Loire Basin Research Articles

Human genetic structure in Northwest France provides new insights into West European historical demography

The demographical history of France remains largely understudied despite its central role toward understanding modern population structure across Western Europe. Here, by exploring publicly available Europe-wide genotype datasets together with the genomes of 3234 present-day and six newly sequenced medieval individuals from Northern France, we found extensive fine-scale population structure across Brittany and the downstream Loire basin and increased population differentiation between the northern and southern sides of the river Loire, associated with higher proportions of steppe vs. Neolithic-related ancestry. We also found increased allele sharing between individuals from Western Brittany and those associated with the Bell Beaker complex. Our results emphasise the need for investigating local populations to better understand the distribution of rare (putatively deleterious) variants across space and the importance of common genetic legacy in understanding the sharing of disease-related alleles between Brittany and people from western Britain and Ireland.

Development of a flow system for decentralized electrochemical analysis of heavy metals using screen-printed electrodes: the importance of sensor stability.

Year after year, the need for decentralized tools to tackle the monitoring of heavy metal levels in the environment gradually increases. In this context, suitable electrochemical methodologies are widely established and particularly attractive for the production of low-cost miniaturized field-deployable analytical platforms. This work focused on the development of an automatable portable system based on square-wave anodic stripping voltammetry (SWASV) for the on-line detection of heavy metals. The surface of the sensors is appropriately modified and coupled with a fluidic system equipped with an ad-hoc designed flow cell. A custom software tool was introduced to handle the remote-controlled potentiostat and automate the various steps of the procedure, including stirring operations, cleaning phases, SWASV measurements, and data collection. After studying technical and analytical challenges, the final system developed was applied to the simultaneous detection of Cd(II), Pb(II), and Cu(II) in solution, achieving sub-ppb detection limits. Additionally, the practical applicability of the method was successfully applied to river water samples collected from the Loire basin in France.

Past and future discharge and stream temperature at high spatial resolution in a large European basin (Loire basin, France)

Abstract. This paper presents retrospective simulations (1963–2019) and future projections (1976–2100) of daily time series of discharge and stream temperature for 52 278 reaches (median length of 1.3 km) over the Loire River basin (105 km2) in France, using a physical process-based thermal model coupled with a semi-distributed hydrological model. Retrospective simulations are based on the 8 km gridded Safran meteorological reanalysis over France. Twenty-first century projections are based on a subset of the 8 km gridded and bias-corrected DRIAS-2020 dataset over France. The discharge and stream temperature dataset stands out from existing ones thanks to its large scale and its high spatial resolution and the use of a physical process-based thermal model. The whole dataset is freely available and can be downloaded in NetCDF format from https://doi.org/10.57745/LBPGFS (Seyedhashemi et al., 2022a).

Regional, multi-decadal analysis on the Loire River basin reveals that stream temperature increases faster than air temperature

Abstract. Stream temperature appears to be increasing globally, but its rate remains poorly constrained due to a paucity of long-term data and difficulty in parsing effects of hydroclimate and landscape variability. Here, we address these issues using the physically based thermal model T-NET (Temperature-NETwork) coupled with the EROS semi-distributed hydrological model to reconstruct past daily stream temperature and streamflow at the scale of the entire Loire River basin in France (105 km2 with 52 278 reaches). Stream temperature increased for almost all reaches in all seasons (mean =+0.38 ∘C decade−1) over the 1963–2019 period. Increases were greatest in spring and summer, with a median increase of + 0.38 ∘C (range =+0.11 to +0.76 ∘C) and +0.44 ∘C (+0.08 to +1.02 ∘C) per decade, respectively. Rates of stream temperature increases were greater than for air temperature across seasons for the majority of reaches. Spring and summer increases were typically greatest in the southern part of the Loire basin (up to +1 ∘C decade−1) and in the largest rivers (Strahler order ≥5). Importantly, air temperature and streamflow could exert a joint influence on stream temperature trends, where the greatest stream temperature increases were accompanied by similar trends in air temperature (up to +0.71 ∘C decade−1) and the greatest decreases in streamflow (up to −16 % decade−1). Indeed, for the majority of reaches, positive stream temperature anomalies exhibited synchrony with positive anomalies in air temperature and negative anomalies in streamflow, highlighting the dual control exerted by these hydroclimatic drivers. Moreover, spring and summer stream temperature, air temperature, and streamflow time series exhibited common change points occurring in the late 1980s, suggesting a temporal coherence between changes in the hydroclimatic drivers and a rapid stream temperature response. Critically, riparian vegetation shading mitigated stream temperature increases by up to 0.16 ∘C decade−1 in smaller streams (i.e. < 30 km from the source). Our results provide strong support for basin-wide increases in stream temperature due to joint effects of rising air temperature and reduced streamflow. We suggest that some of these climate change-induced effects can be mitigated through the restoration and maintenance of riparian forests.

Pond Energy Dynamics, Evaporation Rate and Ensemble Deep Learning Evaporation Prediction: Case Study of the Thomas Pond—Brenne Natural Regional Park (France)

The energy of water masses is a first-order factor that controls the essential physicochemical dynamics of a water body. Its study allows one to understand the roots of the processes that occur at the water-mass, water-atmosphere and water-sediment interfaces. The analysis of the Thomas Pond in the Brenne region gives a valuable overview of energy stock evolution on a yearly scale. It highlights the direct impact of this evolution on thermal stratification and the potential for evaporation and exchange with the atmosphere. The study of evaporation remains challenging due to the complexity of the energy processes and factors involved. Its estimation using formulas, which are mostly empirical, is one of the most used means for studying the process. The studied pond shows a natural stratification during the summer season, however often fragile and disturbed by other climatic factors such as wind and precipitation. This disruption leads to increased exchanges between the pond and the atmosphere. The methods used to estimate pond-atmosphere exchanges, namely evaporation, vary in values ranging between 1 mm/d to > 15 mm/d. Among these methods, three stand out and seem to give reasonable values. This observation is based on the noticeable drop of the pond’s water level during the period of non-communication with the outside, which corresponds to 65 mm. The energy required for this evaporation varies between 600 W/m2 and 1500 W/m2, except for the Smith model, that slightly overestimates this parameter. The regulation of ponds’ water volumes by managers, the increased duration of bungs closure and the intermittence of precipitations in recent years exacerbate the reduction of direct inputs to ponds and the aggravates the impacts of a changing climate. Under the effect of increasing air temperatures, losses by evaporation will also increase significantly. If we generalise the results obtained to all of the Brenne Park water bodies (4500 ponds of the park), losses by evaporation will lead to a significant water deficit of the Loire basin. From this study, the use of deep learning ensemble models was found to provide better short-term predictions (RMSE between 0.003 and 0.006 for all methods), thus confirming the effectiveness of these methods for similar applications.

Biogeography of northeastern Atlantic Neogene chitons (Mollusca, Polyplacophora): New data from the Pliocene of Portugal

AbstractBased on extensive new material, 2088 valves resulting from search sampling of ~500 kg of sediment, the Pliocene chiton biodiversity of the Mondego Basin (Portugal) is reassessed. Twelve species were identified, assigned to seven genera. Eight species are new for the Pliocene of Portugal, as well as two of the genera: Hanleya, Acanthochitona. Two taxa are described as new: Ischnochiton loureiroi n. sp. and Lepidochitona rochae n. sp. Until now, the polyplacophoran European Neogene record was too poorly known to be of help in generating a clear picture of the Miocene to present-day biogeography of the group. This new wealth of data from western Iberia, in conjunction with recent data from the Loire Basin Upper Miocene assemblages (France), allows clarification the Late Miocene to Recent eastern Atlantic and Mediterranean biogeography of the Polyplacophora. The northern range of warm-water northeast Atlantic and Mediterranean Polyplacophora experienced a sharp contraction since, at least, Late Miocene to Early Pliocene times. Warm-water chiton species represented in the Upper Miocene of the Loire Basin of NE France (European-West African Province) and the Pliocene of the Mondego Basin of central-west Portugal (Pliocene French-Iberian Province) are today confined to the southern Mediterranean-Moroccan Molluscan Province.UUID: http://zoobank.org/a2a550c0-caed-449a-aa45-9492c45f882e

Lithium isotopes in the Loire River Basin (France): Hydrogeochemical characterizations at two complementary scales

We illustrate two different, but complementary, applications of lithium (Li) isotope tracers for river-basin characterization at two different scales within the Loire River basin (LRB) in France. The first example deals with the behaviour of Li and the fractionation of its isotopes during river weathering at the basin scale of the LRB (117,800 km2). The wide δ7Li range (+5.0 to +13.3‰) in Loire basin streams, spatialized between the headwaters and the lowlands, is consistent with distinct weathering conditions and the distribution of Li from bedrock in the basin between the rivers and secondary mineral phases during water/rock interaction. Additionally, suspended sediments in the LRB streams are significantly 6Li enriched (δ7Li from −8.7 to −7.6‰) compared to average river waters that range from +5.0 to +13.3‰. The second example focuses on the smaller scale Egoutier watershed (13 km2), part of the LRB, which shows that Li isotopes can be useful for distinguishing between natural input and anthropogenic pollution, like effluents from a water treatment plant connected to a hospital. Overall, we confirm that Li isotopes cannot be used as lithological tracers for river waters. However, we did find that Li isotopes can be good tracers of weathering conditions and of anthropogenic sources in an urbanized watershed.

Microscale distribution of trace elements: a methodology for accessing major bearing phases in stream sediments as applied to the Loire basin (France)

The threat of trace elements (TE) stored in sediments depends on total concentrations, their chemical form, and also on the type of TE–particle association and their resultant stability. The present study aimed at identifying the major TE-bearing phases in river sediments and quantifying their in situ concentrations once total concentrations of TE had been determined in order to understand potential TE mobility and ensuing environmental risk during early diagenesis mechanisms and the sediment cascade. Several TE-enriched layers of sediment cores were selected in a polymetallic-contaminated river basin (Loire basin, France). Selected samples were taken from up- and downstream areas far from sites of specific mining, or heavy industrial or urban activities. They thus represent non-site-dependent sediments which were not modulated or controlled by specific mineralogy or anthropogenic activities. Detailed microscale investigation techniques (SEM, EPMA, and μSXRD) were used to characterize directly the complex TE–solid phase association within river sediments. Despite Bi, Cd, and Hg representing the highest enrichment of the studied sediment layers, these elements were not detected at a microscale and only ubiquitous TE such as As, Cu, Pb, and Zn could be quantified on polished thin sections (EPMA quantification limit = 1000 mg kg−1, n = 111). Three mineralogical groups were evidenced by PCA, EPMA, and μSXRD data. (i) Fine-grained aggregates of aluminosilicates were frequently detected, appearing multiphased in organic matrices. They were mostly enriched with Zn and Pb without any As or Cu. (ii) (Mn, Ti)-rich Fe oxyhydroxides were predominantly SEM observed, either as isolated grains, silicate coatings, or included in aggregates. They represented the highest detected in situ concentrations for all the studied TE. And finally, (iii) Mn-rich particles were not frequently observed with SEM but when present were characterized by the highest TE concentrations. Phosphates, carbonates, and S-rich particles (sulfides and/or sulfates) were also determined by PCA as a potential mineralogical group. However, due to their very low TE concentrations and frequency, they could not be considered representative of a TE-bearing mineralogical group. This fine sorting classification, combining different techniques at the particle scale, was used to visualize and quantify complex mineralogy and particle associations of TE-bearing phases in river bed sediments under no specific mineralogical control. It represents an interesting approach to understand TE mobility during sediment cascade and post-depositional processes in sediments.

Anisodon (Perissodactyla, Chalicotheriinae) from the middle Miocene locality Gračanica (Bugojno Basin, Gornji Vakuf, Bosnia and Herzegovina)

The fossil mammal fauna of the Gracanica coal mine in central Bosnia and Herzegovina includes dental remains of Anisodon (Perissodactyla, Chalicotheriidae, Chalicotheriinae). These teeth most closely resemble those of Anisodon grande from Sansan (France, MN6) and Neudorf an der March (Slovakia, MN6), and are tentatively referred to that species. Anisodon is first known in Europe from the Loire Basin (France), which has been dated as MN5. Given that the Gracanica fauna is considered to be MN5 or earliest MN6 (Langhian), the Gracanica chalicothere represents one of the earlier known finds of both the Chalicotheriinae and Anisodon in Europe. The first known members of the Chalicotheriinae are from the earliest Miocene of Asia. By the middle Miocene, Anisodon had appeared and is known from Asia and Europe, to which it had recently immigrated.

Does Loire grayling represent a distinct species ?

Does Loire grayling represent a distinct species ?

1500 ans d’histoire fluviale dans la vallée du Gage (bassin supérieur de la Loire, sud-est du Massif central, France) : approche pluridisciplinaire

L’etude multi-proxies (releves litho-stratigraphiques, susceptibilite magnetique, estimation de la matiere organique, paleoecologie) des depots organo-detritiques de la vallee du Gage permet de preciser l’evolution de cette petite plaine alluviale de moyenne montagne au cours des 1 500 dernieres annees (bassin de la Loire superieure, Ardeche, France). Des VIe-VIIe siecles au XIIIe siecle apres J.‑C., les depots organiques inferieurs montrent une periode de stabilite des flux hydro-sedimentaires. Les macro-restes illustrent une plaine d’inondation marecageuse bordee d’une ripisylve. Les indices paleoecologiques et archeologiques soulignent aussi une anthropisation notable des cette periode (sites d’habitat et paysage agro-pastoral). Une phase d’aggradation associee a des ecoulements de plus en plus energiques survient durant la premiere moitie du XVe siecle avec l’entree dans le Petit Âge Glaciaire (PAG 1). Elle conduit a un exhaussement rapide de la plaine alluviale par des depots grossiers. Ces derniers sont re-incises par un chenal emboite au cours du XVIe siecle. Les XVIIe et XVIIIe siecles (PAG 2) correspondent a la phase de comblement de ce chenal par un materiel sablo-silteux a passees graveleuses. L’absence d’aggradation grossiere au cours du XIXe siecle (second paroxysme du PAG 2) suggere une forte connectivite amont-aval precedant ou accompagnant l’incision du chenal actuel du Gage (fin XIXe - debut XXe siecle). Ce sequencage de l’evolution recente de la plaine alluviale du Gage enrichit le corpus des observations qui temoignent des fluctuations climatiques, morpho-dynamiques et paysageres caracterisant le PAG dans le sud-est du Massif central et permet de proposer des paralleles avec la vallee du Rhone notamment.

Validation of a Rapid Attribution of the May/June 2016 Flood-Inducing Precipitation in France to Climate Change

AbstractThe extreme precipitation that resulted in historic flooding in central-northern France began 26 May 2016 and was linked to a large cutoff low. The floods caused some casualties and over a billion euros in damage. To objectively answer the question of whether anthropogenic climate change played a role, a near-real-time “rapid” attribution analysis was performed, using well-established event attribution methods, best available observational data, and as many climate simulations as possible within that time frame. This study confirms the results of the rapid attribution study. We estimate how anthropogenic climate change has affected the likelihood of exceedance of the observed amount of 3-day precipitation in April–June for the Seine and Loire basins. We find that the observed precipitation in the Seine basin was very rare, with a return period of hundreds of years. It was less rare on the Loire—roughly 1 in 20 years. We evaluated five climate model ensembles for 3-day basin-averaged precipitation extremes in April–June. The four ensembles that simulated the statistics agree well. Combining the results reduces the uncertainty and indicates that the probability of such rainfall has increased over the last century by about a factor of 2.2 (>1.4) on the Seine and 1.9 (>1.5) on the Loire due to anthropogenic emissions. These numbers are virtually the same as those in the near-real-time attribution study by van Oldenborgh et al. Together with the evaluation of the attribution of Storm Desmond by Otto et al., this shows that, for these types of events, near-real-time attribution studies are now possible.

Middle Pleistocene hominin behavior at the 700ka Acheulean site of la Noira (France)

Middle Pleistocene hominins occupied Europe as early as 700 ka. Data on subsistence and adaptation to environment remain limited due to the small number of sites, especially from 700 to 500 ka. Current consensus suggests that Middle Pleistocene populations periodically peopled and depopulated areas of Europe in response to climatic fluctuations. Most occupations are located in the South, while the North-West was only occupied during favorable climatic periods. During this time, significant behavioral changes occur, such as bifacial technology and more complex modes of flaking. Further north in France, in the Loire basin, the site of la Noira has well-developed bifacial tools at around 700 ka, The site is located along a river with abundant millstone slabs which were flaked on the site suggesting it may have served partially as a lithic workshop. We employ use-wear and residue analysis (optical light and scanning electron microscopy) of stone tools to reconstruct early Acheulean hominin behavior. While the lithics are composed largely of retouched and unretouched debitage, large cutting tools (bifaces and cleavers) are also present. We demonstrate that la Noira was not only a lithic workshop, but that a broad range of resources were being used by the hominins at the site, including wood, plants, mammals, and possibly birds and fish. Finally, we compare our results with contemporary sites and suggest that, in the early European Acheulean, Middle Pleistocene hominins had detailed local environmental knowledge, and were able to adapt to a wide range of environments, including cool, temperate, and Mediterranean.

Tracing surface water mixing and groundwater inputs using chemical and isotope fingerprints (δ18O-δ2H, 87Sr/86Sr) at basin scale: The Loire River (France)

The spatial and temporal distributions of major elements, stable isotopes of water molecule and strontium isotope ratios were investigated in the surface waters of the Loire River basin. The present study, using a coupled hydrological and geochemical approach, focuses on surface water mixing and the interactions between ground- and surface water. Stable isotopes (δ18O, δ2H) provide good evidence for the complex hydrological behavior of the Loire River system at the basin scale, and if binary mixing of surface water masses explain the longitudinal evolution of the Loire signature in the upstream part of the basin, groundwater contributions are required to explain locally the Loire signature. The water chemistry in the different zones of the basin shows large variations in major-element contents. The NO3 content in the Loire River roughly increases from up-to downstream and is mainly controlled by the input from tributaries. The highest concentrations are observed in the middle part of the Loire basin, in close relation with the diffuse agricultural sources. In terms of water-rock interaction, using Na as the reference element, the Loire Basin data are scattered between the three main end-members representing the major lithologies i.e. basalts, granite/gneiss and carbonate. Strontium-isotope ratios measured in water range from 0.70691 to 0.71395 and plotted vs. the Ca/Na ratios, the 87Sr/86Sr ratios clearly discriminate the three main lithological endmembers. In the Middle Loire section, the Loire flow rate increases without significant inputs of surface water, previous studies attributed this increase to groundwater inputs. The relationship between 87Sr/86Sr and the Cl/Sr ratios clearly shows the groundwater inputs from the Beauce carbonate aquifer along a 90 km river profile, between Orléans and Amboise. These conservative tracers can be used to calculate up to 20% groundwater mixing during low flow period.

Interspecific competition between restocked 0+ salmon parr (Salmo salar) and native fish species in a large European river

AbstractAtlantic salmon populations have experienced strong declines in most large European rivers. In the Loire Basin, France, a major restocking effort has been carried out on the Allier River to reduce the wild population decline. This study aimed at investigating the trophic insertion of hatchery‐reared salmon parr and whether they compete for resources with native fish species. For this purpose, two riffles located in the upstream and downstream parts of the restocked area have been surveyed monthly following the initial 0+ salmon fry release. 0+ parr densities remained high upstream, with autumnal values greater than those recommended to maximise smolt production. In contrast, downstream densities declined to weak values despite a faster increase in size, probably mainly due to summer temperatures rising above the discomfort threshold. By analysing the vulnerability to predation of ingested invertebrate prey, we highlighted the role of habitat constraints in driving most of the different fish species to a likely opportunistic utilisation of available food resources. As a result, species such as stone loaches and barbel juveniles exhibited narrow trophic niches and high overlaps with 0+ parr. Nonetheless, both abundant prey resources and spatial or temporal habitat segregation have limited interspecific competition, enabling competitive coexistence of sympatric species, except for barbel juveniles in certain circumstances. Therefore, our findings suggest that future restocking programmes should carefully consider the thermal and hydraulic conditions regarding further smolt production as well as their general trophic context, according to the potential inconvenience of restocked salmon fry arrival relative to native species.

New varanid remains from the Miocene (MN4–MN5) of France: inferring fossil lizard phylogeny from subsets of large morphological data sets

ABSTRACTFossil vertebrae from the early Miocene of France (Loire Basin) are described. They show several characters generally regarded as varanid synapomorphies. A phylogenetic analysis of these vertebrae is performed with a subset of morphological data taken from several large morphological data sets (vertebral characters) and it confirms an attribution to varanid lizards. Moreover, referral of isolated vertebrae from the Eocene–Oligocene of Egypt to varanids is confirmed. The use of subsets of large morphological data sets in phylogenetic analysis of fossils (especially incomplete remains) is discussed and advocated for, and we argue that convergence between tree topologies obtained from different kinds of data sets is a key issue in inferring the phylogenetic position of fossil taxa.Citation for this article: Augé, M. L., and B. Guével. 2018. New varanid remains from the Miocene (MN4–MN5) of France: inferring fossil lizard phylogeny from subsets of large morphological data sets. Journal of Vertebrate Paleontology. DOI:10.1080/02724634.2017.1410483.

T‐NET, a dynamic model for simulating daily stream temperature at the regional scale based on a network topology

AbstractCurrently, the distribution areas of aquatic species are studied by using air temperature as a proxy of water temperature, which is not available at a regional scale. To simulate water temperature at a regional scale, a physically based model using the equilibrium temperature concept and including upstream‐downstream propagation of the thermal signal is proposed. This model, called Temperature‐NETwork (T‐NET), is based on a hydrographical network topology and was tested at the Loire basin scale (105 km2). The T‐NET model obtained a mean root mean square error of 1.6 °C at a daily time step on the basis of 128 water temperature stations (2008–2012). The model obtained excellent performance at stations located on small and medium rivers (distance from headwater <100 km) that are strongly influenced by headwater conditions (median root mean square error of 1.8 °C). The shading factor and the headwater temperature were the most important variables on the mean simulated temperature, while the river discharge influenced the daily temperature variation and diurnal amplitude. The T‐NET model simulates specific events, such as temperature of the Loire during the floods of June 1992 and the thermal regime response of streams during the heatwave of August 2003, much more efficiently than a simple point‐scale heat balance model. The T‐NET model is very consistent at a regional scale and could easily be transposed to changing forcing conditions and to other catchments. Copyright © 2016 John Wiley & Sons, Ltd.

Dynamics of metallic contaminants at a basin scale — Spatial and temporal reconstruction from four sediment cores (Loire fluvial system, France)

From the 19th century, the Loire basin (France) presents potentially pollutant activities such as mining and heavy industries. This paper shows spatio-temporal distribution of trace elements in sediments at a basin-scale, based on a comparison of archived temporal signals recorded in four sedimentary cores. Anthropogenic sources contributing to sediment contamination are also characterized, using geochemical signatures recorded in river bank sediments of the most industrialized tributaries. This study highlights upstream-downstream differences concerning recorded contamination phases in terms of spatial influence and temporality of archiving processes. Such differences were related to (i) various spatial influences of contamination sources and (ii) polluted sediments dispersion controlled by transport capacity of metal-carrier phases and hydrosedimentary dynamics.

Storage and source of polycyclic aromatic hydrocarbons in sediments downstream of a major coal district in France

During the 20th century, the local economy of the Upper Loire Basin (ULB) was essentially based on industrial coal mining extraction. One of the major French coal districts with associated urban/industrial activities and numerous coking/gas plants were developed in the Ondaine-Furan subbasins, two tributaries of the upper Loire main stream. To determine the compositional assemblage, the level and the potential sources of contamination, the historical sedimentary chronicle of the 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) has been investigated. PAH concentrations were determined using gas chromatography/mass spectrometry (GC/MS) in a dated core, sampled in the Villerest flood-control reservoir located downstream of the Ondaine-Furan corridor (OFC). The most contaminated sediments were deposited prior to 1983 (Σ16PAHs ca. 4429–13,348 ng/g) and during flood events (Σ16PAHs ca. 6380 ng/g – 1996 flood; 5360 ng/g – 2003 flood; 6075 ng/g – 2008 flood), especially in medium and high molecular weight PAHs. Among them, typical pyrogenic PAHs such as FLT, PYR, BbF and BaP were prevalent in most of the core samples. In addition, some PAHs last decade data is available from the Loire Bretagne Water Agency and were analyzed using high-performance liquid chromatography with postcolumn fluorescence derivatization (HPLC/FLD). These results confirm that the most highly contaminated sediments were found downstream of OFC (Σ16PAHs ca. 2264–7460 ng/g). According to the observed molecular distribution, PAHs are originated largely from high-temperature pyrolytic processes. Major sources of pyrogenic PAHs have been emphasized by calculation of specific ratios and by comparison to reported data. Atmospheric deposition of urban and industrial areas, wood combustion and degraded coal tar derived from former factories of coking/gas plants seem to be the major pyrogenic sources. Specifically, particular solid transport conditions that can occur during major flood events lead us to emphasize weathering of former contamination sources, such as more preserved coal tar.

ESR as a method for the characterization of alluvial sediments

The possibility of using the parameters involved in the ESR dating of optically bleached quartz grains in a purpose of source determination was checked. In that aim, samples previously taken in different sedimentary formations of the Middle Loire Basin (Central France) and dated by ESR have been observed. First discrimination was made using the thorium and potassium content in the sediments obtained by gamma spectrometry. The plot of these 119 data on the Th/K Schlumberger diagram clearly demonstrated that it was possible to discriminate the clays associations included in the sediment from which the dated quartz are extracted. Clay's nature could then be indicative of the geological nature of the substratum of rivers from their sources. Second discrimination was made using the ESR intensities calculated from Al, Ti–H and Ti–Li paramagnetic centres on 18 samples. It appears that the combination of the non-bleachable aluminum trap (DAT) saturation intensity and the Ti–H/Ti–Li ratio intensities make possible the discrimination of the two main sources of the sediment: Massif Central and Paris Basin. More deeply, The Ti/OBAT (Optically bleachable aluminum traps) intensities made possible the discrimination of quartz grains of different geological sources or with different geothermal history within the Massif Central group.