A strong CO2 sink enhanced by eutrophication in a tropical coastal embayment (Guanabara Bay, Rio de Janeiro, Brazil)
Abstract. In contrast to its small surface area, the coastal zone plays a disproportionate role in the global carbon cycle. Carbon production, transformation, emission and burial rates at the land–ocean interface are significant at the global scale but still poorly known, especially in tropical regions. Surface water pCO2 and ancillary parameters were monitored during nine field campaigns between April 2013 and April 2014 in Guanabara Bay, a tropical eutrophic to hypertrophic semi-enclosed estuarine embayment surrounded by the city of Rio de Janeiro, southeast Brazil. Water pCO2 varied between 22 and 3715 ppmv in the bay, showing spatial, diurnal and seasonal trends that mirrored those of dissolved oxygen (DO) and chlorophyll a (Chl a). Marked pCO2 undersaturation was prevalent in the shallow, confined and thermally stratified waters of the upper bay, whereas pCO2 oversaturation was restricted to sites close to the small river mouths and small sewage channels, which covered only 10 % of the bay's area. Substantial daily variations in pCO2 (up to 395 ppmv between dawn and dusk) were also registered and could be integrated temporally and spatially for the establishment of net diurnal, seasonal and annual CO2 fluxes. In contrast to other estuaries worldwide, Guanabara Bay behaved as a net sink of atmospheric CO2, a property enhanced by the concomitant effects of strong radiation intensity, thermal stratification, and high availability of nutrients, which promotes phytoplankton development and net autotrophy. The calculated CO2 fluxes for Guanabara Bay ranged between −9.6 and −18.3 mol C m$^{−2}$ yr$^{−1}$, of the same order of magnitude as the organic carbon burial and organic carbon inputs from the watershed. The positive and high net community production (52.1 mol C m$^{−2}$ yr$^{−1}$) confirms the high carbon production in the bay. This autotrophic metabolism is apparently enhanced by eutrophication. Our results show that global CO2 budgetary assertions still lack information on tropical, marine-dominated estuarine systems, which are affected by thermal stratification and eutrophication and behave specifically with respect to atmospheric CO2.
(Biogeosciences. vol. 12, n° 1726-4170, pp. 6125-6146, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UFF
Technical Note: Large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwaters
Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atmosphere at the global scale. Fluxes of CO2 between aquatic systems and the atmosphere are calculated from the gas transfer velocity and the water–air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calculated from temperature, pH and total alkalinity (TA). Here, we compare calculated (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L−1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved organic carbon (DOC) (29 to 3970 μmol L−1). Calculated pCO2 were >10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calculated pCO2 compared to measured pCO2 of 2560 ppmv) and were >100% higher in the 25% most organic-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calculated pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of organic acids anions to TA in waters with low carbonate alkalinity and high DOC concentrations; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calculated pCO2 to TA in acidic and organic-rich waters. No empirical relationship could be derived from our data set in order to correct calculated pCO2 for this bias. Owing to the widespread distribution of acidic, organic-rich freshwaters, we conclude that regional and global estimates of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quantitative analysis. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.
(Biogeosciences. vol. 12, n° 1726-4170, pp. 67–78, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULiège, KU Leuven
Environmental concentrations of benz[a]anthracene induce developmental defects and DNA damage and impair photomotor response in Japanese medaka larvae.
Benz[a]anthracene (BaA) is a ubiquitous polycyclic aromatic hydrocarbon found in numerous aquatic ecosystems. However, ecotoxicological data in aquatic organisms are scarce. To remedy this lack of data, Japanese medaka (Oryzias latipes) embryos were exposed to BaA and toxic effects were investigated at multiple toxicological endpoints. Japanese medaka embryos were incubated onto BaA-spiked artificial sediment for 9 days at low or moderate environmental concentrations ranging from 0.9 to 12µgg(-1) dw. BaA-exposed embryos exhibited significant tachycardia. BaA exposure was also shown to increase CYP1A activity in the hepato-biliary tissue as well as craniofacial deformities and DNA damage in pro-larvae. The photomotor response of BaA-exposed larvae was reduced in comparison to the control group. According to this set of tests, the lowest tested and observed effect concentration (LOEC) for Japanese medaka early life stages was equivalent to 0.92µgg(-1) dw of BaA. This concentration fall into the range of concentrations frequently encountered in sediments of polluted aquatic ecosystems. Taking into consideration these results, BaA represents a threat for fish early life stages in particular those developing onto or into contaminated sediments.
(Ecotoxicology and Environmental Safety. vol. 113C, n° 0147-6513, pp. 321-328, 23/06/2026)
UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPGP, INRA, Biosit : Biologie - Santé - Innovation Technologique, BE, IFREMER
Position paper on passive sampling techniques for the monitoring of contaminants in the aquatic environment - Achievements to date and perspectives
This paper, based on the outcome of discussions at a NORMAN Network-supported workshop in Lyon (France) in November 2014 aims to provide a common position of passive sampling community experts regarding concrete actions required to foster the use of passive sampling techniques in support of contaminant risk assessment and management and for routine monitoring of contaminants in aquatic systems. The brief roadmap presented here focusses on the identification of robust passive sampling methodology, technology that requires further development or that has yet to be developed, our current knowledge of the evaluation of uncertainties when calculating a freely dissolved concentration, the relationship between data from PS and that obtained through biomonitoring. A tiered approach to identifying areas of potential environmental quality standard (EQS) exceedances is also shown. Finally, we propose a list of recommended actions to improve the acceptance of passive sampling by policy-makers. These include the drafting of guidelines, quality assurance and control procedures, developing demonstration projects where biomonitoring and passive sampling are undertaken alongside, organising proficiency testing schemes and interlaboratory comparison and, finally, establishing passive sampler-based assessment criteria in relation to existing EQS.
(Trends in environmental analytical chemistry. vol. 8, pp. 20-26, 23/06/2026)
UR MALY, IRSTEA, UR EABX, IRSTEA, NIVA, INERIS, MU / MUNI, IFREMER, EAWAG, CEFAS, EPA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM, ONEMA, LERPAC, COAST, IFREMER
Hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry for acidic herbicides and metabolites analysis in fresh water
Theoretical papers and environmental applications of hydrophilic interaction liquid chromatography (HILIC) have been published for a wide range of analytes, but to our knowledge, no study focused on acidic herbicides (e.g., triketones, phenoxy acids, sulfonylurea, and acidic metabolites of chloroacetanilides). Matrix effects are the main obstacle to natural sample analysis by liquid chromatography coupled with tandem mass spectrometry (MS) via an electrospray ionization (ESI) interface. Therefore, we paid particular attention on limiting interference by (i) adapting the emerging HILIC technique, which is generally considered more sensitive than conventional reversed phase liquid chromatography and (ii) optimizing the solid phase extraction (SPE) step using a design of experiment. A rapid and reliable off line SPE-HILIC-ESI-MS/MS method was thus developed for the quantification of acidic herbicides in fresh water, with limits of quantifications (LOQs) ranging from 5 to 22 ng l1 . Then, the analysis of freshwater samples highlighted the robustness of the method, and the importance of the chloroacetanilides metabolites among the studied analytes.
(Environmental Science and Pollution Research. vol. 22, n° 0944-1344, pp. 3988-3996, 23/06/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Statistical modeling of Southern Ocean marine diatom proxy and winter sea ice data: Model comparison and developments
We compare the performance of the modern analog technique (MAT), the Imbrie and Kipp transfer function (IKTF), the generalized additive model (GAM) and weighted averaging partial least squares (WA PLS) on a southern hemisphere diatom relative abundance and winter sea ice concentration training data set. All relevant model assumptions are tested with a random 10-fold cross-validation, whilst a hold out cross-validation tested the explanatory power of each model on spatially independent validation data. We used auto correlograms on model residuals, variance partitioning, and principal coordinates analysis of neighbor matrices (PCNM) to investigate the importance of the spatial structure of our training database. A set of hierarchical logistic regression models (or Huisman–Olff–Fresco models) are used to infer the response of each diatom species along the winter sea ice gradient. Our analyses suggest that IKTF is an inappropriate sea ice estimation approach as its underlying statistical assumptions do not hold and the fit of IKTF to our data under cross-validation was poor. We conclude that MAT may be biased by spatial autocorrelation, and together with IKTF fails to provide unbiased estimates of winter sea ice. We find GAM and WA PLS are more appropriate than IKTF and MAT for the estimation of paleo winter sea ice cover throughout the Southern Ocean. However, as WA PLS is based on a unimodal species response, which is rarely exhibited by diatoms along the winter sea ice gradient, we ultimately advocate the application of GAM. GAM only uses diatoms with a statistically significant association, and ecologically based link, with sea ice. GAM outperformed all other models under cross-validation in terms of performance statistics, the fit of GAM to the training dataset and diagnostic tests for model assumptions. We also demonstrate that GAM provides a more detailed and potentially more accurate (based on a comparison with New Zealand and southeast Australian paleo climatic records) paleo winter sea ice record for the southwestern Pacific Ocean in comparison with IKTF, MAT and WA PLS.
(Progress in Oceanography. vol. 131, n° 0079-6611, pp. 100-112, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
First records of winter sea ice concentration in the southwest Pacific sector of the Southern Ocean
We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27-23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27-23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub-Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136-111 and E27-23 over the last 220 and 52,000 years, respectively.
(Paleoceanography. vol. 30, n° 0883-8305, pp. 1525-1539, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UTAS, ANSTO
Increased aridity in southwestern Africa during the warmest periods of the last interglacial
Terrestrial and marine climatic tracers from marine core MD96-2098 were used to reconstruct glacial–interglacial climate variability in southwestern Africa between 194 and 24 thousand years before present. The pollen record documented three pronounced expansions of Nama-karoo and fine-leaved savanna during the last interglacial (Marine Isotopic Stage 5 – MIS 5). These Nama-karoo and fine-leaved savanna expansions were linked to increased aridity during the three warmest substadials of MIS 5. Enhanced aridity potentially resulted from a combination of reduced Benguela Upwelling, expanded subtropical high-pressure cells, and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone. Decreased austral-winter precipitation was likely linked to a southern displacement of the westerlies. In contrast, during glacial isotopic stages MIS 6, 4 and 3, fynbos expanded at the expense of Nama-karoo and fine-leaved savanna indicating a relative increase in precipitation probably concentrated during the austral winter months. Our record also suggested that warm–cold or cold–warm transitions between isotopic stages and substages were punctuated by short increases in humidity. Increased aridity during MIS 5e, 5c and 5a warm substages coincided with minima in both precessional index and global ice volume. On the other hand, austral-winter precipitation increases were associated with precession maxima at the time of well-developed Northern Hemisphere ice caps.
(Climate of the Past. vol. 11, n° 1814-9324, pp. 1417-1431, 23/06/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Qu'est-ce qu'une eau de bonne qualité ?
Normes et définitions de la qualité de l'eau vis à vis des usages et limites.
(pp. 212-213, 23/06/2026)
UR ETBX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS
Pression de sélection des barrages aquatiques sur la migration des civelles : approche moléculaire et comportementale
L’anguille européenne est une espèce amphihaline à migration catadrome facultative et à reproduction panmictique dans la mer de Sargasses. La dynamique de sa population est en fort déclin depuis les années 80. Parmi les facteurs qui ont pu contribuer à la disparition de l’espèce, on peut citer la pollution, la surpêche et la fragmentation de l’habitat. Ce dernier est intimement lié à la construction des barrages aquatiques. En effet, les rivières aménagées créent un obstacle au déplacement des anguilles dans les deux sens, c’est-à-dire lors de leur migration de croissance (en amont) ou de reproduction (en aval). Beaucoup d’efforts ont été faits afin d’augmenter la transparence de ces ouvrages. Par exemple, la migration en amont des jeunes stades d’anguilles est facilitée par la construction des passes à civelles, dont le design est adapté à leur taille et comportement. D’une manière générale, l’évaluation de l’impact des barrages, mais aussi de l’efficacité des passes à civelles est quantitative, où seule la proportion des poissons présents dans la parte amont du barrage/passe est comparée au nombre des poissons présents au pied du barrage ou s’engageant dans la passe. Malheureusement, la variabilité entre les individus pour les traits comme la capacité de nage ou d’escalade, la motivation, l’activité ou le comportement exploratoire est rarement prise en compte dans ce contexte. Cependant, certains traits pourraient faciliter le succès de passage par les obstacles, ce qui aboutirait à une sélection Afin d’évaluer si les barrages exercent une pression de sélection sur les civelles migrantes, une étude qualitative à été réalisée sur des groupes des civelles présentes d’une part et d’autre des obstacles. Tout d’abord, une approche par puce ADN a été adoptée pour identifier sans à priori les traits différant entre les groupes amont et aval. Ensuite, les tests expérimentaux ont été réalisés afin d’associer le phénotype moléculaire (expression des gènes) au phénotype organismique (comportement). Parmi les trois tissus étudiés ; le muscle, le foie et le cerveau, seul ce dernier a montré des différences significatives entre les groupes amont et aval des obstacles. Les gènes surexprimés des les parties amont des barrages sont impliqués dans la régulation de la plasticité synaptique et du développement neuronal, qui à son tour sont sollicités dans les processus de cognition, apprentissage et mémorisation. Le comportement d’escalade des parois verticales, souvent effectué en dehors de l’eau, est une condition à laquelle les civelles sont soumises pour la première fois de leur vie, ce qui peut suggérer que le processus d’apprentissage s’est mis en place à ce moment précis. Un tri comportemental effectué dans les conditions expérimentales confirme en partie l’association entre l’expression des gènes de plasticité synaptique et le comportement d’escalade individuel.
(pp. 1, 23/06/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EDF [E.D.F.]