Light-driven processes: key players of the functional biodiversity in microalgae

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Halogénures de lanthane dopés cérium (des scintillateurs rapides pour l'imagerie médicale)

Ce travail concerne l étude de cristaux scintillateurs inorganiques découverts récemment : LaCl3:Ce3+ et LaBr3:Ce3+, caractérisés par une réponse rapide, un rendement lumineux élevé et une excellente résolution énergétique, et particulièrement intéressants pour l imagerie médicale. La forte hygroscopie de ces matériaux nécessite l adaptation des modes opératoires habituels pour la détermination des caractéristiques physico-chimiques.. La bonne compréhension du mécanisme de scintillation et de l effet des défauts présents dans le matériau permet d envisager des pistes pour l optimisation des performances du scintillateur. Dans ce sens, plusieurs techniques sont utilisées (RPE, radioluminescence, excitation laser, thermoluminescence,...). La connaissance des divers processus impliqués dans le mécanisme de scintillation conduit à prévoir l effet de la température et du taux de dopage sur les performances du scintillateur.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Evaluating downscaling methods of GRACE (Gravity Recovery and Climate Experiment) data: a case study over a fractured crystalline aquifer in southern India

International audienceGRACE (Gravity Recovery and Climate Experiment) and its follow-on mission have provided since 2002 monthly anomalies of total water storage (TWS), which are very relevant to assess the evolution of groundwater storage (GWS) at global and regional scales. However, the use of GRACE data for groundwater irrigation management is limited by their coarse (≃300 km) resolution. The last decade has thus seen numerous attempts to downscale GRACE data at higher – typically several tens of kilometres – resolution and to compare the downscaled GWS data with in situ measurements. Such comparison has been classically made in time, offering an estimate of the static performance of downscaling (classic validation). The point is that the performance of GWS downscaling methods may vary in time due to changes in the dominant hydrological processes through the seasons. To fill the gap, this study investigates the dynamic performance of GWS downscaling by developing a new metric for estimating the downscaling gain (new validation) against non-downscaled GWS. The new validation approach is tested over a 113 000 km2 fractured granitic aquifer in southern India. GRACE TWS data are downscaled at 0.5∘ (≃50 km) resolution with a data-driven method based on random forest. The downscaling performance is evaluated by comparing the downscaled versus in situ GWS data over a total of 38 pixels at 0.5∘ resolution. The spatial mean of the temporal Pearson correlation coefficient (R) and the root mean square error (RMSE) are 0.79 and 7.9 cm respectively (classic validation). Confronting the downscaled results with the non-downscaling case indicates that the downscaling method allows a general improvement in terms of temporal agreement with in situ measurements (R=0.76 and RMSE = 8.2 cm for the non-downscaling case). However, the downscaling gain (new validation) is not static. The mean downscaling gain in R is about +30 % or larger from August to March, including both the wet and dry (irrigated) agricultural seasons, and falls to about +10 % from April to July during a transition period including the driest months (April–May) and the beginning of monsoon (June–July). The new validation approach hence offers for the first time a standardized and comprehensive framework to interpret spatially and temporally the quality and uncertainty of the downscaled GRACE-derived GWS products, supporting future efforts in GRACE downscaling methods in various hydrological contexts

Indicator of Flood-Irrigated Crops From SMOS and SMAP Soil Moisture Products in Southern India

Spaceborne L-band data have the potential to monitor flooded and irrigated areas. However, further studies are needed to assess in real cases the impact of flood-irrigated crops on soil moisture and ocean salinity (SMOS) and soil moisture active passive (SMAP) surface soil moisture (SSM) data. This letter demonstrates the ability of SMOS/SMAP SSM retrievals to quantify the fraction of flood-irrigated areas at the seasonal scale and at a 25-km resolution in the Telangana State in southern India. Over irrigated areas, both SMOS level 3 (L3) SSM and SMAP L3 enhanced SSM products present a bimodal annual cycle, with a peak of SSM during the monsoon (wet) season corresponding to rainfall and irrigation, and a peak during the dry season due to irrigation activities solely. The second peak is absent or has a very small amplitude in areas where rice represents a small fraction (typically below 5%–10%). More importantly, the amplitude of the second SSM peak is significantly correlated with the rice cover fraction within 25×25 km2 pixels ( R=0.81 for SMOS and 0.77 for SMAP), showing its potential to assess crop fraction and hence the water used for irrigation. The SMOS/SMAP L3 SSM peak during the dry period occurs several months before the harvest, constituting an indicator for rice stocks at the end of the season. However, the irrigation signature is absent from the SMAP level 4 SSM product derived from the assimilation of SMAP brightness temperatures (Tbs) in a land surface model, which indicates that the data assimilation scheme is inefficient to restitute irrigation information

Recharge heterogeneity at the catchment scale in fractured crystalline rock aquifers

International audienceFactors governing recharge in fractured crystalline rock aquifers are poorly understood. It is unclear whether recharge is primarily controlled by the properties of the heterogeneous underlying aquifer or the overlying soil characteristics, which can also be strongly heterogeneous. Further, in semi-arid and arid environments, soil properties vary strongly and non-linearly as a function of soil moisture. Soil moisture is controlled in part by soil water retention properties and rainfall intensity, but also, increasingly, by land use and human influence. Current large-scale hydrological models often do not account for heterogeneity and the nonlinear variability of soil hydraulic properties. The aim of this study is to identify and quantify the driving forces that shape spatial recharge patterns in crystalline rock aquifers, while critically assessing the models used, model uncertainty and parameter sensibility.Reference recharge maps were obtained previously by applying an improved water table fluctuation (WTF) technique to a well-characterized and continuously monitored catchment in South India at a 685x685m scale (a scale at which underground lateral transfers are assumed to be negligible). Land use maps, irrigation practices, soil maps and associated hydraulic properties are well documented from previous studies. The first step of this study was to calibrate a simple soil moisture balance model (SMBM) against WTF recharge estimates, but it quickly became apparent that assuming constant hydraulic properties for the whole observation period lead to over- or underestimation of recharge relative to soil moisture conditions. Thus, in a second stage, a very simple pseudo-2D physically based unsaturated flow model was applied at a 100x100m scale. This permitted the model to incorporate time-variable water retention properties, and smaller-scale land use and soil type patterns. It was found that land use had a strong effect on recharge, more than soil type distribution. Soils which are kept flooded for rice cultivation are generally poorly transmissive, although, counter-intuitively, these act as zones of enhanced recharge. This is due to their high water content, which increases the effective soil permeability. Parameter uncertainty and the possible existence of lateral transfers are also discussed

Assimilation of the plutonic roots of the Andean arc controls variations in U-series disequilibria at Volcan Llaima, Chile

U-series disequilibria provide important constraints on the processes and time scales of melt production, differentiation, and transport in subduction settings. Such constraints, which are essential for understanding the chemical evolution of the continental crust, are conventionally based on the assumption that the U-series disequilibria measured in mafic lavas are produced during mantle metasomatism and melting, and that intracrustal differentiation and assimilation have limited impacts. Here we show that mantle-derived U-series disequilibria in mafic lavas erupted at Volcán Llaima, Chile are significantly diminished by assimilation of plutonic rocks forming Llaima's subvolcanic basement. This contamination process is extremely subtle in terms of “classical” indicators of crustal assimilation like Sr, Nd or Pb isotopes because it is a manifestation of assimilative recycling of the plutonic roots of the arc. This process results in variations in U-series disequilibria and incompatible trace element ratios that are significant compared to regional and global variability in arc magmas. Furthermore, it yields linear correlations between U-series excesses and incompatible trace element ratios that are generally interpreted as slab-fluid indicators and chronometers, or tracers of sediment recycling in subduction zone. Cannibalization of ancestral magmas by ascending melts warrants careful evaluation when considering the components and chemical fluxes in subduction zones. Linear arrays defined by activity ratios of U-series nuclides with different half-lives may be the most reliable indicators of assimilative recycling of ancestral intrusive magmas

Natural recharge heterogeneity at the catchment scale, in fractured crystalline rock aquifers

International audienceFactors governing recharge in fractured crystalline rock aquifers are poorly understood. It is unclear whether recharge is primarily controlled by the properties of the heterogeneous underlying aquifer or the overlying soil characteristics, which can also be strongly heterogeneous. Further, in semi-arid and arid environments, soil properties vary strongly and non-linearly as a function of soil moisture. Soil moisture is controlled in part by soil water retention properties and rainfall intensity, but also, increasingly, by land use and human influence. Current large-scale hydrological models often do not account for heterogeneity and the nonlinear variability of soil hydraulic properties. The aim of this study is to identify and quantify the driving forces that shape spatial recharge patterns in crystalline rock aquifers, while critically assessing the models used, model uncertainty and parameter sensibility. Reference recharge maps were obtained previously by applying an improved water table fluctuation (WTF) technique to a well-characterized and continuously monitored catchment in South India at a 685x685m scale (a scale at which underground lateral transfers are assumed to be negligible). Land use maps, irrigation practices, soil maps and associated hydraulic properties are well documented from previous studies. The first step of this study was to calibrate a simple soil moisture balance model (SMBM) against WTF recharge estimates, but it quickly became apparent that assuming constant hydraulic properties for the whole observation period lead to over- or underestimation of recharge relative to soil moisture conditions. Thus, in a second stage, a very simple pseudo-2D physically based unsaturated flow model was applied at a 100x100m scale. This permitted the model to incorporate time-variable water retention properties, and smaller-scale land use and soil type patterns. It was found that land use had a strong effect on recharge, more than soil type distribution. Soils which are kept flooded for rice cultivation are generally poorly transmissive, although, counter-intuitively, these act as zones of enhanced recharge. This is due to their high water content, which increases the effective soil permeability. Parameter uncertainty and the possible existence of lateral transfers are also discussed

Impact of sub-horizontal discontinuities and vertical heterogeneities onrecharge processes in a weathered crystalline aquifer in southern India

International audienceIn the face of increasing demands for irrigated agriculture, many states in India are facing water scarcity issues,leading to severe groundwater depletion. Because perennial water resources in southern India consist mainly ofcrystalline aquifers, understanding how recharge takes place and the role of preferential flow zones in such het-erogeneous media is of prime importance for successful and sustainable aquifer management. Here we investigatehow vertical heterogeneities and highly transmissive sub-horizontal discontinuities may control groundwater flowsand recharge dynamics. Recharge processes in the vadose zone were examined by analysing the propagation ofan infiltration front and mass transfers resulting from the implementation of a managed aquifer recharge (MAR)structure. Said structure was set up in the Experimental Hydrogeological Park in Telangana (Southern India), awell-equipped and continuously monitored site, which is periodically supplied with surface water deviated fromthe nearby Musi river, downstream of Hyderabad.An initial volume balance equation was applied to quantify the overall inputs from the MAR structure intothe groundwater system, which was confirmed using a chloride mass balance approach. To understand how thisincoming mass is then distributed within the aquifer, we monitored the evolution of water volumes in the tank, andthe resulting lateral propagation front observed in the surrounding borehole network. Borehole logs of temperatureand conductivity were regularly performed to identify preferential flow paths. As a result we observed that masstransfers take place in the way of preferential lateral flow through the most transmissive zones of the profile.These include the interface between the lower portion of the upper weathered horizon (the saprolite) and theupper part of the underlying fissured granite, as well as the first flowing fractures. This leads to a rapid lateraltransfer of recharge, which allows quick replenishment of aquifers but may have severe implications regardinggroundwater quality, whether contaminants originate from diffuse sources (such as fertilizers), or a localizedinjection of polluted surface water. These findings confirm previous studies about the non-linear behaviour ofhard rock aquifers (Guihéneuf et al., 2014) and recharge processes (Boisson et al., 2015; Alazard et al., 2015).Depending on water level conditions, the aquifer shifts from a regional flow system (when superficial moreconnected and weathered levels are saturated), to independent local flow systems (when only the lower lesserfractured portion is saturated). Thus recharge seems to be controlled by the existence of (i) vertical heterogeneitieswithin the unsaturated zone and (ii) highly transmissive sub-horizontal discontinuities, both of which controllinggroundwater flows and recharge dynamics

Delineation of groundwater potential zones using non-invasive techniques to improve conceptual modelling of recharge in a non-instrumented weathered crystalline aquifer in South India

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