Comparison of kernel density estimators with assumption on number of modes
A data-driven bandwidth choice for a kernel density estimator called critical bandwidth is investigated. This procedure allows the estimation to have as many modes as assumed for the density to estimate. Both Gaussian and uniform kernels are considered. For the Gaussian kernel, asymptotic results are given. For the uniform kernel, an argument against these properties is mentioned. These theoretical results are illustrated with a simulation study which compare the kernel estimators that rely on critical bandwidth with another one which uses a plug-in method to select its bandwidth. An estimator that consists in estimates of density contour clusters and takes assumptions on number of modes into account is also considered. Finally, the methodology is illustrated using environment monitoring data.
(Communications in Statistics - Simulation and Computation. vol. 44, n° 0361-0918, pp. 196-216, 23/06/2026)
IMB, UB, Bordeaux INP, CNRS, CQFD, IMB, UB, Bordeaux INP, CNRS, Inria, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LMBA, UBS, UBO EPE, CNRS
Specific Effects of Dietary Methylmercury and Inorganic Mercury in Zebrafish (Danio rerio) Determined by Genetic, Histological, and Metallothionein Responses
A multidisciplinary approach is proposed here to compare toxicity mechanisms of methylmercury (MeHg) and inorganic mercury (iHg) in muscle, liver, and brain from zebrafish (Danio rerio). Animals were dietary exposed to (1) 50 ng Hg g-1, 80% as MeHg; (2) diet enriched in MeHg 10000 ng Hg g-1, 95% as MeHg; (3) diet enriched in iHg 10000 ng Hg g-1, 99% as iHg, for two months. Hg species specific bioaccumulation pathways were highlighted, with a preferential bioaccumulation of MeHg in brain and iHg in liver. In the same way, differences in genetic pattern were observed for both Hg species, (an early genetic response (7 days) for both species in the three organs and a late genetic response (62 days) for iHg) and revealed a dissimilar metabolization of both Hg species. Among the 18 studied genes involved in key metabolic pathways of the cell, major genetic responses were observed in muscle. Electron microscopy revealed damage mainly because of MeHg in muscle and also in liver tissue. In brain, high MeHg and iHg concentrations induced metallothionein production. Finally, the importance of the fish origin in ecotoxicological studies, here the seventh descent of a zebrafish line, is discussed. © 2015 American Chemical Society.
(Environmental Science and Technology. vol. 49, n° 0013-936X, pp. 14560--14569, 23/06/2026)
IPREM, UPPA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPREM, UPPA, INC-CNRS, CNRS, LCABIE, UPPA, CNRS
The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO2 fluxes in a tropical hydropower reservoir
Abundant research has been devoted to understanding the complexity of the biogeochemical and physical processes that are responsible for greenhouse gas (GHG) emissions from hydropower reservoirs. These systems may have spatially complex and heterogeneous GHG emissions due to flooded biomass, river inflows, primary production and dam operation. In this study, we investigated the relationships between the water–air CO2 fluxes and the phytoplanktonic biomass in the Funil Reservoir, which is an old, stratified tropical reservoir that exhibits intense phytoplankton blooms and a low partial pressure of CO2 (pCO2). Our results indicated that the seasonal and spatial variability of chlorophyll concentrations (Chl) and pCO2 in the Funil Reservoir are related more to changes in the river inflow over the year than to environmental factors such as air temperature and solar radiation. Field data and hydro\\-dynamic simulations revealed that river inflow contributes to increased heterogeneity during the dry season due to variations in the reservoir retention time and river temperature. Contradictory conclusions could be drawn if only temporal data collected near the dam were considered without spatial data to represent CO2 fluxes throughout the reservoir. During periods of high retention, the average CO2 fluxes were 10.3 mmol m−2 d−1 based on temporal data near the dam versus −7.2 mmol m−2 d−1 with spatial data from along the reservoir surface. In this case, the use of solely temporal data to calculate CO2 fluxes results in the reservoir acting as a CO2 source rather than a sink. This finding suggests that the lack of spatial data in reservoir C budget calculations can affect regional and global estimates. Our results support the idea that the Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in the river inflow and retention time are potentially a more important force driving both the Chl and pCO2 spatial variability than the in-system ecological factors.
(Biogeosciences. vol. 12, n° 1726-4170, pp. 147-162, 23/06/2026)
INPE, MCTI, UFIJ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Quels micropolluants peut-on éliminer par les procédés extensifs de traitement des eaux usées domestiques ?
Cet article documente l’élimination de 59 micropolluants (16 métaux et 43 micropolluants organiques) par différentes procédés de traitement extensifs, construits en traitement secondaire ou en traitement complémentaire. Les eaux brutes et traitées de 5 stations de traitement des eaux usées des zones rurales ou péri-urbaines ont été étudiées par temps sec à l’aide d’échantillons prélevés avec du matériel spécifique. 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. En traitement secondaire, la moitié des rendements obtenus sont supérieurs à 70% dès lors qu'un traitement biologique avec nitrification et une élimination des matières en suspension sont appliqués. Les valeurs de rendements obtenues pour les différents procédés extensifs étudiés sont voisines de celles déterminées pour les boues activées aération prolongée. Concernant les traitements complémentaires, les deux procédés extensifs classiques (filtres horizontaux à gravier ou apatite) étudiés, ainsi que le fossé (temps de séjour de 10 min), ont une contribution très faible dans le traitement des micropolluants réfractaires aux traitements secondaires. L’élimination de ces micropolluants nécessite des procédés spécifiques avec des temps de séjour élevés pour mobiliser la photodégradation naturelle, ou avec l’utilisation de matériaux adsorbants. L’argile expansée est efficace à faible niveaux de concentration, tandis que celle de la zéolite clinoptilolite s’avère intéressante lorsque les micropolluants sont présents à fortes concentrations. Malgré leur faible coût d’achat, mais du fait du temps de séjour élevé nécessaire et de la capacité d’adsorption assez faible, le calcul technico-économique reste favorable au charbon actif en grain pour une utilisation de tels matériaux dans des filtres horizontaux. Nos futures recherches visent à étudier les processus impliqués pour l’élimination des micropolluants dans les zones de rejet végétalisées.
(TSM. Techniques Sciences Méthodes, n° 0299-7258, pp. 51-66, 23/06/2026)
UR MALY, IRSTEA, UR REVERSAAL, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The coccolithophores Emiliania huxleyi and Coccolithus pelagicus: Extant populations from the Norwegian–Iceland Seas and Fram Strait
The distributions of the coccolithophore species Emiliania huxleyi and Coccolithus pelagicus (heterococcolith-bearing phase) in the northern North Atlantic were investigated along two zonal transects crossing Fram Strait and the Norwegian–Iceland Sea, respectively, each conducted during both July 2011 and September–October 2007. Remote-sensing images as well as CTD and ARGO profiles were used to constrain the physico-chemical state of the surface water and surface mixed layer at the time of sampling. Strong seasonal differences in bulk coccolithophore standing stocks characterized the northern and southern transects, where the maximum values of 53×103 cells/l (fall) and 70×103 cells/l (summer), respectively, were essentially explained by E. huxleyi. This pattern confirms previous findings of a summer to fall northwestward shift in peak coccolithophore cell densities within the Nordic Seas. While depicting an overall zonal shift in high cell densities between the summer (Norwegian Sea) and fall (northern Iceland Sea) conditions, the southern transects were additionally characterized by local peak coccolithophore concentrations associated with a geographically and temporally restricted convective process (Lofoten Gyre, summer), as well as an island mass effect (in the vicinity of Jan Mayen Island, fall). Maximum coccolithophore abundances within Fram Strait were found during both seasons close to the western frontal zone (Polar and Arctic Fronts) an area of strong density gradients where physical and chemical properties of the surface mixed layer are prone to enhance phytoplankton biomass and productivity. Here, changes in species dominance from E. huxleyi in summer, to C. pelagicus in fall, were related to the strengthened influence during summer, of surface AW, as well as to high July solar irradiance, within an area usually characterized by C. pelagicus-dominated low density populations.
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 98, n° 0967-0637, pp. 1-9, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UiT
Unexpected Levels of Biological Activity during the Polar Night Offer New Perspectives on a Warming Arctic
Summary The current understanding of Arctic ecosystems is deeply rooted in the classical view of a bottom-up controlled system with strong physical forcing and seasonality in primary-production regimes. Consequently, the Arctic polar night is commonly disregarded as a time of year when biological activities are reduced to a minimum due to a reduced food supply. Here, based upon a multidisciplinary ecosystem-scale study from the polar night at 79°N, we present an entirely different view. Instead of an ecosystem that has entered a resting state, we document a system with high activity levels and biological interactions across most trophic levels. In some habitats, biological diversity and presence of juvenile stages were elevated in winter months compared to the more productive and sunlit periods. Ultimately, our results suggest a different perspective regarding ecosystem function that will be of importance for future environmental management and decision making, especially at a time when Arctic regions are experiencing accelerated environmental change.
(Current Biology. vol. 25, n° 0960-9822, pp. 2555-2561, 23/06/2026)
UiT, UNIS, NIVA, SAMS, CEOE, NTNU, NTNU, SPBU, LEMAR, IRD, IFREMER, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, AWI
Phytoplankton versus macrophyte contribution to primary production and biogeochemical cycles of a coastal mesotidal system. A modelling approach
This study presents an assessment of the contributions of various primary producers to the global annual production and N/P cycles of a coastal system, namely the Arcachon Bay, by means of a numerical model. This 3D model fully couples hydrodynamic with ecological processes and simulates nitrogen, silicon and phosphorus cycles as well as phytoplankton, macroalgae and seagrasses. Total annual production rates for the different components were calculated for different years (2005, 2007 and 2009) during a time period of drastic reduction in seagrass beds since 2005. The total demand of nitrogen and phosphorus was also calculated and discussed with regards to the riverine inputs. Moreover, this study presents the first estimation of particulate organic carbon export to the adjacent open ocean.
The calculated annual net production for the Arcachon Bay (except microphytobenthos, not included in the model) ranges between 22,850 and 35,300 tons of carbon. The main producers are seagrasses in all the years considered with a contribution ranging from 56% to 81% of global production. According to our model, the -30% reduction in seagrass bed surface between 2005 and 2007, led to an approximate 55% reduction in seagrass production, while during the same period of time, macroalgae and phytoplankton enhanced their productions by about +83% and +46% respectively. Nonetheless, the phytoplankton production remains about eightfold higher than the macroalgae production. Our results also highlight the importance of remineralisation inside the Bay, since riverine inputs only fulfill at maximum 73% nitrogen and 13% phosphorus demands during the years 2005, 2007 and 2009. Calculated advection allowed a rough estimate of the organic matter export: about 10% of the total production in the bay was exported, originating mainly from the seagrass compartment, since most of the labile organic matter was remineralised inside the bay.(Estuarine, Coastal and Shelf Science. vol. 165, n° 0272-7714, pp. 52-60, 23/06/2026)
IFREMER, 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, 23/06/2026)
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
The most vagile host as the main determinant of population connectivity in marine macroparasites
Although molecular ecology of macroparasites is still in its infancy, general patterns are beginning to emerge, e.g. that the most vagile host in a complex life cycle is the main determinant of the population genetic structure of their parasites. This insight stems from the observation that populations of parasites with only freshwater hosts are more structured than those with terrestrial or airborne hosts. Until now, the same has not been tested for marine systems, where, in theory, a fully marine life cycle might sustain high dispersal rates because of the absence of obvious physical barriers in the sea. Here, we tested whether a marine trematode parasite that utilises migratory birds exhibited weaker population genetic structure than those whose life cycle utilises marine fish as the vagile host. Part of the mitochondrial cytochrome c oxidase 1 (COI) gene was sequenced from individual sporocysts from populations along the Atlantic coast of Europe and North Africa. Strong population structure (Φst = 0.25, p < 0.0001) was found in the fully marine trematode Bucephalus minimus (hosted by fish), while no significant structure (Φst = 0.015, p = 0.19257) was detected in Gymnophallus choledochus (hosted by birds). However, demographic models indicate recent colonisation rather than high dispersal as an alternative explanation of the low levels of structure observed in G. choledochus. Our study is the first to identify significant genetic population structure in a marine autogenic parasite, suggesting that connectivity between populations of marine parasites can be limited despite the general potential for high dispersal of their hosts in the marine environment.
(Marine Ecology Progress Series. vol. 520, n° 0171-8630, pp. 85-99, 23/06/2026)
NIOZ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UM5, UCC
Glacial ice and atmospheric forcing on the Mertz Glacier Polynya over the past 250 years
The Mertz Glacier Polynya off George V Land, East Antarctica, is a source of Adélie Land Bottom Water, which contributes up to B25% of the Antarctic Bottom Water. This major polynya is closely linked to the presence of the Mertz Glacier Tongue that traps pack ice upstream. In 2010, the Mertz Glacier calved a massive iceberg, deeply impacting local sea ice conditions and dense shelf water formation. Here we provide the first detailed 250-year long reconstruction of local sea ice and bottom water conditions. Spectral analysis of the data sets reveals large and abrupt changes in sea surface and bottom water conditions with a B70-year cyclicity, associated with the Mertz Glacier Tongue calving and regrowth dynamics. Geological data and atmospheric reanalysis, however, suggest that sea ice conditions in the polynya were also very sensitive to changes in surface winds in relation to the recent intensification of the Southern Annular Mode.
(Nature Communications. vol. 6, n° 2041-1723, pp. 6642, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULaval, INSU - CNRS, CNRS, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, VOG, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, BTP, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS