Article

Soil organic matter (SOM) characterization by Rock-Eval pyrolysis :

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Application of Rock-Eval pyrolysis to soil organic matter (SOM) quantitation and characterization has been explored by the study of about 100 soil samples taken from a variety of soil profiles from different ecosystems at different latitudes. A straightforward illustration of these possibilities can be obtained from a Hydrogen Index (HI in mg hydrocarbons g−1 TOC) vs. Total Organic Carbon (TOC) diagram that effectively allows one to follow simultaneously the main qualitative (SOM hydrogen richness given by HI values) and quantitative (TOC) changes that affect SOM with increasing depth and humification, in the soil profiles. In addition, abnormally high Oxygen Index (OI in mg CO, CO2 or O2 g−1 TOC) values are fully diagnostic of extensive SOM alteration, as frequently observed in podzol B horizons. More detailed information on the heterogeneity of SOM and on its degree of evolution, can be gained from the shape of the pyrolysis S2 peak recorded in the course of programmed pyrolysis in an inert atmosphere (N2) and/or from its maximum temperature "Tpeak". All these parameters and others, all determined rapidly and automatically, are particularly useful to screen major SOM variations within large sets of samples

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... The Rock-Eval (RE) method was used on the same 52 samples at the ISTeP Laboratory with an RE turbo device (Vinci Technologies, France; see Behar et al. (2001) for details on the equipment). The analytical procedure was adapted from the procedure developed for the analysis of soil organic matter by Disnar et al. (2003). Briefly, approximately 60 mg of ground sample was subjected to two consecutive heating treatments, first in a pyrolysis oven (200-650 • C; thermal ramping rate, 30 • C⋅min − 1 ; under N 2 atmosphere) then in a combustion oven (300-850 • C; thermal ramping rate, 20 • C⋅min − 1 ; under laboratory air atmosphere). ...
... The pyrolysis effluents (mostly HC) were quantified with flame ionization detection, while CO and CO 2 were quantified using infrared detection during both the pyrolysis and oxidation stages. One of the major advantages of the RE method is that it provides TOC values without preliminary treatment such as decarbonation as required for the determination of the OC using classic combustion techniques (Disnar et al., 2003;Baudin et al., 2015). ...
... Here, the RE method (see Cécillon et al., 2018;Cécillon et al., 2021) again appeared to be an efficient and rapid tool for directly determining these two stable and active carbon pools characterizing the 52 agricultural soils, and for running the AMG model. In addition, RE can evaluate the total OC with a difference of about 10% or less (9%: Disnar et al., 2003;6%: Behar et al., 2001). ...
Article
Few studies have simultaneously addressed the issue of the short- and long-term hydrological control of organic carbon (OC) export from soils and the role of the leaching process in the long-term dynamics of the soil OC pool. We combined short- and long-term approaches by investigating dissolved organic carbon (DOC) at the outlet of a small drainage catchment and establishing a relationship between DOC concentrations (3.5 ± 1.8 mgC L⁻¹ on average) and subsurface runoff (175 mm yr⁻¹ on average). We then calculated the annual DOC export as a function of average annual water runoff for a 9-year period. We assumed that the annual flux of leaching is proportional to the active soil OC stock, which we compared with data from the literature. We added a leaching function to the AMG two-compartment model of soil carbon dynamics. The innovative use of the Rock–Eval method for agricultural soils made it possible to determine the stable and active carbon fractions (OCp and OCA, respectively), necessary to characterize the system in the model, for 52 plots in organic and conventional agricultural farms in the Seine Basin. No significant difference was found in OC for the two agricultural systems (11.4 ± 2.5 gC kg⁻¹ vs. 12.3 ± 4.2 gC kg⁻¹, respectively, for the 0 to 30 cm layer). Using the AMG model with its leaching function, we calculated the equilibrium value of OCA, representing the size of the OCA pool that would be reached in the long term under constant farming practices and hydrological conditions in a given plot. Deviation from this equilibrium indicates whether carbon storage or loss occurs. Overall, for the plots sampled in the Seine Basin, an annual carbon loss of ∼−0.24 % yr⁻¹ of the total OC pool was found. This may increase by 15% (i.e., to ∼−0.28% yr⁻¹) under higher subsurface runoff, which is plausible under ongoing climate change (e.g., 600 mm yr⁻¹ vs. 175 mm yr⁻¹ currently observed).
... Пиролитический анализ Rock-Eval -традиционный метод в нефтяной геологии, используемый для оценки нефтегенерационного потенциала осадочных пород [5][6][7][8]. Тем не менее в настоящее время он все чаще используется и для исследований органической компоненты почв и современных осадков [9][10][11][12][13][14]. В приведенных работах показано, что с помощью пиролитического анализа незрелого органического материала можно получить данные о доле морского и терригенного ОВ и степени его диагенетической преобразованности. ...
... 1). Традиционное графическое отображение данных пиролиза Rock-Eval представлено на рис. 2. Подобная интерпретация проведена на основе классификации керогена по типу исходного ОВ на основе соотношений O/C и H/C [9], применяемого при оценке нефтегенерационного потенциала материнских пород. Значения HI лежат в пределах 100-200 HC мг/г TOC, при этом значения OI находятся в диапазоне 180-310 CO 2 мг/г TOС. ...
... Интерпретация значений Tpeak основана на термической стабильности различных органических соединений, присутствующих в осадочном веществе. Так, низкие температуры, как правило, характерны для свежесинтезированного ОВ, в том числе биомакромолекул, таких как целлюлоза и лигнин [9]; углеводородов морского ОВ [24]; низкие значения Tpeak также фиксируются при высоком содержании дезоксисахаров, образующихся в процессе активного микробиального окисления во взвешенном ОВ [30]. Отметим, что для станций 6505 и 6016, находящихся в зоне сноса осадочного материала с близлежащих Новосибирских островов, ремобилизованного в результате береговой эрозии, характерны высокие значения Tpeak и повышение значений OI. ...
Article
Full-text available
Актуальность исследования обусловлена необходимостью всестороннего изучения процессов, ответственных за изменения биогеохимического режима арктического региона. Увеличение темпов деградации прибрежной и подводной мерзлоты на Восточно-Сибирском шельфе приводит к вовлечению в современный биогеохимический цикл большого объема ремобилизованного органического углерода. Изучение особенностей его транспорта и преобразования в системе суша–шельф играет важную роль для оценки функционирования крайне хрупкой арктической экосистемы. Цель: изучение геохимических характеристик органического вещества, прослеживаемых по профилю от береговой зоны к континентальному склону моря Лаптевых с применением метода Rock-Eval и оценка их взаимосвязи с литологическими свойствами вмещающих осадков. Объектом исследования явились пробы донных осадков, взятые с поверхностного горизонта (0–2 см). Отбор проб проводился в морских арктических экспедициях 2018–2019 гг. на НИС «Академик Мстислав Келдыш». Результаты. На основе результатов пиролитического анализа дана геохимическая характеристика органического вещества, содержащегося в донных осадках моря Лаптевых. Органическое вещество, экспортируемое с речным стоком и продуктами береговой эрозии, характеризуется относительно низким кислородным (OI) и водородным (HI) индексами в прибрежной зоне и на глубинах до нескольких десятков метров. В районе среднего шельфа существенное влияние на состав органического вещества, по всей видимости, оказывает снос осадочного вещества с Новосибирских островов, где активно действуют термоабразионные процессы (снижение значений HI и увеличение OI). Высказано предположение, что для продуктов, выносимых речным стоком, и продуктов эрозии берегов характерны различные пиролитические параметры, определяемые методом Rock-Eval (в частности, значения HI, OI и Tpeak).
... En effet, le domaine d'application de la Pyrolyse Rock-Eval a été élargi au cours des deux dernières décennies compte tenu de la fiabilité des informations apportées et sa facilité d'utilisation. La pyrolyse aborde, entre autres, l'étude de la MO des sols et des humus (Di- Giovanni et al., 1998 ;Disnar et al., 2003 ;Sebag et al., 2006, des sédiments lacustres et marins (Botz et al., 2007), des tourbières Gogo et al., 2010 ;Delarue et al., 2013). Elle est effectuée sur un appareil Rock-Eval VI. ...
... Ce qui a conduit à la mise au point de nombreuses techniques physicochimiques, dont la combinaison est généralement recommandée (Kögel-Knabner, 2000). Actuellement, les approches montrent que l'analyse thermique est appropriée pour une évaluation globale de la stabilité biogéochimique de la MOS (Disnar et al., 2003 ;Plante et al., 2011). Il s'agit de la technique de pyrolyse Rock-Eval (P-RE), initialement développée à des fins d'exploration pétrolière pour analyser le potentiel des roches-mères (Espitalié et al., 1985). ...
... Utilisée pour étudier la MO sédimentaire (i.e. Giovanni et al., 1999 ;Macaire et al., 2005 ;Copard et al., 2006) elle a montré son intérêt pour analyser la composition de la MOS et des litières (Baudin et al., 2015 ;Carrie et al., 2012 ;Delarue et al., 2013 ;Disnar et al., 2003 ;Obame et al., 2014 ;Saenger et al., 2013 ;Sebag et al. 2006Sebag et al. , 2013aSebag et al. , 2013bVolland-Tuduri, 2005). ...
Thesis
Full-text available
En régions arides et semi-arides, la gestion du carbone (C) du sol est inséparable des contraintes thermo-hydriques. Le concept de la séquestration du C pour ces régions est encore trop peu connu ou compris, en raison du manque des données expérimentales.Avant de pouvoir effectuer un bilan C à l’échelle des profils de sols et du paysage interdunaire, l’évaluation du stock de C du sol est nécessaire ainsi que la caractérisation de sa stabilité. L’étude a été conduite sur les sites des polders de Bol, nord-est du lac Tchad. Une chronoséquence par « approche synchronique » a été choisie selon les différents âges de poldérisation et de mise en culture ; les sites sélectionnés t0, t10, t60, t62 et à t65 correspondent à un historique de 0 à 65 ans. Le t0 représente le site de référence de sédiment récent. Les sols étudiés sont chimiquement fertiles ; ils se différencient sur les formations quaternaires anciennes de la cuvette tchadienne. Ce sont des sols d’apports alluviaux, hydromorphes, localement salés, cultivés de manière intensive. Dans ce dispositif, 36 profils pédologiques ont été creusés et décrits, y compris 3 profils dans la zone alluviale t0. Les sols ont été échantillonnés de la surface jusqu’à 1 m de profondeur, par incréments de 0,1 m.Les stocks de C organique (COS) (0-1 m) se différencient selon les traitements: à t0 200 ± 0,8 ; t10 241 ± 0,9 ; t60 183 ± 34 ; t62 174 ± 0,3 et à t65 189 ± 1,1 MgC ha-1 (P=0,004) ; les stocks de C inorganiques (CIS) pour la même profondeur sont négligeables et varient de façon significative entre traitements (P = 0,03) de 1 pour t0 à 6 MgC ha-1 pour t65 représentant environ 5 % de stocks de COS. Pour la couche de sol 0-0,3 m, les stocks de COS exprimés en masse de sol varient en moyenne de 53 à 64 MgC ha-1 entre t65 à t0 avec un taux de perte moyenne annuelle de -0,17 MgC ha-1 an-1. L’analyse par pyrolyse Rock-Eval confirme le caractère hérité de la matière organique de l’écosystème lacustre. Dans la couche de surface des sols (0-0,4 m), le caractère résistant de cette matière organique a également été révélé par des valeurs élevées observées des stocks de carbone résistant (ResC), entre 62,6 ± 13,8 et 79,9 ± 5,8 Mg C ha-1 de t0 à t65 par rapport à celles de carbone labile (LabC), plus faibles. Le compartiment résistant représente de 17 à 23 % du stock total de C. La relation entre l’acquisition des propriétés des sols suite à la poldérisation a été discutée au regard de la caractérisation physique des sols et de la nature de la matière organique. Après plus d’un demi-siècle de mise en poldérisation, les stocks de COS ont présenté un caractère relativement stable et résistant à la biodégradation dans ce contexte semi-aride.
... Indeed, these thermal indices are, by construction, highly correlated if the stabilization processes are driven by the gradual decomposition of thermally labile fractions (Albrecht et al., 2015;Sebag et al., 2016;Matteodo et al., 2018;Thoumazeau et al., 2020). This relationship is especially observed in OM-rich samples and interpreted as a consequence of the progressive In addition to these standard parameters, Disnar et al. (2003) proposed to use the shape of thermograms in order to get additional information about SOM quality. In this study, we used R-index (R) to measure the contribution of resistant and refractory C pools, and the I-index (I) to quantify the preservation of the labile C pool (Sebag et al 2016). ...
... Both indices are derived from integrated S2 areas between specific bounds (200-400 °C, 400-460 °C, and above 460 °C), usually interpreted as specific thresholds in thermal stability of organic compounds, separating thermally labile, resistant, and refractory C pools (fig. SM1 and SM2;Disnar et al., 2003;Sebag et al., 2006;Saenger et al., 2013Saenger et al., , 2015. Both indices are calculated from S2 thermograms (i.e., hydrocarbon compound released by thermal cracking under pyrolytic conditions) that seem little or not sensitive to interference with mineral matrix and catalytic reactions. ...
... 1-2, Tab. 1) related to decomposition and changes in chemical composition of soil OM. The results are in agreement with previous Rock-Eval ® studies (e.g., Di-Giovanni et al., 1998;Disnar et al., 2003;Sebag et al., 2006Sebag et al., , 2016Saenger et al., 2013). ...
Article
Soil organic matter (OM) is a complex heterogeneous mixture: resulting from decomposition and organo-mineral interactions, it challenges characterization in terms of composition and biogeochemical stability. From this perspective, the Rock-Eval® method is a rapid and efficient thermal analysis, which combines quantitative and qualitative information on soil OM, including several parameters related to thermal stability. This approach has already been used to monitor changes in OM properties at landscape, cropland, and profile scales. This study aims to assess the stability of soil organic matter pools by characterizing grain-size fractions from forest litters and topsoils using Rock-Eval® thermal analyses. Organic and topsoil samples were selected from a beech forest located in Normandy (France), whose management has been documented for the last 200 years. Fractionation by wet sieving was used to separate large debris (>2000 μm), coarse (200–2000 μm), and fine particulate organic matter (50–200 μm) in organic samples, and coarse (200–2000 μm), medium (50–200 μm), and fine (<50 μm) fractions in topsoils. Rock-Eval® was able to provide thermal parameters sensitive enough to study fine-scale soil processes. In organic layers, quantitative and qualitative changes are all explained by progressive decomposition of labile organic compounds from plant debris to the finest organic particles. On the other hand, the grain size fractions of the topsoil display different characteristics: indeed, the coarse organo-mineral fractions show high C contents, but with a different composition and a higher thermal stability and degree of decomposition than the plant debris forming the organic layers. These results are consistent with previous studies concluding that the microbial activity is more effective in this fraction. The finest fractions of topsoil reveal low C contents and the highest thermal stability, but also a low degree of decomposition, which can be explained by stronger interactions with the mineral matrix. Therefore, it is suggested that the dynamics of OM present in the different size fractions be interpreted in the light of a plant-microbes-soil continuum. Finally, three distinct thermal stability C pools are highlighted through the grain-size heterogeneity of soil OM: free-coarse organic matter (large debris, coarse and fine particles), weakly-protected organic matter in (bio)aggregates (coarse fraction of topsoil), and stabilized organic matter in fine fractions of topsoil, the latter resulting from interactions inside organo-mineral complexes. These results allow Rock-Eval® thermal parameters to be used in order to empirically illustrate the conceptual models emphasizing the role of drivers played by the gradual decomposition and protection of the most thermally labile organic constituents.
... The S2 peak is non-Gaussian and is accompanied by shoulders for the immature samples. The different peaks and shoulders correspond to the cracking of the different organic compounds (Disnar 1982;Disnard and Trichet 1984;Disnar et al., 2003). The literature concerning the shape of the pyrolysis S2 peak is mainly focused on soils samples. ...
... The S2 peak shows a broad shape and two T peak at 370 • C and 460 • C (C3 and C4) (Fig. 5a), typical of a soil sample and in agreement with the bulk RE results. The cluster C3, at 370 • C can be attributed to the thermal breakdown of biological constituents such as polysaccharides and lignin (Disnar et al., 2003). The C4 cluster shows more preserved OM. ...
... The R400 parameter (proportion of the S2 peak integrated before 400 • C, Disnar et al., 2003) and depending on the proportion of labile and probably more diagenetically reactive biomolecules was also calculated (supplementary data 1). This parameter varied between 0.1 and 0.6 and was higher for surface samples (0.6 at 0-30 cm) indicating the presence of 60% of labile OM in the surface. ...
Article
Samples of Albian Tégulines Clay outcropping near Brienne-le-Château in the eastern part of the Paris Basin were subjected to a geochemical characterization of organic matter (OM), combining OM bulk Rock-Eval analysis (RE), organic petrography and molecular analysis. In this study, the objective was to investigate the oxidation of natural organic matter in critical zone developed in early reduced marine clay formation. For that purpose, core samples from three boreholes crosscutting the Tégulines Clay formation down to the Greensands were selected. Several meters of Brienne marls preserved Tégulines Clay from atmosphere and therefore from high weathering and high oxidation in AUB240 borehole, whereas Tégulines Clay were weathered in their upper part in AUB1010 and in AUB230 boreholes as a result to their vicinity to the surface. The results showed that the Total Organic Carbon (TOC) contents in all clays are very low, ranging between 0.3 and 0.7 wt%. The RE bulk data and Tmax parameter of OM in preserved Tégulines Clay indicate that the OM is immature. The organic petrography shows a predominance of gel-like amorphous OM preserved by natural sulphurisation in anoxic environments. Organic matter in Tégulines Clay from the AUB230 and AUB1010 boreholes show similar characteristics. The OM at the top of Tégulines Clay contains large amounts of oxidized lignocellulosic debris and has high RE Oxygen-Index values. In the first upper 10 m of the clays, the RE bulk, organic petrography and molecular data revealed oxidative events (high OI and high oxidized debris contents). Below 10 m, the OM is almost preserved. The OM in the reduced marine Tégulines Clay formation is very little functionalized and seems to be slightly reactive but not negligibly with the inorganic fractions in presence of oxygen.
... Originally developed to provide information on the content of hydrocarbons and the kerogen type in sedimentary rocks, as well as determine the maturity of the kerogen (Disnar, 1994;Lafargue et al., 1998), Rock-Eval analysis has become an attractive and fast alternative for the analysis of organic matter in soils and sediments compared to conventional methods due to the lack of sample preparation (Disnar et al., 2003;Sebag et al., 2006). Rock-Eval analysis provides not only the quantity of organic carbon but also information on the elemental composition of the OM. ...
... The representation of the HI against TOC allows the estimation of the soil OM quality, which is usually determined by the mineralization of the soil OM and the dilution by the mineral matrix. Fresh and fragmented litter usually shows high TOC levels (10 %-40 %) and HI values greater than 300 (Disnar et al., 2003). This results from the material consisting primarily of unconverted biopolymers such as lignin, cellulose, and hemicellulose. ...
... The socalled S2 peak integrates the quantity of pyrolyzed emission products between 200 and 650 • C. Utilizing mathematical deconvolution determines individual peaks within the S2 peak. Fractions of OM differing in thermal stability are assignable to the resulting temperature intervals: (A1) 200-340 • C, thermally unstable biological macromolecules, like saccharides; (A2) 340-400 • C, stable biological macromolecules, like cellulose and/or lignin or polypeptides; (A3) 400-460 • C, immature geological macromolecules, like humic substances; (A4) 460-520 • C, re-fractory geological macromolecules; and (A5) 520-650 • C, highly refractory pool (Disnar et al., 2003;Sebag et al., 2006Sebag et al., , 2016. Investigations of composts using 13 C nuclear magnetic resonance (NMR) showed that the thermal stability separating the mentioned groups also correlates with the chemical stability (Albrecht et al., 2015). ...
Article
Sedimentary organic matter (OM) analyses along a 130 km long transect of the Mkhuze River from the Lebombo Mountains to its outlet into Lake St Lucia, Africa's most extensive estuarine system, revealed the present active trapping function of a terminal freshwater wetland. Combining bulk OM analyses, such as Rock-Eval®, and source-specific biomarker analyses of plant-wax n-alkanes and their stable carbon (δ13C) and hydrogen (δD) isotopic composition showed that fluvial sedimentary OM originating from inland areas is mainly deposited in the floodplain and swamp area of the wetland system but not in the downstream lake area. A distinctly less degraded OM signature, i.e., a considerably lower degree of transformation of unstable components (higher I index) and lower contribution of refractory and persistent fractions (lower R index) as well as recognizably higher δD values compared to samples from upstream sub-environments, characterizes surface sediments of Lake St Lucia. The offset in δD indicates that the contributing vegetation, although similar to upstream vegetation inputs in terms of photosynthetic pathway (δ13C) and alkane distribution pattern, experienced different hydrological growth conditions. The results suggest that under current conditions hinterland sedimentary OM is deposited throughout the wetland system up to the Mkhuze Swamps, which ultimately captures the transported OM. Consequently, samples from the downstream located Lake St Lucia show locally derived signals instead of integrated signals encompassing the river catchment. This finding raises important constraints for future environmental studies as the assumption of watershed-integrated signals in sedimentary archives retrieved from downstream lakes or offshore might not hold true in certain settings.
... The Rock-Eval® pyrolysis, developed by IFPEN for petroleum industry (Espitalie et al., 1986;Lafargue et al., 1998), is a simple, fast, cost-effective method for obtaining information on the carbon content, composition, and thermal stability of OM. In the context of soil science, it is recommended for quantitative and qualitative characterization of SOM (Derenne and Quenea, 2015;Disnar et al., 2003;Feller et al., 2010). The literature has shown that the thermal status of SOM during Rock-Eval® pyrolysis provides an overall approximation of its biogeochemical stability (Barré et al., 2016;Fernández et al., 2011;Gregorich et al., 2015;Plante et al., 2011). ...
... In this study, thermal status of SOM was characterized by combining two indexes (denoted R and I) calculated from five subdivided areas of the S2 thermograms related to HC (Disnar et al., 2003;Sebag et al., 2006Sebag et al., , 2016. Areas were calculated between the following bounds (or nodes): 200−340°C for A1, 340−400°C for A2, 400−460°C for A3, 460−520°C for A4, and 520−650°C for A5. ...
... Areas were calculated between the following bounds (or nodes): 200−340°C for A1, 340−400°C for A2, 400−460°C for A3, 460−520°C for A4, and 520−650°C for A5. The forms of S2 thermograms depend upon the OM cracking temperature, as expressed through five pools corresponding to the sections of the thermograms: highly labile (A1), labile (A2), resistant (A3), refractory (A4) and highly refractory (A5) (Disnar et al., 2003;Sebag et al., 2016Sebag et al., , 2006. ...
... Moreover, the indicator developed by Hurisso et al. (2016) has not been validated adequately by comparison with other more conventional methods for assessing SOC dynamics. To explore how the in-field indicator is related to soil carbon dynamics, we chose Rock-Eval® pyrolysis method which is based on the thermal analysis of SOC (Disnar et al., 2003). Rock-Eval® pyrolysis has been identified as one of the most promising methods for assessing SOC dynamics (Barré et al., 2016). ...
... Qualitative and quantitative parameters are calculated by integrating the amounts of hydrocarbons, CO, and CO 2 produced during thermal cracking of organic matter, between defined temperature limits (Behar et al., 2001;Lafargue et al., 1998). This technique has been recommended for characterizing soil organic matter (Derenne and Quénéa, 2015;Disnar et al., 2003). In this study, soil organic matter dynamics was analyzed through the combination of two indices (I and R) calculated from five areas of the hydrocarbon thermograms, according to predefined temperature thresholds (Disnar et al., 2003;Sebag et al., 2016Sebag et al., , 2006. ...
... This technique has been recommended for characterizing soil organic matter (Derenne and Quénéa, 2015;Disnar et al., 2003). In this study, soil organic matter dynamics was analyzed through the combination of two indices (I and R) calculated from five areas of the hydrocarbon thermograms, according to predefined temperature thresholds (Disnar et al., 2003;Sebag et al., 2016Sebag et al., , 2006. By construction, the R-index is related to the most thermally refractory fraction of organic matter, while the I-index is related to the most thermally labile one (see Sebag et al. (2016) for details). ...
Article
The assessment of the impacts of land-use and management on soil organic carbon (SOC) dynamics is a major environmental concern, as the soil carbon cycle underpins key ecosystem services. However, assessments based on short-term SOC dynamics face methodological and experimental difficulties. Hurisso et al. (2016) proposed a method to assess SOC dynamics by coupling two methods: Permanganate Oxidizable Carbon (POXC) and Basal Soil Respiration (BSR). This method has been used in laboratory on dried and re-wetted soil samples from temperate regions mainly. In our study, we adapted this method to the field and proposed a cost-effective in-field indicator combining the POXC and in situ Basal Soil Respiration (SituResp® method). We tested the indicator at four study sites (n = 169 points) within various tropical land-use and management contexts based on rubber, soybean and oil palm cropping systems respectively in Thailand, Cambodia and Indonesia. The results demonstrated the relevance, sensitivity and robustness of the POXC-SituResp® indicator to characterize the impact of a gradient of disturbance on SOC dynamics. The results also highlighted the potential of conservation agriculture (no-tillage and crops residues) and compost amendments to accumulate SOC. Rock-Eval® analysis showed that POXC-SituResp® indicator is negatively linked to excess of potentially mineralizable labile carbon. Carbon pools targeted by the POXC were specified by Rock-Eval® pyrolysis measurements to be a rather thermal resistant pool of SOC. Our study confirms that the integrated indicator based on POXC and BSR assess a relative carbon stabilization of SOC pools. This indicator can be measured in the field by a rapid and cost-effective method.
... Persistence is expected to depend on three major processes (Sollins et al., 1996): (i) physical protection (Balesdent et al., 2000), (ii) physico-chemical protection (von Lützow et al., 2006) and (iii) chemical recalcitrance (Angst et al., 2016). (i) The physical protection is related to the accessibility of SOC to decomposers, either depending on the distance between SOC particles, limiting the likelihood of degradation by microorganisms (Don et al., 2013), or on the formation of clay-sized aggregates, entrapping SOC and making it inaccessible to microorganisms (Chenu et al., 2009). (ii) The interaction between SOC and mineral particles determines an energy barrier inducing the physico-chemical protection of organic matter (OM) against decomposition (Mikutta and Kaiser, 2011). ...
... In addition to thermal characterization of SOC, information on OM chemistry can be obtained (Saenger et al., 2013). Chemical indices can be derived from the analysis and related to OM stoichiometry (Disnar et al., 2003). Specifically, PyOC being a substantial SOC component in several LTBF samples (Lutfalla et al., 2017), it gives the possibility of focusing on the origin of long-term persistence of PyOC compounds. ...
Article
Full-text available
Evolution of organic carbon content in soils has the potential to be a major driver of atmospheric greenhouse gas concentrations over the next century. Understanding soil carbon dynamics is a challenge due to a wide range of residence times of soil organic matter and limited constraints on the mechanisms influencing its persistence. In particular, large uncertainties exist regarding the persistence of pyrogenic organic carbon in soils. In order to characterize organic matter with varying degrees of persistence and to distinguish pyrogenic organic carbon, we combined Rock-Eval analysis, a thermo-chemical method, with the benzene polycarboxylic acid molecular marker method and Raman spectroscopy to characterize samples from long-term bare-fallow experiments, progressively depleted in the most labile organic carbon over time. Considering the heterogeneity of soil samples, size fractions have been separated to distinguish pools of organic carbon with distinct properties. We observe that organic carbon dynamics is dependent on granulometry. A pool of organic carbon with intermediate residence times, from years to a few decades, representing ca. 65 % of the bulk soil organic carbon stock, is mainly associated with fine fractions ( 20 µm) are rich in centennially persistent organic carbon, representing ca. 20 % of the initial organic carbon stock, due to the chemical recalcitrance of organic matter in these fractions, dominated by pyrogenic organic carbon. A second pool of persistent organic carbon, representing ca. 15 % of the initial organic carbon stock, is associated with the clay fraction, indicating mechanisms of protection occurring at the submicron scale (
... Generally T peak measurements represent the thermal stability of OM compounds indicating its potential source. The high T peak results are typical for decomposition of immature humic substances (420-470 • C), which were detected for organo-mineral soil horizons by [75]. Nevertheless, some regional contrasts for the ESAS permafrost carbon pools should be addressed. ...
... The shift from high T peak values near the coastlines to low T peak range on the outer shelf reflects an increasing contribution of labile autochthonous compounds and shorter hydrocarbon chains. Low temperatures are typical for more recent organic matter reflecting the thermal breakdown of biological constituents such as polysaccharides and lignin and/or cellulose [75] or high deoxy sugar content associated with active microbial degradation in fine particulate OM as proposed by [31,77]. The abundances of lignin phenol proxies across the East Siberian Arctic shelf have been widely investigated by previous researchers [11][12][13]78,79]. ...
Article
Full-text available
Global warming in high latitudes causes destabilization of vulnerable permafrost deposits followed by massive thaw-release of organic carbon. Permafrost-derived carbon may be buried in the nearshore sediments, transported towards the deeper basins or degraded into the greenhouse gases, potentially initiating a positive feedback to climate change. In the present study, we aim to identify the sources, distribution and degradation state of organic matter (OM) stored in the surface sediments of the Laptev Sea (LS), which receives a large input of terrestrial carbon from both Lena River discharge and intense coastal erosion. We applied a suite of geochemical indicators including the Rock Eval parameters, traditionally used for the matured OM characterization, and terrestrial lipid biomarkers. In addition, we analyzed a comprehensive grain size data in order to assess hydrodynamic sedimentation regime across the LS shelf. Rock-Eval (RE) data characterize LS sedimentary OM with generally low hydrogen index (100–200 mg HC/g TOC) and oxygen index (200 and 300 CO2/g TOC) both increasing off to the continental slope. According to Tpeak values, there is a clear regional distinction between two groups (369–401 °C for the inner and mid shelf; 451–464 °C for the outer shelf). We suggest that permafrost-derived OM is traced across the shallow and mid depths with high Tpeak and slightly elevated HI values if compared to other Arctic continental margins. Molecular-based degradation indicators show a trend to more degraded terrestrial OC with increasing distance from the coast corroborating with RE results. However, we observed much less variation of the degradation markers down to the deeper sampling horizons, which supports the notion that the most active OM degradation in LS land-shelf system takes part during the cross-shelf transport, not while getting buried deeper.
... It indicates how terrigenous in origin the organic matter is (Fahl and Stein, 1999;Lafargue et al., 1998). However, a study on soil organic matter shows that lipids degrade first, derived from a decrease in HI values down core concurrent with increasing OI values (Disnar et al., 2003). Thus, this can also be interpreted as selective preservation of compounds or a change in the organic matter source. ...
... The relatively high HI in this upper most part of the core could potentially be the result of lower organic matter degradation and therefore would not be an indication of increased marine productivity alone. Elevated HI values in the upper parts of sediments cores have been recorded in other studies and interpreted to result from lower degradation of fresh labile organic matter in the top samples (Bailey et al., 2013;Carrie et al., 2012;Disnar et al., 2003;Sanei et al., 2005;Wagner and Henrich, 1994). ...
Article
Full-text available
Radiocarbon dating of Arctic marine sediment is often challenging due to the low availability of calcareous fossils. Consequently, bulk organic matter dating has at times been used to establish sediment core chronologies. Yet, radiocarbon dates based on bulk organic matter often appear to deviate vastly from dates based on fossils, mainly caused by input of allochthounous carbon, including terrigenous organic matter. In this study, we aim to examine the link between the composition of the bulk organic matter and the age offsets between the bulk radiocarbon dates and those obtained from calcareous foraminiferal tests. All samples are taken from the marine sediment core AMD14-204C from offshore Upernavik (eastern Baffin Bay). The radiocarbon dates for bulk organic matter are on average ∼3000 years older than the radiocarbon dates based on foraminifera, but with changing age offsets throughout the record. To investigate the cause of this age offset and its variations over time, we applied core scanning, X-ray Fluorescence analysis, stable isotopes, organic pyrolysis and microscopic organic petrology to examine the distribution and characterization of the organic matter. The results show that the older organic matter includes clastic input of reworked sedimentary rocks potentially originating from West Greenland and/or the Canadian Arctic Archipelago. Changes in the input of contemporary marine algal produced organic matter versus both terrigenous input and reworked ancient organic matter appear to control the age offsets between the bulk and foraminifera dates. A low Hydrogen Index and low δ¹³Corg values together with a high Oxygen Index, indicative of high influence of terrigenous organic matter, seem to correspond to samples with the largest age offsets; 1000–2000 years greater than in other samples. To examine the cause of the variations in the age offsets, a new quantification of the autochthonous organic matter as a fraction of the TOC was calculated. This shows that samples with the largest age offsets contained the lowest fraction (as low as ∼12%) of autochthonous organic matter in the TOC.
... Catena 190 (2020) 104513 ( Fig. 9A), reflecting the input of material from a terrestrial origin (Carrie et al., 2012). In detail, the values of these two indicators of OM quality reflect an organo-mineral soil horizons origin (A horizon) (Disnar et al., 2003). Conversely, the U1 facies of both ponds are characterised by an HI/OI ratio of approximately 2 (Fig. 9A), suggesting that the OM origin is either aquatic (Carrie et al., 2012) or, with respect to the HI and OI values, detrital (OH or A horizons) (Disnar et al., 2003). ...
... In detail, the values of these two indicators of OM quality reflect an organo-mineral soil horizons origin (A horizon) (Disnar et al., 2003). Conversely, the U1 facies of both ponds are characterised by an HI/OI ratio of approximately 2 (Fig. 9A), suggesting that the OM origin is either aquatic (Carrie et al., 2012) or, with respect to the HI and OI values, detrital (OH or A horizons) (Disnar et al., 2003). Therefore, OM in the U1 facies is less altered and may have a mix aquatic/terrestrial origin, than that stored in the U2 facies. ...
Article
Full-text available
Most rivers worldwide are contaminated by various trace metals from different origins, which may be stored for considerable periods of time in depositional areas. Most of these studies are focused on the main river of a watershed and the tributaries are often neglected which can be important sources of contamination. The aim of this study was to reconstruct the anthropogenic activities that occurred in the Eure River, tributary of the Seine Estuary, since the 1940s using "legacy sediments". The results showed that the temporal trends of trace metals were not related to detrital inputs and TOC variations but with the industrial history of the Eure River watershed. The high levels of Zn, Cu, and Ni during the 1950s and the 1960s, and the decrease with the decline of the probable main source of release showed the watershed reactivity to anthropogenic activities. The high levels of Pb during the 1990s and the 2000s showed that the watershed reacted immediately to anthropogenic pressures. The Pb levels remained important after the cease of industrial activity, showing that a resilience period is necessary for the system, and that interactions between human activities and the environment go beyond of the activities themselves.
... Qualitative and quantitative parameters are calculated by integrating the amounts of hydrocarbons, CO, and CO2 produced during thermal cracking of organic matter, between defined temperature limits (Behar et al., 2001;Feller et al., 2010;Lafargue et al., 1998a). This technique has been recommended for the characterisation of soil organic matter (Derenne and Quénéa, 2015;Disnar et al., 2003) and recently proved to be relevant in a similar context (Thoumazeau et al., 2020). ...
... Soil organic carbon quality was assessed with the R-index calculated as the relative HC contribution of the most thermally resistant organic fraction (i.e. thermal cracking above 400°C; see Disnar et al., 2003;Sebag et al., 2016Sebag et al., , 2006. The higher the R-index, the more organic fractions are thermally resistant. ...
Article
Full-text available
Rubber tree plantations (Hevea brasiliensis) cover large areas in the tropics. In historical producing regions like South Thailand, rubber has been planted by smallholders for three successive rotations lasting a total of 75 years. Despite possible consequences on topsoil, the long-term impacts of repeated rubber plantations on soil quality remain unknown. This study aims to better understand how various factors linked to long-term rubber land use and land use change affect topsoil physico-chemical properties and soil organic carbon (SOC) thermal stability. We focus on the effects of three factors: i. deforestation (change from forest to first rubber plantation); ii. the age of the rubber stand (immature vs mature); and iii. Long-term rubber cultivation (first, second or third successive rotation) over a chronosequence in farmers plots. Our results show that soil was deeply degraded after deforestation to a rubber plantation. Long-term rubber cultivation is also detrimental for the soil and has a more negative impact on soil physico-chemical properties and carbon dynamics, than the age of the rubber stand (e.g. on average, decrease of 50% of SOC content between forest and third rotation). At the third rotation, after 50 years of rubber cultivation, the quality of the 0–10 cm soil layer was very low, with an increase in SOC thermal stability. At this stage, logging practices upset the sustainability of the system. These impacts could be limited by less destructive practices during planting. This article is protected by copyright. All rights reserved.
... Free hydrocarbon (HC) effluents were also measured during the pyrolysis step by a flame ionization detector (FID). Several standard parameters referring to OM chemistry were computed (Disnar et al., 2003;Schomburg et al., 2018), including: total organic carbon (TOC), pyrolysable carbon (PC), residual carbon (RC), hydrogen index (HI) and oxygen index (OI). Several additional RE6 parameters indicative of OM stability were also calculated. ...
... The S2 signal, released during the pyrolysis phase, showed peaks corresponding to the successive cracking of organic compounds of different thermal stability (Disnar et al., 2003;Copard et al., 2006;Saenger et al., 2013). The R-index is related to the contribution of OM compounds with higher thermal stability. ...
Article
Stabilization of organic matter (OM) against decomposition and its de-stabilization leading to mineralization are important processes controlling greenhouse gas emissions and carbon sequestration in soils. Soil organisms, particularly earthworms, may greatly influence these processes through their potential impact on the interaction of OM with clay minerals, a mechanism which may protect OM at medium (years) to long (decades, centuries) time scales. The aim of this study was to use earthworms and pure minerals in order to enhance carbon sequestration through the formation of aggregates containing particulate OM and organo-mineral associations during a composting experiment. To this end we compared OM transformations in composting treatments with and without (i) clay minerals (montmorillonite) and (ii) epigeic earthworms (Eisenia andrei and Eisenia foetida). We used density fractionation of the end-products to quantify the amount of aggregates including organo-mineral associations formed during 196 days. Their chemical composition and stability were analyzed by elemental analyses, Rock-Eval 6 thermal analysis and solid-state ¹³C nuclear magnetic resonance spectrometry. Our results indicated that the addition of minerals led to the formation of heavy fractions most probably containing aggregates and organo-mineral associations in treatments with and without earthworms. While OM showed higher oxidative transformation in all treatments, addition of earthworms changed organic carbon (OC) and nitrogen (N) concentrations in specific density fractions and increased the thermal stability of OM in heavy density fractions. These fractions contained higher proportions of aromatic and proteinaceous material. We conclude that earthworms under composting conditions may be able to effectively stabilize OM, though the formation of aggregates and/or organo-mineral associations containing greater proportions of microbial-derived material.
... Persistence is expected to depend on three major processes (Sollins et al., 1996): (i) physical protection (Balesdent et al., 2000), (ii) physico-chemical protection (von Lützow et al., 2006) and (iii) chemical recalcitrance (Angst et al., 2016). (i) The physical protection is related to the accessibility of SOC to decomposers, either depending on the distance between SOC particles, limiting the likelihood of degradation by microorganisms (Don et al., 2013), or on the formation of clay-sized aggregates, entrapping SOC and making it inaccessible to microorganisms (Chenu et al., 2009). (ii) The interaction between SOC and mineral particles determines an energy barrier inducing the physico-chemical protection of organic matter (OM) against decomposition (Mikutta and Kaiser, 2011). ...
... In addition to thermal characterization of SOC, information on OM chemistry can be obtained (Saenger et al., 2013). Chemical indices can be derived from the analysis and related to OM stoichiometry (Disnar et al., 2003). Specifically, PyOC being a substantial SOC component in several LTBF samples (Lutfalla et al., 2017), it gives the possibility of focusing on the origin of long-term persistence of PyOC compounds. ...
... Hydrocarbon biomarkers. The traditional method for study of molecular OM composition of oil source rocks is pyrolysis in the version of Rock-Eval (RE-pyrolysis) and the method of Chromato-Mass-Spectrometry (Pyr-GC MS), which, due to its simplicity and reliability began to be widely used for study of immature OM in samples of soils and recent lacustrine sediments (Disnar et al., 2003). This is based on the fact that pyrolysis of OM sample of recent sediment may be represented as a complex process comprised of a series of consecutive stages of decomposition of some OM components differing in nature and thermal stability and, consequently, in temperature intervals of their decomposition. ...
Article
—We present results of study of the chemical composition of organic matter (C, H, N, and S) from Holocene sections of lake sapropels with undisturbed stratification penetrated by vibratory drilling of the bottom sediments, down to the underlying rocks, of Lakes Bol’shie Toroki (1.8 m), Minzelinskoe (5 m), Ochki (4.5 m), Dukhovoe (7 m), and Kotokel’ (6 m). We consider methodological approaches to the identification of the sources and genesis of buried organic matter in marine and lacustrine sediments by a number of organogeochemical indicators: data of a biological analysis (biostratification based on layer-by-layer determination of organic relics in bottom sediment sections); hydrocarbon biomarkers (molecular composition of normal aliphatic hydrocarbons (n-alkanes), nitrogen compounds of a protein complex, etc.); and C/N ratio reflecting a difference in the biochemical compositions of bioproducers. The results of biological analysis (biostratification) show that planktonogenic sapropel (phyto- and zooplankton, the autochthonous source of organic matter) in Lake Ochki formed for 10,760 years, and sphagnum and hypnum moss were supplied from the bogged shores (allochthonous source of organic matter). In Lake Minzelinskoe, peaty sapropel formed at the stage of a flooded lowland bog (5905 years ago); since 3980 years ago and till the present, macrophytogenic sapropel has formed. Pyrolytic study (RE pyrolysis and Pyr–GC–MS analysis) of bioproducers and sapropel from Lake Ochki has shown that phytoplankton and zooplankton were the main autochthonous source of OM in the lake, which is confirmed by the identified macromolecules of nitrogen compounds of different compositions. The presence of hopanes indicates the contribution of microorganisms to the formation of OM in the sediments. The organic matter of sapropel has a terrigenous component, which is confirmed by the presence of high-molecular odd-numbered n-alkanes, ketones, and methyl esters of fatty acid. The C/N ratios in the stratified sections of macrophytogenic sapropels of Lakes Bol’shie Toroki and Minzelinskoe fall in the range of values specific to higher aquatic and terrestrial vegetation (C/N = 15–18), whereas the C/N ratios in planktonogenic sapropel of Lake Dukhovoe are typical of marine and lake plankton (C/N = 5.7–8.6).
... We used a Rock-Eval 6 turbo device (Behar et al., 2001) for the thermal analysis of bulk samples. We adapted the procedure developed for the analysis of SOM proposed by Disnar et al. (2003) as specified in Souc� emarianadin et al. (2018). Briefly, about 60 mg of ground sample were subjected to two consecutive thermal treatments: first, samples were transferred to a pyrolysis oven (under N 2 atmosphere) then to a combustion oven (under laboratory air atmosphere). ...
Article
The fate of organic matter (OM) occluded in earthworm casts during the casts' lifetime is poorly known. We collected casts produced by the anecic earthworm Amynthas khami in tropical woodland in Northern Vietnam at different times after their production. The aim of this study was to assess the (1) the effect of earthworms on biogeochemical OM properties compared to control aggregates, separated from the surrounding soil and (2) the fate of OM during cast ageing. We analyzed five cast ageing stages for elemental content, OM chemical composition by analytical pyrolysis and stability by Rock-Eval thermal analysis. Moreover, we assessed the distribution of organic carbon (OC) in density fractions. Compared to control aggregates, fresh casts had higher OC values (5.3 vs. 2.6%) and increased OC in all density fractions. Cast OM had more lignin (1.1 vs.<0.1%), similar polysaccharide and N-compound contribution and was more thermally labile than those of control aggregates. Changes in OM composition and content during cast ageing appeared at the end of the casts’ lifetime, when they were broken into small sized aggregates (10–13 mm). At these latest stages, OC content decreased (1.5-fold); along with OM in macro-aggregates (2.2-fold) and microaggregates (6.8-fold). Reduced mineral-associated OC was also recorded (1.3-fold). During ageing, the percentage of lignin decreased (5.5-fold) while the thermal stability of OM increased. Most properties were still significantly different between the oldest ageing stage and control aggregates. This study highlights that the impact of earthworms on OM storage goes beyond cast disintegration and that there is a need to better understand their influence on soil organic matter stabilization processes and in particular the formation and stability of organo-mineral associations.
... In addition to thermal characterisation of SOC, information on OM chemistry can be obtained (Saenger et al., 2013). Chemical indices can be derived from the analysis and related to OM stoichiometry (Disnar et al., 2003). Specifically, PyOC being a substantial SOC component in several LTBF 15 samples (Lutfalla et al., 2017), it gives the possibility to focus on the origin of long term persistence of PyOC compounds. ...
Preprint
Full-text available
Evolution of organic carbon content in soils has the potential to be a major driver of atmospheric greenhouse gas concentrations over the next century. Understanding soil carbon dynamics is a challenge due to a wide range of residence time of soil organic matter and limited constraints on the mechanisms influencing its persistence. In particular, large uncertainties exist on the persistence of pyrogenic organic carbon in soils. In order to characterise organic matter with varying degrees of persistence and distinguish pyrogenic organic carbon, we combined Rock-Eval analysis, a thermo-chemical method, with the benzene polycarboxylic acid molecular marker method and Raman spectroscopy, to characterise samples from long-term bare fallow experiments, progressively depleted in the most labile organic carbon over time. Considering the heterogeneity of soil samples, size fractions have been separated to distinguish pools of organic carbon with distinct properties. We observe that organic carbon dynamics is dependent on granulometry. A pool of organic carbon with intermediate residence time, from years to a few decades, representing ca 65 % of the bulk soil organic carbon stock, is mainly associated to fine fractions ( 20 µm) are rich in centennially-persistent organic carbon, representing ca 20 % of the initial organic carbon stock, due to the chemical recalcitrance of organic matter in these fractions, dominated by pyrogenic organic carbon. A second pool of persistent organic carbon, representing ca 15 % of the initial organic carbon stock, is associated with the clay fraction, indicating mechanisms of protection occurring at the submicron scale (
... Recent years have seen extended application of Rock-Eval for CBM and shale gas unconventional hydrocarbon reservoir characterization (Jarvie 2012;Carvajal-Ortiz and Gentzis 2015;Romero-Sarmiento et al. 2016). Furthermore, the device has also been extended for characterization of mangrove sediments (Marchand et al. 2005(Marchand et al. , 2008 of soil organic-matter characterization (Meyers and Lallier-Vergès 1999;Disnar et al. 2003;Sebag et al. 2006Sebag et al. , 2013Carrie et al. 2012;Hare et al. 2014) and even black carbon in soil (Poot et al. 2009). Furthermore, Poot et al. (2014) used Rock-Eval to predict PAH partitioning and desorption kinetic parameters of sedimentary organic-matter. ...
Article
The Rock-Eval technique has been conventionally used for source-rock analysis. In this work we document the importance of Rock-Eval S4 oxidation graphics and S4-Tpeak as indicators for coal reactivity and thermal maturity. Two non-coking coals (lower maturity), one coking coal (higher maturity), and one jhama (intrusion-induced metamorphosed coal), were collected and studied in terms of their reactivity and combustion properties. Our results indicate that Rock-Eval S4-Tpeak can be convincingly used to decipher the thermal maturity level of a coal sample. The two non-coking coals owing to their higher reactivity and corresponding lower activation energies, combusted at lower temperatures, almost entirely below 650 °C, and showed lower Rock-Eval S4-Tpeak. The coking coal sample on the other hand due to its higher thermal maturity level and lower reactivity, combusted at higher temperature, showing higher S4-Tpeak. While the S2 Tmax showed higher maturity for the coking coal than the jhama, the S4 oxidation graphics and S4-Tpeak clearly revealed higher thermal maturity of the jhama relative to the other samples. With increasing sample weights, the S4CO2 curves were observed to be broader, and consequently the S4-Tpeak was observed to be higher and erroneous, the errors being more for the more-mature coking coal and jhama. With lowering sample weights, the curves became tighter and the S4-Tpeak became lower and more precise. Parameters calculated using TG-DTG-DSC were observed to complement the data from Rock-Eval oxidation-stage, and revealed higher maturity, less reactivity, higher temperatures of ignition and burn out for the jhama, followed by the coking coal. Our results also indicate the suitability of applying Rock-Eval for combustion-profiling of coals, beyond source-rock characterization and CBM reservoir analysis.
... Therefore, this S3 fraction is used to calculate the oxygen index (OI). The HI decreases, and the OI increases as the OM undergoes greater degradation and oxidation (Carrie, Sanei, & Stern, 2012;Disnar, Guillet, Keravis, Di-Giovanni, & Sebag, 2003). ...
Article
Full-text available
We studied the drying behavior of slurries of Markermeer sediments in the Netherlands having different solid compositions. Natural processes such as sand–mud segregation and oxidation of organic matter were mimicked to analyze the effect of changes in sediment composition. Evaporation experiments were performed with soft slurry samples using the Hyprop setup. Soil water retention curves (SWRCs) and hydraulic conductivity curves (HCCs) were determined as a function of the water ratio (WR, defined as volume of water/volume of solids). The sediment remained close to saturation until the end of the experiments. The Atterberg limits reduced significantly after sediment treatment involving drying at 50 °C, rewetting, and chemical oxidation. Furthermore, the oxidized sediment lost capacity to retain water. The SWRCs of sandy and oxidized clays were steeper, and fine‐textured sediments showed large water ratios. At low matric suctions, the water retention capacity of the upper sediment samples containing more labile organic matter was larger than that of the sediment underneath. Clear correlations were found between van Genuchten parameters and the degree of degradation of the organic matter. The hydraulic conductivity of fine‐textured samples with less labile organics was larger. The results give insight into the drying behavior of Markermeer sediment, currently used to build wetlands.
... Turbo device (Vinci Technologies). This technique, which does not require any chemical pre-treatment of the soil sample, involves the measurement of carbon as gaseous effluent during two phases (Behar et al., 2001;Cécillon et al., 2018;Disnar et al., 2003). The first phase is a pyrolysis stage (200-650°C) in a N 2 atmosphere, during which CO and CO 2 gases are quantified with an infrared detector and volatile hydrocarbon effluents (CH) are quantified using a flame ionization detector. ...
Article
Full-text available
Since the last glacial maximum, soil formation related to ice‐cover shrinkage has been one major sink of carbon accumulating as soil organic matter (SOM), a phenomenon accelerated by the ongoing global warming. In recently deglacierized forelands, processes of SOM accumulation, including those that control carbon and nitrogen sequestration rates and biogeochemical stability of newly sequestered carbon, remain poorly understood. Here, we investigate the build‐up of SOM during the initial stages (up to 410 years) of topsoil development in ten glacier forelands distributed on four continents. We test whether the net accumulation of SOM on glacier forelands (i) depends on the time since deglacierization and local climatic conditions (temperature and precipitation); (ii) is accompanied by a decrease in its stability; (iii) is mostly due to an increasing contribution of organic matter from plant origin. We measured total SOM concentration (carbon, nitrogen), its relative hydrogen/oxygen enrichment, stable isotopic (13C, 15N) and carbon functional groups (C‐H, C=O, C=C) compositions, and its distribution in carbon pools of different thermal stability. We show that SOM content increases with time and is faster on forelands experiencing warmer climates. The build‐up of SOM pools shows consistent trends across the studied soil chronosequences. During the first decades of soil development, the low amount of SOM is dominated by a thermally stable carbon pool with a small and highly thermolabile pool. The stability of SOM decreases with soil age at all sites, indicating that SOM storage is dominated by the accumulation of labile SOM during the first centuries of soil development, and suggesting plant carbon inputs to soil (SOM depleted in nitrogen, enriched in hydrogen and in aromatic carbon). Our findings highlight the potential vulnerability of SOM stocks from proglacial areas to decomposition and suggest that their durability largely depends on the relative contribution of carbon inputs from plants.
... As presented in Fig. 9, the %Ro values of the Alès outcrop samples are relatively constant in each of the two wells, while the Tmax values can be enhanced by over 100 degrees depending on the degree of weathering. More case studies on soil organic matter (Disnar et al., 2003), Longmaxi Shale (Silurian, South China) (Tang et al., 2018), and the Eagle Ford Shale (Carboniferous, USA) (Kuske et al., 2019) confirmed these systematic changes in Rock-Eval parameters in response to weathering. ...
... Subsequently, the aged powder was separated from the solution with a filter paper and dried in an oven at 333 K for 1 hr. Finally, 64 ± 3 mg of this aged powder was pyrolysed, at 200-650°C, at a heating rate of 30°C/min; under N 2 atmosphere [57]. The pure quartz still contained five ppm of organic matter, which increased up to 1400 ppm after ageing with 100 mg/L humic acids ( Table 2). ...
Article
Hypothesis Millions of tons of CO2 are stored in CO2 geological storage (CGS) formations (depleted oil reservoirs and deep saline aquifers) every year. These CGS formations naturally contain small concentrations of water-soluble organic components in particular humic acid (HA), which may drastically affect the rock wettability − a significant factor determining storage capacities and containment security. Hence, it is essential to characterise the effect of humic acid concentration on CO2-wettability and its associated impact on storage capacity. Experimental To achieve this, we measured advancing and receding contact angles at reservoir conditions using the pendant drop tilted plate method for various humic acid concentrations (1, 10, and 100 mg/L) as a function of pressure (0.1-25 MPa), temperature (303-333 K), and brine salinity (0-0.3 M NaCl). Further, the influence of humic acid adsorption on the mineral’s surface was examined by several independent techniques. Results Our results demonstrate that humic acid significantly changes rock wettability from water-wet (0-50o) towards CO2-wet (90-110o). An increase in pressure, temperature, and salinity had a similar effect. Humic acid adsorption also increased the surface roughness of the substrates. We conclude that even trace amounts of humic acid (i.e. 1 mg/L), which exist in storage aquifers, significantly increase CO2-wettability and thus reduce structural and residual trapping capacities. Therefore, it is pertinent to account for these humic acid concentrations to de-risk CGS projects.
... Tmax values of 345 C and 420 C are typical of an immature organic matter. Nevertheless, the higher Tmax values in Units 2 and 3 (420 C) could indicate slightly more degraded organic matter (Disnar et al., 2003) than in Unit 1 that contains relatively fresh organic matter (Tmax =345 C). This is confirmed by the higher OI values in Units 2 and 3 that could denote slightly more oxygenated/oxidized organic matter than in Unit 1, i.e. organic matter that has suffered more degradation, for example soil organic matter or reworked organic matter that underwent early diagenesis. ...
Article
To test the extent to which sediments accumulated in sewers may serve as high-resolution archives of urban evolution, this study examined a sedimentary succession deposited in a decantation tank of the combined sewer network of Orléans (France). The focus was on a 1.43 m sediment core drilled after 10 months of operation since the last cleaning. Sediments were stratigraphically organised into three distinct facies. The lower unit comprised organic remains, the middle unit gravels and sands and the upper unit was fine sands. The evolution of radionuclide activities, bile acid concentrations, and glass microspheres enabled sediments from wastewater and stormwater inputs to be distinguished. Precipitation events that affected the area were the main control on sediment deposition with organic-rich sediments accumulating from wastewater during dry weather and coarser, mineral sediments accumulating from stormwater during precipitation events. These results enable development of a chronological framework for sediment deposition. These findings reveal the potential of sewer sediment accumulations to record relevant information on the evolution of urban socio-ecosystems on monthly to annual scales with a relatively high time resolution.
... stability, and in recent years, thermogravimetry, differential scanning calorimetry and temperature-controlled thermal analysis (e.g. Rock Eval pyrolysis) have been found to be promising high-throughput approaches (Peltre et al., 2013, Barré et al., 2016, Disnar et al., 2003. Several indices from temperaturecontrolled thermal analysis have been developed to successfully describe in situ biogeochemical stability (Cécillon et al., 2018. ...
Chapter
Full-text available
Accurate estimation of soil organic carbon (SOC) stocks and dynamics along the soil profile is challenging due to the immense diversity and complexity of soils leading to the spatio-temporal variability of the parameters of interest. It is conducted in a wide range of different frameworks with diverse conceptual and analytical approaches. Our purpose in this chapter is to give a broad overview on methods for monitoring, reporting and verifying SOC stocks and their dynamics. This includes sampling and sensing techniques, SOC stock calculation, as well as SOC fractionation and assessment of SOC turnover along the soil profile using stable isotopes and alternative approaches. It is highlighted that certain key operational challenges need to be overcome for the determination of bulk SOC stocks and changes. Some of these issues, e.g. the depth vs. mass-based comparisons were discussed for several decades, while others have been less addressed so far.
... During both stages, CO and CO 2 emissions were measured by infrared detection. Hydrocarbon effluents were also measured during the pyrolysis step by a flame ionization detector (Disnar et al., 2003;Schomburg et al., 2018). The total OC of earthworm casts and control soil aggregates was determined using the Rock Eval (RE6) signals. ...
Article
Full-text available
The role of earthworms on biogeochemical carbon cycling is a major knowledge gap resulting from the difficulty of isolating and exploring the effects provided by the diversity of organisms. In this study, we investigated the effect of six earthworm species belonging to three ecological categories on soil organic carbon (SOC) mineralization. To this end, we produced casts in microcosms with the six species in the same soil and with the same litter material. The casts were subjected to laboratory ageing for 140 days. During this process, we monitored physicochemical parameters, CO2 emissions and determined the micro-scale organization of the casts’ particulate organic matter and pores using X-ray microtomography. Our results showed contrasting properties of fresh casts of the three ecological categories, in accordance with the earthworm species’ morphological or behavioral strategies, indicating that those were maintained in artificial environments. However, species-specific changes in cast properties throughout ageing increased intragroup variability among ecological categories. As a result we observed earthworm species-specific evolution of CO2 mineralization rates during casts ageing. We found that at least half of the variability in CO2 emissions was explained by cast microstructural changes, related to the spatial arrangement between particulate organic matter, porosity, and mineral particles. We conclude that earthworm species-specific traits may play a role in organic carbon protection through their impact on microstructural cast properties.
... The samples were first 140 pyrolyzed in an inert N2 atmosphere, then oxidized under ambient air (O2). The heating routine applied during pyrolysis was as described in (Disnar et al., 2003), starting with a three-minute isotherm at 200 °C followed by a heating ramp of 30 °C•min −1 up to 650 °C. For the oxidation step, a one-minute isotherm was kept at 300 °C and was directly followed by a 1968 1970 2000 1967 1998 1958 1978 1975 1972 Simulated period 1975-2010 1970-2011 2000-2018 1977-1989 1998-2019 1989-2008 1978-2005 1975-1992 1976-1997 Number of treatments 4 12 1 2 2 2 5 2 2 ...
Preprint
Full-text available
Changes in soil organic carbon (SOC) stocks are a major source of uncertainty for the evolution of atmospheric CO2 concentration during the 21st century. They are usually simulated by models dividing SOC into conceptual pools with contrasted turnover times. The lack of reliable methods to initialize these models, by correctly distributing soil carbon amongst their kinetic pools, strongly limits the accuracy of their simulations. Here, we demonstrate that PARTYsoc, a machine-learning model based on Rock-Eval® thermal analysis optimally partitions the active and stable SOC pools of AMG, a simple and well validated SOC dynamics model, accounting for effects of soil management history. Furthermore, we found that initializing the SOC pool sizes of AMG using machine-learning strongly improves its accuracy when reproducing the observed SOC dynamics in nine independent French long-term agricultural experiments. Our results indicate that multi-compartmental models of SOC dynamics combined with a robust initialization can simulate observed SOC stock changes with excellent precision. We recommend exploring their potential before a new generation of models of greater complexity becomes operational. The approach proposed here can be easily implemented on soil monitoring networks, paving the way towards precise predictions of SOC stock changes over the next decades.
... Subsequently, the aged powder was separated from the solution with a filter paper and dried in an oven at 333 K for 1 hr. Finally, 64 ± 3 mg of this aged powder was pyrolysed, at 200-650°C, at a heating rate of 30°C/min; under N 2 atmosphere [57]. The pure quartz still contained five ppm of organic matter, which increased up to 1400 ppm after ageing with 100 mg/L humic acids ( Table 2). ...
Article
Carbon Geo Sequestration (CGS) is considered an effective way to reduce anthropogenic greenhouse gas emission into the atmosphere. The storage of captured CO2 is mainly geological. Several researchers confirmed Humic Acid (HA) concentration in the deep aquifer at high temperature and high-pressure conditions, which may affect the rock wettability and reduce storage capacities and containment security. One key parameter which affects the wettability of formation in the presence of humic acid is pH. However, there is a lack of information on the relationship of pH, humic acid and wettability of CO2 in storage formation. We measured the effect of pH on the CO2 wettability of storage formation in the presence of humic acid. Advancing and receding contact angles were measured at HPHT conditions (pressure of 12 MPa and temperature of 323 K), using the pendant drop tilted-plate method for various pH (2 to 12) at the humic acid concentration (25 mg/L) and brine salinities (0 and 0.2 M NaCl). We concluded that decreasing pH significantly impacts rock wettability; and shifts water-wet to CO2-wet, thus reducing structural and residual trapping capacities. Therefore, presence of organic acids in reservoir geochemical conditions should be considered to de-risk the development of CGS projects.
... The Rock-Eval® device has also been used and developed for many different matrices to detect and quantify the total organic carbon (TOC) and the mineral carbon (MINC) contents. This analytical technique has been used increasingly in other geoscience applications including: (1) the characterization of organic matter in soils (e.g., Di-Giovanni et al., 2000;Disnar et al., 2003;Hetényi et al., 2005;Sebag et al., 2006;Saenger et al., 2013); (2) the study of recent lacustrine sediments (e.g., Campy et al., 1994;Di-Giovanni et al., 1998;Jacob et al., 2004;Sanei et al., 2005); (3) the evaluation of recent marine sediments (e.g., Peters and Simoneit, 1982;Hussain and Warren, 1991;Calvert et al., 1992;Ganeshram et al., 1999;Tribovillard et al., 2008Tribovillard et al., , 2009); (4) the study of past climate changes and global carbon cycle (e.g. Baudin et al., 2007Baudin et al., , 2010Rohais et al., 2019), and many other applications. ...
Article
In this work, artificial thermal degradation experiments using the Rock-Eval® device were performed on selected polymer microsphere samples (PE, PP, PE100, PA6, PA11, PFA and PET). The main idea of this work is first to create a database of different polymer standard responses using the specific Rock-Eval® FID/IR peak signals. Several specific Rock-Eval® parameters are now defined to characterize each polymer family. For instance, each polymer is characterized by specific quantified parameters like Total HCpolymer, Total COpolymer, TotalCO2polymer, Tpeakpolymer, among others. This study attempts to demonstrate if this quick thermal degradation method can be also used to characterize the plastic contents (detection, type, and quantity) in sedimentary samples. Results indicate that each investigated polymer shows specific Rock-Eval® parameters that can be considered as useful characteristics of polymer families (mainly Tpeakpolymer, TOCpolymer, PCpolymer, RCpolymer, total HCpolymer, total COpolymer and total CO2polymer parameters). Samples containing different mineral matrices (e.g. sand, shale, marl and carbonate) were also mixed with polymers at different concentrations varying between 0.2 and 4.2 wt%. These composite samples were also analyzed in order to evaluate their thermal degradation comparing their specific Rock-Eval® FID/IR signatures. For example, most composite samples show an excellent linear correlation between TOC, PC, RC, total HC, CO and CO2 parameters versus the amount polymer at different concentrations. Although more work is still needed, a methodology is here proposed to distinguish and quantify the presence of plastics in the environment applying the proposed polymer Rock-Eval® database.
... The total C org content in the rock samples (TOC) before and after hydrothermal experiments was evaluated by the Rock-Eval pyrolysis method in HAWK (Wild Cat Technologies, USA). Moreover, other pyrolysis parameters that characterize oil generating potential of the given rock samples were also considered [35]: S 1 -content of free HC, mg HC/gr rock; S 2 -content of kerogen, mg HC/gr rock; S 3 -content of CО 2 , mg CО 2 /gr rock; TOC-total C org content %; РI = S 1 /(S 1 + S 2 )-productivity index; T max -temperature of maximum HC yield during kerogen pyrolysis, • C; НI and OI-hydrogen and oxygen indices, mg HC/gr C org .; OSI-oil saturation index, mg HC/gr C org .; ...
Article
Full-text available
The hydrocarbon compositions of shale oils, generated from two different lithological–facial Domanic deposits of the Tatarstan Republic (Russia), were studied under hydrothermal impact with 30% of water addition in a 350 °С and CO2 environment. The samples were extracted from carbonate–siliceous rocks of the Semiluky–Mendym deposits of the Berezovskaya area, and carbonate deposits of the Dankovo–Lebedyan horizon of the Zelenogorskaya area of the Romashkino oil field. The distinctive features of rocks are in the composition and content of organic matter (OM), its thermal stability, as well as the structural-group composition of the shale oil products. The hydrothermal treatment of the rock samples increased the content of saturates and decreased the content of aromatics, resins and asphaltenes in the composition of crude oil. The decomposition of the polymer-like kerogen structure and destruction processes of high-molecular compounds, such as resins and asphaltenes, are accompanied with the formation of substances highly rich in carbons—carbenes and carboids. The contents of n-alkanes and acyclic isoprenoids increase in the composition of saturated hydrocarbons. According to the chemical classification of Al. A. Petrov, the character of the molecular mass distribution of such substances corresponds to oil type A1, which is considered paraffinic. The contents of dibenzothiophene, naphthalene and phenanthrene are increased in the composition of aromatic hydrocarbons, while the contents of tri-methyl-alkyl-benzene and benzothiophene are decreased. The increase in the aryl isoprenoid ratio (AIR = С13–С17/С18–С22) and maturity parameter (4-MDBT/1-MDBT) under the influences of hydrothermal factors indicates the increasing thermal maturity degree of the hydrocarbon system. The differences in the distribution behavior of saturated and aromatic hydrocarbons—biomarkers in rocks of various lithological-facies types, which are reasoned by different conditions of initial organic matter transformation as well as under the impact of hydrothermal factors—were revealed.
... The samples were first pyrolysed in an inert N 2 atmosphere, then oxidized under ambient air (O 2 ). The heating routine applied during pyrolysis was as described in Disnar et al. (2003), starting with a 3 min isotherm at 200 • C followed by a heating ramp of 30 • C min −1 up to 650 • C. For the oxidation step, a 1 min isotherm was kept at 300 • C and was directly followed by a heating ramp of 20 • C min −1 until 850 • C was reached, followed by a 5 min isotherm at 850 • C (Baudin et al., 2015; adapted from Behar et al., 2001). ...
Article
Full-text available
Changes in soil organic carbon (SOC) stocks are a major source of uncertainty for the evolution of atmospheric CO2 concentration during the 21st century. They are usually simulated by models dividing SOC into conceptual pools with contrasted turnover times. The lack of reliable methods to initialize these models, by correctly distributing soil carbon amongst their kinetic pools, strongly limits the accuracy of their simulations. Here, we demonstrate that PARTYSOC, a machine-learning model based on Rock-Eval® thermal analysis, optimally partitions the active- and stable-SOC pools of AMG, a simple and well-validated SOC dynamics model, accounting for effects of soil management history. Furthermore, we found that initializing the SOC pool sizes of AMG using machine learning strongly improves its accuracy when reproducing the observed SOC dynamics in nine independent French long-term agricultural experiments. Our results indicate that multi-compartmental models of SOC dynamics combined with a robust initialization can simulate observed SOC stock changes with excellent precision. We recommend exploring their potential before a new generation of models of greater complexity becomes operational. The approach proposed here can be easily implemented on soil monitoring networks, paving the way towards precise predictions of SOC stock changes over the next decades.
... Rock-Eval pyrolysis is a technique used to trace changes in bulk organic matter composition and degree of decomposition (Disnar, Guillet, Keravis, Di-Giovanni, & Sebag, 2003;Newell, Vane, Sorensen, Moss-Hayes, & Gooddy, 2016). It predicts soil carbon contents reliably and is an appropriate tool for assessing the vulnerability of SOC stocks to microbial degradation (Saenger et al., 2013;Soucémarianadin et al., 2018;Upton, Vane, Girkin, Turner, & Sjögersten, 2018). ...
Article
Contrasting tillage strategies not only affect the stability and formation of soil aggregates but also modify the concentration and thermostability of soil organic matter associated with soil aggregates. Understanding the thermostability and carbon retention ability of aggregates under different tillage systems is essential to ascertain potential terrestrial carbon storage. We characterised the concentration and thermostability of soil organic carbon (SOC) within various aggregate size classes under both zero and conventional tillage using novel Rock‐Eval pyrolysis. The nature of the pore systems was visualised and quantified by X‐ray Computed Tomography to link soil structure to organic carbon preservation and thermostability. Soil samples were collected from experimental fields in Botucatu, Brazil, which had been under zero‐tillage for 2, 15 and 31 years, along with adjacent fields under conventional tillage. Soils under zero‐tillage significantly increased pore connectivity whilst simultaneously decreasing inter‐aggregate porosity, providing a potential physical mechanism for protection of soil organic carbon in the 0‐20 cm soil layer. Changes in the soil physical characteristics associated with the adoption of zero‐tillage resulted in improved aggregate formation compared to conventionally tilled soils, especially when implemented for at least 15 years. In addition, we identified a chemical change in composition of organic carbon to a more recalcitrant fraction following conversion to zero‐tillage, suggesting aggregates were accumulating rather than mineralising soil organic carbon. These data reveal profound effects of different tillage systems upon soil structural modification, with important implications for the potential of zero‐tillage to increase carbon sequestration compared to conventional tillage. This article is protected by copyright. All rights reserved.
... This choice was possible for reference topsoil samples for which Rock-Eval ® analyses showed a good organic carbon yield (TOC RE6 divided by SOC EA and multiplied by 100). This is generally the case for most soils, with typical organic carbon yields from Rock-Eval ® ranging from 90 to 100 % SOC EA (Disnar et al., 2003). For the topsoils of the sites of Grignon, Rothamsted, Ultuna, and Versailles used in the first version of PARTY SOC , the organic carbon yield from Rock-Eval ® was greater than 96 % (linear regression model, R 2 = 0.97, n = 118; Cécillon et al., 2018). ...
Article
Full-text available
Partitioning soil organic carbon (SOC) into two kinetically different fractions that are stable or active on a century scale is key for an improved monitoring of soil health and for more accurate models of the carbon cycle. However, all existing SOC fractionation methods isolate SOC fractions that are mixtures of centennially stable and active SOC. If the stable SOC fraction cannot be isolated, it has specific chemical and thermal characteristics that are quickly (ca. 1 h per sample) measurable using Rock-Eval® thermal analysis. An alternative would thus be to (1) train a machine-learning model on the Rock-Eval® thermal analysis data for soil samples from long-term experiments for which the size of the centennially stable and active SOC fractions can be estimated and (2) apply this model to the Rock-Eval® data for unknown soils to partition SOC into its centennially stable and active fractions. Here, we significantly extend the validity range of a previously published machine-learning model (Cécillon et al., 2018) that is built upon this strategy. The second version of this model, which we propose to name PARTYSOC, uses six European long-term agricultural sites including a bare fallow treatment and one South American vegetation change (C4 to C3 plants) site as reference sites. The European version of the model (PARTYSOCv2.0EU) predicts the proportion of the centennially stable SOC fraction with a root mean square error of 0.15 (relative root mean square error of 0.27) at six independent validation sites. More specifically, our results show that PARTYSOCv2.0EU reliably partitions SOC kinetic fractions at its northwestern European validation sites on Cambisols and Luvisols, which are the two dominant soil groups in this region. We plan future developments of the PARTYSOC global model using additional reference soils developed under diverse pedoclimates and ecosystems to further expand its domain of application while reducing its prediction error.
... A classical presentation of RE data is in the form of a pseudo-Van Krevelen diagram, which plots the OI and HI against each other in a manner analogous to the atomic O/C and H/C ratios used to classify kerogens [23,28]. The ratio diagram of hydrogen and oxygen indices (HI/OI) is shown in Figure 3. Right: HI, mg HC/g Corg as a function of Tpeak,°С. ...
Article
Full-text available
Rapid warming of the Arctic provokes large-scale degradation of permafrost on land terrestrial and in submarines. A vast amount of remobilized organic matter (OM) is involved in the modern biogeochemical cycle. Understanding of the fate of terrestrial OM moving from the land to the Arctic shelf is essential for predicting the potential feedback of Arctic ecosystems. In our research, an attempt was made to characterize the modern OM stored in the surface sediments of the Laptev Sea to estimate its composition variability and to identify the OM sources along with the “coastline - outer shelf” profile. Here we discuss the OM features revealed by Rock-Eval pyrolysis (RE) and the distribution of n-alkanes in combination with sediment grain-size analysis. The GC/MS records are directly comparable with RE data tracing the terrestrial OM along with the entire studied profile. However, we observe both a significant decline of terrestrial input and the rise of hydrobiont in the outer shelf zone. We assume that different OM sources may produce different ranges of RE values.
... The thermal stability of OM has also been proposed as a proxy for SOC dynamics (Plante et al. 2009;Sanderman and Grandy 2020). Among thermal analysis techniques, Rock-EvalÒ analysis can provide insights into OM quality changes (Disnar et al. 2003;Matteodo et al. 2018;Poeplau et al. 2017). In particular, the I and R Index scores, calculated from the amounts of hydrocarbon compounds released during pyrolysis, have been proposed as an indicator of variations in the OM quality of diverse soils (Sebag et al. 2006;Sebag et al. 2016). ...
Article
Full-text available
Geochemical indicators are emerging as important predictors of soil organic carbon (SOC) dynamics, but evidence concerning the role of calcium (Ca) is scarce. This study investigates the role of Ca prevalence in SOC accumulation by comparing otherwise similar sites with (CaCO3-bearing) or without carbonates (CaCO3-free). We measured the SOC content and indicators of organic matter quality (C stable isotope composition, expressed as δ 13C values, and thermal stability) in bulk soil samples. We then used sequential sonication and density fractionation (DF) to separate two occluded pools from free and mineral-associated SOC. The SOC content, mass, and δ 13C values were determined in all the fractions. X-ray photoelectron spectroscopy was used to investigate the surface chemistry of selected fractions. Our hypothesis was that occlusion would be more prevalent at the CaCO3-bearing site due to the influence of Ca on aggregation, inhibiting oxidative transformation, and preserving lower δ 13C values. Bulk SOC content was twice as high in the CaCO3-bearing profiles, which also had lower bulk δ 13C values, and more occluded SOC. Yet, contrary to our hypothesis, occlusion only accounted for a small proportion of total SOC (< 10%). Instead, it was the heavy fraction (HF), containing mineral-associated organic C, which accounted for the majority of total SOC and for the lower bulk δ 13C values. Overall, an increased Ca prevalence was associated with a near-doubling of mineral-associated SOC content. Future investigations should now aim to isolate Ca-mediated complexation processes that increase organo-mineral association and preserve organic matter with lower δ 13C values. Supplementary information: The online version of this article (10.1007/s10533-021-00779-7) contains supplementary material, which is available to authorized users.
... First, the sample underwent pyrolysis in an inert (N 2 ) atmosphere, and then oxidation in the presence of O 2 (ambient air). The heating routine applied during pyrolysis was as proposed by Disnar et al. (2003), including a three-minute isotherm at 200 • C, succeeded by a heating ramp of 30 • C•min − 1 up to 650 • C. Oxidation started with a one-minute 300 • C isotherm followed by a heating ramp of 20 • C•min − 1 up to 850 • C and a final five-minute isotherm at 850 • C (oxidation routine presented in Baudin et al. (2015) as "bulk rock/basic" method). Simultaneous detection of effluents during both analysis steps generated five thermograms per sample in total describing the evolution of hydrocarbons during pyrolysis (HC_PYR), and CO and CO 2 during both pyrolysis and oxidation steps (CO_PYR, CO2_PYR, CO_OX, CO2_OX). ...
Article
Soil sampling depths strongly vary across soil studies. Stocks of elements (such as C, N) or organic matter in a soil layer can be simply calculated from stocks measured in its sublayers. This calculation is less obvious for other soil characteristics, such as soil organic carbon (SOC) persistence, complicating the comparison of results from different studies. Here, we tested whether Rock-Eval® parameters of a soil layer, characterizing soil organic matter and its biogeochemical stability, can be determined using Rock-Eval® data measured on its sublayers. Soil samples collected in 10 plots located in eight French forest sites, taken up at two different depths (0–30 cm, 30–50 cm), and their mixtures were analysed with Rock-Eval®. Expected values for the Rock-Eval® parameters of the soil mixtures were calculated either: (1) as the weighted mean of Rock-Eval® parameters measured on the two sublayers, or (2) based on a signal reconstructed as the weighted mean of Rock-Eval® thermograms recorded on the two sublayers. Our results showed a good agreement between measured and expected Rock-Eval® parameter values. However, when the clay content strongly differed between the two soil sublayers, the amount of pyrolyzed hydrocarbons measured on the soil mixtures was slightly lower than expected. We conclude that it is reasonable to calculate Rock-Eval® parameters of a soil layer, from the Rock-Eval® signature of its sublayers. Our findings facilitate the harmonization of Rock-Eval® data from large scale soil studies using different sampling depths.
Article
The Rock-Eval® device has been widely used to identify the type and the thermal maturity of sedimentary organic matter as well as quantifying the total organic carbon content. Traditionally, it is a screening tool to estimate the petroleum generation potential of source rocks using standardize parameters. More recently, a new Rock-Eval® method (Shale PlayTM) was proposed to investigate the hydrocarbon content in liquid-rich tight rock samples. In this study, we describe a dual vacuum and on-line system that was developed to recover most compounds that are thermally released during a Rock-Eval® Shale PlayTM analysis. Thermally vaporized products are divided so that half is analyzed by the Rock-Eval® flame ionization detector (FID) while the other portion is cryogenically trapped in the on-line recovery system. The trapped products can then be transferred via a vacuum line system into a sample vial for subsequent molecular and/or isotopic composition analyses. The recovery vacuum line volumes were calibrated using known quantities of gas (CH4 and CO2). Sample transfer from without isotopic fractionation was demonstrated for CO2 evolved from Rock-Eval® preparation of pure carbonate standards (siderite, magnesite and azurite). Recovery efficiencies were first measured on C8-C16n-alkane standards and then on produced oil samples. Results indicate a high quantitative recovery and an accurate mass balance of most compounds released during the Shale PlayTM Sh0 thermovaporization step (100-200°C). Thermally vaporized compounds released at higher temperatures Sh1 (200-350°C) are recovered at lower efficiencies but are still suitable for subsequent characterization. The coupled Rock-Eval® and recovery system could have applications beyond petroleum geochemistry.
Article
In the Majerda delta, the largest wadi in Tunisia, a study is being conducted on the flow of organic matter at the old and new mouths of this wadi (NMM, OMM). This study explores the sources, distribution, evolution, and diagenesis of organic matter in recent sediments by means of Rock–Eval. The pyrolysis results are interpreted in relation to particle size, carbonates, N, Mn, and Fe. Sediments from both cores are predominantly clastic and consist of clay and silt with fragments of higher plants. TOC content varies from 1.13 to 1.59% in the NMM core compared to 1.22 and 2.63 in the OMM core, and C/N ratios range from 9 to 13 for NMM and 11 to 73 for ONM. The C/N ratio < 10 indicates that OM is rapidly decomposed by biomass and mineralized, while a C/N > 10 indicates that OM is preserved. According to the HI vs. OI diagram, there are two distinct OM groups in the delta of Majerda. Temperatures above 300 °C indicate that OM has not been profoundly altered in this delta; however, a high C/N ratio and a low Mn/Fe ratio indicate that OM tends to be lignin rich in the deep sediments of OMM. The low values of HI/OI ratio (0.2 < HI/OI < 0.4) in the new and old Majerda mouths with the lowest C/N and Fe/Mn ratios are due to microbial oxidative diagenesis and reflect a highly oxidizing environment. During OM degradation and progressive oxidation, the labile and lignocellulosic components disappear, leaving stabilized residues.
Article
Soil organic carbon (SOC) plays key roles in determining soil properties, plant nutrients, and land-atmosphere carbon exchange, yet is affected by various natural and anthropogenic perturbations such as wildfire, climate change, land use change and pollution. Herein, we review perturbation types and SOC response mechanisms, as well as new technologies to measure SOC stability, highlighting the resistance and resilience of SOC. Although there is great controversy on the nature and structure of SOC, it has been recognized that the SOC stability not only depends on physiochemical characteristics of SOC, but also on soil microenvironment, soil microbial community composition, and types of perturbations. Based on ecosystem stability theories, the change of SOC stability under perturbation can be keeping stable states, changing to an alternative stable states or system collapse. For future studies, we suggest that understanding responses of soil biogeochemical processes to multiple perturbations, well-designed experiments to quantify threshold and uncertainty of SOC, and integration of novel biological approaches besides physicochemical characterizations into SOC stability are needed. This review helps to better understand the process of SOC stabilization and reduce the uncertainties in assessments of global carbon stocks, not only for mitigating the effects of climate change through negative feedbacks but also for maintaining soil functions such as soil fertility, water quality, and resistance to erosion.
Article
In the present study, shale samples from Rajmahal Basin, India, were analysed in terms of their source rock properties using an open-system programmed pyrolysis instrument (Rock–Eval 6). Comprehensive analysis of the different Rock–Eval graphics was conducted for the samples under consideration. Construction of S2 (mg HC/g rock) vs. total organic carbon (wt%) cross-plot using iso-HI (iso-hydrogen index) lines classified the studied suit of samples into three zones with increasing hydrogen index (Zone A < Zone B < Zone C). Analysis of S2 curves of samples from different zones revealed distinctive features attributed to the variable nature of kerogen present within the sample as well as the levels of S2 and HI. S2 curves of sample with higher Tmax were observed to be asymmetric, broad, and marked by lower flame ionization detector signals. However, for those samples, the S4 Tpeak was observed to be similar to that of the other samples. On the other hand, the higher S2 Tmax of some samples coincided with higher S4 Tpeak indicating the samples to be more mature. Additionally, samples with higher levels of oxygen index (OI), and siderite content, were observed to have S3′ curve marked by pronounced release of CO2 above 400 °C, whereas the samples with higher OI but without any presence of siderite were marked by noisy curves due to low IR CO2 signal. The results reiterated the importance of careful monitoring of the different curves obtained during the pyrolysis and oxidation stage so that erroneous characterization of the samples could be avoided.
Article
The characterization of organic matter (OM) composition, physico-chemical, geochemical, and mineralogical studies of sedimentary core can help to better understand the paleoclimates and the depositional environments. The purpose of this work is to identify the factors monitoring the mineralogical composition and the sedimentation of sebkha Mhabeul sediments (southeastern Tunisia), during the Holocene. A 100.5 cm core (Mh 1) collected from this sebkha was analyzed for the determination of chemical composition by X-ray fluorescence (XRF), carbonate content by Bernard calcimetry, grain-sized sediments by AFNOR sieves, OM content by Rock-Eval 6 Pyrolysis, and mineralogical composition by X-ray diffraction (XRD), scanning electronic microscope (SEM), and infrared spectroscopy (IR). The sedimentary fillings of this sebkha, constituted by fine fractions, are characterized by the dominance of the detrital minerals (72–96 %) with high quartz percentages (42.2–91.5 %). The mineralogical composition of the studied sediments included detrital minerals (clay minerals, quartz, and feldspars), carbonate minerals (ankerite, dolomite, and calcite), and evaporitic minerals (halite, bassanite). The clay minerals (11–14%) are composed of a mixture of kaolinite, illite and palygorskite. Fourier transform infrared (FTIR) absorption spectra of all sediment samples confirm the mineralogical composition obtained by XRD and the existence of OM, by defining the band assignments for OM and different minerals as quartz, feldspar, clay, and carbonate minerals. The Rock Eval pyrolysis shows that the OM is immature and has a mixed origin (terrestrial and aquatic). The statistical analyses prove the results of geochemical and mineralogical studies. Indeed, the principal component analysis (PCA) of geochemical and mineralogical data and the depth help to prove the relationships between minerals and chemical elements. Moreover, the negative correlation between the Rock Eval Pyrolysis parameters and the depth shows a homogenous statistical group.
Article
The Northern coastline, from Kayar to Saint Louis (Senegal) is characterized by a succession of dunes and inter-dunes. Coastal wetlands located in the inter-dunes which bear Organic Matter (OM) rich soil where market garden agriculture is the main activity. These zones locally called “Niayes” are characterized by shallow groundwater table threatened by anthropogenic pressure, climate and environmental impacts. The scientific interest of this research work is to characterize the composition of soil OM to discuss its origin, composition, and diagenetic evolution in this depositional environment of Mboro research site with regard to natural and anthropogenic pressure. Three selected core samples with depth interval of 5 cm aligned in along a slope transect in the Mboro wetland were carried out. Soil OM were analyzed for Particulate OM, C/N, Rock-Eval HI and OI, δ¹³C, δ¹⁵N whereas sediments and water were respectively analyzed for grain size distribution, water contents and redox potential down to 50 cm depth. We have demonstrated through the results a vertical variability in the content, the nature and preservation quality of sedimentary OM with the occurrence of a peat storage zone. The isotopic markers depict a strong contribution of C3 plants, macrophytes and to a lesser extent of algae and microbial organic materials. High concentrations of dissolved nutrients occurring mainly on the surface slope may derive from the use of fertilizers to improve agricultural yields. These results constitute an added value in the scientific knowledge of this sector of the Niaye of Senegal.
Thesis
lors que de nombreuses études paléoenvironnementales traitent de l’évolution du climat et de la végétation au cours de l’Holocene, il n’existe que très peu d’études portant sur l’évolution des sols au cours de cette même période. Cependant, les propriétés physiques et chimiques des sols ayant un rôle clef au sein d’un écosystème, la reconstitution de l’histoire des sols constitue un enjeu important pour comprendre les changements environnementaux passés. Un des facteurs limitant pour reconstituer l’histoire des sols réside dans l’absence d’enregistrement continu des processus pédologiques sur de longues échelles de temps (103 à 104 ans). Notre intérêt s’est donc porté sur l’utilisation d’archives sédimentaires lacustres dans le but de reconstruire l’histoire de la couverture pédologique en lien avec celle de l’écosystème. Cette étude a été menée sur deux petites dépressions lacustres de l’étage subalpin (Vallée de la Maurienne, Savoie) ayant a priori des histoires de l’occupation humaine différentes. A Dans un premier temps, une approche géochimique a été appliquée sur des sols actuels afin de caractériser les pédosignatures des processus de podzolisation et d’altération chimique. Il en résulte que les terres rares (numéros atomiques de 57 à 71) constituent un indicateur du degré d’altération chimique tandis que les proportions des complexes organo-métalliques d’Al et Fe permettent de tracer l’intensité de la podzolisation. Dans un deuxième temps, ces mêmes traceurs ont été mesurés sur deux séquences sédimentaires couvrant 4500 ans Cal. BP (lac du Thyl) et 13500 ans (lac du Loup). La comparaison de ces pédosignatures avec des marqueurs indépendants (végétation, climat, feux) révèle des pédogenèses progressives et régressives après la déglaciation de la fin du Tardiglaciaire. Les sols et l’environnement du lac du Loup sont caractérisés par une évolution progressive et stable menant aux forets de résineux et aux podzols actuels. L’enregistrement du lac du Thyl est plus contrasté : le développement progressif d’une forêt de pin cembro associé au processus de podzolisation est suivi par des perturbations secondaires (principalement l’augmentation du régime des feux) qui pourraient expliquer la mise en place d’une végétation semi-ouverte associée à des processus de dépodzolisation. Finalement, ce travail a permit d’ajouter un volet pédologique aux études aléoenvironnementales classiques. Il en résulte que les deux schémas d’évolution des sols sont très cohérents avec les marqueurs indépendants et qu’ils offrent
Thesis
Les dynamiques de constitution des stocks de matière organique des sols, leur variabilité et leurs relations avec les autres composantes biotiques et abiotiques des écosystèmes sont insuffisamment connues à l’échelle du paysage. Or cette compréhension des interdépendances entre le système pédologique et les autres compartiments environnementaux est cruciale pour prévoir les changements globaux et mesurer l’impact des activités anthropiques. Les milieux de montagnes présentent dans ce contexte des spécificités fortes dues au fait de leur importante variabilité spatiale, des stocks élevés de matière organique contenus dans leurs sols et de leur vulnérabilité aux changements globaux. Par ailleurs, ils subissent intensément les effets du changement climatique. Pour toutes ces raisons, ils offrent un grand intérêt pour l’étude temporelle des dynamiques écosystémiques.En étudiant des sols de montagne aux situations environnementales contrastées, nous avons tenté de comprendre quelles étaient les dynamiques qualitative et quantitative de la matière organique au cours du temps. Pour cela, cette thèse s’est appuyée sur (i) l’étude de sols récemment formés le long de chronoséquences, (ii) de climatoséquences pour l’examen de la variabilité de la matière organique à l’échelle du paysage dans des sols ayant suivis des trajectoires différentes et enfin (iii) sur des simulations expérimentales de changement pédoclimatique pour analyser la réactivité du carbone organique stocké à la surface de sols de prairies de haute altitude.Nos résultats ont mis en évidence, indépendamment des conditions locales de chaque site, un schéma commun d’accumulation de la matière organique lors des phases initiales de formation d’un nouvel écosystème terrestre après retrait glaciaire en différents points du monde. Cette accumulation est affectée par le temps et accélérée par un climat plus chaud. La végétation contribue alors largement à l’incorporation de matière organique relativement labile dans ces sols nouvellement formés. Dans les écosystèmes plus évolués, la stabilisation environnementale par le climat structure en partie la variabilité quantitative et qualitative de la matière organique des sols en montagne à l’échelle du paysage. L’importance de cette structuration par le climat est plus forte dans les horizons de surface des sols qu’en profondeur. La stabilisation environnementale par le climat maintient dans les sols de montagne du carbone organique particulièrement réactif en préservant de la dégradation une matière organique vulnérable à haute altitude. En simulant un réchauffement de 3°C par transplantation d’un sol alpin à l’étage subalpin, nous avons effectivement démontré le rapide relargage de ce carbone organique labile.Ces résultats offrent un éclairage nouveau, à la fois sur la nature de la matière organique des sols de montagne, et aussi sur sa dynamique à-travers le temps et l’espace. La stabilité de la matière organique dans les sols est bien une fonction de l’écosystème.
Article
A quantitative assessment of historical sediment yields (SY) was performed using sediment budgets from lacustrine records located in the Mont Dore and Cezallier volcanic provinces (French Massif Central). A source-to-sink approach combining hydro-acoustic images, organic geochemistry (Rock-Eval and quantitative organic petrography) and radiocarbon dating of sediment cores has been adopted on three lake-catchment systems, namely Pavin, Chauvet and Montcineyre. SY was estimated from the quantification of red Amorphous Particles (rAP), a terrigenous organic tracer identified in both soils and sediments. Historical SY range between 3 and 320 t km⁻².yr⁻¹, which is comparable to the magnitude reached in other European lake-based SY records in similar geographical and climatic settings. Comparison of recent SY with predicted values of soil erosion rates from the RUSLE2015 model highlights large differences linked to scale differences between the model at plot scale and lake-based SY reflecting erosion export from the catchment to the lake. In this sense, the role of peatlands as sediment traps within two studied catchments must be considered to explain the large differences between modelled soil erosion rates and reconstructed SY data. SY differences between sites can be firstly attributed to morphology, size and lithology of the catchments as well as to vegetation cover whereas fluctuations reconstructed for each record seem to be mainly related to human-induced land use management. Historical SY from Chauvet and Montcineyre synchronously recorded two events in 850 CE and 1450 CE, respectively. The first marked the rise of SY to their maxima following land-use changes in the catchments. Nearby palaeoenvironmental records from Lake Aydat, Chambedaze peatland, and Espinasse marsh suggest this rise was consecutive to intensification of agro-pastoral activities recorded at regional scale. The second event followed a land-use shift characterized by a ten to fifteen-fold decrease in SY values. The driver remains unclear but could be possibly related to historical events causing a demographic decline (i.e., the Black Plague and/or the Hundred Years War) and/or cultural adaption in response to the onset of the Little Ice Age. Overall, both records suggest erosion in the area has been historically more susceptible to human-induced land use change rather than to precipitation and temperature changes induced by climate variability of the past millennium.
Thesis
Full-text available
Ferruginous conditions were a prominent feature of the oceans throughout the Precambrian Eons and thus throughout much of Earth’s history. Organic matter mineralization and diagenesis within the ferruginous sediments that deposited from Earth’s early oceans likely played a key role in global biogeochemical cycling. Knowledge of organic matter mineralization in ferruginous sediments, however, remains almost entirely conceptual, as modern analogue environments are extremely rare and largely unstudied, to date. Lake Towuti on the island of Sulawesi, Indonesia is such an analogue environment and the purpose of this PhD project was to investigate the rates and pathways of organic matter mineralization in its ferruginous sediments. Lake Towuti is the largest tectonic lake in Southeast Asia and is hosted in the mafic and ultramafic rocks of the East Sulawesi Ophiolite. It has a maximum water depth of 203 m and is weakly thermally stratified. A well-oygenated surface layer extends to 70 m depth, while waters below 130 m are persistently anoxic. Intensive weathering of the ultramafic catchment feeds the lake with large amounts of iron(oxy)hydroxides while the runoff contains only little sulfate, leading to sulfate-poor (< 20 µM) lake water and anoxic ferruginous conditions below 130 m. Such conditions are analogous to the ferruginous water columns that persisted throughout much of the Archean and Proterozoic eons. Short (< 35 cm) sediment cores were collected from different water depths corresponding to different bottom water redox conditions. Also, a drilling campaign of the International Continental Scientific Drilling Program (ICDP) retrieved a 114 m long sediment core dedicated for geomicrobiological investigations from a water depth of 153 m, well below the depth of oxygen penetration at the time of sampling. Samples collected from these sediment cores form the fundament of this thesis and were used to perform a suite of biogeochemical and microbiological analyses. Geomirobiological investigations depend on uncontaminated samples. However, exploration of subsurface environments relies on drilling, which requires the use of a drilling fluid. Drilling fluid infiltration during drilling can not be avoided. Thus, in order to trace contamination of the sediment core and to identify uncontaminated samples for further analyses a simple and inexpensive technique for assessing contamination during drilling operations was developed and applied during the ICDP drilling campaign. This approach uses an aqeous fluorescent pigment dispersion commonly used in the paint industry as a particulate tracer. It has the same physical properties as conventionally used particulate tracers. However, the price is nearly four orders of magnitude lower solving the main problem of particulate tracer approaches. The approach requires only a minimum of equipment and allows for a rapid contamination assessment potentially even directly on site, while the senstitivity is in the range of already established approaches. Contaminated samples in the drill core were identified and not included for further geomicrobiological investigations. Biogeochemical analyses of short sediment cores showed that Lake Towutis sediments are strongly depleted in electron acceptors commonly used in microbial organic matter mineralization (i.e. oxygen, nitrate, sulfate). Still, the sediments harbor high microbial cell densities, which are a function of redox conditions of Lake Towuti’s bottom water. In shallow water depths bottom water oxygenation leads to a higher input of labile organic matter and electron acceptors like sulfate and iron, which promotes a higher microbial abundance. Microbial analyses showed that a versatile microbial community with a potential to perform metabolisms related to iron and sulfate reduction, fermentation as well as methanogenesis inhabits Lake Towuti’s surface sediments. Biogeochemical investigations of the upper 12 m of the 114 m sediment core showed that Lake Towuti’s sediment is extremely rich in iron with total concentrations up to 2500 µmol cm-3 (20 wt. %), which makes it the natural sedimentary environment with the highest total iron concentrations studied to date. In the complete or near absence of oxygen, nitrate and sulfate, organic matter mineralization in ferruginous sediments would be expected to proceed anaerobically via the energetically most favorable terminal electron acceptors available - in this case ferric iron. Astonishingly, however, methanogenesis is the dominant (>85 %) organic matter mineralization process in Lake Towuti’s sediment. Reactive ferric iron known to be available for microbial iron reduction is highly abundant throughout the upper 12 m and thus remained stable for at least 60.000 years. The produced methane is not oxidized anaerobically and diffuses out of the sediment into the water column. The proclivity towards methanogenesis, in these very iron-rich modern sediments, implies that methanogenesis may have played a more important role in organic matter mineralization thoughout the Precambrian than previously thought and thus could have been a key contributor to Earth’s early climate dynamics. Over the whole sequence of the 114 m long sediment core siderites were identified and characterized using high-resolution microscopic and spectroscopic imaging together with microchemical and geochemical analyses. The data show early diagenetic growth of siderite crystals as a response to sedimentary organic matter mineralization. Microchemical zoning was identified in all siderite crystals. Siderite thus likely forms during diagenesis through growth on primary existing phases and the mineralogical and chemical features of these siderites are a function of changes in redox conditions of the pore water and sediment over time. Identification of microchemical zoning in ancient siderites deposited in the Precambrian may thus also be used to infer siderite growth histories in ancient sedimentary rocks including sedimentary iron formations.
Article
Full-text available
Here we present lithological and geochemical characteristics of the core drilled in coastal part of the Laptev Sea (Ivashkina Lagoon, Bykovsky Peninsula). It is shown that for sediments accumulated in specific lagoon conditions the increased content of organic carbon is confined to fine-grained lacustrine and lagoonal sediments in the uppermost layers. Pyrolytic analysis results indicate a sharp variability in the content of total organic carbon and volatile organic compounds across the studied horizons. The distribution of n-alkanes is characterized by the dominance of high molecular weight homologues, which indicates the ubiquitous contribution of higher terrestrial vegetation discharged with river and coastal thermo abrasion fluxes to the organic matter of bottom sediments.
Article
Vitrain is one of the most important lithotype for the end utilization of humic coals in relevant industries. In this work, we examine the thermal, structural and pyrolysis properties of vitrains, manually isolated from coals of three distinct thermal maturity levels (rank). The high volatile bituminous (HvbA) vitrain showed highest moisture content and reactivity during combustion, while showing least Rock-Eval S2 Tmax and S4 Tpeak. On the other hand, the low volatile (Lvb) sample showed properties exact opposite to that of the HvbA sample. Thus, the rank of the vitrains was observed to directly control their behaviour. Owing to their inherently lower ash content, all the vitrains during thermogravimetric analysis developed smooth thermograms, indicating easy burning. Interlayer spacing (d002), obtained from XRD displayed a strong decrease with increasing coal rank, indicating formation of condensed stacking structures with increasing rank. On the other hand, other XRD parameters, viz., the crystallite height (Lc) and the crystallite diameter (La) were not correlated with the rank of the samples. Rock-Eval S2 pyrograms depicted distinctive responses for the vitrains. While smooth curves were observed for the HvbA vitrain, the pyrograms showed unevenness and spikes for the Mvb and Lvb vitrains. We interpret these spikes or ruggedness to be caused due to melt formation during pyrolysis of Lvb and Mvb vitrains, and concomitant gas/bubble-bursting. We back our results with distinctive observations from the field emission scanning electron microscope (FE-SEM) of the pyrolysis-residues of the vitrains. We interpret that the distinctive S2 signatures shown by coals can be useful in predicting their end usage.
Article
Full-text available
An African oxalogenic tree, the iroko tree (Milicia excelsa), has the property to enhance carbonate precipitation in tropical oxisols, where such accumulations are not expected due to the theoretical acidic conditions of these soils. This uncommon process is linked to the oxalate-carbonate pathway, which increases soil pH through oxalate oxidation. In order to investigate the oxalate-carbonate pathway in the iroko system, fluxes of matter have been identified, described, and evaluated from field to microscopic scales. In the first centimeters of the soil profile, decaying of the organic matter allows the release of whewellite crystals, mainly due to the action of termites and saprophytic fungi. Regarding the carbonate flux, another direct consequence of wood feeding is a concomitant flux of carbonate formed in wood tissues, which is not consumed by termites. Nevertheless, calcite biomineralization of the tree is not a consequence of in situ oxalate consumption, but rather related to the oxalate oxidation inside the upper part of the soil. The consequence of this oxidation is the presence of carbonate ions in the soil solution pumped through the roots, leading to preferential mineralization of the roots and the trunk base. An ideal scenario for the iroko biomineralization and soil carbonate accumulation starts with oxalatization: as the iroko tree grows, the organic matter flux to the soil constitutes the litter. Therefore, an oxalate pool is formed on the forest ground. Then, wood rotting gents (mainly termites, fungi, and bacteria) release significant amounts of oxalate crystals from decaying plant tissues. In addition some of these gents are themselves producers of oxalate (fungi). Both processes contribute to a soil pool of "available" oxalate crystals. Oxalate consumption by oxalotrophic bacteria can start. Carbonate and calcium ions present in the soil solution represent the end products of the oxalate-carbonate pathway. The solution is pumped through the roots, leading to carbonate precipitation. The main pools of carbon are clearly identified as the organic matter (the tree and its organic products), the oxalate crystals, and the various carbonate features. A functional model based on field observations and diagenetic investigations with δ <sup>13</sup>C signatures of the various compartments involved in the local carbon cycle is proposed. It suggests that the iroko ecosystem can act as a long-term carbon sink, as long as the calcium source is related to non-carbonate rocks. Consequently, this carbon sink, driven by the oxalate carbonate pathway around an iroko tree, constitutes a true carbon trapping ecosystem as define by the ecological theory.
Article
Full-text available
In mine soil, quantification of soil organic carbon (OC) derived recently from biomass decomposition is complicated by the presence of fossil (geogenic) C derived from coal, oil shale, or similar material in the overburden. The only reliable method for such measurement is 14C analysis (i.e. radiocarbon dating) using instrumentation such as accelerator mass spectrometry, which is too expensive for routine laboratory analysis. We tested two previously used and two new methods for recent C quantification and compared them with 14C AMS radiocarbon dating as a reference using a set of soil samples (n = 14) from Sokolov, Czech Republic: (i) 13C isotope ratio composition, (ii) cross polarization magic angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy, (iii) near infrared spectroscopy (NIRS) coupled with partial least squares regression and (iv) Rock–Eval pyrolysis. Conventional methods for OC determination (dry combustion, wet dichromate oxidation, loss-on-ignition) were also compared to quantify any bias connected with their use. All the methods provided acceptable recent carbon estimates in the presence of mostly aliphatic fossil C from kerogen. However, the most accurate predictions were obtained with two approaches using Rock–Eval pyrolysis parameters as predictors, namely (i) S2 curve components and (ii) oxygen index (OI). The S2 curve approach is based on the lower thermal stability of recent vs. fossil organic matter. The OI approach corresponded well with 13C NMR spectra, which showed that samples rich in recent C were richer in carboxyl C and O-alkyl C. These two methods showed the greatest potential as routine methods for recent C quantification.
Article
Full-text available
Current interest in carbon (C) exchange processes between terrestrial ecosystems and the atmosphere have identified a need to assess soil C stocks or inventories for specific soil types and climates. In this study, the mean store of C and nitrogen (N) was determined in the soil profile of several Gleysolic, Podzolic, Luvisolic, and Brunisolic soils under different agricultural management systems, in the cool, humid region of eastern Canada. Based on a total of 69 management treatments from 16 agroecosystem sites, mean soil C and N densities (to a soil depth of 60 cm) ranged from 3.1 to 13.1 kg C m ⁻² and from 0.36 to 1.05 kg N m ⁻² The C:N ratio ranged from 8.3 to 17.1. Distribution of C and N down the soil profile showed a relatively regular pattern of C and N decrease with depth. Estimated C stocks or storage for the 1-m soil depth ranged from 8.3 to 13.3 kg C m ⁻² for the Gleysolic soils, and 5.4 to 10.5 kg C m ⁻² for the Podzolic soils, with an overall range and mean for all soils of 3 to 16 kg C m ⁻² and 9.8 kg C m ⁻² ± 2.8 This indicates that some agricultural soils in eastern Canada possess a relatively high potential for organic matter storage. Key words: Organic carbon and nitrogen storage, agroecosystem, Gleysol, Podzol, Luvisol, Brunisol, cool-humid climate
Article
Full-text available
The response of soil carbon dynamics to climate and land-use change will affect both the future climate and the quality of ecosystems. Deep soil carbon (> 20cm) is the primary component of the soil carbon pool, but the dynamics of deep soil carbon remains poorly understood. Therefore, radiocarbon activity (ΔD(14) C), which is a function of the age of carbon, may help to understand rates of soil carbon biodegradation and stabilization. We analyzed the published (14) C contents in 122 profiles of mineral soil that were well distributed in most of the large world biomes, except for the boreal zone. With a multivariate extension of a linear mixed effects model whose inference was based on the parallel combination of two algorithms, the Expectation-Maximization (EM) and the Metropolis-Hasting algorithms, we expressed soil Δ(14) C profiles as a four-parameter function of depth. The four-parameter model produced insightful predictions of soil Δ(14) C as dependent on depth, soil type, climate, vegetation, land-use and date of sampling (R2 = 0.68). Further analysis with the model showed that the age of topsoil carbon was primarily affected by climate and cultivation. By contrast, the age of deep soil carbon was affected more by soil taxa than by climate and thus illustrated the strong dependence of soil carbon dynamics on other pedologic traits such as clay content and mineralogy. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
Article
Full-text available
The Rock-Eval 6 apparatus is the latest version of the Rock-Eval product line, commercialized since 1996 by Vinci Technologies. The present work describes the methodology developed at IFP for reliable data acquisition and endorses the quality of geochemical parameters acquired with Rock-Eval 6. Data were obtained on 147 source rocks from various sedimentary basins, of different organic matter types and maturity stages. Intrinsic correlations for two different Rock-Eval 6 apparatus were performed and the obtained data set shows an excellent consistency and good reproducibility conditions for the whole set of Rock-Eval parameters. Complete recovery of total carbon (TC) by Rock-Eval 6 was confirmed by comparison with elemental analysis. In order to check the carbon partition (mineral vs. organic) determined by Rock-Eval 6, measurements of mineral carbon (MinC) and total organic carbon (TOC) were performed by alternative techniques. TOC measured by Rock-Eval 6 was compared to that obtained either by: the Leco apparatus for bulk rocks; elemental analysis for kerogens; and calculation from the mass balance determined after destruction of mineral matrix and the carbon concentration determined by elemental analysis on recovered kerogens for bulk rocks. The results display a good correlation for the whole concentration range (0-90 wt% TOC), when comparing elemental analysis and Rock-Eval 6 for source rocks and kerogens. However, comparison of Rock-Eval 6 with Leco data leads to larger deviations while correlation factors are still good. For a subset of kerogen samples, preparative pyrolysis was performed in order to confirm the value of 83 wt% for the organic carbon of the total S2 peak for any rock with any organic type and to check the absolute value of the S2 peak by gas chromatography analysis of pyrolysis by-product. MinC measured with Rock-Eval 6 was compared to that determined: weight loss after HCl treatment; the acidimetry technique; and calculation after TC, mass balance from kerogen isolation and organic carbon measurement on kerogen by elemental analysis. The results displays a good correlation for the whole concentration range (0-12 wt% MinC), when comparing elemental analyses and Rock-Eval 6. However, comparison of Rock-Eval 6 with acidimetry data leads to larger deviations while correlation factors are still good while comparison with weight loss is poor. As a whole an excellent reliability of TOC and MinC obtained by Rock-Eval 6 was demonstrated, and consequently, it is now possible to get at once the total organic and mineral carbon mass balance for a given rock. Recommendations are proposed regarding the standard samples and analytical methods selected for calibrating the Rock-Eval 6 over a large mineral and organic carbon range. Consistency between S2 and Tmax measured by Rock-Eval 2 and Rock-Eval 6 for Types I and II bulk rocks was also checked. A good correlation was obtained for S2, even though S2 values are slightly higher while measured with Rock-Eval 2. It was demonstrated that this is due to carrier gas(nitrogen vs. helium) by running measurements with a Rock-Eval 6 under helium, the difference ranging from 5 to 10 relative wt% for most studied samples. For Tmax correlation, data are much more scattered and as a general trend Tmax obtained by Rock-Eval 6 are higher than T-max obtained by Rock-Eval 2 and the difference increases with Tmax: this is due to the fact that the probe measuring the temperature in the Rock-Eval 2 is located in the oven wall, consequently Tmax determination is highly dependent in the Rock-Eval 6, where the probe is in contact with the crucible containing the sample, leading to much more reliable data.
Chapter
Full-text available
Introduction Although fungi are generally disregarded in the biogeochemical literature, they undoubtedly constitute crucial biogeochemical factors in many elemental cycles. This fact, combined with their abundance in the soil warrants greater detailed study into their geoecological impact. The network formed by fungal filaments can represent 10 000 km of thread-like mycelia in 1 m 2 of fertile soil. Their mass is evaluated at 3500 kg ha À1 at a depth of 20 cm in an average continental soil, i.e. taking into account all the different terrestrial environments on the Earth (Gobat et al., 2004). In comparison, bacteria and algae would represent 1500 and 10–1000 kg ha À1 respectively, in the same virtual average soil. Fungi are not only biologically important as saprophytes in the recycling of organic matter, but also play a geological role by excreting notable amounts of organic acids, among which oxalic acid is particularly important (Gadd, 1999), contributing to continental weathering as well as to mineral neogenesis (Verrecchia & Dumont, 1996; Verrecchia, 2000; Burford et al., 2003 a, b). The first fossil fungi have been identified in rocks dated from the Ordovician, i.e. 460 to 455 Ma ago (Redecker et al., 2000). However, molecular clock estimates for the evolution of fungi have suggested a Late Precambrian (600 Ma) colonization on land (Berbee & Taylor 2000). Recent molecular studies, based on protein sequence analysis, indicate that fungi were present on continents 1 billion years ago and possibly affected (together with plants) the evolution of Earth's atmosphere and climate since 700 Ma (Heckman et al., 2001). Therefore, if fungi have been present on the Earth's surface for such a long time, producing large amounts of oxalic acid able to precipitate as metal oxalates, why is there no evidence of oxalate accumulation in paleosols?
Article
Full-text available
The soil is important in sequestering atmospheric CO2 and in emitting trace gases (e.g. CO2, CH4 and N2O) that are radiatively active and enhance the ‘greenhouse’ effect. Land use changes and predicted global warming, through their effects on net primary productivity, the plant community and soil conditions, may have important effects on the size of the organic matter pool in the soil and directly affect the atmospheric concentration of these trace gases. A discrepancy of approximately 350 × 1015 g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo-referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project. This database holds 4353 soil profiles distributed globally which are considered to represent the soil units shown on a 1/2° latitude by 1/2° longitude version of the corrected and digitized 1:5 M FAO–UNESCO Soil Map of the World. Total soil carbon pools for the entire land area of the world, excluding carbon held in the litter layer and charcoal, amounts to 2157–2293 Pg of C in the upper 100 cm. Soil organic carbon is estimated to be 684–724 Pg of C in the upper 30 cm, 1462–1548 Pg of C in the upper 100 cm, and 2376–2456 Pg of C in the upper 200 cm. Although deforestation, changes in land use and predicted climate change can alter the amount of organic carbon held in the superficial soil layers rapidly, this is less so for the soil carbonate carbon. An estimated 695–748 Pg of carbonate-C is held in the upper 100 cm of the world's soils. Mean C: N ratios of soil organic matter range from 9.9 for arid Yermosols to 25.8 for Histosols. Global amounts of soil nitrogen are estimated to be 133–140 Pg of N for the upper 100 cm. Possible changes in soil organic carbon and nitrogen dynamics caused by increased concentrations of atmospheric CO2 and the predicted associated rise in temperature are discussed.
Article
Full-text available
Variations in the abundance of soil organic matter (SOM) constituents with different stability have a major impact on important environmental processes, e.g., carbon dioxide (CO2) fluxes between the soil and the atmosphere. Recently, besides the bulk Rock-Eval (RE) data, the mathematical deconvolution of the signals derived from hydrocarbon-like compounds released by thermal cracking of SOM during RE pyrolysis has been increasingly used to estimate the relative contribution of the major SOM classes differing in origin and preservation. This study applied the mathematical deconvolution of the S3 and S4 signals of carbon monoxide (CO) and CO2, produced both by the pyrolysis of the oxygen-containing moieties and by the oxidation of the residual highly resistant organic matter, to characterize the stability of these components. Our results suggested that the stability of the oxygen-containing moieties was controlled by the precursor material and was strongly affected by the land use and the presence of humic substances in the surface horizon of some main soil types in Hungary. In consistence with the bulk RE data, results of the mathematical deconvolution also proved to be diagnostic markers for discriminating the aquatic or terrigenous plants as the main sources of SOM. The mathematical deconvolution of S4 signals derived from the highly resistant SOM fraction allowed us to quantify the contribution of constituents with different stability. Furthermore, the results of this study displayed that the stability of this highly abundant SOM fraction in the surface soil samples depended on source biomass and intensity of leaching.
Article
Full-text available
This paper reviews the role of alluvial soils in vegetated gravelly river braid plains. When considering decadal time scales of river evolution, we argue that it becomes vital to consider soil development as an emergent property of the developing ecosystem. Soil processes have been relatively overlooked in accounts of the interactions between braided river processes and vegetation, although soils have been observed on vegetated fluvial landforms. We hypothesise that soil development plays a major role in the transition (speed and pathway) from a fresh sediment deposit to a vegetated soil-covered landform. Disturbance (erosion and/or deposition), vertical sediment structure (process history), vegetation succession, biological activity and water table fluctuation are seen as the main controls on early alluvial soil evolution. Erosion and deposition processes may not only act as soil disturbing agents, but also as suppliers of ecosystem resources, because of their role in delivering and changing access (e.g. through avulsion) to fluxes of water, fine sediments and organic matter. In turn, the associated initial ecosystem may influence further fluvial landform development, such as through the trapping of fine-grained sediments (e.g. sand) by the engineering action of vegetation and the deposit stabilisation by the developing above and belowground biomass. This may create a strong feedback between geomorphological processes, vegetation succession and soil evolution which we summarise in a conceptual model. We illustrate this model by an example from the Allondon River (CH) and identify the research questions that follow. This article is protected by copyright. All rights reserved.
Article
Full-text available
Organic matter (OM) is a key component of soils but information on its chemistry and behavior in soils is still incomplete. Numerous methods are commonly used to characterize and monitor OM dynamics, but only a few include the qualities required to become routine techniques i.e. simple, rapid, accurate and at low cost. Rock–Eval pyrolysis (RE pyrolysis) is a good candidate, as it provides an overview of OM properties by monitoring four com- ponents related to the main major classes of organic constituents (from A1 for the labile biological constit- uents to A4 for the mature refractory fraction). However, a question is still pending: do these four major classes used in the literature reflect a pertinent compositional chemical counterpart? 13C Nuclear Magnetic Resonance Spectroscopy in the solid state (13C CPMAS NMR) has been used to answer this question by collecting information on structural and conformational characteristics of OM. Moreover, in order to avoid the blurring effect of pedogenesis on OM dynamics, a ‘‘less complex OM’’ source, i.e. compost samples, has been used. Results showed significant and high determination coefficients between classes, indi- ces (of transformation of plant biopolymers, humifi- cation...) from RE pyrolysis, and the main classes of OM characterized by 13C NMR, e.g. A1 & A2 with labile/easily degradable components (alkyl C et O-alkyl C), A3 & A4 with humified OM (with aromatic C and phenolic C). The R index (contribution of bio- macromolecules) is correlated with phenolic and aromatic C, whereas the I index (related to immature OM) refers to labile––easily degradable components (alkyl C et O-alkyl C). The results confirm the pertinence of RE pyrolysis to monitor OM dynamics.
Article
Full-text available
Rock-Eval pyrolysis is used to rapidly evaluate the petroleum-generative potential and thermal maturity of rocks. Accurate conclusions require pyrograms every 30-60 ft (9-18 m), understanding of interpretive pitfalls, and supporting data, such as visual kerogen, vitrinite reflectance, and elemental analyses. The generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography. Most coals show high S2/S3 (> 5) and low Hi values (< 300 mg HC/g TOC). Migrated oil and mud additives, which alter Rock-eval data, can sometimes be removed by special processing. For immature rocks, bimodal S2 peaks and PI values over 0.2 indicate contamination. Pyrolysis downgrades organic-poor, clay-rich rocks, which show lower HI and higher T/sub max/ values than isolated kerogen because of adsorption of pyrolyzate on the clays. T/sub max/ values for small S2 peaks (< 0.2 mg HC/g TOC) are unreliable. T/sub max/ is affected by maturation, organic matter type, contamination, and the mineral matrix. S3 is sensitive to inorganic and adsorbed carbon dioxide, and to instrumentation problems. Acidification of carbonate-rich samples and proper maintenance improves S3 measurement. Constant sample weights (100 mg) are recommended. Below a threshold weight, T/sub max/ increases by up to 10/sup 0/C, and other parameters decrease. Organic-rich samples, which overload the detector, can be diluted with carbonate. Detector linearity is determined by pyrolyzing various weights of an organic-rich rock. 15 figures, 4 tables.
Article
The role of forest age as a potential driver of intraspecific variation in leaf litter quality, that is a key plant trait determining ecosystem functioning, has largely been neglected. Using a set of fully replicated pure beech (Fagus sylvatica) forest stands differing in age (15, 65, 95 and 130 years), we quantified the forest stand age related variability of twelve leaf litter quality traits. Litter Mg, N and K showed significantly higher concentrations in litter from 15-yrs-old stands and decreased with increasing stand age. Mn was the only nutrient analyzed that was highest in the oldest stands. Hemicellulose and cellulose were lowest, and lignin and lignin/N ratio were highest in stands of intermediate age. The amount of N within the litter lignin fraction was highest in the 95-yrs-old stands (51% of total N) and lowest in the oldest stands (34% of total N). The amount of N associated within the hemicellulose fraction (<3%) showed the opposite pattern along the forest stand age gradient compared to lignin. Using Partial Least Squares regressions, we showed that litter N, C/N, lignin/N, K, Mn and Mg were the most important predictors of litter decomposition along the chronosequence. In contrast the proportions of C fractions and the amount of N within these C fractions were the most significant variables explaining the variation in final litter N content after one year of decomposition. N mineralization in ground litter was highly related to the proportion of total N within lignin and humus N mineralization was mostly explained by Mn and the lignin/N ratio. We showed that forest age is an important driver of litter quality variation and contributed considerably to the overall variation of F. sylvatica leaf litter quality traits observed from a reviewed data of published studies conducted at the continental scale. Furthermore, intraspecific litter quality variation greatly impacted belowground processes. Accounting for forest age related litter trait variation, and for the crucial role of the distribution of N within different litter C fractions, may improve the mechanistic understanding of ecosystem functioning.
Article
The exchange of nutrients, energy and carbon between soil organic matter, the soil environment, aquatic systems and the atmosphere is important for agricultural productivity, water quality and climate. Long-standing theory suggests that soil organic matter is composed of inherently stable and chemically unique compounds. Here we argue that the available evidence does not support the formation of large-molecular-size and persistent 'humic substances' in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds. We discuss implications of this view of the nature of soil organic matter for aquatic health, soil carbon-climate interactions and land management.
Article
Considers the significance of organic soil C to water and nutrient supply, soil development, and ecosystem function and productivity. Illustrates this through both chronosequence studies and designed experiments using the state factor approach. Emphasis is placed on forms and pool sizes of organic C at the ecosystem level across a range of climatic and management regimes. -from Authors