Carbon fixation and emission within dense aquatic weed mats of a temperate shallow lake
Dense aquatic weed mats are likely to enhance oxygen depletion and build-up of organic matter. As a result of a thick biomass layer, water flow is reduced and hypoxic conditions prevail; the imbalance between aerobic and anaerobic processes can influence the net ecosystem metabolism and its carbon budget. We here present results from a multi-year investigation (2013-2015) carried out on a mesotrophic shallow lake of south-west of France (Lacanau Lake), where 10% of surface is occupied by dense beds of Egeria densa and Lagarosiphon major. Investigations were carried out through multiple approaches, such as 24h-cycle water collection, GIS mapping, growth rates measurements and sedimentary organic matter assessment. Results from this study revealed that, thanks to advantageous hydrodynamics local conditions (strong wind), those plants do not necessarily trigger water stagnation and hypoxia. Nevertheless, their fast growth generates the accumulation of a huge quantity of labile litter, which feeds respiration processes and methanogenesis on the bottom of the macrophytes bed. Our study underlines that dense aquatic weed mats may constitute important hotspots for greenhouse gases emissions at our latitude, notably enhanced by mild temperature and strong irradiation all over the year.
(pp. 17, 23/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Radar altimetry backscattering signatures at Ka, Ku, C, and S bands over West Africa
This study presents a comprehensive comparison of radar altimetry signatures at Ka-, Ku-, C-, and S-bands using SARAL, ENVISAT and Jason-2 data over the major bioclimatic zones, soil and vegetation types encountered in West-Africa, with an emphasis on the new information at Ka-band provided by the recently launched SARAL–Altika mission. Spatio-temporal variations of the radar altimetry responses were related to changes in surface roughness, land cover and soil wetness. Analysis of time series of backscattering coefficients along the West African bioclimatic gradient shows that radar echoes at nadir incidence are well correlated to soil moisture in semi-arid savannah environments. Radar altimeters are able to detect the presence of water even under a dense canopy cover at all frequencies. But only measurements at Ka-band are able to penetrate underneath the canopy of non-inundated tropical evergreen forests.
(Physics and Chemistry of the Earth. Parts A/B/C. vol. 83-84, n° 1474-7065, pp. 96-110, 23/04/2026)
GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, USTTB
Atlas des diatomées des eaux douces de la Réunion
L’ile de la Réunion, de par son caractère insulaire et son isolement, présente de grandes particularités des assemblages biologiques, doublée d’un fort taux d’endémisme. Les diatomées des cours d’eau ne font pas exception à ce constat, et étaient fortement méconnues jusqu’à un passé récent. Or la connaissance des espèces présentes et de leur écologie est le premier pas pour leur protection face aux pollutions et aux pressions qui s’exercent sur leurs habitats. Un programme de recherche-développement financé par l’Office de l’Eau de la Réunion, la DEAL Réunion, le FEDER et l’ONEMA a été lancé à partir de 2008 et a duré jusqu’à fin 2013. Il a été conduit par le consortium Asconit-Cemagref (devenu depuis Irstea). Le but était d’identifier les espèces diatomiques locales, de les nommer, de leur affecter une écologie et une écologie de l’altération, de fonder un nouvel indice diatomique adapté à l’évaluation des cours d’eau de la Réunion (l’IDR) et de transférer cette nouvelle méthode avec la production des documents et outils d’accompagnement (guide méthodologique, guide taxonomique, outil de calcul sous R et sa notice d’utilisation etc. Au cours de ce programme, 343 taxons ont pu être identifiés ou reconnus à l’espèce, certains non trouvés dans la littérature taxonomique mondiale se voyant affecter un code de genre et un numéro d’espèce. Le présent Atlas taxonomique édité par l’Office de l’Eau de la Réunion contient un grand nombre de fiches-taxons décrivant la plupart de ces espèces locales, avec des indications morphologiques et des supports iconographiques au microscope optique et électronique permettant de les reconnaître et de les déterminer : des cartes chorologiques permettant de résumer à quels sites ou dans quels cours d’eau on les trouve, de façon différenciée aux deux saisons ; et enfin, des figurations permettant de situer et de résumer leurs caractéristiques autoécologiques par rapport à des variables abiotiques naturelles et à d’autres sous forte influence des altérations anthropiques.
(pp. 230, 23/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse
Climbing experience in glass eels: a cognitive task or a matter of physical capacities?
The European eel is a panmictic species, whose decline has been recorded since the last 30 years. Among human induced environmental factors of decline, the impact of water dams during species migration is questioned. Indeed, water impoundments can be a severe obstacle for young eels trying to reach the upstream freshwater zones, even if they are equipped with fish-friendly passes. The passage by such devices could be an important event shaping the outcome of the future life and life history traits of eels. We studied what phenotypic traits were associated with the event of experience of passage by water obstacles. We analyzed specific enzyme activities and/or gene transcription levels in the muscle and brain to test whether the obstacle passage is rather a physical or cognitive task.Wefound that after a long period of maintenance under homogenous conditions, transcription levels of several genes linked to synaptic plasticity, neurogenesis and thyroid activity differed among the field-experience groups. In contrast, muscle gene transcription levels or enzymatic activities did not show any differences among fish groups.We suggest that cognitive processes such as learning and memory acquisition rather than swimming-related metabolic capacities are involved in passage of water obstacles by young eels.
(Physiology & behavior. vol. 151, n° 0031-9384, pp. 448-455, 23/04/2026)
UR EABX, IRSTEA, SEEM, UT3, Comue de Toulouse, CNRS, EDB, IRD, UT3, Comue de Toulouse, CNRS, EDF [E.D.F.], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Evaluation technique, économique et environnementale de procédés de traitement complémentaire avancés pour l’élimination des micropolluants
Cet article documente l’élimination de 64 micropolluants (15 métaux et 49 substances organiques) par 5 procédés de traitement complémentaire : adsorption sur charbon actif en grain, ozone, ozone/ H2O2, ozone/UV et UV/H2O2. Des méthodes analytiques validées ont été mises en ½uvre, avec de faibles limites de quantification (i.e. proches du nanogramme par litre) et des incertitudes maîtrisées. Les traitements complémentaires étudiés aux conditions d’application utilisées ont été trouvés efficaces pour l’élimination de la plupart des micropolluants quantifiés dans cette étude, excepté les métaux. Le charbon actif et l’ozone ont permis d’éliminer à plus de 70% plus de 2/3 des substances organiques quantifiées dans cette étude. L’ajout de peroxyde d’hydrogène à l’ozone a augmenté le nombre de substances bien éliminées (Rw>70%), mais n’a pas permis d’augmenter le rendement d’élimination des substances réactives à l’ozone. Les autres POA (ozone/H2O2 et UV/H2O2) n’ont pas permis d’augmenter le nombre de substances organiques bien éliminées par rapport à l’ozone seul. Les 5 technologies étudiées ont été dimensionnées à pleine échelle afin d’évaluer leurs coûts d’investissement et d’exploitation pour deux tailles de STEU différentes. Selon cette étude, la mise en place de traitements complémentaires intensifs sur une STEU de 60 000 ou de 200 000 EH entraînerait un surcoût de traitement d’environ 2 à 20 centimes d’euros par m3 traité, selon la technologie mise en place, la liste des substances choisie et l’objectif visé.
(TSM. Techniques Sciences Méthodes – Génie urbain, génie rural, n° 0299-7258, pp. 67-83, 23/04/2026)
IRSTEA, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR MALY, IRSTEA
Stratification of surface waters during the last glacial millennial climatic events: a key factor in subsurface and deep-water mass dynamics
The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich and Dansgaard–Oeschger events. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high-resolution analyses were conducted on the 12–42 ka BP section of core MD99-2281 retrieved southwest of the Faeroe Islands, and combined with analyses conducted in two previous studies (Zumaque et al., 2012; Caulle et al., 2013). Such a multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep-water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials, while surface conditions progressively deteriorate throughout these cold episodes; conversely, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes, with progressively milder surface conditions and gradual intensification of the deep circulation, while the vigor of the subsurface northward Atlantic flow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HSs): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation during the middle of the event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.
(Climate of the Past. vol. 11, n° 1814-9324, pp. 1507-1525, 23/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UQAM, IFREMER, LDO, INSU - CNRS, UBO EPE, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Spatial heterogeneity of benthic biogeochemistry in two contrasted marine environments (Arcachon Bay and Bay of Biscay, SW France)
We have studied the heterogeneity of vertical profiles of biogeochemical components obtained from sediment core slicing. Sediment cores were collected in the intertidal zone of the Arcachon Bay and on the continental slope of the Bay of Biscay, at 550 and 1000 m depth. At each station of the Arcachon Bay, five 1 m-side zones were delimited at low tide. In each square, 3 cores were collected. Spatial heterogeneity on the continental slope was obtained from the study of 3 cores of multi-corer while 2 or 3 multi-corer deployments were used during the same oceanographic cruise. Similarity between profiles was determined to estimate the spatial heterogeneity at different scales. In the Arcachon Bay, results showed a spatial heterogeneity at a decimetre scale on apparently homogeneous areas. Despite the spatial variability, all the replicated profiles in Arcachon Bay sediments had similar trends, suggesting homogeneous benthic properties. However, a sampling with replicate cores handling is required for seasonal monitoring or study of biogeochemical mechanisms in coastal environments. We observe that the spatial variability on the continental margin of the Bay of Biscay is lower than in coastal environment of the Arcachon Bay. Heterogeneity is equivalent at a decimetre scale and at a hundred meters scale, which is the precision of the sampling positioning due to the drift of the boat and the tilt of the corer cable. In addition, our 10-year-long database for the Bay of Biscay showed that differences in the shape of profiles obtained in sediment cores collected at the same stations throughout this long period may not be interpreted in terms of evolution with time, because the observed variability is as high as the spatial heterogeneity.
(Estuarine, Coastal and Shelf Science, n° 0272-7714, pp. 51–65, 23/04/2026)
BIAF, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Programme PIREN-Seine - Phase 6 Axe 4 : « Ecologie & Ecotoxicologie » Les déterminants de la qualité écologique du milieu aquatique
Les organismes vivants dans le milieu aquatique sont soumis à de multiples pressions combinées : chimique, hydro- morphologique, thermique, trophique (matière organique, eutrophisation...), qui impactent, et éventuellement perturbent leur fonctionnement. La santé des individus qui composent la biocénose peut aussi être altérée par ces différentes pressions. S'il est possible de faire des relations causales entre une pression et une réponse biologique, l'enjeu aujourd'hui est de pouvoir prédire les conséquences sur les différentes composantes de la biocénose de l'ensemble des pressions qui interagissent. L'observation des organismes vivants, à différents niveaux d'organisation (la cellule, l'organe, l'organisme, la population, ou la communauté) est proposée depuis plusieurs années pour renseigner sur l'état de santé des organismes, des communautés (bio- indication de type DCE), sur l'état écologique global du milieu, ou sur l'impact des contaminants chimiques (biomarqueurs en écotoxicologie). Au cours de la phase 6 PIREN -Seine, nous avons étudié à la fois comment les observations faites sur la biocénose peuvent nous renseigner sur les impacts des différentes pressions, y compris la pression chimique (domaine de l'écotoxicologie), mais aussi comment la multiplicité de ces pressions (caractéristique d'un bassin versant très anthropisé comme l'est celui de la Seine), ou les modifications de ces pressions, impactent le vivant.
(pp. 172, 23/04/2026)
SEBIO, INERIS, URCA, ULH, NU, URCA, CNRS, UR HBAN, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULB, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LSPE - UP-S, UR MALY, IRSTEA
La restauration écologique comme nouveau paradigme d'aménagement ?
Bien que les politiques aménagistes aient permis d'améliorer la maîtrise globale des fleuves, elles ont également généré de nombreuses perturbations et altérations. Aujourd'hui, la restauration des cours d'eau fait l'objet de nouvelles expérimentations. Dans le sud-ouest de la France, sur le fleuve Garonne et l'estuaire de la Gironde, elles se traduisent notamment par des remises en eau des marais liées au passage de tempêtes (dynamique de dépoldérisation). Plus en amont, dans la moyenne Garonne toulousaine, les réflexions en cours concernent la réouverture de bras morts ou la création de zones d'expansion de crues. Nous proposons, de questionner l'émergence de ce nouveau paradigme, dans une perspective pluridisciplinaire, par une évaluation géohistorique, géochimique, écologique et sociologique.
(Cahiers de géographie du Québec. vol. 59, n° 0007-9766, pp. 293-314, 23/04/2026)
GEODE, UT2J, Comue de Toulouse, CNRS, UR ETBX, IRSTEA, UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS
Rapid longitudinal migrations of the filament front off Namibia (SE Atlantic) during the past 70 kyr
Although productivity variations in coastal upwelling areas are mostly attributed to changes in wind strength, productivity dynamics in the Benguela Upwelling System (BUS) is less straightforward due to its complex atmospheric and hydrographic settings. In view of these settings, past productivity variations in the BUS can be better investigated with downcore sediments representing different productivity regimes. In this study, two sediment cores retrieved at ca. 25°-26°S in the BUS and representing different productivity regimes were studied. By using micropaleontological, geochemical and temperature proxies measured on core MD96-2098, recovered at 2910 m water depth in the bathypelagic zone at 26°S off Namibia, variations of filament front location, productivity and temperature in the central BUS over the past 70 kyr were reconstructed. The comparison with newly-generated alkenone-based sea-surface temperature (SST) and previously obtained data at site GeoB3606-1 (~ 25°S; ca. 50 km shoreward from MD96-2098) allowed the recognition of four main phases: (1) upwelling front above the mid slope (70 kyr-44 kyr), (2) seaward displacement of the upwelling front beyond the mid slope (44 kyr-31 kyr), (3) main upwelling front over the hemipelagial (31 kyr-19 kyr), and (4) shoreward contraction of the upwelling filament, and decreased upwelling strength over most of the uppermost bathypelagic (19 kyr-6 kyr). The latitudinal migration of the Southern Hemisphere westerlies and the consequent contractions and expansions of the subpolar gyre played a significant role in millennial and submillennial variability of SST off Namibia. The strength of the southeasterly trade winds, rapid sea-level variations and the equatorward leakage of Antarctic silicate might have acted as amplifiers. Although late Quaternary variations of productivity and upwelling intensity in eastern boundary current systems are thought to be primarily linked to the variability in wind stress, this multi-parameter reconstruction shows that interplaying mechanisms defined the temporal variation pattern of the filament front migrations and the diatom production off Namibia during the past 70 kyr.
(Global and Planetary Change. vol. 125, n° 0921-8181, pp. 1-12, 23/04/2026)
IACT, CSIC, UGR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NIOZ, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS