Comparative analysis of molecular biomarkers in the sediments of two artificial urban lakes in Orléans, France

International audienceThe onset of the Anthropocene, a new geological Era characterized by human activities being the dominant geological process affecting the Earth surface, will soon be defined by the International Commission on Stratigraphy in 1950 AD (Zalasiewicz, 2015). For palaeoenvironmentalists, the Anthropocene opens a new and very exciting challenge: decrypt geological archives by using various tracers over unusual time scales (days, seasons, years, decades) and take into account the major forcing factor: human activities. As for longer time periods and more natural contexts, organic geochemistry will have to contribute and will be confronted to emerging issues: (1) to which extent organic tracers and proxies developed for longer time scales, in more natural ecosystems, can be transferred and applied in hyper-anthropized socio-ecosystems such as urban areas?; (2) human activities produce novel materials and organic compounds such as emerging pollutants that could be readily considered as novel tracers for a large set of socioeconomic concerns, thus establishing new connections between paleoenvironmentalists and researchers engaged into pollution studies. We have analysed molecular biomarkers preserved in the sediments of two artificial lakes of Orléans: Lac de l'Université (LU) and Lac de l'Orée de Sologne (LOS) in order to determine their potential as sedimentary archives, through the presence of both sedimentary accumulations and specific tracers in order to reconstruct the recent history of their surroundings, and evaluate to which extent molecular imprints reflect local environmental conditions. Those two lakes collect local rainwaters and were clean out around 1990. Only few centimetres could be collected in LOS whereas LU afforded 30 cm constituted by 6 cm of sand with gravels (TOC400°C), then 16 cm of black organic clay and finally 8 cm of greenish organic clay (TOC> 5%, IH>400 mgHC/COT, IO~150 mgO2/COT, Tmax>400°C). The strong contribution of vascular plants to the sediment is not only attested by Rock-Eval values but also by the distribution of n-alkanes that maximize at n-C27 with a strong odd/even predominance. In LOS minor amounts of short-chain n-alkanes attest to a bacterial/algal contribution. The ketone fraction afforded a large diversity of compounds such as pentacyclic triterpenones (taraxerone, β-and α-amyrenones, germanicone, lupanone, glutinone and friedelin). In addition, LOS sample displayed abietic acid and a series of four methoxy-serratenes (two dimethoxy and two keto-methoxy; LeMilbeau et al., 2013). LOS sample was also characterized by the presence of four compounds of which the mass spectra displayed M + at m/z 378 or 392 and intense m/z at 199 and 225 that are interpreted as diagenetic derivatives of pentacyclic triterpenes bearing a ketone function (Tris-nor-olea-trien-2-one, Tris-nor-ursa-trien-2-one, Bis-nor-olea-trien-2-one and Bis-nor-ursa-trien-2-one). The alcohol fraction contained the alcohol equivalent to triterpene ketones such as taraxerol, β-, δ-and α-amyrins, germanicol and glutinol, as well as a keto-methoxy-serratene and a hydroxy-methoxy-serratenes in LOS. Again, LOS displayed original pentacyclic triterpenes constituted by diketo Δ 12 (Bandaranayake, 1980) and

STEROLS AND BILE ACIDS IN URBAN AND RURAL SOILS AS FAECAL MARKERS OF LAND-USE SINCE THE BRONZE AGE

International audienceFor ancient societies, the control of agriculture and animal domestication were extremely important to their development. After having domesticated different animals as livestock, ancient societies developed techniques such as manuring to improve culture yields. There are numerous evidences in archaeological records of animal breeding (bones, coprolithes, spherolites). Reversely, despite few studies dedicated to buildings and caves, the only evidence for manuring and breeding out of archaeological context, were acquired on recent soils (Bull et al., 1998; Birk et al., 2011). The aim of this study is to test the potential of faecal biomarkers preserved in soils to spatially resolve (at the field-scale) the strategies of land use (buildings, breeding and manuring) in ancient times. For this, faecal biomarkers (sterols and bile acids) of animals (Humans, cow, horse, pig and sheep), sediments from a septic tank (beginning of 19th century) and soils of distinct land use (pasture and forest) were characterized. Then, archaeogical samples were analysed: (i) agricultural soils, middens and settlement layers dated back to the Bronze Age in Lake Bourget shore, (ii) settlement layers recovered during excavations in a medieval building (15th century, Orléans). Sterols and bile acids were isolated from archaeogical samples following Zocatelli et al. (2012). Neutral fraction was further separated by flash chromatography. The alcohol fraction was silylated and analysed by GC-MS with a Polaris TRACE-GCQ. From the twenty sterols and bile acids identified, the following faecal biomarkers were found: coprostanol (Cp), methyl-coprostanol (mCp), ethyl-coprostanol (eCp), lithocholic acid (LC), deoxycholic acid (DOC), cholic acid (C), chenodeoxycholic acid (CDOC), hyodeoxycholic acid (HDOC), ursodeoxycholic acid (UDOC) and 3α-hydroxy-12-oxo-5β-cholanoic acid (oxoDOC). To identify possible sources of faecal compounds, bile acid imprints and sterol ratios were employed: 1) (Cp+epi-Cp)/(eCp+epi-eCp); 2) (Cp+epi-Cp)/(Cp+epi-Cp+5α-cholestanol); 3) (Cp+epi-Cp)/cholesterol. Sterol content of animal faeces clearly distinguished two groups: omnivores (Humans and pig) and herbivores (cow, horse and sheep). Then, Human and pig imprints were distinguished from bile acids. Faecal biomarkers were detected in all archaeogical samples (i and ii) and allowed the distinction between omnivores, herbivores and mixed faecal biomarker imprints in the sample set. Samples from middens of Lake Bourget catchment contained a mixture of Human and breeding faecal sterols. Bile acids corroborated these results. Furthermore, faecal biomarkers detected Le Bourget catchment soils formerly cultivated for millet, evidenced past manuring practices (mCp, eCp and DOC). High contents of coprostanols (Cp and eCp) and bile acids (LC, DOC and C) in settlement layers from Lake Le Bourget shore evidenced the co-occurrence of animals in the same area. Analysis of faecal materials from a medieval building in Orléans revealed only Human occupation (Cp, LC, DOC, CDOC, C and oxoDOC). Finally, this study showed that faecal biomarkers are efficient to provide information on the use of space in areas inhabited by humans. From a more general point of view, these results illustrateed that faecal biomarkers could reveal how Human societies shaped their environment through times

Lipids and clays interactions in a productive marine water column (Antofagasta Bay, Chile)

International audienceOrgano-Clay Interactions (OCIs) are a poorly investigated topic despite the potential benefits in both fundamental and industrial studies fields. Indeed, Organic Matter (OM) sorption on clays is a mechanism involved in several research areas: past and actual environmental problematics, hydrocarbons sources rocks or soil sciences considerations. In actual environmental issues, new research axes are emerging on OCIs applications on organic pollutants treatments. In the actual environmental management field, OCIs are investigated in order to characterize the role of clay minerals on landfill barriers strengthening (Sánchez-Jiménez et al., 2011). OCIs investigations in paleoenvironmental field are primordial for the calibration of climatical and paleoecological biomarkers proxies. On the topic of formation and evolution of hydrocarbon source rocks, OCIs play an important role on the early steps of diagenetic processes. Several models of OM preservation paths are already admitted (Boussafir and Lallier-Verges, 1997). However, those schemes do not consider the function of the mineral fraction and particularly the role of the clayey fraction on sedimentation and preservation of organic matter. In order to test the role of clays on early stages of petroleum source rocks genesis, our study aims to investigate the efficiency of three clays on OM sorption in a marine productive water column. This study was carried out off the eastern Pacific upwelling (Antofagasta bay, Chile) which is considered as one of the four most productive up-welling areas of the South American coast. A combined system of upwelling and surface currents (Humboldt current) sustains a proliferating biomass. Natural and synthetic montmorillonites and natural kaolinite samples have been disposed along the oceanic water column at three depths corresponding to different water oxygenic conditions (oxic, transition and anoxic). After different times of exposure, the samples have been removed and characterized via different analytical methods (Py-GC-MS, Dissoveld Organic Carbon Analyser, XRD and infrared spectroscopy). The contributions of this work can be declined in three points: (i) we observed an increase of the dissolved organic carbon (DOC) concentrations in the water of clay traps compared to marine ones. This evidence has been detected in the traps water after 2 days of interactions, demonstrating a good attraction effect of clays on ambient organic material. Drouin (2007) observed similar result in lacustrine area. (ii) The py-GC-MS molecular results show that fatty acids are the preferentially adsorbed molecular lipids family during the interaction process. The anoxic zone of the water column has been defined as the most propitious area for the organo-clay aggregation process. (iii) X-ray analysis have highlighted an extension of montmorillonites (001) plans spacing suggesting the intercalation of some organic compounds. However, previous studies (Drouin et al., 2010) and some of our results suggest that clays specific surfaces play a major role on the organic sorption. A comparison between theoretically absorbable amount of organic material and effectively quantified ones permitted us to conclude that organic molecules occupied a little part of external clay surface area

Combined δ13C - δD analysis of pentacyclic triterpenes and their derivatives

International audienceCompound-specific carbon and hydrogen analyses have been proposed to quantify environmental variables because they afford a remarkable constrain on the biological source through the selection of specific biomarkers

Molecular signature of Late Bronze Age archaeological layers preserved in littoral settings in Lake le Bourget (French Alps).

International audienceThe Final Bronze Age was a key period for Human history in the Alps since numerous human occupations developed on lake shores attest to an increased anthropication of alpine ecosystems at that time [1]. Successions of abandonment and occupations were most probably climatically-driven through lacustrine level variations [2]. Our recent results on a sediment core drilled in Lake le Bourget provide a detailed record of the evolution of past human activities for this period by using a molecular biomarker specific of millet cultivation [3]. These original results motivated the research of new molecular biomarkers of human activities

CHEMICAL DIVERSITY OF SOIL LIPIDS REFLECTS SURROUNDING BIODIVERSITY IN A FRENCH PEATBOG

International audienceThe aims of this study are to characterize the spatial variability of biomarker imprints in a peatland and to test to which extent this variability can be related to the surrounding vegetation. Since the mid 1970’s La Guette peatland (région Centre, France) has been colonized by vascular plants. Nowadays it is totally colonized by Molina caerulea and, to varying extent, by Pinus sylvestris and Betula pendula. In nine stations representative of distinct vegetation cover, we analysed the lipid composition of soil developed under Molinia caerulea. The lipids of the six most abundant plants encountered in the peatland were analysed as reference samples: Sphagnum rubellum, Erica tetralix, Calluna vulgaris, Molinia caerulea, Betula pendula and Pinus sylvestris. For all these samples, lipids were ultrasonically extracted with DCM and then separated into neutral, acidic and polar compounds. The neutral fraction was further separated by flash chromatography to afford (i) aliphatics and aromatics; (ii) ethers, esters, ketones and acetates and (iii) alcohols. 5α-cholestane was added prior to analysis for quantitation. Lipid fractions were then identified and quantified by gas chromatography-mass spectrometry. In order to quantify their density, trees were counted within circles of increasing radius (giving areas of 3.14; 12.6; 28.3; 50.3 and 78.5 m2) around the sampling plot. After counting, total tree density was determined as well as individual P. sylvestris and B. pendula density. For each sample (n=9) regressions were calculated between (i) lipids and (ii) the density of the tree (n=9). This calculation was reproduced for each counting surface. Then, the resulting regression coefficient was plotted against each surface of counting. Apart from ubiquist compounds such as n-alkanes and triterpenoid ketones, we found in soils several biomarkers for which the source could be constrained. Taraxeryl, friedelanyl and moretenyl acetates were detected. Friedelanyl and moretenyl acetates were found in high amounts in open vegetation plots (9.7 and 2.9 µg.g soil-1, respectively). They were also detected in E. tetralix and C. vulgaris (Ericaceae) and, probably due to contamination, in S. rubellum. Multiflorenyl and two unknown acetates, also present in low contents, may originate from undetermined, less abundant plant. Four methoxy-serratenes (Le Milbeau et al., 2013) and seven tricyclic diterpenes were detected in both soils and P. sylvestris needles. Strong correlation (r = 0.997; p ≤ 0.0001) of their respective abundances in soils attest to their common origin and similar conservation potential. The presence of betulin and related compounds in soil samples and in B. pendula leaves are in agreement with the admitted use of these biomarkers to track the former presence Betula species in soils and sediments (i.e. Otto and Simoneit, 2001). The source of these biomarkers being defined, we then assessed their spatial distribution at the nine sampling sites. Although not abundant, triterpenyl acetates, methoxy-serratenes, diterpenes and betulin derivatives exhibit a higher coefficient of variation along sampling sites than other compound such as n-alkanes or triterpenoid ketones.The correlation between methoxy-serratenes and the number of P. sylvestris in the nine sampling sites increases with the surface used for the calculation (r = 0.93, p<0.022). These values indicate that specific biomarkers of P. sylvestris in soil samples and surrounding vegetation are spatially linked. The same applies for B. pendula and betulin derivatives (r = 0.96, p<0.008). The degradability of the betulin and its relatively high solubility may induce lost and leaching out of the sampling point. Our results provide evidence that selected biomarkers in soil samples can give a reliable picture of the surrounding vegetation. It also quantifies the area of influence of trees on the soil lipid composition, over 20 m². The approach combining tree counting and quantitation of specific biomarkers that was developed in the frame of this study proved to be efficient in evidencing the spatial control of the surrounding vegetation on lipids distribution in a peatland invaded by vascular plants.REFERENCESLe Milbeau, C., Lavrieux, M., Jacob, J., Bréheret, J.G., Zocatelli, R., Disnar, J.R., 2013. Diversity of methoxy-serratenes in a soil under a conifer forest and their potential as biomarkers of Pinaceae. Organic Geochemistry 55, 45-54.Otto, A., Simoneit, B.R.T., 2001. Chemosystematics and diagenesis of terpenoids in fossil conifer species and sediment from the Eocene Zeitz formation, Saxony, Germany. Geochimica et Cosmochimica Acta 65:20, 3505–3527

Spatial variability of soil lipids reflects vegetation cover in a French peatland

International audienceThe purpose of this study was to show how current vegetation in a peatland is imprinted in the lipid fraction of the underlying soil. La Guette is a fen peatland in Central France dominated by Sphagnum spp. and ericaceous shrubs, colonized by sedges (Molinia caerulea) and trees since the 1970s (Betula pendula and Pinus sylvestris). Lipid were identified and quantified in the most abundant plants and in samples collected at the base of M. caerulea tussocks. Among relevant biomarkers, tricyclic diterpenes and methoxy-serratenes stood out as specific for P. sylvestris, betulin derivatives as specific for B. pendula, and some pentacyclic triterpene ketones and acetates as biomarkers of Ericaceae. Multivariate analysis applied to biomarker concentration in soil samples from several sites permitted distinguishing three different vegetation types: vegetation cover: (i) closed vegetation dominated by P. sylvestris; (ii) closed vegetation dominated B. pendula and (iii) open vegetation or semi-open vegetation (early colonization by trees) constituted mainly by Ericaceae, Sphagnum and graminoids. Comparison of tree-specific biomarker concentrations with estimates of tree biomass allowed establishing of quantitative relationships that were valid over at least 80 m2 around the sampling site. Although preliminary, the results are promising in attempting to relate biomarker concentrations in geological archives to paleo-biomass

Preservation of an ancient grassland biomarker signature in a forest soil from the French Massif Central

International audienceIn response to the lack of studies focussing on the residence time of molecular biomarkers in soils, the lipid content of three soil profiles from the French Massif Central with different land use history were examined. The free neutral lipid content of two reference soil profiles developed under grassland and forest vegetation, and of a former grassland soil converted to forest about 60 years ago, was analysed using gas chromatography - mass spectrometry (GC-MS). Wax esters as well as the ratio of major homologues of n-alkanes and n-alkan-2-ones could be used to characterize the overlying vegetation in the reference forest and grassland soil profiles, but failed to distinguish the respective grassland and forest contributions to the profile of the soil that had changed use. For n-alkanes and n-alkan-2-ones, the failure might be attributed either to mixing of the molecular patterns inherited for the former and current plant cover, whereas for compounds such as wax esters simple degradation is likely to be involved. Conversely, iso- and anteiso- C15:0 fatty acid methyl esters (FAMEs; of bacterial origin), steroids (tracing cattle faecal contamination), tricyclic diterpenoids and their oxygenated derivatives, as well as methoxyserratenes (inherited from Pinaceae) and triterpenyl acetates (specific to the Asteraceae), proved to be effective in distinguishing current land use for the reference soil profilesand for the converted soil. The persistence of these compounds in the changed use soil allowed us to estimate their residence time in soil

Distribution of miliacin (olean-18-en-3β-ol methyl ether) and related compounds in broomcorn millet (Panicum miliaceum) and other reputed sources: Implications for the use of sedimentary miliacin as a tracer of millet

International audienceUsing sedimentary miliacin (olean-18-en-3β-ol methyl ether) as a molecular tracer of the history of Panicum miliaceum (broomcorn millet) cultivation depends upon broomcorn millet being sedimentary miliacin's dominant source. It also requires knowledge of the variability in miliacin concentration in broomcorn millet. Finally, it is affected by the presence of other pentacyclic triterpene methyl ethers (PTMEs) that may exist in conjunction with miliacin in other sources but not in broomcorn millet. Miliacin biosynthesis has been proposed for other Panicum species, Setaria italica (Italian or foxtail millet), Pennisetum sp., and Chaetomium olivaceum (an olive green mold). We found miliacin concentration in seeds of different varieties of P. miliaceum to be similarly high (with trace amounts of β- and α-amyrin methyl ethers). It was absent from hulls and roots, and nominally present in leaves and stems. The transfer of miliacin from plant to sediments is therefore mostly from seeds. it was abundant (often with larger amounts of β- and α-amyrin methyl ethers) in all other Panicum species studied, but only in some species of the genus Pennisetum and was absent from Setaria italica. Neither C. olivaceum nor its growth medium (rice) showed any trace of miliacin. Our results, with miliacin absent from S. italica and C. olivaceum, its high miliacin in seed of P. miliaceum relative to other PTMEs and to other grasses and, considering the high biomass that cultivated broomcorn millet has relative to other potential plant sources, support the use of sedimentary records of miliacin in some contexts to track past millet agricultural dynamics

First detection of triterpenyl acetates in soils: sources and potential as new palaeoenvironmental biomarkers

International audienceUnderstanding past reactions of ecosystems under natural and anthropic constraints is of crucial importance to anticipate the consequences of the current global changes. Unraveling natural and anthropic impacts on environments requires the reconstruction of ancient land-uses. As a part of a larger project aiming at developing new molecular biomarkers in soils that could be specific of their overlying vegetation, we have analyzed the neutral lipid content of soils developed under distinct types of plants. Soils were sampled around Lake Aydat, in Central France, of which the catchment is covered with pastures/meadows, forests and moors. The ketone/ester lipid fraction from soils under pastures or meadows contains a series of 14 pentacyclic triterpenyl acetates with a large structural diversity (Fig. 1). This discovery motivated an extensive phytochemical literature survey (240 references) that showed restricted potential sources of triterpenyl acetates. -amyrin, taraxeryl, glutinyl, -amyrin, and multiflorenyl, acetates are found in very distinct taxa and are thus poorly informative. Conversely, lupeyl, bauerenyl, isobauerenyl, taraxasteryl and -taraxasteryl acetates appear more specific since they are majoritary reported in Asteraceae. Pichierenyl, isopichierenyl and gammacerenyl acetates seem to be the more specific ones since they are produced by a single known species, Picris hieracioides L. (hawkweed oxtongue, Asteraceae)