Loire Research Articles

Nutrient inputs and hydrology together determine biogeochemical status of the Loire River (France): Current situation and possible future scenarios

The Grafs-Seneque/Riverstrahler model was implemented for the first time on the Loire River for the 2002–2014 period, to explore eutrophication after improvement of wastewater treatments. The model reproduced the interannual levels and seasonal trends of the major water quality variables. Although eutrophication has been impressively reduced in the drainage network, a eutrophication risk still exists at the coast, as shown by the N-ICEP indicator, pointing out an excess of nitrogen over silica and phosphorus. From maximum biomass exceeding 120 μgChla l−1 in the 1980's, we observed decreasing maximum values from 80 to 30 μgChla l−1 during the period studied.Several scenarios were explored. Regarding nutrient point sources, a low wastewater treatment scenario, similar to the situation in the 1980's, was elaborated, representing much greater pollution than the reference period (2002–2014). For diffuse sources, two agricultural scenarios were elaborated for reducing nitrogen, one with a strict application of the agricultural directives and another investigating the impact of radical structural changes in agriculture and the population's diet. Although reduced, a risk of eutrophication would remain, even with the most drastic scenario. In addition, a pristine scenario, with no human activity within the basin, was devised to assess water quality in a natural state. The impact of a change in hydrology on the Loire biogeochemical functioning was also explored according to the effect of climate change by the end of the 21st century. The EROS hydrological model was used to force Riverstrahler, considering the most pessimistic SRES A2 scenario run with the ARPEGE model. Nutrient fluxes all decreased due to a >50% reduction in the average annual discharge, overall reducing the risk of coastal eutrophication, but worsening the water quality status of the river network.The Riverstrahler model could be useful to help water managers contend with future threats in the Loire River, at the scale of its basin and at smaller nested scales.

QUAL-NET, a high temporal-resolution eutrophication model for large hydrographic networks

Abstract. To allow climate change impact assessment of water quality in river systems, the scientific community lacks efficient deterministic models able to simulate hydrological and biogeochemical processes in drainage networks at the regional scale, with high temporal resolution and water temperature explicitly determined. The model QUALity-NETwork (QUAL-NET) was developed and tested on the Middle Loire River Corridor, a sub-catchment of the Loire River in France, prone to eutrophication. Hourly variations computed efficiently by the model helped disentangle the complex interactions existing between hydrological and biological processes across different timescales. Phosphorus (P) availability was the most constraining factor for phytoplankton development in the Loire River, but simulating bacterial dynamics in QUAL-NET surprisingly evidenced large amounts of organic matter recycled within the water column through the microbial loop, which delivered significant fluxes of available P and enhanced phytoplankton growth. This explained why severe blooms still occur in the Loire River despite large P input reductions since 1990. QUAL-NET could be used to study past evolutions or predict future trajectories under climate change and land use scenarios.

Investigation of hydraulic regime at middle part of the Loire River in context of floods and low flow events

Significant variability characterizes natural streams in space and time that describe hydraulic regime of the entire stream. In this paper, the importance of investigation and assessment of hydraulic system in the context of management of surface water resources is discussed. The objective of this study is to investigate hydraulic regime in the middle part of Loire River located in France. Loire River basin is the largest river basin in France and origin of many potential flood events. Investigation of a hydraulic regime of the Loire River is conducted using traditional hydraulic simulation model HEC-RAS. Hydraulic modeling of the river is carried out by considering two different datasets (i.e. flood and low flow events). A certain number of hydraulic structures, which have the significant effect on the hydraulic regime of the river, is considered as well. Through Froude number computation, it is noticed that middle part of the Loire River demonstrates subcritical regime. Accurate calibration and validation of the model are performed by changing Manning coefficient along the riverbed. Computation carried out for both data sets; show that there are no big differences between observed and simulated water levels, results obtained are satisfactory. Therefore, to get more accurate information about the hydraulic regime at the middle part at of Loire River, the further simulation needs to be done by considering an additional dataset of floods and low flow events.

Topos et mémoires des deux rives de La Loire amont (XVIIIe–XXe siècles)

Dans le bassin amont de la Loire, la plaine alluviale situee entre Chassenard (Auvergne-Rhone-Alpes, Allier) et Digoin (Bourgogne-Franche-Comte, Saone-et-Loire) offre un cadre privilegie pour discuter des divagations recentes du fleuve et de leur prise en compte memorielle par les communautes riveraines. Nous proposons une approche croisee de geographie physique et sociale, pour mettre en relief les procedes – volontaires ou inconscients – utilises par ces populations pour conserver en memoire les fluctuations spatiales du cours d’eau. Notre etude s’appuie sur une analyse geohistorique des toponymes, qui souligne l’origine moderne, voire contemporaine (XVIIIe-XXe siecles) d’une majorite de noms de lieux dans cette section de la Loire Amont. Ils rappellent la presence de meandres abandonnes, de terres fertiles, de zones de franchissement du fleuve ou de protection face aux crues passees comme actuelles. Cette analyse est etayee par d’autres temoignages oraux et ecrits, dont de nombreuses marques de crues datees du XIXe siecle, qui montrent que les crues exceptionnelles et historiques constituent l’un des points marquants de la memoire collective, mais selective des communautes ligeriennes. Connectes par cette discussion transversale, ces diffe­rents exemples mettent en evidence que la mobilite du trace du fleuve, au-dela du risque qu’il represente, constitue aussi un lien symbiotique et un heritage spatio-memoriel tres fort.

Mathematical modeling of oval arches. A study of the George V and Neuilly Bridges

Abstract In this work we approach the mathematical modeling of oval arches of n centers and we present an analytical study of their geometry given the expressions of the elements that define them and the tangency points as a function of span, sagita and the radius of the circumferences of which they are formed, using Mathematica software to perform interactive graphs and calculations. This allows to mathematically model an existing arch or to design the construction of a new one. We apply the results obtained in the modeling of the Orleans Bridge over the River Loire (1751–1760) whose construction — initiated by Hupeau and completed by Perronet — made of three-centered oval arches and in the Neuilly Bridge over the River Seine, close to Paris, which is formed of eleven-centered oval arches.

Suspended particulate matter determines physical speciation of Fe, Mn, and trace metals in surface waters of Loire watershed

This study investigates the spatiotemporal variability of major and trace elements, dissolved organic carbon (DOC), total dissolved solids (TDS), and suspended particulate matter (SPM) in surface waters of several hydrosystems of the Loire River watershed in France. In particular, this study aims to delineate the impact of the abovementioned water physicochemical parameters on natural iron and manganese physical speciation (homoaggregation/heteroaggregation) among fine colloidal and dissolved (< 10nm), colloidal (10-450nm) and particulate (> 450nm) phases in Loire River watershed. Results show that the chemistry of the Loire River watershed is controlled by two end members: magmatic and metamorphic petrographic context on the upper part of the watershed; and sedimentary rocks for the middle and low part of the Loire. The percentage of particulate Fe and Mn increased downstream concurrent with the increase in SPM and major cations concentration, whereas the percentage of colloidal Fe and Mn decreased downstream. Transmission electron microscopy analyses of the colloidal and particulate fractions (from the non-filtered water sample) revealed that heteroaggregation of Fe and Mn rich natural nanoparticles and natural organic matter to the particulate phase is the dominant mechanism. The heteroaggregation controls the partitioning of Fe and Mn in the different fractions, potentially due to the increase in the ionic strength, and divalent cations concentration downstream, and SPM concentration. These findings imply that SPM concentration plays an important role in controlling the fate and behavior of Fe and Mn in various sized fractions. Graphical abstract Physical speciation by heteroaggregation of (Fe-Mn) compounds: high [SPM] → [Fe-Mn] particulate faction; low {SPM] → [Fe-Mn] colloid-dissolved fraction.

Influence of hydrology, sediment supply and sediment gradation on river bar morphodynamics: application to the Loire River at Bréhémont (France)

Rivers inherently show heterogeneous sediment sizes and can also show a strong sediment supply variability in time because of natural episodic events or as a consequence of human activities, which alter the characteristics and dynamics of alluvial bars at the macro-scale. The impact of the combination between sediment size heterogeneity and sediment supply variation, or even with other forcings (i.e. hydrology, channel geometry) remains poorly documented. In this work, a physics-based numerical model is applied on a trained reach of a sandy-gravel bed river to investigate the combination of these parameters on bar morphodynamics. The morphodynamic computations are performed with a two-dimensional depth-averaged hydrodynamic solver, internally coupled to a sediment transport and bed evolution module, which estimate the transport of graded sediment and model bed stratigraphy, respectively. A 1 km long reach of the Loire River at Bréhémont (France) is selected to conduct the numerical investigations. The interaction between several forcing mechanisms induces highly complex bar morphodynamic processes in this area.A comprehensive set of high-definition data is available, which allows to study the river morphodynamics for a succession of three flooding events and a period of low flows. Based on this model, a variety of scenarios is presented with the aim of exploring the implications of sediment gradation, geometrical and boundary forcing effects on in situ bars morphodynamics.

Héritages et influences contemporaines des anciens ouvrages de navigation de la Loire moyenne (France)

Levées, duits et chevrettes imprègnent fortement les paysages fluviaux de la vallée de la Loire, par leur omniprésence et leur intégration aux structures des villes ligériennes, anciennes cités portuaires. Ces ouvrages opérationnels au temps de la navigation ligérienne et aujourd’hui révolus perturbent toujours la dynamique fluviale : influence des conditions d’écoulements, impacts sur la dynamique sédimentaire, végétalisation du lit entre levées. Ces objets fluviaux ont contribué au réajustement fluvial toujours en cours. L'approche géohistorique du XIXe au XXIe siècle montre que le paysage fluvial du lit entre levées s’est profondément modifié en réponse à l’arrêt brutal de la navigation et des modes d’entretien des chenaux à la fin du XIXe siècle. Pour illustrer l’impact de ces friches hydrauliques sur le paysage fluvial, nous nous intéressons aux digues submersibles de deux sites de la Loire moyenne : La Charité-sur-Loire et sa chevrette, Orléans et ses duits. Des conflits naissent et des enjeux apparaissent à l’issue de cette trajectoire paysagère : entretenir et restaurer le lit fluvial, maintenir ou supprimer des aménagements fluviaux, valoriser le patrimoine de navigation.

Improving representation of riparian vegetation shading in a regional stream temperature model using LiDAR data

Modelling river temperature at the catchment scale is needed to understand how aquatic communities may adapt to current and projected climate change. In small and medium rivers, riparian vegetation can greatly reduce maximum water temperature by providing shade. It is thus important that river temperature models are able to correctly characterise the impact of this riparian shading. In this study, we describe the use of a spatially-explicit method using LiDAR-derived data for computing the riparian shading on direct and diffuse solar radiation. The resulting data are used in the T-NET one-dimensional stream temperature model to simulate water temperature from August 2007 to July 2014 for 270km of the Loir River, an indirect tributary of the Loire River (France). Validation is achieved with 4 temperature monitoring stations spread along the Loir River. The vegetation characterised with the LiDAR approach provides a cooling effect on maximum daily temperature (Tmax) ranging from 3.0°C (upstream) to 1.3°C (downstream) in late August 2009. Compared to two other riparian shading routines that are less computationally-intensive, the use of our LiDAR-based methodology improves the bias of Tmax simulated by the T-NET model by 0.62°C on average between April and September. However, difference between the shading routines reaches up to 2°C (monthly average) at the upstream-most station. Standard deviation of errors on Tmax is not improved. Computing the impact of riparian vegetation at the hourly timescale using reach-averaged parameters provides results close to the LiDAR-based approach, as long as it is supplied with accurate vegetation cover data. Improving the quality of riparian vegetation data should therefore be a priority to increase the accuracy of stream temperature modelling at the regional scale.

Diagnosis of the Tropical Moisture Exports to the Mid-Latitudes and the Role of Atmospheric Steering in the Extreme Precipitation

Three river basins, i.e., the Yangtze river, the Mississippi river and the Loire river, were presented as case studies to explore the association among atmospheric circulations, moisture exports and extreme precipitations in the mid-latitudes. The major moisture source regions in the tropics for the three river basins are first identified using the Tropical Moisture Exports (TMEs) dataset. The space-time characteristics of their respective moisture sources are presented. Then, the trajectory curve clustering analysis is applied to the TMEs tracks originating from the identified source regions during each basin’s peak TMEs activity and flood seasons. Our results show that the moisture tracks for each basin can be categorized into 3 or 4 clusters with distinct spatial trajectory features. Our further analysis on these clustered trajectories reveals that the contributions of moisture release from different clusters are associated with their trajectory features and travel speeds. In order to understand the role of associated atmospheric steering, daily composites of the geopotential heights anomalies and the vertical integral of moisture flux anomalies from 7 days ahead to the extreme precipitation days (top 5%) are examined. The evolutions of the atmospheric circulation patterns and the moisture fluxes are both consistent with the TMEs tracks that contribute more moisture releases to the study regions. The findings imply that atmospheric steering plays an important role in the moisture transport and release, especially for the extreme precipitations. We also find that the association between TMEs moisture release and precipitation is nonlinear. The extreme precipitation is associated with high TMEs moisture release for all of the three study regions.

A Châtelperronian Open-air Site in the Paris Basin: les Bossats at Ormesson (Seine-et-Marne)

Les Bossats site at Ormesson, in addition to its Badegoulian, Solutrean, Gravettian and Mousterian levels, has also delivered a Châtelperronian occupation over a large area, in the form of a thin layer and whose integrity has not suffered from mixtures, or to a very limited extent, with older or newer layers. This occupation has been excavated in two test-pits, test-pits 3 and 50 of respectively 16 and 2 square meters, but with an estimated surface area of 150 square meters. This level already delivers a certain amount of information concerning the lithic industry but also the colouring materials, already present at Ormesson in the Mousterian level, as well as on animal and vegetable resources. If in the years to come efforts are directed towards the exploitation of the younger levels, we plan an extensive excavation of the Châtelperronian in 4 to 5 years. In the meantime, this article is intended as a first presentation of this new Châtelperronian occupation, the northernmost one known at the present time. But it also lays down a certain number of milestones concerning the characteristics of the lithic industry, especially the blade production, through the realization of numerous explicit refits and also the presence and role of bladelet production. In this sense, the Ormesson site is an obvious part of the debate concerning the microlithic productions of the Châtelperronian and the relations which this so-called transitional industry was able to maintain with the Mousterian, as well as with the Proto-Aurignacian.Like their Mousterian predecessors, but also like the groups that occupied the site after them, the Châtelperronians from Ormesson undoubtedly benefited from a particular topography of the valley at this point, favourable to the driving of game. Like them, they were also able to find water, vegetal resources and flint nearby. Like them, their occupation was rapidly covered by sediments, sandy in this case, which allows a relatively new palethnographic analysis for this period. The small size of the surface presently excavated is certainly a limitation to the overall economic and functional interpretation of this level, but it does not prevent a fairly detailed questioning of the various categories of tools represented (knives, burins) or absent (end-scrapers) in the current state of the excavation. The first results of the faunal and charcoal analysis are presented, enriching this documentation, on the technical side, with more contextual data.In spite of a certain geographical isolation, les Bossats are nonetheless part of a “northern” Châtelperronian territory which includes the famous Renne at Arcy-sur-Cure or Roche-au-Loup at Merry-sur-Yonne (Yonne) caves. Some initial comparisons are outlined with these two sites. A discussion is also initiated about this apparent scarcity in Châtelperronian sites north of the Loire River, which is perhaps more related to the actual state of research rather than to a real lack of occupations.

Hydro‐sedimentary Dynamics of a Drained Agricultural Headwater Catchment: A Nested Monitoring Approach

Core Ideas Discharge and sediment concentrations were measured in a drained catchment. The impact of tile drainage at the catchment scale was analyzed with a nested approach. The major part of sediment fluxes occurred during winter floods. Sediment transfer in the tile drain was episodic although significant. Soil erosion and sediment transfer are extensive in lowland agricultural catchments. In these environments, high‐frequency datasets of both water discharge and suspended sediment concentrations are often lacking. In particular, the impact of tile drainage networks on sediment fluxes in these catchments is poorly understood. Our research quantified sediment fluxes between 2013 and 2016 at five nested stations including a tile drain outlet across a small (25‐km2) agricultural catchment (located in the Loire River basin, France) representative of lowland cultivated environments of the middle part of this basin. Sediment fluxes varied from 1 to 38 t km−2 yr−1 across the monitored subcatchments. Most of sediment fluxes (79 ± 9%) were measured during flood events (n = 44), mostly occurring in winter (75%) and spring (20%). Seasonality controlled most of the variations of sediment fluxes. Sediment transfers in tile drains occurred episodically. Flows were measured during 11.4% of the monitoring time. A mean time lag of 80 min was recorded between the peak discharge at the drain outlet and the downstream river station. At the event scale, sediment fluxes exported from the tile drain varied between 1.1 × 10−4 and 2.5 t km−2 and remained of the same order of magnitude as those measured at the downstream river station, although the latter were on average 53% lower. Results suggest significant storage of sediment material in the river channel and its export during the most intense flood events. Our research emphasizes the need for continuous monitoring of water and sediment transfers in agricultural catchments equipped with tile drains.

Prospections systématiques d’une vallée entre Rhône et Loire (France). Une cartographie de l’occupation à la fin de l’Acheuléen ?

Systematic surveys on the Rhins Valley, a little tributary of the Loire River (South East France), have yielded lithic assemblages for more than 20 years. The number of open-air localities totals at that moment 28. The assemblages are composed for the most of bifaces, cores, including many Levallois cores, and flakes. Although the number of pieces varies in localities, data recorded for more than 20 years are enough to map a small size territory and compare assemblages attributed to the end of the “Acheulean”. Comparison of strategies, debitage and façonnage, provides hypotheses on the type of occupation of the valley, with living spots located on the flint outcrops and asking both a heavy-duty component and flaking products. Some main categories of bifacial tools are present, mainly on flint. The ratio of bifaces and intensity of shaping seems to distinguish the series. The Levallois core technology is used in large quantity associated to diverse other core technologies. These sites located on the plateaus bordering the valley offer the opportunity to describe human occupations on a micro-regional scale, occupations sharing technological common features. These occupations are located between the Saône-Rhône corridor and the isolated basins of the Massif Central. The rhodanian corridor has yielded at that moment few evidence of Acheulean open-air human occupations. These sites attest that systematic surveys have to continue on these areas to complete the knowledge on the occupations.

The diked-up middle Loire river bed: from a wild river image to the recognition of its anthropogenic character

Les espaces fluviaux font l’objet d’usages diversifies et en evolution ; cette diversite d’usages, sur des espaces relativement reduits, ne va pas sans conflits et sans poser des problemes de gouvernance. La Loire a ete investie, depuis une trentaine d’annees, d’une valeur ecologique et patrimoniale qui l’a identifiee comme un fleuve « sauvage », representation liee a l’absence de grands ouvrages et au declin des activites traditionnellement fluviales. Ce caractere « sauvage » de la Loire est plus particulierement attache a son lit endigue. Reconnaitre la diversite des usages et des fonctions d’un espace est un prealable pour l’envisager comme un socio-ecosysteme. L’objectif du travail presente ici est de proposer une demarche pour caracteriser la diversite du lit endigue de la Loire moyenne, a partir de la base de donnees du SIEL (Systeme d’Information sur l’Evolution du Lit de la Loire), seule base de donnees incluant les communautes herbacees. La diversite de l’espace inondable a ete mise en relation avec ses dimensions longitudinale et transversale, en testant le lien entre l’occupation du sol, issue de descripteurs des communautes vegetales, et des indicateurs de la distance amont/aval et de la largeur de l’espace fluvial. Nos resultats montrent que le gradient amont/aval est preponderant, le lit endigue presentant plus de forets, de prairies et de sables a l’aval et plus de surfaces artificialisees a l’amont. La largeur du lit endigue est correlee avec la part de cultures, presentes en proportion non negligeable dans le lit endigue, et localisees de preference la ou le lit est le plus large. A travers l’exploration spatiale de la diversite du lit endigue de la Loire moyenne, nous avons mis en evidence les usages que traduisent certains habitats de cet espace fluvial, qui ne se presente donc pas comme l’espace « sauvage » de representations sociales.

Aspects méthodologiques de l’approche intégrée des comblements postglaciaires : apports pour la reconstitution de la dynamique fluviale de la Loire au cours de l’Holocène

Cet article methodologique propose d’illustrer l’interet du couplage des analyses morphologiques planaires, de l’etude d’anomalies topographiques et des donnees sedimentologiques pour documenter l’evolution spatio-temporelle d’un troncon pluri-kilometrique de la plaine alluviale ligerienne au cours des derniers millenaires. Ce travail de reconstitution debute par l’etude des transformations les plus recentes grâce a un corpus de plans anciens, georeferences puis digitalises, qui permet de quantifier l’evolution de la forme en plan du fleuve a l’echelle centennale a l’aide de parametres morphometriques. On etablit ensuite la chronologie relative des grandes etapes du comblement postglaciaire par l'analyse geomorphologique de la surface du lit majeur. Afin de s’affranchir de l’effet de la pente du fleuve, le plan de declivite de la ligne d’eau actuelle a ete soustrait au releve LiDAR (Light Detection And Ranging). On obtient ainsi une representation des altitudes relatives du lit majeur, qui aide a definir des familles de paleochenaux et par consequent des sequences de depot telles que definies par la stratigraphie sequentielle. Ces corps sedimentaires refletant une partie de l’histoire du remplissage sont ensuite decrits en des points juges pertinents (carottages, coupes) et leur geometrie affinee par des profils de tomographie electrique. La systematisation des datations radiocarbone donne des âges absolus aux grandes phases mises en evidence. La synthese des resultats revele les principales transformations du cours d’eau et de sa plaine alluviale sur les derniers millenaires. Elles sont principalement controlees par les variations climatiques de l’Holocene, notamment le PAG (Petit Âge Glaciaire), dernier evenement climatique majeur dans la genese des paysages alluviaux europeens. En definitive, l’approche integree permet de decrire le rythme, l’intensite et le temps de reaction de la dynamique alluviale a l’echelle de la vallee holocene, et ce quel que soit le cours d’eau etudie.

Network analysis for species management in rivers networks: Application to the Loire River

Forecasting the colonization process is important for wildlife managers who supervise the reintroduction of endangered species or control the spread of invasive species. Patch connectivity is thus critical to predicting the fates of expanding populations. Connectivity in river networks results from river dendritic structure and dispersal modality of organisms. Both factors may strongly affect the colonization process and the efficiency of conservation action plans. Based on empirical data, we simulated, using a simplified model with limited number of parameters, the colonization of a large river network, the Loire River, by the native Eurasian beaver and the invasive African clawed frog. For each species, we inferred model parameters (dispersal behavior and distances) by comparing the simulated and the observed distributions. Using network theory, we evaluated the efficiency of alternative conservation strategies to prevent or promote colonization of the river network. Network robustness to fragmentation and disturbance was also assessed. The model accurately predicted >70% of the observed species ranges. Conservation strategies that selectively protect habitat patches with the highest connectivity values provide a weak advantage at preventing connectivity loss compared to random protection strategies. In contrast, the targeted destruction of highly connected patches had a much stronger effect on the fragmentation of the network than the random removal of habitat patches. Spatial network topology strongly contributes to determining colonization patterns of large river watersheds. Network theory allows tests for robustness of rivers to fragmentation and disturbance, and identification of strategies for conservation planning.

Rediscovery of the endangered species Harpalus flavescens (Coleoptera: Carabidae) in the Loire River

Abstract The Loire River is one of the last European large rivers with important sediment dynamics and numerous sandbanks. The extraction of sediment from the riverbed during decades and the construction of levees for flood prevention have strongly affected and shaped the biodiversity of the Loire River. Many species from pioneer riverbanks have been impacted with particular consequences for psammophilous insects. The ground beetle Harpalus (Acardystus) flavescens (Piller &amp; Mitterpacher, 1783), is considered to have disappeared from the Middle Loire River for 40 years and is endangered everywhere in Europe. In 2012 and 2013, we recorded two specimens of H. flavescens in Région Centre‐Val de Loire (France), in the course of a survey dedicated to evaluating the impact of fluvial maintenance operations upon sediment and biodiversity dynamics. The presence of H. flavescens may be linked to the interruption of riverbed extractions and the vegetation removal of sandbanks of the Loire River (ecosystem restoration).

Assessing long‐term effects of multiple, potentially confounded drivers in ecosystems from species traits

Although species traits have the potential to disentangle long-term effects of multiple, potentially confounded drivers in ecosystems, this issue has received very little attention in the literature. We aimed at filling this gap by assessing the relative effects of hydroclimatic and water quality factors on the trait composition of invertebrate assemblages over 30years in the Middle Loire River (France). Using a priori predictions on the long-term variation of trait-based adaptations over the three decades, we evaluated the ability of invertebrate traits to indicate the effects of warming, discharge reduction and water quality improvement. Hydroclimatic and water quality factors contributed to up to 65% of the variation in trait composition. More than 70% of the initial trait response predictions made according to observed long-term hydroclimatic changes were confirmed. They supported a general climate-induced trend involving adapted resistance and resilience strategies. A partial confounding effect of water quality improvement acting on trophic processes was also highlighted, indicating that improved water quality management can significantly help to reduce some adverse effects of climate change. This trait-based approach can have wider implications for investigating long-term changes driven by multiple, potentially confounded factors, as frequently encountered in the context of global change.

Tracing Mixings and Water-rock Interactions in the Loire River Basin (France): δ18O-δ2H and 87Sr/86Sr

The Loire River drains more than 1/5thof the French territory and flows into the Atlantic Ocean through plutonic and volcanic rocks in the upper and lower parts and a large sedimentary basin. Through sampling of the Loire River along its main course and its main tributaries during 2 snapshot campaigns at the basin scale (one during a flood event and the other during the following low flow period), the behavior of the stable and Sr isotopes during water mixing and water/rock interactions at the scale of a large river basin having various lithologies is reported. This study highlighted the complex functioning of the river system and the key issue of the relation between surface and groundwater that must be more investigated, especially regarding water resources management.

Rivers of Risk and Redemption in Gregory of Tours’ Writings

Rivers of Risk and Redemption in Gregory of Tours’ Writings