Évaluation des risques de contamination des eaux de surface par les produits phytosanitaires : application à un bassin versant viticole (projet PhytoCOTE)
L'évolution de la production qualitative viticole, s'est faite durant plusieurs décennies par l'usage souvent excessif de produits phytosanitaires. L'objectif était la lutte contre les cryptogames, les ravageurs des plantes et la gestion de la concurrence des adventices concernant les éléments minéraux, l'eau, l'espace de développement. Ces pesticides, faciles à utiliser et très efficaces, ont été appliqués durant cette période de façon systématique suivant des recommandations, généralement à l'encontre de considérations agronomiques et écologiques. Mais l'usage bénéfique de ces molécules pour les agrosystèmes trouve aussi ses conséquences dans la contamination des écosystèmes et particulièrement les hydrosystèmes, ainsi que sur la santé humaine. Le projet pluridisciplinaire PhytoCOTE (agronomie, hydrobiologie, chimie environnementale, écotoxicologie, économie) étudie l'usage des produits phytosanitaires dans les agrosystèmes viticoles, leurs transferts dans les écosystèmes connexes (eau, air, sol), leur bioaccumulation et leur potentiel toxique chez les organismes aquatiques. Le site d'étude est localisé dans le Blayais, région viticole située sur la rive droite de l'estuaire de la Gironde. Les recherches ont d'abord permis d'évaluer la contribution de parcelles viticoles aux risques de contamination des eaux de surface par les produits phytosanitaires utilisés en viticulture, en tenant compte de critères descriptifs du milieu (sols, relief, connectivité des parcelles par rapport aux cours d'eau) et des pratiques viticoles (pression phytosanitaire, degré d'enherbement des parcelles, zones tampons). Des cartes de ces risques au niveau du parcellaire ont pu être établies. Parallèlement, un suivi annuel de la variabilité spatio-temporelle des concentrations en pesticides a été mis en place dans les différents compartiments environnementaux. Le suivi des cours d'eau permanents repose notamment sur le déploiement de capteurs passifs POCIS (Polar Organic Chemical Integrative Samplers) classiques à une fréquence mensuelle et de prélèvements d'eau ponctuels (bi-mensuels). L'analyse de la cartographie des risques, de la concentration en pesticides, de la modélisation des modes de conduite viticole (conventionnel, agrobiologie, agroécologie,...) et du comportement décisionnel des agriculteurs face aux choix des méthodes de protection phytosanitaire, devrait permettre d'établir des scenarii de changements de ces pratiques. Le but in fine est de proposer aux viticulteurs des mesures concrètes de nature agro-écologiques pour une réduction des usages de ces produits phytosanitaires et d'analyser comment ces mesures pourraient être influencées par les politiques publiques.
(pp. 12 p., 29/04/2026)
UR ETBX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Développement et validation d'une méthode d'analyse des chloroalcanes à chaine courte et moyenne dans le biote. Application à la détermination de l'état de contamination de tissus de poissons d'eau douce
La Directive 2013/39 /UE modifiant les Directives 2000/60/CE et 2008/105/CE concernant les substances prioritaires dans le domaine de l'eau a introduit quinze nouvelles substances prioritaires au niveau communautaire, et promulgué les normes de qualité environnementale (NQE) correspondantes. Parmi les substances récemment introduites, on trouve les chloroalcanes dits « à chaine courte » (C10 à C13), constitués de mélanges complexes de n-alcanes polychlorés, composés répondant aux critères PBT (persistants, bioaccumulables et toxiques). Ces composés, ainsi que les chloroalcanes à chaine moyenne (C14-C17) et longue (C20-C30), sont hydrophobes, chimiquement et thermiquement stables, sont ou ont été employés dans de nombreuses applications industrielles. Les données existantes suggèrent le caractère ubiquiste de ces composés produits en quantité importantes à l'échelle globale ; ces données demeurent néanmoins relativement fragmentaires en raison de la difficulté à analyser et quantifier ces composés. Les travaux réalisés dans le cadre de cette étude ont permis le développement et la validation d'une méthode de dosage des chloroalcanes à chaine longue et moyenne dans les tissus de poisson. Cette méthode repose sur l'utilisation de l'extraction assistée par micro-ondes, sur la purification des extraits organiques par chromatographie d'adsorption et sur l'utilisation de la chromatographie en phase gazeuse couplée à la spectrométrie de masse haute résolution de type « temps de vol » (résolution de 15000 à m/z = 400) pour la détection des analytes. L'optimisation de la méthode a permis l'obtention de limites de détection dans la gamme 0,03-0,4 ng.g-1 pf pour les différents groupes (CnH2n+2-zClz), compatibles avec les niveaux environnementaux attendus. L'application de cette méthode à l'analyse de tissus de poisson (barbeau) prélevés dans le bassin du Rhône a permis de confirmer le caractère ubiquiste de ces micropolluants ; dans les échantillons sélectionnés, les niveaux de MCCP (1,25 - 72,7) apparaissent 2 à 57 fois plus élevés que ceux des SCCP (0,16 - 10,6 ng.g-1 poids frais), ces derniers étant systématiquement inférieurs à la NQEbiote applicable aux SCCP (16,6 µg.g-1 pf).
(pp. 19, 29/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSTEA
On the influence of reflection over a rhythmic swash zone on surf zone dynamics
The reflection of incident gravity waves over an irregular swash zone morphology and the resulting influence on surf zone dynamics remains mostly unexplored. The wave-phase resolving SWASH model is applied to investigate this feedback using realistic low-tide terraced beach morphology with well-developed beach cusps. The rhythmic reflection generates a standing wave that mimics a subharmonic edge wave, from the superimposition of incident and two-dimensional reflected waves. This mechanism is enhanced by shore-normal, narrow-banded waves in both direction and frequency. Our study suggests that wave reflection over steep beaches could be a mechanism for the development of rhythmic morphological features such as beach cusps and rip currents.
(Ocean Dynamics. vol. 68, n° 1616-7341, pp. 899-909, 29/04/2026)
LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Quantitative comparison of taxa and taxon concepts in the diatom genus Fragilariopsis : a case study on using slide scanning, multiexpert image annotation, and image analysis in taxonomy 1
Semiautomated methods for microscopic image acquisition, image analysis, and taxonomic identification have repeatedly received attention in diatom analysis. Less well studied is the question whether and how such methods might prove useful for clarifying the delimitation of species that are difficult to separate for human taxonomists. To try to answer this question, three very similar Fragilariopsis species endemic to the Southern Ocean were targeted in this study: F. obliquecostata, F. ritscheri, and F. sublinearis. A set of 501 extended focus depth specimen images were obtained using a standardized, semiautomated microscopic procedure. Twelve diatomists independently identified these specimen images in order to reconcile taxonomic opinions and agree upon a taxonomic gold standard. Using image analyses, we then extracted morphometric features representing taxonomic characters of the target taxa. The discriminating ability of individual morphometric features was tested visually and statistically, and multivariate classification experiments were performed to test the agreement of the quantitatively defined taxa assignments with expert consensus opinion. Beyond an updated differential diagnosis of the studied taxa, our study also shows that automated imaging and image analysis procedures for diatoms are coming close to reaching a broad applicability for routine use.
(European Journal of Phycology. vol. 54, n° 0967-0262, pp. 703-719, 29/04/2026)
AWI, BAS, NERC, UNLP, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MPI-BGC
Variation of the isotopic composition of dissolved organic carbon during the runoff cycle in the Amazon River and the floodplains
Given the relative scarcity of stable isotope data on dissolved organic carbon (DOC) in the Amazon Basin, we hypothesized that the variability in DOC sources may be underestimated in such major river basins. To explore the links between the mainstem and tributaries and the floodplain, particular efforts were made during five distinct cruises at different stages of the hydrograph between October 2008 and January 2011, to document the spatial and temporal variation of DOC concentrations and δ13C-DOC in the central Amazon River system (Brazil). Based on more than 200 data, the spatial and temporal variability of δ13C-DOC values was found to be larger than previously reported in the same area. Although a small range of variation was observed throughout the hydrological cycle in the upper reach of the studied section (–29.2 to –29.5‰ in the Rio Negro and –28.7 to –29.0‰ in the Rio Solimões), a much larger one (–28.0 to –34.6‰) was found in the lower reach of the river, as the proportion of open lakes increased downstream in the floodplains. The low variability in the upper reaches suggests constant and homogeneous DOC sources from upland soils and flooded forest, while lower δ13C-DOC values recorded in the lower reach mainstem at high and falling waters can be attributed to a greater export of plankton-derived 13C-depleted DOC from flooded lakes. Noteworthy are the higher δ13C-DOC values measured in the Rio Madeira and the associated flooded lakes (–26.5 to –28.8‰), which may reflect the imprint from upland headwaters and a weaker density of flooded forest in the watershed. The higher δ13C-DOC values observed in the lower reach during low waters are still not fully understood. Floating meadows principally consisting of C4 macrophytes were found to increase δ13C-DOC values by ∼1.5‰ in their vicinity, but this impact was no longer noticeable at distances of ∼10 m from the plant rafts. This rather modest 13C-enrichment suggests rapid decomposition and/or dilution of this wetland-derived DOC.
(Comptes Rendus. Géoscience. vol. 350, n° 1631-0713, pp. 65-75, 29/04/2026)
ISTO, BRGM, INSU - CNRS, UO, CNRS, ISTO, BRGM, INSU - CNRS, UO, CNRS, UFF, GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, EES, KU Leuven, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, PSL, UVSQ, CEA, INSU - CNRS, X, IP Paris, CNES, SU, CNRS, UPCité
Le Golfe de Gascogne: zone clef pour tester les fonctions de transfert d´eriv´ees des microfossiles planctoniques
(29/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, HESAM, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS
Intraspecific trade-offs between facilitation and competition in the non-native mollusc Crepidula fornicata
We tested the hypothesis that high-density populations of the non-indigenous gastropod Crepidula fornicata increase settlement of conspecific recruits (facilitation process), and that this facilitation is balanced by competition processes. To verify our hypothesis, we sampled C. fornicata at 2 drastically different densities for 10 yr. We found that at high densities, the number of 1 yr old individuals per square meter colonizing the habitat and individual growth performances were higher in comparison with the low-density condition (Allee effect). In contrast, the production/biomass ratio (P/B), a good indicator of population fitness, was lower at higher densities. We relate this lower P/B ratio to the deficit of young individuals compared to adult biomass. We conclude that the net effect of high density on the conspecific colonization processes of the population is positive, thanks to the higher available hard substrate for larvae (facilitation). However, intraspecific competition also occurs and mitigates this positive effect. Therefore, we suggest that it is particularly important to take into account the ‘net’ balance between costs and benefits (i.e. what we observe) when analyzing population growth, in order to better understand its dynamics.
(Marine Ecology Progress Series. vol. 604, n° 0171-8630, pp. 163-171, 29/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMN, UMN
Microbial Dark Matter Investigations: How Microbial Studies Transform Biological Knowledge and Empirically Sketch a Logic of Scientific Discovery
Microbes are the oldest and most widespread, phylogenetically and metabolically diverse life forms on Earth. However, they have been discovered only 334 years ago, and their diversity started to become seriously investigated even later. For these reasons, microbial studies that unveil novel microbial lineages and processes affecting or involving microbes deeply (and repeatedly) transform knowledge in biology. Considering the quantitative prevalence of taxonomically and functionally unassigned sequences in environmental genomics data sets, and that of uncultured microbes on the planet, we propose that unraveling the microbial dark matter should be identified as a central priority for biologists. Based on former empirical findings of microbial studies, we sketch a logic of discovery with the potential to further highlight the microbial unknowns.
(Genome Biology and Evolution. vol. 10, n° 1759-6653, pp. 707 - 715, 29/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, AIRE, UAG, UPMC, UNS, CNRS
High-Content Screening of Plankton Alkaline Phosphatase Activity in Microfluidics
One way for phytoplankton to survive orthophosphate depletion is to utilize dissolved organic phosphorus by expressing alkaline phosphatase. The actual methods to assay alkaline phosphate activity—either in bulk or as a presence/absence of enzyme activity—fail to provide information on individual living cells. In this context, we develop a new microfluidic method to compartmentalize cells in 0.5 nL water-in-oil droplets and measure alkaline phosphatase activity at the single-cell level. We use enzyme-labeled fluorescence (ELF), which is based on the hydrolysis of ELF-P substrate, to monitor in real time and at the single-cell level both qualitative and quantitative information on cell physiology (i.e., localization and number of active enzyme sites and alkaline phosphatase kinetics). We assay the alkaline phosphatase activity of Tetraselmis sp. as a function of the dissolved inorganic phosphorus concentration and show that the time scale of the kinetics spans 1 order of magnitude. The advantages of subnanoliter-scale compartmentalization in droplet-based microfluidics provide a precise characterization of a population with single-cell resolution. Our results highlight the key role of cell physiology to efficiently access dissolved organic phosphorus.
(Analytical Chemistry. vol. 90, n° 0003-2700, pp. 4174 - 4181, 29/04/2026)
CRPP, UB, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Unraveling the forcings controlling the vegetation and climate of the best orbital analogues for the present interglacial in SW Europe
The suitability of MIS 11c and MIS 19c as analogues of our present interglacial and its natural evolution is still debated. Here we examine the regional expression of the Holocene and its orbital analogues over SW Iberia using a model-data comparison approach. Regional tree fraction and climate based on snapshot and transient experiments using the LOVECLIM model are evaluated against the terrestrial-marine profiles from Site U1385 documenting the regional vegetation and climatic changes. The pollen-based reconstructions show a larger forest optimum during the Holocene compared to MIS 11c and MIS 19c, putting into question their analogy in SW Europe. Pollen-based and model results indicate reduced MIS 11c forest cover compared to the Holocene primarily driven by lower winter precipitation, which is critical for Mediterranean forest development. Decreased precipitation was possibly induced by the amplified MIS 11c latitudinal insolation and temperature gradient that shifted the westerlies northwards. In contrast, the reconstructed lower forest optimum at MIS 19c is not reproduced by the simulations probably due to the lack of Eurasian ice sheets and its related feedbacks in the model. Transient experiments with time-varying insolation and CO2 reveal that the SW Iberian forest dynamics over the interglacials are mostly coupled to changes in winter precipitation mainly controlled by precession, CO2 playing a negligible role. Model simulations reproduce the observed persistent vegetation changes at millennial time scales in SW Iberia and the strong forest reductions marking the end of the interglacial "optimum".
(Climate Dynamics. vol. 51, n° 0930-7575, pp. 667-686, 29/04/2026)
EPHE, PSL, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS