Recent comparability of oceanographic nutrients data: Results of a 2003 intercomparison exercise using reference materials

An intercomparison exercise was conducted using the recently developed Reference Material for Nutrients in Seawater (RMNS). Discrepancies of reported values among laboratories were greater than the homogeneity of RMNS samples and the reported analytical precision of nutrients. The variability of in-house standards of the participating laboratories might be the most likely source of interlaboratory discrepancies. Therefore, the use of common reference materials, i.e. certified RM, is essential to establish and improve the comparability of nutrient data of the world's oceans

2008 Inter-laboratory Comparison Study of a Reference Material for Nutrients in Seawater

Autoclaved natural seawater collected in the North Pacific Ocean was used as a reference material for nutrients in seawater (RMNS) during an inter-laboratory comparison (I/C) study conducted in 2008. This study was a follow-up to previous studies conducted in 2003 and 2006. A set of six samples was distributed to each of 58 laboratories in 15 countries around the globe, and results were returned by 54 of those laboratories (15 countries). The homogeneities of samples used in the 2008 I/C study, based on analyses for three determinants, were improved compared to those of samples used in the 2003 and 2006 I/C studies. Results of these I/C studies indicate that most of the participating laboratories have an analytical technique for nutrients that is sufficient to provide data of high comparability. The differences between reported concentrations from the same laboratories in the 2006 and 2008 I/C studies for the same batch of RMNS indicate that most of the laboratories have been maintaining internal comparability for two years. Thus, with the current high level of performance in the participating laboratories, the use of a common reference material and the adaptation of an internationally accepted nutrient scale system would increase comparability among laboratories worldwide, and the use of a certified reference material would establish traceability. In the 2008 I/C study we observed a problem of non-linearity of the instruments of the participating laboratories similar to that observed among the laboratories in the 2006 I/C study. This problem of non-linearity should be investigated and discussed to improve comparability for the full range of nutrient concentrations. For silicate comparability in particular, we see relatively larger consensus standard deviations than those for nitrate and phosphate

Addressing the measurement of particulate organic and inorganic phosphorus in estuarine and coastal waters

The speciation of particulate phosphorus (TPP) into inorganic (PIP) and organic phosphorus (POP), has been scarcely investigated in suspended particulate matter (SPM), contrary to numerous sediment studies. This work evaluates the actual capacity of methods for TPP, POP and PIP determination in SPM to measure efficiently and specifically each pool. Methods were tested on a range of plankton-associated organic and inorganic P compounds, on microalgal cultures and estuarine samples. Then results are specifically discussed reviewing P speciation in phytoplankton. For TPP analysis, the method of Solorzano and Sharp (1980) is recommended compared with that of Aspila et al. (1976), originally dedicated to sediment, as there is one step less, the protocol is more explicit (use of MgSO4) and it provides the best results. The application of the original protocol of the Aspila method for TPP (no MgSO4) results in underestimated and highly variable values. For POP, the CWO (Chemical Wet Oxidation) method tested here succeeds in providing sufficient oxidation of organic P, but, inorganic polyphosphate is yet too significantly hydrolysed, and intracellular phosphate, an underestimated PIP fraction, contributes to the POP pool with this method. Finally the Aspila method for PIP. is the best compromise in estimating the contribution of PIP to TPP and POP by difference. Even if particulate polyphosphate is only partially hydrolysed (41-49%), intracellular phosphate is included and only a very low percentage of organic P, essentially nucleotidic P, is attacked. In any case, our findings show clear evidence of the necessity to fully describe the procedure when P speciation methods are used

Effect of P depletion on the functional pools of diatom carbohydrates, and their utilization by bacterial communities

Phosphorus (P) limitation of phytoplankton growth is known to affect the accumulation and release of carbohydrates (CHO) by micro-algae. However, relatively little is known about the fate of algal exudates, notably their bacterial degradation. The CHO chemical characterization is also not exhaustive, especially in ‘functional’ pools relevant for phytoplankton physiology (particulate reserve [R] or structural [S] CHO) and for bacterial degradation (dissolved mono- [MDCHO] and polysaccharides [P-DCHO]). In this study, we investigated how P depletion and repletion affect the CHO composition in diatom Thalassiosira weissflogii cultures, and the shortterm response of free and diatom-attached bacteria in terms of abundance and potential βglucosidase activity (βGlc). The bacterial inoculum was composed of the bacterial consortiums of diatom precultures and a natural bacterial community from the Bay of Brest. P depletion favored CHO accumulation in diatom cells, mainly as R i.e. soluble CHO accumulated in cytoplasm, but also as S, polysaccharides linked to the cell wall. The R:S ratio was high in the present diatom cultures. The high M-DCHO observed in P-deplete cultures (twice that of P-replete cultures) when P-DCHO remained quite similar is explained both by active polysaccharide hydrolysis (very high potential βGlc of attached bacteria) and reduced uptake of M-DCHO by Pdepleted bacteria. P depletion of heterotrophic bacteria favors labile CHO accumulation, which may affect particle potential aggregation. However, the remarkably constant M-DCHO concentration over time for both conditions suggests tight coupling between phytoplankton accumulation, release, polymer hydrolysis and monomer uptake by bacteria

Impact of Oyster Farming on Diagenetic Processes and the Phosphorus Cycle in Two Estuaries (Britanny, France)

This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size, organic matter parameters), and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations of sulfide and Fe concentrations in pore waters, as well as Fe-P concentrations in the solid-phase highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulphate reduction (Beneath Oyster). This could be partly explained by the increase in labile organic matter (ie, biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4475 µmol l-1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron sulfide compounds (FeS, FeS2). In the Aber Benoît, dissolved Fe/PO4 ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO4 ratios in the summer indicated higher effluxes of phosphate towards the water column (up to 47 µmol m-2 h-1). At other periods, Fe/PO4 ratios higher than 2 mol:mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO4 ratios more difficult in terms of indicators of phosphate release

Recent Comparability of Oceanographic Nutrients Data: Results of a 2003 Intercomparison Exercise using Reference Materials

An intercomparison exercise was conducted using the recently developed Reference Material for Nutrients in Seawater (RMNS). Discrepancies of reported values among laboratories were greater than the homogeneity of RMNS samples and the reported analytical precision of nutrients. The variability of in-house standards of the participating laboratories might be the most likely source of interlaboratory discrepancies. Therefore, the use of common reference materials, i.e. certified RM, is essential to establish and improve the comparability of nutrient data of the world's oceans

Étude sur la prolifération de la micro algue Alexandrium minutum en rade de Brest

Suite à l’événement de grande ampleur d’efflorescence d’Alexandrium minutum et des toxicités associées en Rade de Brest en 2012, un projet a été élaboré avec la Région Bretagne dans le cadre du développement du port de Brest. L’Ifremer a organisé un échantillonnage dans l’estuaire de la rivière de Daoulas, zone la plus touchée en 2012, au cours des printemps-été 2013 et 2014. Un suivi de la présence d’A. minutum dans les sédiments a également été réalisé en hiver 2014. De ces suivis, des mesures réalisées au laboratoire à ce jour, des simulations du modèle Prévimer ainsi que des résultats du réseau Rephy et Velyger, il ressort que: * La rade de Brest peut aujourd’hui être considérée comme une zone à risque pour Alexandrium minutum. En effet, depuis 2012 les blooms sont récurrents, dépassant le seuil d’alerte et entrainant une toxicité des coquillages. L’ensemble de la rade présente des sédiments contaminés par la présence d’A. minutum. * La période à risque s’étend de mi-mai à fin août. Les estuaires du fond de rade, ainsi que le Sillon des Anglais sont les zones les plus touchées. En Baie de Daoulas et au Sillon des Anglais, l’année 2014 a été une année présentant un développement d’A. minutum, ainsi que des toxicités, sur une période très longue par rapport à 2012 et 2013. Le secteur Elorn a vu des concentrations en A. minutum ponctuellement supérieures au seuil d’alerte mais pas de toxicité. * Le suivi Daoulex a mis en évidence l’importance de la température de l’eau pour le démarrage du bloom. 2014 est une année où les températures de l’eau ont été plus chaudes au printemps ce qui coïncide avec un démarrage beaucoup plus précoce, dès mi-mai du bloom. C’était la situation opposée en 2013. * Les apports de nutriments par la rivière Mignonne semblent aussi être un facteur non négligeable, 2014 se situant entre les forts débits de 2012 et les débits plus faibles de 2013. L’intensité du bloom d’A. minutum présente cette même différence interannuelle. * Les blooms d’A. minutum présentent des maxima pour les faibles coefficients de marée, c’est-à-dire lorsque les courants sont plus faibles et permettent un maintien du bloom dans les fonds d’estuaires, plus favorables à la croissance d’A. minutum. * L’hydrodynamique de la rade seule ne peut expliquer la distribution d’A. minutum dans l’ensemble de la rade à partir d’un seul point de germination et de développement. Il s’agit vraisemblablement de plusieurs foyers de germination et de développement, qui ensuite vont contaminer, à de plus faibles abondances, le reste de la rade. * Alexandrium minutum n’est qu’une espèce parmi l’ensemble de la communauté microphytoplanctonique mais elle peut devenir dominante au sein de cette communauté, comme en 2012 et 2014. * Le séquençage de l’ensemble des ARN messagers de souches d’A. minutum a mis en évidence une diversité intra-spécifique extrêmement importante à la fois entre souches isolées au cours d’efflorescences distinctes (à la fois dans l’espace et dans le temps), mais également au sein d’une même efflorescence. L’impact de cette diversité sur la dynamique des efflorescences reste méconnu. * Une approche de génétique des populations a pu mettre en évidence des différences de fréquences alléliques entre sites Bretons touchés par des efflorescences à A. minutum. Ceci indique que ces efflorescences se développent de manière indépendante, sans qu’il existe de forts flux de gènes entre sites. * Les populations d’A. minutum de la rade synthétisent plusieurs types de toxines PSP au cours du bloom. * Un test bandelette de détection et quantification d’A. minutum est en cours de développement

Vertical and horizontal controls on a haptophyte thin layer in the Bay of Biscay.

Investigations into the phytoplankton of the Bay of Biscay in July 2006 revealed an extensive bloom of an unidentified haptophyte species. High-resolution sampling techniques identified the region in the vicinity of the mouth of the Loire estuary as an area of high ... cell densities of the haptophyte in a thin sub-surface layer. This organism dominated the phytoplankton population regionally. Measurements of the vertical distribution of horizontal shear showed that the population, located at ca. 20 m depth, was confined to a layer lying between two density discontinuities with high shear. Physical measurements indicated that the population was being advected southeastwards, along the coast. Seaward spreading of the population was also noted during the survey. Horizontal diffusion could be derived from the changes in the offshore gradient in the population's distribution with time, with estimates ofKx, the horizontal diffusion coefficient, of the order of 100 m...The magnitude of horizontal dispersion is compared with that of horizontal advectiveflux, vertical dispersion and growth.Versión del editor