E and A) over another. Using this new method, the following optimum values were obtained for the carbon at a heating rate of 25°Cmin−1: E=129.4kJmol−1 and ln(A/s−1)=10.4. These results are very similar to those calculated for the same material using more time consuming and less accurate isothermal TGA methods. It is therefore proposed that this new analysis method might be an improvement on conventional techniques to determine the intrinsic oxidation reactivity in air of coal chars.
High-resolution solid-phase 13C NMR spectra were obtained on celluloses from cotton linters, ramie, hydrocellulose prepared from cotton linters, Acetobacter xylinum, and Valonia ventricosa. The spectra from cotton, ramie, and hydrocellulose are virtually identical. Peak positions for all peaks are the same for the cotton, Acetobacter, and Valonia celluloses although there are differences in resolution and in the intensity of two broad resonances attributed to C-4 and C-6. These differences are ascribed to differences in the morphology of the samples. The higher resolution obtained in the NMR spectra of Acetobacter and Valonia celluloses plus the improved resolution obtained at an applied field of 4.7 T relative to 1.4 T shows definite multiplicity in the resonances assigned to C-1 and C-4. It is argued that this multiplicity is higher than two and reflects the fact that there must be more than two anhydroglucose residues per unit cell in the crystal structure of cellulose I.
With the use of cross-polarization, high-power decoupling, and "magic-angle" spinning techniques, high-resolution 13C NMR spectra have been obtained for the solid crystalline π-π molecular complexes of the donor molecule hexamethylbenzene with a series of acceptor molecules. Small shifts were found for the aromatic carbon resonance of the hexamethylbenzene moiety in the complexes compared to that for solid hexamethylbenzene itself. The shifts were roughly proportional to the electron affinities of the acceptor molecules, indicating a small degree of electron transfer in the ground state for these compounds. With the use of chemical shift1charge density relationships determined from solution NMR studies, the degree of electron transfer was estimated at ≤10% for the complexes studied.
Recent advances in experimental methods and computer modeling have shed new light on the kinetics of cellulose pyrolysis. The rich slate of reaction products that evolve when cellulose is heated implies that the pyrolysis chemistry is exceedingly complex. Nevertheless, a simple, first order, high activation energy (ca. 238 kJ/mol) model accurately describes the pyrolytic decomposition of an extraordinary variety of cellulosic substrates. Secondary vapor-solid interactions are the main source of char formed during cellulose pyrolysis. When a whole biomass substrate is pretreated to remove mineral matter, the pyrolysis kinetics of its cellulose component are very similar to those of pure cellulose. Future work should focus on the effects of mineral matter on pyrolysis, and the secondary vapor-solid reactions which govern char formation.
In this paper, samples o cellulose, hemicellulose, lignin, and nine species of whole biomass are pyrolyzed in sealed reactors. Very high charcoal yields (e.g., 40% from cellulose, 48% from Eucalyptus gummifera) were obtained. Higher sample loading (sample mass per unit reactor volume) increased charcoal yield and the associated exothermic heat release and lowered the reaction onset temperature. These effects were induced by the vapor-phase concentrations of the volatile products, and not the system pressure. Addition of water catalyzed the reaction and increased the char yield. These observations suggest that charcoal formation is autocatalyzed by water, an initial pyrolysis product. When whole biomass was used as a feedstock, higher charcoal yields were obtained from species with high lignin and/or low hemicellulose content.
Hard and softwood and wood constituent polymers (cellulose and lignin) were studied using Fourier transform infrared (FTIR) spectroscopy. The hollocellulose-to-lignin ratio was estimated for some of the timber species. The structural difference between Klason lignin isolated from softwood (Pinus roxberghii and cupressus lusitanica) and hard wood (Acacia auriculaeformis and Eucalyptus tereticornis) species was studied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1969–1975, 1999
We report here on the use of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to contrast the average chemical composition of modern degraded gymnosperm woods with fossil gymnosperm woods from Australian brown coals (Miocene). We first established the quantitative nature of the NMR techniques for these samples so that the conventional solid-state 13C NMR spectra and the dipolar dephasing NMR spectra could be used with a high degree of reliability to depict average chemical compositions. The NMR results provide some valuable insights about the early coalification of xylem tissue from gymnosperms. Though the cellulosic components of wood are degraded to varying degrees during peatification and ensuing coalification, it is unlikely that they play a major role in the formation of aromatic structures in coalified woods. The NMR data show that gynmosperm lignin, the primary aromatic contribution to the coal, is altered in part by demethylation of guaiacyl-units to catechol-like structures. The dipolar dephasing NMR data indicate that the lignin also becomes more cross-linked or condensed.
Cellulose pyrolysis has been investigated by combined TGA/DTA applying constant heating rates between 0.14 and 105 K min−1. The experiments entailed variation of initial mass and initial bulk density of the cellulose samples. The final mass depended on the heating rate as well as on the initial mass and bulk density and was reproducible when these parameters were carefully controlled. Mass transport resistance is a dominating factor increasing the char yield even in samples of 1 mg significantly at all heating rates. At higher initial sample masses, the char yield is determined by meshed heat and mass transport phenomena. Exothermic secondary reactions form additional char and change the overall heat of reaction. The heat released by secondary reactions promotes the volatilization of primary tars which in turn reduces the char yield. Fitting global reaction models to the experimental TGA results assuming a single first-order reaction yielded apparent kinetic parameters which were strongly correlated, but varied in a broad range depending in a complicated manner on heating rate and initial sample mass. This, together with the inherent impossibility to predict changes in product distribution, results in the restricted applicability of a single first-order reaction as predictive model for reactor analysis and design. Multi-step models with a modified Broido-Shafizadeh mechanism are more successful in describing experimental results for small sample masses. Nevertheless, they can not be extended to conditions under which secondary char is formed due to the lack of kinetic data in the literature.
The slow pyrolysis of biomass in the form of pine wood was investigated in a static batch reactor at pyrolysis temperatures from 300 to 720°C and heating rates from 5 to 80 K min−1. The compositions and properties of the derived gases, pyrolytic oils and solid char were determined in relation to pyrolysis temperatures and heating rates. In addition, the wood and the major components of the wood—cellulose, hemicellulose and lignin—were pyrolysed in a thermogravimetric analyser (TGA) under the same experimental conditions as in the static batch reactor. The static batch reactor results showed that as the pyrolysis temperature was increased, the percentage mass of solid char decreased, while gas and oil products increased. There was a small effect of heating rate on product yield. The lower temperature regime of decomposition of wood showed that mainly H2O, CO2 and CO were evolved and at the higher temperature regime, the main decomposition products were oil, H2O, H2, hydrocarbon gases and lower concentrations of CO and CO2. Fourier transformation infra-red spectroscopy and elemental analysis of the oils showed they were highly oxygenated. The TGA results for wood showed two main regimes of weight loss, the lower temperature regime could be correlated with the decomposition of hemicellulose and the initial stages of cellulose decomposition whilst the upper temperature regime correlated mainly with the later stages of cellulose decomposition. Lignin thermal decomposition occurred throughout the temperature range of pyrolysis.
The long-term role of fire in coastal temperate rain forest is poorly under-stood. To determine the historical role of fire on western Vancouver Island (British Co-lumbia, Canada), we constructed a long-term spatially explicit fire history and examined the spatial and temporal distribution of fire during the Holocene. Two fire-history parameters (time-since-fire [TSF] and fire extent) were related to three landscape parameters (landform [hill slope or terrace], aspect, and forest composition) at 83 sites in a 730-ha low-elevation (less than 200 m) area of a mountainous watershed. We dated fires using tree rings (18 sites) and 120 soil-charcoal radiocarbon dates (65 sites). Comparisons among multiple radiocarbon dates indicated a high probability that the charcoal dated at each site represented the most recent fire, though we expect greater error in TSF estimates at sites where charcoal was very old (6000 yr) and was restricted to mineral soil horizons. TSF estimates ranged from 64 to 12 220 yr; 45% of the sites have burned in the last 1000 yr, whereas 20% of the sites have not burned for over 6000 yr. Differences in median TSF were more significant between landform types or across aspects than among forest types. Median TSF was sig-nificantly greater on terraces (4410 yr) than on hill slopes (740 yr). On hill slopes, all south-facing and southwest-facing sites have burned within the last 1000 yr compared to only 27% of north-and east-facing sites burning over the same period. Comparison of fire dates among neighboring sites indicated that fires rarely extended 250 m. During the late Holocene, landform controls have been strong, resulting in the bias of fires to south-facing hillslopes and thus allowing late-successional forest structure to persist for thousands of years in a large portion of the watershed. In contrast, the early Holocene regional climate and forest composition likely resulted in larger landscape fires that were not strongly controlled by landform factors. The millennial-scale TSF detected in this study supports the distinction of coastal temperate rain forest as being under a fundamentally different disturbance regime than other Pacific Northwest forests to the east and south.
Stable carbon isotope analysis of tree rings has become a widely used proxy in environmental and palaeoclimatological studies. In those studies, a-cellulose has often been the preferred material because of its singular composition and its immobility in wood. However, cellulose extraction is a time-consuming procedure and since the development of on-line isotope ratio mass spectrometers has become the time-limiting step in the isotopic analysis of wood samples for dendrochemical purposes. In this study we evaluate the necessity of cellulose extraction for isotopic analysis of tree rings in a tropical mangrove tree, Rhizophora mucronata Lam. Comparison between the d 13 C of extracted a-cellulose and bulk wood material revealed a highly significant linear relationship (d 13 C bulk wood = 0.92 (F 0.08) * d 13 C a-cellulose À 2.91 (F 2.04); p b 0.001) for a-cellulose values between À24x and À27x. However a-cellulose was on average 0.97 F 0.03x enriched in 13 C as compared to bulk wood. The slope of the regression was not significantly different from one (p b 0.05). Furthermore, no significant difference was found between either the d 13 C bulk wood À d 13 C a-cellulose slopes for earlywood and latewood or between the slopes for samples from trees growing in contrasting environmental conditions. These results indicate that bulk wood can be used instead of a-cellulose when measuring stable carbon isotopes in the sapwood of R. mucronata in the context of a dendrochronological investigation. D 2005 Elsevier B.V. All rights reserved.
Atmospheric aerosol samples were collected in the Ivory Coast, primarily at Lamto (6N, 5W) between 1979 and 1981. The samples were analysed for total particulate carbon concentration and isotopic composition (13C/12C) by mass spectrometry. Observed concentrations were found high compared to values reported for temperate regions. Fine particulate carbon in the submicrometersize range accounted for 50 to 80% of the reported concentrations. At Lamto, both particulate carbon concentrations and isotopic ratios exhibit a large temporal variability which is shown to reflect the diversity of sources and their seasonal evolution. Natural emissions from the equatorial forest during the wet season, and biomass burning during the dry season, appear to be the major sources. The latter, though active during only a third of the year, is, on an annual basis, the most important source. Based on the data obtained at Lamto, an attempt has been made to estimate the flux of fine particulate carbon emitted from the tropical regions into the global troposphere. This flux, which is of the order of 201012 g C/yr, appears to be equivalent to the flux of fine particulate carbon emitted from industrial sources. These results suggest that the tropospheric burden of fine particulate carbon in lowlatitude regions is dominated by the long-range transport of carbonaceous aerosols originating from the Tropics.
An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by13C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the amorphous region between 79 and 86 ppm in the13C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing amorphous cellulose mainly as surface layers and induced reversible lattice distortions.
Solid-state NMR spectroscopy and Fourier transform IR (FTIR) spectroscopy have been used to study the degradation of cellulose in the form of transformer insulating paper and Whatman filter paper in air at temperatures from 200°C to 550°C for 1 h with and without 0.01 wt.% NaCl, ZnCl2 and CuCl2. The NMR studies included 1H wide line measurements of the spin-lattice relaxation time (T1) and spin-lattice relaxation time in the rotating frame (T1ρ), and 13C magic-angle spinning experiments. The 1H spectra and relaxation times indicated the presence of absorbed water and oxygen in the papers. On degradation, the 1H intensity and line width decreased, indicating the loss of hydrogen nuclei, and the 1H relaxation times decreased due to the formation of paramagnetic species. The 13C-NMR spectra and FTIR spectra indicated the formation of aromatic structures on degradation above 250°C, the conversion being essentially complete at 450°C. The presence of the salts had little or no effect on the rate or mechanism of degradation.
The cellulose fraction of botanicals recovered from archaeologically defined strata may be suitable for stable isotope-based palaeoclimatology in much the same manner as cellulose from tree rings has been utilized. However, manipulation by humans is a distinct possibility with such specimens and constitutes a potential source of isotopic alteration early in the post-mortem history of the samples. We studied the susceptibility of plant cellulose to isotopic alteration caused by manipulations related to food processing to determine if discarded plant foods recovered from archaeological contexts are suitable substrates for isotopic palaeoclimatic studies. The carbon and hydrogen isotope ratios of cellulose nitrate and the oxygen isotope ratios of cellulose were determined for Zea mays cobs, Helianthus annus seeds, Agave americana leaves, Pachyrrhizus erosus tubers and a cellulose standard before and after a variety of treatments, including boiling, roasting, fermentation, liming, molding and carbonization. The oxygen and hydrogen isotope ratios (which are climatically sensitive in all plants) and the carbon isotope ratios (which reflect climate only in certain plants) of all samples, except for Agave, were conserved during various food-processing steps. Thus, it appears that the isotope ratios of cellulose and cellulose nitrate prepared from many archaeological food plants, whether processed or uncooked, will reflect in vivo values and can be used to reconstruct aspects of palaeoclimate. Such isotopic palaeoclimatic studies will extend the utility and value of existing collections of ecofacts by opening a unique window for the study of the relationships among climate, plants and man.
Hydropyrolysis (hypy) as a fast means for preparing lignin concentrates for stable carbon isotope analysis was evaluated by performing hypy at different temperatures (200–500 °C) on Klason lignin concentrates, cellulose, and wood samples followed by bulk stable carbon isotope analysis of the solid residues. The δ13C values of cellulose, Klason lignin and their hypy residues revealed that hypy does not produce isotopic fractionation throughout the temperature range explored. The δ13C of hypy residues from cellulose-Klason lignin physical mixtures obtained at 500 °C were in the value range of the corresponding Klason lignin indicating that cellulose decomposed completely and that no major structural rearrangements, which could lead to carbon cross-linking between these two moieties are produced by hypy. The hypy residues obtained from wood samples at 500 °C were consistently depleted in 13C by 0.8‰ and enriched by 1.6‰ relative to the original wood and Klason lignin, respectively. This finding results from polysaccharide derivatives remaining in the wood residue, with a percentage of polysaccharide derived carbon 1.9 and 3.7 times higher than expected at 300 and 350 °C, respectively. It is concluded that the results presented here provide an indicator of the extent of cross-linking between lignin and polysaccharides (hemicellulose) in the native wood forming lignin–carbohydrate complexes.
To define the decomposition patterns of wood cell wall, three economically important brown-rot fungi, Coniophora puteana, Postia placenta, and Gloeophyllum trabeum were studied. Degraded Scots pine (Pinus sylvestris L.) sapwood blocks were analysed using 13C NMR spectroscopy, chemical, and water vapor sorption methods. C. puteana caused the most wood decay (55%) after 50 days of exposure, while the destructive abilities of P. placenta and G. trabeum were 32 and 30%, respectively. Hemicellulose was removed preferably to cellulose, but the intensity of depletion depended on the fungus species rather than the mass loss. P. placenta and C. puteana removed 11.8 and 14.7% of the lignin, respectively, while G. trabeum removed 25.2%. The possible re-polymerization of lignin stopped any further lignin degradation during attack by C. puteana and P. placenta, while G. trabeum continued to degrade lignin until the end of the test. Removal of lignin metoxyl groups and formation of the reactive phenolic hydroxyl groups can be coupled to the reactions of Fenton reagents or other powerful oxidants in acidic conditions. Removal of hemicellulose and lignin (primarily methoxyl groups) will promote further access of fungal metabolites to cellulose fibers. A common regularity of the surface A accessible to water molecules and the losses of the wood weight was obtained. The mass hydrophilicity of sorbent am in brown-rotted wood tended to decrease as the share of lignin increased.
The changes induced by thermal modification in the chemical structure of spruce [Picea abies (L.) Karst.], birch (Betula pendula), aspen (Populus tremula) and oak (Quercus robur) were studied by 13C CPMAS NMR spectroscopy. Spruce, birch and aspen were thermally modified at ∼195 °C and oak at ∼160 °C, under steam, according to an industrial-scale heat treatment process. In both hard- and softwood samples, 13C CPMAS NMR measurements revealed a degradation of less ordered carbohydrates (i.e. hemicelluloses and amorphous cellulose) in the thermally modified wood, which resulted in an increase in the cellulose crystallinity. Furthermore, thermal modification induced changes in the lignin structure by a cleavage of the β-O-4 linkages. In the softwood lignin, a decrease also occurred in the methoxyl group content leading to a more condensed lignin structure.
We investigated the δ13C values of pyrolysis products from cellulose and lignin, the main components of wood, to prove that in the pyrolysis process no isotope exchange between different pyrolysis products appears and that hence pyrolysis products represent the isotope content of their precursors. Two cellulose samples and a lignin sample with δ13C values of −23, −12 and −28‰, respectively, were pyrolysed using Curie point pyrolysis simultaneously coupled to GC/MS and GC/IRMS. All samples were pyrolysed individually and in mixtures of lignin with both isotopically different celluloses in two mixing ratios, e.g. 1:1 and 4:1; the latter is representative for wood. No intermolecular isotope exchange between pyrolysis products from cellulose and lignin was observed. This proves that Curie point pyrolysis is suitable for investigating the isotope content of pyrolysis products in complex mixtures like wood. Pyrolysis products from both celluloses and lignin have δ13C values similar to the bulk δ13C value of the respective sample. In mixtures of cellulose and lignin δ13C values of some pyrolysis products change slightly due to peak overlap and higher background signals. However, detected changes were independent from the isotopic difference between the mixing partners. Pyrolysis products such as 2,6-dimethoxyphenol, 4-methyl-2,6-dimethoxyphenol and trans-4-(2-propenyl)-2,6-dimethoxyphenol for lignin and 2-hydroxymethyl-5-hydroxy-2,3-dihydro-(4H)-pyrane-4-one and levoglucosane for cellulose were found to represent the isotopic signature from cellulose and lignin in mixtures regardless of the composition of the mixture.
It is generally accepted that thermal treatment of wood by mild pyrolysis (retification or torrefaction) improves its durability to fungal degradation. However, this property has recently been questioned in the literature and definitely needs further investigation. The increase in durability conferred by thermal treatment is generally explained by four hypotheses: the low affinity of heat-treated wood to water; the generation of toxic compounds during heating; the chemical modification of the main wood polymers and the degradation of hemicelluloses. This study was undertaken to understand the reasons for durability of heat-treated beech wood. In order to confirm or not the above mentioned hypotheses, the durability of heat-treated beech wood towards Coriolus versicolor was evaluated according to different parameters like mass loss, wettability or chemical composition. The heat treatment was carried out in a temperature range of 20–280 °C under inert atmosphere for 10 different temperatures. The results show clearly an important correlation between the temperature of treatment and the fungal durability. At the same time, there was insufficient evidence to support the hypothesis of improved decay resistance due to generation of fungicidal compounds or due to the hydrophobic character of wood. Finally, the most plausible hypothesis to explain improvement of wood durability concerns its chemical modifications. Indeed, degradation of hemicellulose associated with other chemical modifications appearing during treatment could be the origin of improved durability. There is a good correlation between decay resistance and mass loss measurements which are directly correlated to hemicellulose degradation.