Jérémy Jacob

Impacts of new agricultural practices on soil erosion during the Bronze Age in the French Prealps

In order to better understand the evolution of past climate—human—environment interactions in the northwestern Alps during the Holocene, we have analysed the lipid content of two cores taken from the sediments of Lake le Bourget (French Alps). By using a specific molecular biomarker of Panicum miliaceum (broomcorn millet) previously defined and a new molecular marker of soil erosion, we demonstrate that the onset of millet cultivation coincides with the onset of major soil erosion in the catchment during the Middle Bronze Age. Although archaeological and archaeobotanical investigations indicate a discrete human occupation of the lakeshores at this period, they also point to a regional change in agricultural practices that deeply affected soils. The evolution of millet cultivation appears in strong connection with climatic variations, estimated in the same cores from the variations in titanium, a proxy of hydrological changes in the region. Social and cultural triggers cannot be discarded at this stage. Such an approach applied to more sedimentary archives shows high potential to unravel the temporal and spatial dynamics of human land use.

6700 yr sedimentary record of climatic and anthropogenic signals in Lake Aydat (French Massif Central)

A 19 m long sedimentary record retrieved in Lake Aydat (French Massif Central) covers the last 6700 yr at a high resolution. A multiproxy 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 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 c. 8550 years ago. Two contrasted periods (6700±200 to 3180±90 cal. BP, and 1770±60 cal. BP to present) 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 c. 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 c. 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 c. 150 cal. BP.

Sedimentary cannabinol tracks the history of hemp retting

Hemp (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 is specific to the plant. Here we report on the detection of one of these chemicals, cannabinol (CBN), preserved in a sediment record from a lake in the French Massif Central covering the past 1800 yr. 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. A.D. 1850. These findings, supported by pollen analyses and historical data, show that this novel sedimentary tracer can help to better constrain past impacts of human activities on the environment.

Free fatty acids in Lake Aydat catchment soils (French Massif Central): sources, distributions and potential use as sediment biomarkers

PurposeEighteen 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 methodsThe 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 discussionFew low molecular weight compounds (LMW; i.e., <C20) were detected; FA distributions were dominated by even numbered-carbon high molecular weight (HMW; ≥C20) normal FAs and difunctionalized FAs that included: dicarboxylic acids (diFAs), n-alkylcarboxylic acids (nFAs), and α- and ω-hydroxycarboxylic acids (αHOFAs and ωHOFAs). The distributions and abundances of HMW terms of all families (which can be all considered as representative of terrestrial OM source) displayed only slight differences. These differences were rationalized by the following ratios: (C26:0 + C28:0)/ΣCeven nFAs, C22/C24 di-FAs, and C20−/C20+ω-HOFAs). Soils from areas that had changed use recently consistently displayed intermediate ratio values typical of their double inheritance. All grassland soils and some samples from intermediate areas contained notable amounts of the bile acid deoxycholic acid that testifies to their present or recent use for cattle breeding.ConclusionsDespite the variety and the abundance of all HMW FAs in soils, work done previously on Lake Aydat sediments found only nFAs (Stefanova, M. and Disnar, J. R. 2000. Composition and early diagenesis of FAs in lacustrine sediments, Lake Aydat (France). Org Geochem 31, 41–55). These results suggest we should question the importance of the watershed contribution, the source (plant or soil) and mode of transportation of the FAs to the lake sediments.

Variation in δD values of a single, species-specific molecular biomarker: a study of miliacin throughout a field of broomcorn millet (Panicum miliaceum L.).

Compound-specific δD analyses of land plant-derived biomarkers preserved in lake sediments are gaining increasing interest in paleoclimatic studies because of their potential to record essential information on the climatic conditions that prevailed at the time of their synthesis. The accuracy of inferences about climate from these analyses could be better constrained with more study of the variability in the δD values of possible inputs at catchment scales. We measured the δD values of miliacin (olean-18-en-3β-ol methyl ether) extracted from the seeds of millet plants collected in 21 stands spatially distributed in a field with visually heterogeneous soil organic matter contents. The use of a single molecular biomarker extracted from a single plant species eliminates the possibility of variability caused by differences in plant type. The δD values differed between plants by as much as 50‰ and the average δD values per stand differed from one another by a maximum of 30‰. Thus, the δD values of a single, species-specific biomarker can vary markedly among plants even within a similar climate. Differences in δD values within stands could be as high as between stands, suggesting that the δD values are not related to macroscale heterogeneities in soil organic matter content. In addition, δD values were unrelated to factors indicative of differences in environment such as plant height, seed weight or miliacin concentration. The average miliacin δD value was representative of the area sampled, however, since it was normally distributed (p < 0.05).

Molecular Biomarkers of Anthropic Impacts in Natural Archives: A Review

Molecular biomarkers are becoming increasingly important tools in paleoenvironmental research, and over recent years have been shown to be useful indicators of human activities. Common indicators of past human impacts include pollen, charcoal, sedimentation rates, and magnetic susceptibility, each of which has its limitations. Thus, the advent of novel molecular markers of human activities provides an additional set of tools to make the difficult distinction between anthropogenic and natural factors that have influenced the environment in the past. Fossil biomarkers preserved in natural archives provide valuable temporal and spatial insights on land use such as cultivation practices and pastoral activities, post-harvesting activities (e.g., retting), and their consequences on the environment and ecosystems. Herein we review the progress that has been made in developing novel biomarkers of human activities, differentiating those indicating environmental changes that can be related to human activities from those unambiguously attributable to human activities. The review ends with a case study highlighting the strengths and weaknesses of the biomarker approach and finally summarizes opportunities for future research.

Miliacin in palaeosols from an Early Iron Age in Ukraine reveal in situ cultivation of broomcorn millet

During the archaeobotanical investigation of Scythian–Sarmatian period (Early Iron Age), pits with crop processing waste, discovered in the floodplain of Donets River, eastern Ukraine, and charred remains of cereal grains, dominated by broomcorn millet, were recorded. The grains from the pits were radiocarbon dated to the fifth to first century BC. Those pits are distant from any known contemporaneous settlement. The apparent disconnection of these pits from any local settlement suggests that (1) millet was brought from other locations by mobile groups, or (2) millet was cultivated locally by populations whose settlements have left no discernible archaeological trace. The analysis of molecular biomarkers preserved in palaeosols that are stratigraphically connected to the pits revealed high levels of miliacin, a molecule that can be preserved in ancient soils and sediments, and that is consistent with broomcorn millet (Panicum miliaceum). High levels in miliacin in soils stratigraphically connected to the pits are interpreted as the result of a large biomass of P. miliaceum produced at time of soil formation. Our biogeochemical results applied to a palaeosol thus attest to the in situ cultivation of crops dominated by the broomcorn millet during the early Iron Age in the floodplain of Donets River. Biochemical examination of soils and palaeosols can thus provide useful information on past dynamics of land-use by ancient population, especially when settlements or macrobotanical remains are absent.

Temporal dynamics of human-excreted pollutants in wastewater treatment plant influents: toward a better knowledge of mass load fluctuations

The occurrence of 25 drug target residues (illicit drugs or pharmaceutically active compounds) was investigated during 85 consecutive days in the influents of a wastewater treatment plant in the Region Centre-Val de Loire, France. This long tracking period allowed a better understanding of the patterns affecting the occurrence of this type of contaminants. Among them, 2 were never detected (i.e. heroin and amphetamine). Concerning illicit drugs two patterns were found. Cocaine and ecstasy median loads varied considerably between weekdays and weekend days (i.e. 18.3 and 35.9% respectively) whereas cannabis and heroin (based on 6-mono-acetylmorphine loads) loads were within the same order of magnitude with a significant statistical correlation with pharmaceuticals such as acetaminophen or ketoprofen. The consumption of selected drugs was back-calculated from the loads. Among illicit drugs the highest consumption was found for cannabis with a median consumption of 51mg·day-1·inhabitant-1 (inh) whereas the median consumption for cocaine (based on benzoylecgonine loads) and ecstasy was 32 and 6mg·day-1·103·inh-1 respectively. The highest consumption values of pharmaceutically active compounds (PACs) were found for acetaminophen and acetylsalicylic acid with 108.8 and 34.1mg·day-1·inh-1 respectively, in good agreement with national sales data. A statistically significant weekly pattern was found for several PACs such as metoprolol and trimethoprim, but with the opposite pattern to that of illicit drugs. The variations in daily PAC loads could provide information about the mobility of people in the catchment, especially on the basis of daily taken PACs (i.e. to treat chronicle diseases).

Conference report on the first meeting of French organic geochemists : Tuesday 30th-Friday 31st August 2012.

Organic geochemistry aims at studying the nature, structure, and chemistry of natural and anthropic organic matters in order to understand their mode of formation or their sources, the processes that allow their transformation, preservation or degradation during diagenesis, and, more generally, their dynamics in natural and human-altered systems. In the field of geosciences, this discipline constitutes a link between biosphere and geosphere. The information provided by organic geochemical studies addresses issues as diversified as the past evolution of climates, ecosystems, and biodiversity, the genesis of petroleum and coal, pollutant dynamics, the carbon cycle, the origin of life. The French community is rich of more than 50 researchers and lecturers. However, these people are disseminated in more than 30 academic and public laboratories scattered all over the territory. Up to now, no structure aims at coordinating this community, except the “Réseau Matières Organiques” (Network for Organic Matters, http://www7.inra.fr/reseau_ matieres_organiques) that organizes summer schools and thematic seminars. Beyond day-to-day collaborations, the only opportunity to gather a large part of the community is the biennial International Meeting of Organic Geochemistry, IMOG, organized by the European Association of Organic Geochemists (EAOG, www.eaog.com). In 2009, a first step into putting together colleagues who identify themselves as organic geochemists was the launching of the “FROGs” internet website (www.geochimie.fr) that offers communicating information and also acts as a platform for discussions. FROGs, in addition to being the classical nickname English people give to French ones, is the acronym for “French Researchers in Organic Geochemistry” (Fig. 1). It is also a nod to the BOGS, the British Organic Geochemical Society, that for years gather the British organic geochemists and organizes an annual meeting in one of the universities that houses an organic geochemistry team. After the last IMOG (Interlaken, September 18–23, 2011), several French organic geochemists have proposed such an event to test whether a true organic geochemical community would exist in France. This proposal having received a large consensus, it was then decided to organize the first meeting in Orléans where the Institut des Sciences de la Terre d’Orléans is for a while one the leading organic geochemistry labs in France and is still very active in the field. The objectives of this first meeting were hence rather ambitious: to identify current fields of research and the geography of organic geochemistry in France, to promote discussions, interactions, and collaborations, to define the analytical facilities available in France and to provide young researchers a first experience in oral presentations.