Organic carbon release by phytoplankton and bacterial reassimilation

The release of organic carbon by phytoplankton and its reassimilation by bacteria were studied in Lake Geneva during four daily kinetics, using¹⁴C techniques. Gentamycin was used to suppress bacterial activity. Size fractionation was used to measure¹⁴C fixation in 2 particulate fractions (≥1 μm and 0.2 to 1 μm) and in a third fraction: dissolved organic carbon. Measurements of bacterial biomass and¹⁴C glucose uptake as the H¹⁴CO ₃ ⁻ uptake by samples prefractionated before incubation showed that the whole algae were retained on 1 μm pore size Nuclepore filters, but bacteria were retained on 1 μm and 0.2 μm filters. Concentration of 20 μg.ml⁻¹ gentamycin resulted in incomplete bacterial inhibition while phytoplankton was affected. Phytoplankton released less of 20% of its photoassimilated carbon of which a large proportion was utilized by bacterioplankton.     

Contamination des sédiments superficiels des principales rivières du Canton de Genève par les Polychlorobiphényles et DDT

The concentrations of PCBs and DDT at the surface of sediments of rivers in the Canton of Geneva were examined. Concentration variations observed along the rivers are discussed. In the case of the Rhône River, recent pollution at the surface of sediments is compared with that of aged underlying layers.     

Evolution estivale de la turbidité dans le lac de Neuchâtel

Some turbiditic measures carried out by a limnological diffusiometer along with the physico-chemical determinations of the Lake of Neuchatel have permitted to subdivide the water column in 4 distinct layers: the Epilimnium, the Clear Water Layer, the Pelagic Nepheloid Layer and the Benthic Nepheloid Layer.      

Le régime thermique des eaux de l'Ardèche dans son cours inférieur

A study of the thermal regime of the Lower Ardeche River was carried out from July 1982 to December 1984 using a chemical method (sucrose inversion) and a continuous temperature recorder. Yearly, monthly and daily temperature fluctuations were analyzed. The main factors that influence thermal variations are air temperature and geomorphology of the canyon. The hydrological regime is responsible of the water temperature fluctuations between years Despite the low winter temperatures, the Lower Ardeche can be classified among Mediterranean rivers, which typically have a very high maximum in summer.      

Cultures monoalgales: courte description et discussion d'une méthode permettant une observation à fort grossissement des cellules avant leur isolement à l'aide d'un emporte-pièce

A method allowing isolation of phytoplancton algae for unialgal cultures is briefly described. Advantages and limits of the method are discussed.     

Application de méthodes d’analyse biochimique à un problème taxonomique: les Corégones du lac de Neuchâtel1, 2, 4

Sans résumé Travail réalisé avec l’appui du Fonds national suisse de la Recherche. La rédaction du présent travail est antérieure au mémoire deDottrens [254]³). La parution du texte de cet auteur a très exactement co?ncidé avec la présentation de notre thèse. Ces deux recherches ont été accomplies indépendamment. D’après les conclusions deDottrens, les Corégones du lac de Neuchatel doivent désormais être désignés par Le mot ?ichtyologie? et les termes de la même famille sont orthographiés avec un seul ?h? en accord avec une décision récente de l’Académie.     

L'aération naturelle et artificielle des lacs

Conclusion Par ce qui précède, on se rend compte que chaque lac constitue un cas particulier qui doit être étudié pour lui-même et que l'aération artificielle d'un lac de grandes dimensions est susceptible d'être réalisée. A notre époque les lacs prennent de plus en plus d'importance comme réservoirs pouvant servir à l'alimentation en eau potable. Pour remplir ce r?le il est indispensable que la qualité de l'eau soit satisfaisante afin d'éviter des traitements co?teux. On peut dire que l'aération artificielle, malgré le co?t initial des installations et la consommation annuelle d'énergie électrique, est le procédé le plus économique pour améliorer l'eau d'un lac eutrophe. Actuellement la consommation de l'eau augmente partout et dépasse parfois dans certaines agglomérations 1000l/habitant/par jour. Dans ces conditions les frais d'exploitation d'une station d'aération conjuguée avec un service important de distribution d'eau ne grèvent le prix de revient du mètre cube que d'un supplément minime. Il est évident que l'emploi de l'aération artificielle pour assainir un lac ne dispense pas de combattre les causes originelles de la pollution des eaux. C'est un procédé auxiliaire précieux qui peut aider un lac à rétablir son équilibre biologique compromis par les conséquences de l'eutrophie. Cet article résume les idées exposées par l'auteur à l'occasion d'un colloque organisé à Zurich le 22 février 1957 par le Prof.Jaag, président de la Commission hydrobiologique de la Société helvétique des sciences naturelles.     

Stable Eocene Magnetization Carried by Magnetite and Iron Sulphides in Marine Marls (Pamplona-Arguis Formation,Southern Pyrenees,Northern Spain)

In order to establish the magnetic carriers and assess the reliability of previous paleomagnetic results obtained for Eocene marine marls from the south Pyrenean basin, we carried out a combined paleo- and rock-magnetic study of the Pamplona-Arguis Formation, which crops out in the western sector of the southern Pyrenees (N Spain). The unblocking temperatures suggest that the characteristic remanent magnetization (ChRM) is carried by magnetite and iron sulphides. The ChRM has both normal and reversed polarities regardless of whether it resides in magnetite or iron sulphides, and represents a primary Eocene magnetization acquired before folding. Rock magnetic results confirm the presence of magnetite and smaller amounts of magnetic iron sulphides, most likely pyrrhotite, in all the studied samples. Framboidal pyrite is ubiquitous in the marls and suggests that iron sulphides formed during early diagenesis under sulphate-reducing conditions. ChRM directions carried by magnetic iron sulphides are consistent with those recorded by magnetite. These observations suggest that magnetic iron sulphides carry a chemical remanent magnetization that coexists with a remanence residing in detrital magnetite. We suggest that the south Pyrenean Eocene marls are suitable for magnetostratigraphic and tectonic purposes but not for studies of polarity transitions, secular variations and geomagnetic excursions, because it is difficult to test for short time differences in remanence lock-in time for the two minerals. The presence of iron sulphide minerals contributing to the primary magnetization in Eocene marine marls reinforces the idea that these minerals can persist over long periods of time in the geological record.     

Masses d'air conditionnées par la fonte des neiges

Summary In the paper it is shown in which manner the cooling of the air due to the melting of snowflakes causes the appearance of special air masses of greater or smaller dimensions. Here some examples are given of the formation of such air masses of melting in Yugoslavia on the north slopes of the Dinarian Alps.

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Zusammenfassung In dieser Arbeit ist gezeigt, auf welche Weise die Abkühlung der Luft, die durch das Schmelzen der Schneeflocken bedingt ist, besondere Luftmassen von grösseren und kleineren Ausdehnungen zur Folge hat. Es sind einige Beispiele von solchen Luftmassen des Schmelzens in Jugoslawien gegeben, die auf der Nordseite der dynarischen Gebirge formiert sind.

     

Geo-Characterization at selected accelerometric stations in Crete (Greece) and comparison of earthquake data recordings with EC8 elastic spectra

To estimate the seismic response according to Eurocode (EC8) and almost all other national codes, site conditions have to be properly characterized so that soil amplification and the corresponding peak ground motion can be calculated. In this work, different geophysical and geotechnical methods are combined in order to define the detailed ground conditions in selected sites of the Hellenic Accelerometric Network (HAN) in Crete. For this purpose, the geological information of the sites and shear wave velocity, calculated from surface wave measurements, is used. Additionally, ground acceleration data recorded through HAN have been utilized from intermediate depth earthquakes in the broader area of South Aegean Sea. Using the recorded ground motion data and the procedure defined in EC8, the corresponding elastic response spectrum is calculated for the selected sites. The resulting information is compared to the values defined in the corresponding EC8 spectrum for the seismic zone that includes the island of Crete. The comparison shows that accurate definition of ground type through geological, geotechnical and geophysical investigations is important. However, our current comparison focuses on the distribution of values rather than the absolute values of EC8-prescribed spectra, and the results should be considered in this context.