words)A 19-meter-long sedimentary record retrieved in Lake Aydat (French Massif Central) covers the last 6700 yrs at a high-resolution. A multi-proxy approach (density, magnetic susceptibility, XRF, Rock-Eval, pollen and non-pollen palynomorph analyses and a historical archives study) was used to characterise and propose a model of sedimentation. The high 2 deposition rate results from the combined effects of the high suspension load of the river, autochthonous production and the narrow shape of the incised fluvial valley dammed by a lava flow ca. 8550 years ago. Two contrasted periods (6700±200 -3180±90 cal. BP, and 1770±60 cal. BP-now) were characterized. The lower unit (mid-Holocene) displays a fine and regular lamination and holds a single, major, flood deposit. This unit is capped by an erosive mass wasting deposit triggered ca. 1770±60 cal. BP. The upper unit (late-Holocene) is made of organic rich and fine grained faintly laminated sediment, with numerous interbedded flood deposits and diatom blooms. The sedimentation was principally controlled by climatic forcings until ca. 1100 cal. BP, accompanied by detrital events linked to human activities around the lake. Then, a more detrital input attested by numerous and recurrent flood deposits can be linked to the intensification of a persistent anthropogenic impact on the catchment.Two phases of lake eutrophication are highlighted: 1200-1130 cal. BP, as a result of increased anthropogenic pressure, and the current phase that could have started ca. 150 cal. BP.

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As a part of a wider study aimed at determining new molecular biomarkers in soils and sediments that could be specific of distinct vegetation types with respect to unravelling past changes in land use, we analysed the neutral lipid content of soil developed in the catchment of a small lake in central France. The ketone/acetate lipid fraction of soil under pasture or meadow contains a series of pentacyclic triterpenyl acetates of wide structural diversity, most being reported in soil for the first time. The restricted number of potential plant sources of triterpenyl acetates (some produced by a single species) underlines the potential of triterpenyl acetates as new biomarkers to track past vegetation change in palaeoenvironmental studies, when found in natural archives such as soil, sediments or peat.

ERODE project funded by the INSU/CNRS and 205 OTARIE project funded by the Région Centre and the European Council. ARTEMIS programInternational audienceHemp (Cannabis sp.) has been a fundamental plant for the development of human societies. Its fibers have long been used for textiles and rope making, which requires prior stem retting. This process is essential for extracting fibers from the stem of the plant, but can adversely affect the quality of surface waters. The history of human activities related to hemp (its domestication, spread, and processing) is frequently reconstructed from seeds and pollen detected in archaeological sites or in sedimentary archives, but this method does not always make it possible to ascertain whether retting took place. Hemp is also known to contain phytocannabinoids, a type of chemicals that are specific to the plant. Here we report on the detection of one of these chemicals, cannabinol (CBN), preserved in a sediment record from a small lake in the French Massif Central covering the last 1800 years. We demonstrate that the presence of this molecule in the sedimentary record is related to retting. Analysis of the evolution of CBN concentrations shows that hemp retting was a significant activity in the area until ca. 1850 AD. These findings are supported by pollen analyses and historical data

International audiencePurpose: Eighteen soils were sampled in the Lake Aydat catchment in order to analyse free fatty acid (FA) content; FAs are considered to be among the most amenable biomarkers to mobilisation by runoff waters. The majority of the study area has soil cover consisting of grasslands or forest since the 2nd World War, although some covers having changed more recently. Material and methods: The soil studied all developed on volcanic rocks (andisols). The bulk organic matter (OM) content of the samples was characterized by Rock-Eval (RE) pyrolysis. The FAs were determined by gas chromatography-mass spectrometry (GC-MS) analysis of isolated and derivatized (methylation and trimethylsilylation) FA fractions. Results and discussion: Few low molecular weight compounds (LMW; i.e.

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International audienceThis paper presents the potential of 5β-stanols and bile acids to act as fecal source biomarkers in order to identify and characterize past agropastoral activities in archaeological and natural archives. First of all, a molecular inventory of 5β-stanols and bile acids was made on fresh fecal human and domestic animal samples, using the same methodology to define the specificity of these molecular biomarkers. The selected species were cow, horse, pig and sheep as they are the major domestic species present in European archaeological sites. To our knowledge, our work constitutes the first report on fecal biomarkers in sheep feces. Bile acids can distinguish diet regime and species having the same diet with greater specificity than 5β-stanols. Fresh human fecal material and historical/archaeological fecal material were analyzed to assess their stability through time by calculating the coprostanol/epi-coprostanol (Cp/epi-Cp) and deoxycholic acid/cholic acid (DOC/C) ratios. Results show that bile acids are more resistant to diagenesis than 5β-stanols, at least on a 700-year time scale. Human and domestic animal fecal molecular imprints were then compared to the molecular content of 65 samples retrieved from archaeological sites, soils and lacustrine sediments to test their ability to trace past land-use dynamics. This study is the first to combine bile acids and 5β-stanols to identify a source of fecal material in lacustrine sediments. The combination of sterols and bile acids can be used in a variety of natural archives and archaeological contexts to define the origin of fecal material, to specify land-use, and to reconstruct past pastoral practices at various spatio-temporal scales

International audienceIn the frame of a study aimed at defining new soil molecular biomarkers that could attest to former land use and that could also be screened in lake sediments for palaeoenvironmental reconstruction, we analysed the 2-4 cm depth layer of a soil developed under a conifer forest in the Lake Aydat catchment (French Massif Central). The lipid fraction of the sample contained 12 serratenoids bearing at least a methoxyl (OMe) group at C-3 or C-21 and various additional functional groups (alcohol, ketone or acetate). A survey of the literature provided indubitable evidence that these compounds are typical for Pinaceae species, in agreement with the surrounding vegetation at the sampling site. Due to the economic and ecological importance of the taxa, the presence of these highly specific compounds in soil, sediments or peat should therefore help in unravelling the timing of forestry activity