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The lateen-rigged barque du Léman (Lake Geneva, France/Switzerland, 19th-20th centuries) was skeleton-built in genuine post-medieval Mediterranean tradition, however, its bottom was constructed in a very particular way: the heavy planks, made of silver fir (Abies pectinata) and almost as thick as the frames were sided, ran uninterrupted over most of the bottom's length. The rest of the planking was made of oak (at the ends of the bottom) and of larch (at the sides). Obviously, the bottom's structural strength mainly depended on these fir planks. La barque du Léman (France/Suisse, xixe-xxe siècles) est une grande embarcation à voile latine, construite sur couple selon la plus authentique tradition méditerranéenne postmédiévale. Cependant, son fond a été construit d'une manière très particulière : les lourds bordés de fond en sapin pectiné (Abies pectinata) sont presque aussi épais que la membrure et courent sans interruption sur presque toute la longueur du fond. Le reste du bordé était en chêne (pour le bouchain) et en mélèze (pour les flancs). De toute évidence, la résistance structurelle du fond dépendait principalement de ces planches de sapin.

Lake Geneva, the largest freshwater lake in Western Europe, is subject to important environmental pressures from its densely populated shores and watershed. To maintain and improve water quality in this lake, as well as in other enclosed or semi‐enclosed basins, it is essential to understand and be able to predict how nutrients and pollutants are transported within it. A 3D numerical modeling study of Lagrangian transport in Lake Geneva is presented, showing the dispersion of water (based on tracking inert water particles) inflowing from the lake's main tributary, the Rhône River. The relation between dominant winds, circulation patterns, and transport was analyzed. The results demonstrated that transport within the lake is highly inhomogeneous in space and intermittent in time, because water mass movements are controlled by the wind‐induced formation of large‐scale gyres and their subsequent breakdown into smaller ones. Particle spreading was shown to be sensitive to the depth of the initial particle release, and to the mean depth of the particles’ trajectory. However, several preferential pathways could be identified. Some water particles rapidly (days) traveled across the entire lake, through the near‐shore region in the upper layer, while others remained trapped for months, particularly in the central region of the lake at depth. Deeper particles tended to remain longer in the lake, due to the insulating effect of stratification, bathymetry obstacles, and slower currents at greater depth.

Ces dernières décennies, différentes approches numériques ont été utilisées afin de reproduire l'hydrodynamique des lacs en pilotage stand alone ou en couplage avec des modèles atmosphériques. L'augmentation de la résolution spatiale de ces modèles a permis d'intégrer un nombre croissant de lacs et de représenter leurs influences. Il s'agit d'effectuer une évaluation d'un modèle de lac 1D utilisé en mode multi-colonnes afin de savoir s'il représente une alternative à un modèle hydrodynamique 3D pour des applications climatiques. Le lac Léman sert de laboratoire d'analyse. Les épisodes transitoires de court terme ne sont pas reproduits fidèlement par le modèle multi-colonnes mais il réussit à représenter la structure thermique moyenne saisonnière. La température de l'eau en surface, la période stratifiée, la stabilité thermique et la thermocline sont reproduits raisonnablement. Il est donc envisageable d'utiliser un tel modèle plutôt qu'un modèle 3D en vue d'un couplage avec un modèle climatique régional.

The shoreline of Thonon-les-Bains and its hinterland, located at the northern end of the French Alps, between Lake Geneva and the foothills of the Chablais mountains, provides a suitable framework for the spatial and diachronic analysis of land use during the Bronze Age. This work is based on the study of ancient discoveries and the results of recent rescue operations. It focuses on the pile-dwelling village of Rives 2, dated between the mid- and end-Late Bronze Age (BF 2b-3b). The study area follows the coastline in both directions from Thonon along a total width of 5 km, and extends 5 km into the hinterland. This territory is located on alluvial terraces of glacial origin which reach an altitude of almost 400 m above the shore, nowadays artificially maintained from 372 m to 750 m. The shoreline is cut by water courses that are tributaries of the Rhône river: the Dranse river to the east, the Pamphiot river to the west, and the Redon river still farther east. On the terraces the glacial retreats left some sinkholes. These were filled by nowadays drained marshlands, which in the past attracted populations because of their environmental resources. People settled there from the Middle Neolithic period, clearing the slopes intensively at the beginning of the Late Bronze Age. For instance, the swamps of Versoie, including the settlements of le Genevray and Aviet, are located on plateaus at a height of 450 m and 600 m respectively. Both are located on the edge of the Pamphiot canyon, which was possibly a communication route when it crossed the barrier topped by the Allinges Middle Age castles, as well as a boundary for east-west circulations. In addition to physical geographic aspects that made it possible to define the limits of this work, distances and elevation gains were also taken into account. Indeed, in accordance with the site catchment analysis theories, we stayed within an area accessed by a one-hour walk, which is the time needed to cover the territory of an agropastoral sedentary community on a daily basis., Le territoire littoral de Thonon-les-Bains (Haute-Savoie) et son arrière-pays, enserrés entre le massif du Chablais et le lac Léman, offrent un cadre propice à une approche spatiale de l’occupation des sols au cours de l’âge du Bronze. D’après les données bibliographiques anciennes, la station lacustre de Rives 2 à Thonon-les-Bains est mentionnée pour la première fois en 1858. Des prospections subaquatiques ont été réalisées par le DRASSM en 1996-1997. L’analyse dendrochronologique des pieux prélevés et les mobiliers céramique et métallique mis au jour s’accordent, désignant les phases moyenne et récente de l’âge du Bronze final alpin. La zone étudiée couvre près de 40 km² et intègre le terroir associé au site de Rives 2, dans le cadre généralement admis de l’heure de marche quotidienne. Ce secteur, tout comme celui de Chens-sur-Léman, présente une forte concentration de données terrestres par rapport au reste de la rive méridionale du Léman. Du village lacustre aux habitats et nécropoles qui s’étagent sur les terrasses glaciaires, sur les rives des marais comblant les anciennes dolines d’Aviet à Allinges et de Versoie au Genevray, une douzaine de sites structurent ainsi un terroir relativement bien documenté, en particulier pour la seconde moitié du Bronze final.

International audience; This dataset corresponds to a data series produced from automated data loggers during the MESOLAC experimental project. Nine pelagic mesocosms (about 3000 L, 3 m depth) were deployed in July 2019 in Lake Geneva near the shore of Thonon les Bains (France), simulating predicted climate scenarios (i.e. intense weather events) by applying a combination of forcing. The design consisted of three treatments each replicated three times: a control treatment (named C - no treatment applied) and two different treatments simulating different intensities of weather events. The high intensity treatment (named H) aimed to reproduce short and intense weather events such as violent storms. It consisted of a short-term stress applied during the first week, with high pulse of dissolved organic carbon (5x increased concentration, i.e. total DOC similar to 6 mg L-1), transmitted light reduced to 15% and water column manual mixing. The medium intensity treatment (named M) simulated less intense and more prolonged exposures such as during flood events. It was maintained during the 4 weeks of the experiment and consisted of 1.5x increased concentration of dissolved organic carbon (i.e. total DOC similar to 2 mg L-1), 70% transmitted light and water column manual mixing. Automated data loggers were placed for the entire period of the experiment in the mesocosms and in the lake for comparison with natural conditions. Temperature, conductivity, dissolved oxygen and CO2 were monitored every 15 min at different depths (0.15, 0.25, 1 and 2 m). This data set aims to contribute our understanding of the effect of environmental forcing on lake ecosystem processes (such as production, respiration and CO2 exchange) under simulated intense weather events and the ability of the planktonic community to recover after perturbation. To a broader extent, the presented data can be used for a wide variety of applications, including monitoring of lake community functioning during a period of high productivity on a large peri-alpine lake and being included in further meta-analysis aiming at generalising the effect of climate change on large lakes.

International audience; When considering microbial biotic interactions, viruses as well as eukaryotic grazers are known to be important components of aquatic microbial food webs. It might be the same for bacterivorous bacteria but these groups have been comparatively less studied. This is typically the case of the Bdellovibrio and like organisms (BALOs), which are obligate bacterial predators of other bacteria. Recently, the abundance and distribution of three families of this functional group were investigated in perialpine lakes, revealing their presence and quantitative importance. Here, a more in-depth analysis is provided for Lake Geneva regarding the diversity of these bacterial predators at different seasons, sites and depths. We reveal a seasonal and spatial (vertical) pattern for BALOs. They were also found to be relatively diverse (especially Bdellovibrionaceae) and assigned to both known and unknown phylogenetic clusters. At last we found that most BALOs were positively correlated to other bacterial groups, mainly Gram-negative, in particular Myxococcales (among which many are predators of other microbes). This study is the first shedding light on this potentially important bacterial killing group in a large and deep lake.

A sampling campaign was carried out in June 2018 thoughout the lake, targeting roaches (N= 27) and burbots (N=18). Mercury, and a range of organic chemicals including polychlorobiphenyls (PCBs), polybrominated phenyl-ethers (PBDEs), hexabromocyclododécane (HBCDD), chlorinated alkanes (C10-C13), perfluoro-octane sulfonate (PFOS) and various flame retardants were analyzed in whole fish. Overall, the approach was derived from the methodological framework elaborated in the European Union for monitoring the chemical contamination of biota. Results were interpreted in terms of risk for piscivorous species. According to the results, PBDEs, HBCDD, chloro-alkanes, PCBs (except dioxin-like PCBs- DL-PCBs) and most halogenated flame retardants displayed low concentrations in fish from Lake Geneva. However, the concentrations exceeded the respective assessment criteria for mercury and DL-PCBs. In the case of PFOS, mean concentrations were clearly lower than the criterion, but some individuals exceeded it. Furthermore, an emerging flame retardant, DBDPE, was also systematically detected in fish samples. The trends for mercury and PCBs, which have been monitored for decades in Lake Geneva fish, show an important decrease, and have seemingly reached a plateau. Data are currently insufficient for determining the trends for PBDEs and PFOS.; Cette campagne de mesures s'est intéressée à la contamination par le mercure et par une gamme étendue de composés organiques, notamment les polychlorbiphényles (PCB), les polybromodiphényl-éthers (PBDE), l'hexabromocyclododécane (HBCDD), les chloroalcanes (C10-C13), le perfluorooctane sulfonate (PFOS), et divers retadateurs de flamme chez des gardons (N= 27) et des lotes (N=18) collectés en juin 2018 dans plusieurs secteurs du lac. La méthodologie s'est inspirée du cadre d'élaboration de la surveillance de l'état chimique dans le biote dans les Etats membres de l'Union Européenne. Les résultats ont été interprétés par rapport au risque pour la faune piscivore. Sur la base des résultats, le Léman apparait peu contaminé en ce qui concerne les PBDE, l'HBCDD, les chloroalcanes, les PCB (sauf ceux de type dioxine, PCB-DL), et la plupart des retardateurs de flamme chlorés et bromés alternatifs aux PBDE. En revanche, les concentrations moyennes dépassent les critères d'évaluation pour le mercure et les PCB-DL. Pour le PFOS, les concentrations moyennes sont inférieures au critère d'évaluation, mais quelques individus le dépassent. Un retardateur de flamme alternatif, le DBDPE, a également été détecté de manière systématique. Les concentrations de mercure et de PCB, qui ont fait l'objet d'un suivi de longue date, ont beaucoup baissé au fil des décennies, et semblent se stabiliser. Il est actuellement prématuré de statuer sur les tendances suivies par les PBDE et le PFOS.

The coastline of Thonon-les-Bains and its hinterland provide a favourable framework to the spatial and diachronic analysis of land use during Protohistory. This synthesis is based on the study of old finds and the results of recent rescue operations, in an area between the Dranse and Redon rivers. About 15 sites form a relatively well-documented micro-region, extending from the piledwellings village of Rives 2 to the settlements and cemeteries stepped on glacial terraces, on the marshlands filling the sinkholes of “ Aviet” in Allinges, and of “ Versoie” next to the Genevray., Le territoire littoral de Thonon-les-Bains et son arrière-pays offrent un cadre propice à une approche spatiale et diachronique de l’occupation des sols au cours de la Protohistoire. La reprise des données anciennes et les résultats des fouilles préventives récentes alimentent ce projet de synthèse portant sur un espace compris entre les rivières Dranse et Redon. Du village lacustre de Rives 2 aux habitats et nécropoles qui s’étagent sur les terrasses glaciaires, sur les rives des marais comblant les anciennes dolines d’«Aviet » à Allinges et de «Versoie » près du Genevray, une quinzaine de sites structurent un terroir relativement bien documenté, en particulier pour la seconde moitié du Bronze final., Landry Christophe,Treffort Jean-Michel,Tremblay-Cormier Laurie,Gisclon Jean-Luc,Henon Philippe,Morin Eymeric,Lalai Dominique,Etien Nathalie,Doyen Elise,Crola Bernard,Berman Laurent,Ticon Joseph. Entre Alpes et Léman, Thonon aux âges des métaux. In: Collection EDYTEM. Cahiers de géographie, numéro 20, 2018. L’Homme dans les Alpes, de la pierre au métal. pp. 295-303.

Artificial stocking practices are widely used by resource managers worldwide, in order\ud to sustain fish populations exploited by both recreational and commercial activities,\ud but their benefits are controversial. Former practices involved exotic strains, although\ud current programs rather consider artificial breeding of local fishes (supportive breeding).\ud Understanding the complex genetic effects of these management strategies is an\ud importan t challenge with economic and conservation implications, especially in the\ud context of population declines. In this study, we focus on the declining Arctic charr\ud (Salvelinus alpinus) population from Lake Geneva (Switzerland and France), which has\ud initially been restocked with allochtonous fishes in the early eighties, followed by supportive\ud breeding. In this context, we conducted a genetic survey to document the\ud evolution of the genetic diversity and structure throughout the last 50 years, before\ud and after the initiation of hatchery supplementation, using contemporary and historical\ud samples. We show that the introduction of exotic fishes was associated with a genetic\ud bottleneck in the 1980–1990s, a break of Hardy–Weinberg Equilibrium (HWE),\ud a reduction in genetic diversity, an increase in genetic structure among spawning sites,\ud and a change in their genetic composition. Together with better environmental conditions,\ud three decades of subsequent supportive breeding using local fishes allowed to\ud re-establish HWE and the initial levels of genetic variation. However, current spawning\ud sites have not fully recovered their original genetic composition and were extensively\ud h omogenized across the lake. Our study demonstrates the drastic genetic\ud consequ e nces of different restocking tactics in a comprehensive spatiotemporal\ud framewo rk and suggests that genetic alteration by nonlocal stocking may be partly\ud reversible through supportive breeding. We recommend that conservation-based programs\ud consider local diversity and implement adequate protocols to limit the genetic\ud homogenization of this Arctic charr population.

International audience

In deep stratified lakes, such as Lake Geneva, flood-driven turbidity currents are thought to contribute to the replenishment of deep oxygen by significant transport of river waters saturated with oxygen into the hypolimnion. The overarching aim of this study was to test this long-standing hypothesis directly. It combines direct observational data collected during an extreme flooding event that occurred in May 2015 with dark bioassays designed to evaluate the consequences of river-borne inputs for the hypolimnetic respiration. The exceptional precipitation events of May 2015 caused floods with an annual return time for the Rhône River, the dominant tributary of Lake Geneva, and with 50-year return time for the Dranse River, the second-most important tributary. Sediment-loaded river flows generated turbidity currents plunging into the lake hypolimnion. The observed river intrusions contributed to the redistribution of dissolved oxygen, with no net gain, when occurring in the lowermost hypolimnetic layer. In the uppermost hypolimnion above the last deep-mixing event, the intrusions coincided with a net oxygen deficit. Consistent with field observations, dark bioassays showed that 1 to 50 % substitution of riverine organic matter to deep (

Lake Geneva became famous in the scientific world since the publication of the pioneer limnology book “Le Léman” by François-Alphonse Forel (Forel 1892-1904). We will take you onboard the Neptune, a boat constructed in 1904, the same year Forel's book was published, for a short journey through the geological and sedimentological history of the lake. We will show you how the Leman and humans societies, including the palafittes (UNESCO world heritage), interacted through time and how several tsunamis swept over the lake. We will also take the opportunity of the breathtaking view over the surrounding landscape to discuss how the Rhone glacier shaped the Geneva basin during the last glaciation. We will finish the visit in the old Town of Geneva visiting the archeological site of St. Peter's cathedral

Viral community structure and dynamics were investigated for the first time in surface waters (0–20 m) of Lake Geneva over a 5-month period between July and November 2011. Abundances of autotrophic picoplankton, heterotrophic bacteria and virus-like particles determined using flow cytometry revealed their predominance during the summer months followed by a slight decrease in fall. Two groups of viruses could be discriminated, referred to as virus-like particles (VLP) group 1 and 2. The abundance of VLP1 correlated significantly with the bacterial abundance, while that of VLP2 correlated with both chlorophyll a and picocyanobacterial abundance suggesting a tight coupling between these viral groups and bacteria or phytoplankton. The abundance of cyanomyoviruses and cyanopodoviruses varied between 7.3 × 102 ml−1 (July) to 1.2 × 104 ml−1 (November) and 5.8 × 103 ml−1 (July) to 2.2 × 104 ml−1 (September), respectively. The abundance of the picocyanobacterial hosts was in concurrence with that of the cyanophages, being higher in late summer. Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) of viral signature genes such as g20, g23, mcp, polB, psbA and psbD revealed a relatively high richness within these genes with their diversity increasing towards the summer months. The diversity of psbD was found to be particularly high and correlated with picocyanobacterial abundance suggesting that cyanophages may be directly responsible for a significant proportion of carbon fixation in Lake Geneva.

International audience; I addressed the effects of taphonomic and early diagenetic processes on the isotope composition of cladoceran remains, using both experimental and field approaches. An experiment was designed to mimic the conditions encountered by cladoceran remains when they settle through the water column and are buried in the sediment. Cladoceran exoskeletons were incubated for 4 months in oxic or anoxic water, and in sediment. Changes in their carbon (C) and nitrogen (N) content and isotope compositions were measured. Most changes in isotope composition of exoskeletons took place when they settled through the water column. Once buried in the sediment, however, the δ13C and δ15N values of cladoceran exoskeletons did not undergo further change. Taphonomic processes resulted in an increase in δ13C and δ15N of the cladoceran remains and this was related to microbial degradation, which selectively removed isotopically light C and N compounds from the remains. For δ13C, changes were minimal (

International audience; We tested the applicability of two available Water Framework Directive (WFD) compliant phytoplankton indices on three large peri-alpine lakes to analyze their suitability for trophic classification. We show that the indices vary in their final resulting Ecological Quality Ratios (EQRs) and are only appropriate to roughly distinguish lakes of different water quality according to OECD criteria (OECD, 1982). Annual mean TP concentration in Lake Geneva was 0.03 mg l-1 in 2006 (Lazzarotto & Rapin, 2007), which marks mesotrophic conditions. According to the tested indices, the lake is of ‘good’ (0.60–0.80) quality after the GermanWFDmethod (PSI) and of ‘moderate’quality according to the Austrian WFD method (BI).We prove that the way how to derive the per annumvalue of the metric ‘Brettum Index’ (BI) in the Austrian WFD method significantly influences the resulting index and the scatter of long-term data. We focused on improvement strategies for this index in terms of calculation and sampling frequency. Contrary to the tested bin, the modified index presents no significant differences between four and six sampling dates per year. In order to improve the significance of the available indices, we propose to modify the way of per annum index calculation for the AustrianWFDmethod as well as to focus on species composition to achieve a high relative proportion of indicator species. A phytoplankton index alone may not be sensitive enough to track the changes that occur within a lake. The results confirm the need to take into account other biological elements such as fish, macrophytes, attached diatoms and macrozoobenthos as suggested by the WFD.

Flow cytometry (FCM) was used to assess microbial community abundances and patterns in three natural, large and deep peri-alpine hydrosystems, i.e., lakes Annecy (oligotrophic), Bourget, and Geneva (mesotrophic). Picocyanobacteria, small eukaryotic autotrophs, heterotrophic prokaryotes, and viruses were studied in the 0–50 m surface layers to highlight the impact of both physical and chemical parameters as well as possible biotic interactions on the functioning of microbial communities. Some specificities were recorded according to the trophic status of each ecosystem such as the higher number of viruses and heterotrophic bacteria in mesotrophic environments (i.e., Lakes Geneva and Bourget) or the higher abundance of picocyanobacteria in the oligotrophic Lake Annecy. However, both seasonal (temperature) and spatial (depth) variations were comparatively more important than the trophic status in driving the microbial communities’ abundances in these three lakes, as revealed by principal component analysis (PCA). A strong viral termination of the heterotrophic bacterial blooms could be observed in autumn for each lake, in parallel to the mixing of the upper lit layers. As virus to bacteria ratio (VBR) was indeed very high at this period with values varying between 87 and 114, such important relationships between viruses and bacteria were likely. The magnitudes of seasonal variations in VBR, with the highest values ever reported so far, were largely greater than the magnitude of theoretical variations due to the trophic status, suggesting also a strong seasonality in virioplankton production associated to prokaryotic dynamics. FCM analyses allowed discriminating several viral groups. Virus-Like Particles group 1 (VLP1) and group 2 (VLP2) were always observed and significantly correlated to bacteria for the former and chlorophyll a and picocyanobacteria for the latter, suggesting that most of VLP1 and VLP2 could be bacteriophages and cyanophages, respectively. On the basis of these results, new ways of investigation emerge concerning the study of relationships between specific picoplanktonic groups; and overall these results provide new evidence of the necessity to consider further viruses for a better understanding of lake plankton ecology.

Turbidity currents, and other types of submarine sediment density flow, redistribute more sediment across the surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The deposits of these flows are of societal importance as imperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understanding field observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than ∼ 0.6°. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low (

Le Léman est devenu célèbre dans le monde scientifique avec la publication de l'ouvrage «Le Léman» (Forel 1892-1904), par l'inventeur de la limnologie François-Alphonse Forel. Nous vous emmènerons à bord de la Neptune, une barque construite en 1904, l'année de parution de l'ouvrage de Forel, pour un court voyage à travers l'histoire géologique et sédimentologique du lac. Nous vous expliquerons comment le Léman et les sociétés humaines, y compris celle des palafittes (inscrits au Patrimoine mondial de l'UNESCO), interagissent dans le temps et comment deux tsunamis ont déferlé sur le lac. Nous prendrons aussi l'occasion de contempler les paysages à couper le souffle de la campagne environnante pour vous donner un aperçu de la géologie régionale (Préalpes, Jura) et discuter comment le glacier du Rhône a sculpté le Bassin lémanique durant la dernière glaciation (dernier maximum glaciaire vers 20'000 BP).

L'article traite de la carte prototype de la région du Léman au 17e siècle, le siècle des grands modèles scientifiques. Première carte en perspective verticale, la représentation de Jacques Goulart (1605) est d'abord éditée dans l'Atlas de Mercator puis dans différentes éditions ultérieures comme celui de Jodocus Hondius (Amsterdam). Elle conserve l'orientation médiévale vers le Sud-Est. Elle est marquée par la religion protestante du cartographe, qui était aussi pasteur, et elle sera un instrument d'identification à la région lémanique dans son ensemble.

In Lake Geneva, the surface water temperature has increased by 1° C over 20 years probably as a result of climate change. The effects of changes in temperature on the reproductive cycle of the roach Rutilus rutilus were assessed in a 19 year survey. Over time, spawning tended to begin earlier. The consequences of temperature changes were assessed on two different stages of the female reproductive cycle: the development of the ovaries from the beginning of autumn to ovulation, and the onset of the spawning period. The development of the ovaries was studied for 7 consecutive years from October to June. From 1 October to the onset of spawning, it was possible to assess the gonado-somatic index (I G ) of females in terms of time expressed as a sum of degree-days. The correlation between I G and the sum of degree-days was +0·97. The onset of the roach spawning period in Lake Geneva was triggered by a thermal threshold (median and range 190 ± 10 degree-days for the 15 previous days). From October to April, climate warming accelerated the development of gonads, then in May, a thermal threshold that triggered the onset of roach spawning occurred earlier.

L'évolution comparée des biocénoses rotatoriennes du Léman et du Lac de Constance montre un parallélisme remarquable lors des changements continus de l'état trophique, tant avant qu'après le niveau maximal d'eutrophisation atteint par ces deux lacs. La comparaison avec un certain nombre d'autres milieux soumis également à un changement de leur niveau trophique met en évidence une variation très nette des effectifs des espèces méso-eutrophes et eutrophes en fonction de la progression ou de la régression de l'eutrophisation; ces changements sont beaucoup moins marqués en ce qui concerne l'association des espèces oligo-mésotrophes., Eutrophication of a lake must be expected to cause both abiotic and biotic responses. The changes in the trophic state of a lake certainly occur at all trophic levels, but to different extents depending on the character of the ecosystem; the subsequent evolution of the rotifer biocenosis is one of the most pronounced features occurring as an indirect consequence of eutrophication.In the last three decades, the rotifer community in Lake Geneva has presented important changes in structure, as a result of continuous changes in the trophism of the lake. This study covered a period of time sufficient to show possible true modifications of the community structure.Lake Geneva has undergone anthropogenic eutrophication since the 1950's. The lake reached its highest nutrient level during 1979-1980, which has decreased though since 1981 with the improvement of phosphorus removal in sewage treatment plants. A similar trend was observed in Lake Constance, with more important quantitative changes connected with previous results dating from the oligotrophic stage of this lake.Table 1 gives the variations in abundance of rotifer species observed during the eutrophication increase and during the decrease of the eutrophication level in some lakes of different trophic status.Figure 1 indicates the quantitative changes of the main rotifer species in Lake Geneva and Lake Constance. Compared to the maximal trophic level (indicated by arrow), data from Lake Geneva for 1959-1987 are similar to those obtained in Lake Constance between 1963 and 1978, if the previous data obtained for this lake during its oligotrophic stage are excluded.Figure 2 presents the general trend observed for the different trophic indicator groups during the increase or decrease of eutrophication. Throughout the eutrophication process, these groups exhibited a general increase for most of the different species, with the ratio "number of increasing species/number of decreasing species" growing from the oligo-mesotrophic group to the eutrophic one. During the decrease of eutrophication, the strength of meso-eutrophic and eutrophic indicator groups diminished more than that of the oligomesotrophic group.Many species have appeared during the eutrophication increase, mainly belonging to meso-eutrophic and eutrophic indicator groups, together with the settlement of some oligo-mesotrophicspecies (Ascomorpha saltans, Synchaeta oblonga, Notholca caudata). The proportion of meso-eutrophic and eutrophic species increased in the two lakes, but there is a trend in populations of the oligo-mesotrophic species to decrease, leading to a precocious disappearance of Ploesoma hudsoni and later of Ascomorpha ovalis, Gastropus stylifer, Ploesoma truncatum in Lake Constance, and of Synchaeta tremula and Notholca foliacea in both lakes.Decreasing eutrophication reduces the number of some mesoeutrophic (Trichocerca longiseta and T. pusilla in Lake Geneva, T. rousseleti in Lake Constance) and eutrophic species (Anuraeopsis fissa and Trichocera cylindrica in Lake Geneva, Pompholyx complanta in Lake Constance). However, the water quality has mot improved enough to allow a further increase in oligo-mesotrophic species, except for Conochilus unicornis in both lakes, and for Ascomorpha ecaudis, Kellicottia longispina and Synchaeta oblonga in Lake Geneva.Since 1981, the oligo-mesotrophic indicator group is numerically dominant in Lake Geneva (BALVAY and LAURENT, 1989c), preceding the euryecious one (Asplanchna priodonta + Keratella cochlearis), white the strength of the meso-eutrophic group decreases and the eutrophic one remains almost steady.

The antifouling herbicide Irgarol 1051 has been detected in recent years in numerous estuaries, marinas, harbors and coastal areas, and in some harbors on Lake Geneva, but so far only a few studies have investigated the ecotoxicological effects of this compound on microalgae. The purpose of this study was to assess the ecotoxicological impact of Irgarol 1051 on the algal communities of Lake Geneva, and to compare its phytotoxicity to that of the common triazine herbicide, atrazine. We investigated the response of phytoplanktonic and periphytonic algal communities and single-species isolates collected from the lake, to the PS II inhibitor Irgarol 1051 (growth, proxy of photosynthetic activity and community structure). A short-term bioassay was developed based on in vivo fluorescence, together with nanocosm experiments with natural algal communities, and single-species tests on algal strains isolated from the lake. The toxicity of Irgarol 1051 towards periphyton and phytoplankton was shown to be higher than that of atrazine. Indications of the tolerance induced by this triazine in the algal communities of Lake Geneva, suggests that even at the levels of contamination reported in some parts of the lake, Irgarol 1051 is already exerting selection pressure. Information about sensitivities, selection and tolerance from laboratory experiments are used to explain the observations in natural microalgal communities from the lake.

Les guerres du XXe siècle ont instauré une nouvelle pratique de déversement dans les points d'eau (mers, océans, lacs) du surplus de matériel de guerre, opérationnel ou obsolète, contenant des substances extrêmement dangereuses (ypérite, vincennite, tabun, etc.). Ces déchets peuvent provoquer des catastrophes environnementales. L'objectif de cette recherche vise à analyser, au travers du prisme du secret, la réémergence sur la scène publique de la thématique des munitions englouties en Suisse, et de comprendre le pourquoi et les implications d'une telle réapparition. De manière plus générale, il s'agit d'analyser la position de la Suisse, qui bien que pays neutre et n'ayant pas pris part aux conflits du XXe, siècle, s'est retrouvée détentrice d'une production excédentaire de munitions (pour assurer sa sécurité intérieure en cas d'attaque), et dont il a fallu se débarrasser. Pour illustrer cette réflexion, le cas d'étude choisi porte sur les immersions des munitions dans le lac Léman.

International audience

Regional cartography has developed since the 16th century, with the «conquest of visible» as well as regional individualization stemming from biographical literature of the Renaissance. An image of the Lake Geneva region was formulated using early regional maps. Their representation codes, especially those of the humanist period of the end of 16th century, are presented in this paper., La cartographie régionale a pris son essor au XVIe siècle, avec la «conquête du visible» et l’individualisation des régions nées de la littérature biographique de la Renaissance. L’image de la région lémanique se forge à travers les premières cartes régionales dont nous restituons ici les codes de représentation, en particulier ceux qui sont issus de la période humaniste de la fin du XVIe siècle., La cartografía regional se desarolla en el siglo XVI, con la «conquista del visible» y la individualización de las regiones nacida de la literatura biográfica del Renacimiento. La imagen de la región lemánica se fragua a través de los primeros mapas regionales cuyos códigos de representación restituimos aquí, especialmente los que resultan del período humanista de finales del siglo XVI., Lévy Bertrand. Les premières cartes régionales du Léman. In: Mappemonde 50, 1998/2. pp. 2-6.

International audience; Dynamic penetrometers reveal information about seafloor strength, stratification, stability, and sediment remobilization. However, positioning is often limited to a range of meters making it difficult to target small-scale geomorphologic features. Deployments from submersed vessels (manned or remotely operated) can extend the possibilities of in situ geotechnical surveying in areas of complex bathymetry. The lightweight dynamic penetrometer Nimrod was modified to enable its deployment from the MIR submersibles, and was deployed during two dives in the Rhône Delta and Vidy Bay (both Lake Geneva). In the Rhône Delta, five positions at the floor/levee complex of a submarine canyon were sampled with ~1 m spacing, with good reproducibility of the results. In Vidy Bay, so-called pillow-hollow structures on the lake bottom with dimensions of about 50 cm were targeted. At both sites, the penetrometer was released from a height of about 1-2 m above the lake bottom using the starboard robotic arm of the MIRs leading to impact velocities of ~ 3 m-1. The probe reached penetration depths of up to 80 cm with maximum decelerations of up to 2.9 g. Stratification in the deceleration versus penetration depth profiles hinted at recent sediment remobilization processes. Pressure transducer results of the probe were suitable to determine water depth, and estimate trends of excess pore pressure. This article describes the modification of the dynamic penetrometer Nimrod for deployments from the MIR submersibles, assesses the deployment performance, validates the results, and gives an outlook on the application of this technique and the results.

La distribution du zooplancton au cours de la periode diurne montre une forte segregation spatiale. Les divers stades de developpement d'une meme espece occupent des strates differentes, les formes juveniles etant generalement localisees dans les couches superieures tandis que les stades âges colonisent principalement les zones profondes. Si la coexistence d'especes a regime alimentaire different est possible dans une meme strate (Eudiaptomus gracilis et Cyclops vicinus), il existe une tres nette segregation spatiale entre Cyclops prealpinus et C. vicinus, la premiere espece ayant toujours une localisation plus profonde durant la journee. II en est de meme pour les nauplii de cyclopides et de calanides. La repartition diurne des daphnies selon l'axe vertical montre une augmentation de la taille moyenne avec la profondeur, les juveniles (ainsi que D. galeata, espece de petite taille) occupant les couches de surface alors que les adultes peuplent preferentiellement les couches profondes ou ils peuvent ainsi echapper a la predation par les poissons planctophages chassant a vue.

Dès le XIXe siècle, les lacs du Plateau suisse ont livré des milliers d'objets en bronze. Témoignant de l'établissement de villages sur les rives à la fin du Bronze final (1050-800 av. J.-C.), la plupart de ces objets ont été immergés volontairement. L'analyse quantitative et qualitative d'un corpus de plus de 17000 objets en bronze, issus de 10 collections palafittiques de Suisse occidentale, indique l'existence de règles spatio-temporelles dans la sélection des pièces immergées. Les comparaisons avec d'autres catégories de sites archéologiques permettent de « décomposer » les collections lacustres en ensembles comparables aux dépôts terrestres et aux découvertes fluviales contemporains. La « superposition » de plusieurs pratiques socialement codifiées dans le périmètre des stations palafittiques soulève de nouvelles questions sur le rôle socio-économique des villages littoraux dans les sociétés du Bronze final au nord des Alpes. Ainsi, les stations de grande superficie semblent avoir attiré les populations sur de grandes distances.

Resume Ce papier presente les resultats d'une etude sur les transferts des nutriments (P, N) et la qualite de l'eau, menee sur un petit bassin versant (14 ha) en milieu rural, situe en bordure du Lac Leman. L'etude du bilan annuel et de la variabilite des concentrations en N et P permet d'evaluer les risques de degradation des eaux lies aux pratiques agricoles. L'analyse d'une vingtaine de crues nous a permis de degager 3 types d'evenements: (1) les crues liees surtout a une mise en charge de la nappe et caracterisees par des exportations limitees de N et de P; (2) les crues a forte composante de ruissellement qui exportent surtout de grandes quantites de P sous forme particulaire; (3) les crues a ecoulement hypodermique important qui exportent beaucoup de N mais aussi de P sous forme soluble. Les flux sortant du bassin experimental s'ecoulent vers un marecage et a l'exutoire de ce marais, on constate une nette amelioration de la qualite de l'eau par denitrification et par insolubilisation et decantation de P. La gestion et la lutte contre la pollution diffuse agricole passe ainsi par un amenagement a la fois de la zone agricole elle-meme et des differentes zones tampons le long du parcours des eaux. Le type d'amenagement n'est pas forcement le meme pour N et pour P. Dans certains cas, il peut meme apparaitre des effets contraires.

International audience; The pollution of lakes and rivers by the agricultural use of pesticides is a growing problem worldwide. As these substances have complex effects on ecosystems, we need to improve our understanding of their fate and their impact on biological communities. With this in mind, we carried out experimental study of the responses of planktonic bacterial communities from lakes and benthic bacterial communities from streams to the fungicide tebuconazol, and of its degradation by these different communities. For each type of ecosystem, communities were collected from pristine environments (Lake Aiguebelette and the upstream segment of the river Morcille, France) and pre-exposed environments (Lake Léman and the downstream segment of the river Morcille, France in which tebuconazol was found). The experiments were carried out in 20L microcosms in which communities from each of the four environments were either not Exposed (control), or exposed to a low (2μg/L) or high (20μg/L) concentration of the fungicide, in order to simulate the contamination levels encountered in aquatic ecosystems. Results obtained after three weeks of incubation showed that 60 to 70% of the initial concentration of tebuconazol had been degraded in the stream microcosms, whereas only minor degradation had occurred in the lake microcosms (15-20%). The fungicide had no significant impact on benthic bacterial abundance, although the proportion of dead bacteria increased. The changes observed in planktonic bacterial abundance and dead bacteria were transient and depended on previous exposure. To complete these findings, the bacterial diversity is characterizing by pyrosequencing of the gene coding for 16S rRNA. This high-throughput sequencing technology provides a deep inventory of the diversity in microbial communities. All the resulting findings will be discussed with regard to the fungicide history of the different communities studied, and to the rate at which these communities degrade the fungicide

International audience

In France, the Arctic charr (Salvelinus alpinus) is native in only two lakes (Lakes Bourget and Geneva), in the most southerly part of its distribution area. It is a profundal morph living at depths of between 30 and 100 m in Lake Geneva. Following considerable stocking of Lake Geneva with juvenile Arctic charr and some good results during the 1980s, catches are currently declining. Several hypotheses have been proposed to explain this decrease, but the potential influence of warming of the lake in the 1990s has not been considered. This article studies the relationship between the strength of the cohorts and the temperature in Lake Geneva from 1992 to 2002, and discusses the various potential causes of the population collapse observed. The findings reveal close correlation between water temperature and the strength of the cohorts. It is concluded that the recent warming of Lake Geneva may have a significant direct or indirect impact on the Arctic charr population.

National audience

La diversité des écosystèmes lacustres s’explique en partie par la variété hydromorphologique des lacs ; la nature et la répartition du substrat qui tapisse leur fond sont des composantes de ce paramètre. C’est pour cela que la Directive Cadre sur l’Eau impose une description de la nature des sédiments des plans d’eau. Plus généralement, la répartition des substrats peut être considérée comme un facteur de structuration des espèces biologiques qu’abrite un lac. Des outils traditionnels comme l’utilisation d’une benne à sédiment ou d’une caméra subaquatique permettent de déterminer la nature des substrats de manière très ponctuelle mais ces techniques atteignent leurs limites lorsque tout un plan d’eau doit être caractérisé. Depuis les années 1980 des méthodes de caractérisation des sédiments utilisant des outils acoustiques qui permettent d’obtenir des informations en continu le long de parcours réalisés par un navire ont été développées et commercialisées. Pour l’application aux écosystèmes lacustres, de part leur mise en oeuvre, les systèmes utilisant les échosondeurs mono‐faisceau paraissent les plus appropriés. Ces appareils permettent de réaliser des cartes de la répartition des substrats à l’échelle du lac. Les informations pertinentes qui permettent de décrire un état biologique potentiel ou de définir un état initial peuvent être ainsi intégrer dans la mise en place des réseaux de suivi de la qualité des milieux. / The lake ecosystem diversity is explained, in part, by the hydromorphological diversity of lakes; nature and repartition of the substrata give information about this parameter. That is the reason why the European Water Framework imposes a substrata nature description of lakes. The substrata repartition could be considered as a factor of the biological structuring presents in lakes. Traditional tools like grab samplers or video cameras enable to determine the substrata nature but they are not appropriate for getting a high resolution description for an entire lake. From the beginning of the 80’s, acoustic devices specialized in seabed classification have been developed and commercialized. For lakebed surveys, systems using single beam sounders seem to be more appropriate; they enable to obtain maps of the lakebed at the whole lake scale. Information which describes a potential biological state can be used for the establishment of a quality monitoring.

National audience; En milieu aquatique, le Trématode Trichobilharzia sp. réalise son cycle en parasitant successivement un oiseau (canard, hôte principal) et un mollusque (limnée, hôte secondaire). La dermatite du baigneur est une affection causée par la cercaire de ce parasite (dénommée puce du canard), quittant le mollusque à la recherche de l’hôte définitif et qui pique l’homme par erreur. La dermatite du baigneur est connue au Léman depuis 1950. Elle est apparue sur les lacs d’Annecy et du Bourget depuis les années 90. Les recherches menées par le laboratoire INRA de Thonon-les-Bains sur les lacs savoyards ont porté sur (1) l’épidémiologie de la dermatite, (2) la détermination des espèces de parasites et de limnées impliquées, (3) la distribution, le cycle de développement et le taux de parasitisme des limnées, (4) le taux de parasitisme chez les canards par la recherche du parasite nasal, (5) la mise en évidence de facteurs environnementaux susceptibles de réguler le problème parasitaire. Les points principaux sont : la description de la cercaire d’une espèce trouvée au Léman (T. cf ocellata, qui sera par la suite rattachée à T szidatii) ; la description du cycle de croissance de la limnée Radix peregra ; la distribution en zone littorale des limnées dans les zones colonisées par la végétation aquatique ; l’émission massive des cercaires pour une température de l’eau avoisinant 22°C, et la relation avec l’augmentation de la pression atmosphérique en période d’orage ; la diminution des problèmes de dermatite au Léman dans les zones colonisées par l’écrevisse signal (Pacifastacus leniusculus), espèce introduite qui continue son expansion le long des rives du lac. Ces travaux ont été réalisés en collaboration avec des organismes de recherche et des universités françaises et suisses.

National audience; Lake Geneva, located at the border between France and Switzerland, is the largest freshwater reserve in Western Europe. In the 70’s the economic importance of the lake made it necessary to develop a monitoring program that is still in action and provides data on physical and chemical characteristics as well on the abundance and species composition of planktonic communities. The analysis of the long-term data reveals important modifications of physico-chemical features of the lake, changes in the abundance, the structure, the phenology and the mechanisms of regulation of the planktonic and fish communities. In the last decades, the lake has undergone both a local anthropogenic pressure (increase and then decrease in phosphorus concentration) and a large scale atmospheric pressure that has induced synchrony in the long-term changes of water temperatures between lakes over the alpine area. These major forces have induced long-term trends in the different trophic levels. There is an increase in the abundance of one of the main planktivorous fish species, a decrease in the abundance of zooplankton and an increase in the biomass of phytoplankton. Such trends suggest a top-down control. However, a more acute analysis indicates complex mechanisms that combine both top-down and bottom-up controls varying in intensity depending on the time scale and population considered.

National audience; Le Léman a évolué d’un stade oligotrophe, jusqu’à la fin des années 50 à eutrophe entre 1970 et 1990, pour revenir à un niveau mésotrophe, actuellement 25 μg P/l). L’abondance du zooplancton a suivi cette évolution. Les populations de perches présentent des évolutions pluri-annuelles cycliques, mises en évidence lors de la reproduction, sur les histogrammes de largeur des rubans d’oeufs et sur les captures de perches, une cohorte forte constituant alors une part importante des captures, surtout la première année. Ces cycles résultent des effets combinés du cannibalisme des 62 grosses perches sur leur descendance et de la pêche qui élimine rapidement ces grosses perches. Le zooplancton est une source essentielle de nourriture pour la perche, particulièrement pour les jeunes stades. Le biovolume de zooplancton produit annuellement par m² a diminué significativement pendant la ré-oligotrophisation, mais il est difficile de faire la part du rôle de l’évolution trophique de celle du broutage exercé par les populations de poissons planctonophages. La relation établie entre le niveau trophique ([P] et l’abondance de nourriture (biovolume de zooplancton en ml/m²) et le niveau des captures des perches est meilleure si l’on se limite aux populations des fortes cohortes. La taille des 0+ est corrélée à la quantité de zooplancton. Cette relation est plus forte pour les fortes cohortes. Compte-tenu de l’abondance des jeunes poissons, la ressource limitée en zooplancton limite alors la taille des jeunes perches, ce qui n’apparaît pas autant pour les perches des cohortes intermédiaires. L’augmentation de la température de surface, en réponse aux changements climatiques (+1 °C en 20 ans), n’a eu aucun impact visible sur la croissance et les captures de perche, masqué par les effets liés à la diminution rapide de la quantité de nourriture disponible survenant pendant la même période. Les captures de perche et leur croissance individuelle sont globalement liées à la ressource alimentaire, fonction de la richesse trophique du milieu. Toutefois, des incidents climatiques prolongés peuvent influer sur la quantité de poissons (période de 1977 à 1980, où les printemps ont été très instables). Mais le recrutement des 0+, très abondant ces dernières années dans le Léman ainsi que dans le lac d’Annecy fortement oligotrophe serait peut être favorisé par la ré-oligotrophisation.

National audience; This poster deals with the use of the oxygen isotopic composition (δ18Op) of dissolved inorganic phosphate (DIP) as a tracer for phosphate sources. Recent studies have shown that δ18Op values can be used as a tracer to identify the sources and cycling of P in different environments including marine and freshwater systems (Paytan and McLaughlin., 2006). Several studies were made for the purification and the analysis of phosphates oxygen isotopic composition since the pioneering works of Tudge 1960. Thus, many methods have been developed for the purification of phosphate from apatite. However, they are not easily applied to DIP purification. In 2004, Karen McLaughlin et al. propose a new method for purifying phosphate by precipitation as cerium phosphate. Currently, this method was never repeated. Here we present the first results of reproducibility and repeatability tests of this method with the goal in mind to apply this one to trace phosphate sources in Lake Geneva.