Les particularités de la société en commandite par actions au regard des conflits d'agence

organisé par l'Institut de Gestion de Rennes (IGR)L'objectif de cette étude est d'analyser les relations entre les gérants, les associés-commandités et les actionnaires-commanditaires de société en commandite par actions (SCA) familiales. Les relations entre ces trois catégories d'acteurs présentent des spécificités originales au regard des conflits d'agence, entre associés et dirigeants (type I), et entre actionnaires majoritaires et minoritaires (type II). Les particularités de la SCA en font un excellent cadre de gouvernance pour les entreprises familiales, notamment en raison de la dissociation entre le pouvoir et la détention du capital

Infiltration processes in karst using an event-based conceptual model of flow and transport of dissolved organic carbon

International audienceThe aim of this study is to characterize karst infiltration processes during flood events using a rainfall-discharge model coupled with a transport model for non-conservative solutes. The modelling approach is based on a classical karst devoted model with three connected reservoirs: SOIL (and epikarst) that feeds the aquifer partitioned into DIFFUSE and CONDUIT. Solute transport is modelled using mixing equations, including an empirical retardation factor in SOIL, as well as a first order solute decay. In order to take into account some specificities commonly observed in karst systems, three parameters are added to simulate overflows, piston-type flows in conduits, and a variation of the recharge area according to the initial hydrological conditions. To validate our approach, we used the dissolved organic carbon (DOC) as tracer, which is a non- conservative compound derived from the enrichment of infiltrated water into soil humic substances. The model was applied on a small karst system at Fertans in the French Jura mountains, where discharge and continuous measurements of DOC fluorescence are recorded. The model was calibrated and validated on a set of 19 flood events, showing that the model adequately simulated hydrographs and delayed chemographs during flood events with various rainfall intensities. A large variability of the recharge area was highlighted according to low and high groundwater level periods, and was attributed to the state of hydraulic connectivity in the unsaturated zone. The model simulate the contributions of pre-event and event waters during flood events and allow to better quantify the available resource considering the mixing effect of DOC. It shows, in particular, that total discharge of some flood events during dry periods are mainly composed by pre-event water via piston flow-type processes. Finally, this study show the ability of mixing model to properly simulate solute transport taking into account degradation and retardation processes

Using IDPR to characterize recharge area of karst aquifers from catchment to regional scales

International audienceThe shape and the nature of hydrographic networks on karst environments are closely linked to the infiltration capacity of geological formations. Thus, the presence or absence of a river in a favorable topographic context can be interpreted in terms of karstic aquifers recharge potential. We present the GIS built index of infiltration and runoff properties of landscape (called IDPR) as an interesting tool for the characterization of the karst extension and for the further recharge estimation of such aquifers. A new version of the IDPR tool has been released over France in 2017 which spatial resolution (25 m) becomes very useful for the detection of contributive zones for karst aquifers recharge. Examples of the IDPR application at the river basin scale (Fontaine de Vaucluse) and at the regional scale (Rhone river basin) will be presented. Base flow estimation methods are used for the calibration of the IDPR index in terms of infiltration capacity, leading the IDPR index to be useful for recharge estimation

Nitrate and phosphorous evolution in surface water and groundwater across space and time scales – the example of the Jura Mountains

International audienceThe aim of this study is to explore the changes in water quality from local to large spatial scale and from short to long term periods, in order to better understand the fate and transport of pollutants. Our work focused on the analysis of nutrients in surface and groundwaters in the karstic catchment of the Loue river (~ 1000 km²) in the French Jura Mountains. The hydrological behavior of this large basin is highly controlled by surface water-groundwater interactions. Recurrent algae proliferation and a scarcity of species considered to be sensitive are indices of a chronic degradation of the water quality.A first analysis of long term evolution of nitrate over 45 yrs in surface water shows that the nitrate concentration in waters (mean value of 10 mg/l) is controlled mainly by a seasonal effect (from 2 to 40 mg/l). A long term component is also observed showing an increase of several mg/l from 70's to 90's and then a decrease from 2000 to present. This long-term evolution is correlated to the annual amount of synthetic fertilizers used in cultivated areas of the Jura Mountains. On the contrary to nitrate, phosphorous evolution shows no long-term trend. Changes are mostly controlled by several peaks often superior to 0.2 mg/l, and occurring more frequently during autumn.A second analysis of short-term evolution was carried out at the seasonal and event-time scales comparing concentrations and fluxes at 5 gauging stations over the catchment. This analysis showed contrasted nitrate and phosphorous evolutions depending the location. High level nitrate concentrations occurred after recharge events in autumn and winter. The nitrate decrease during spring and summer reaches in some locations the detection limit. This pattern is attributed to the biomass productivity during hottest and driest months. Regarding phosphorous evolution, erratic peaks occurred after rainfalls without their amplitude being correlated with that one of the rainfalls, meaning that it originated probably from effluents from wastewater treatment plants.Finally, these first results showed the spatial and temporal variability of water contamination by nutrients, highlighting the complex hydrological and ecological behaviour on the various sub-catchments. The spatio-temporal variability of anthropogenic activities associated with the complexity of transport processes and with the hydrological conditions are the key processes that explain these contrasting responses within the same hydrosystem

Use of continuous measurements of dissolved organic matter fluorescence in groundwater to characterize fast infiltration through an unstable fractured hillslope (Valabres rockfall, French Alps)

International audienceContinuous measurements of natural fluorescence of dissolved organic matter (DOM) in groundwater have been used to characterize infiltration through an unstable fractured hillslope at the event time scale. Within the gneissic Valabres rockfall area in the southern French Alps, two sites, in the unstable massif and in the collapse area, were continuously monitored for electrical conductivity and for DOM natural fluorescence using a field fluorometer, and analyzed weekly for hydrochemical data. Two main results were found. From a methodological point of view, DOM natural fluorescence was a relevant tracer of fast infiltration in fissured media, knowing that continuous measurements improved the study of infiltration processes at the event time scale. From a hydrogeological point of view, the unstable fractured massif showed delayed dilution phenomena and the collapse areas showed fast and slow infiltration by piston-type flows via more or less open fractures. Consequently, from this conceptual model one may suppose that, unlike the collapse zones, the fractured hillslope threatening the valley is not submitted to strong pore-water pressure variations. Des mesures en continu de la fluorescence naturelle de la matière organique dissoute (DOM) dans les eaux souterraines ont été utilisées pour caractériser l'infiltration à travers un versant fracturé instable. Dans la région gneissique de l'éboulement de Valabres dans les Alpes françaises du Sud, deux sites, dans le massif instable et dans la zone de glissement, sont suivis en continu pour des mesures de conductivité électrique et de fluorescence naturelle avec un fluorimètre de terrain, et sont l'objet de mesures hydrochimiques hebdomadaires. D'un point de vue méthodologique, la fluorescence naturelle DOM est un traceur pertinent de l'infiltration rapide en milieu fissuré, sachant que des mesures continues améliorent l'étude du processus d'infiltration à l'échelle de l'évènement. D'un point de vue hydrogéologique, le massif fracturé instable montre des phénomènes de dilution retardée et la zone de glissement montre une infiltration rapide et lente par écoulements de type piston via des fractures plus ou moins ouvertes. En conséquence, à partir de ce modèle conceptuel, on peut supposer que, à la différence des zones de glissement, la porosté de fissure dans le versant fracturé menaçant la vallée n'est pas soumise à de fortes variations de pression d'eau

Comparison of climate change impacts on the recharge of two karst systems computing different modelling approaches

International audienceKarst systems constitute aquifers in which infiltration and groundwater flows are generally complex processes and are characterized by limited knowledge in terms of geometry and structure. Nonetheless, they often represent interesting groundwater resources, some of them being subjected to intensive exploitation and others non exploited due to their poor understanding. In the future, it is likely that climate change impact on water resources will increase the interest for such a kind of aquifers due to their strong infiltration and storage capacity, in a broad context of higher water scarcity.The Lez and the Lison karst systems in Southern and Eastern France, respectively, provide 2 examples of such systems of several km² under two contrasted climate conditions, the first one being heavily exploited. This study presents a comparative climate change assessment onboth karst systems. Nine climate scenarios corresponding to the Fourth assessment report of the IPCC (SRES A1B scenario), downscaled using weather-type methods by the CERFACS, have been applied to various recharge modelling approaches, as standard analytical solutions of recharge estimation and soil-water balance models. Results are compared and discussed in order to assess the influence on climate change impacts of i) the climate conditions(geographic location), ii) the groundwater exploitation and iii) the modelling approach

SNO KARST: a French network of observatories for the multidisciplinary study of critical zone processes in karst watersheds and aquifers

Karst aquifers and watersheds represent a major source of drinking water around the world. They are also known as complex and often highly vulnerable hydrosystems due to strong surface groundwater interactions. Improving the understanding of karst functioning is thus a major issue for an efficient management of karst groundwater resources. A comprehensive understanding of the various processes can be achieved only by studying karst systems over a wide range of spatio-temporal scales under different geological, geomorphological, climatic and soil cover settings. The objective of the French Karst National Observatory Service (SNO Karst) is to supply the international scientific community with appropriate data and tools, with the ambition of i) facilitating the collection of long-term observations of hydro-geo-chemical variables in karst, and ii) promoting knowledge-sharing and developing cross-disciplinary research on karst. The present paper provides an overview of the monitoring sites and of collective achievements such as the KarstMod modular modelling platform and the PaPRIKa toolbox. It also presents the research questions addressed within the framework of SNO Karst, along with major research results regarding i) the hydrological response of karst to climate and anthropogenic changes, ii) the influence of karst on geochemical balance of watersheds in the critical zone, and iii) the relationships between the structure and hydrological functioning of karst aquifers and watersheds