Le phytoplancton du lac de Neuchâtel

Résumé L'analyse du phytoplancton récolté de 1959 à 1962 montre qu'à son tour le lac de Neuchatel a atteint un degré de pollution favorisant l'implantation et l'expansion d'espèces indésirables. Le r?le que jouent actuellementAphanizomenon flos-aquae, Oscillatoria rubescens, O. prolifica, Tabellaria fenestrata, entre autres, ainsi que lesChlorophycées, a rapidement modifié la physionomie de la biocénose. L'inventaire des algues planctoniques dressé parFuhrmann en 1897/1898 fournit d'autre part un élément de comparaison mettant en évidence l'évolution survenue dans ce bassin subjurassien au cours de 65 années. Travail réalisé avec l'appui du Fonds national suisse de la Recherche.     

Le zooplancton du lac de Bret en 1902/03, 1943 et 1951

Summary The Lac de Bret, formerly an “oligotrophic” lake, has by several artificial risings of its level become “eutrophic” with the drawbacks of that state during the summer stagnation. A plant of partial underwater aeration has improved the situation and has been described in this Review (11, 423 [1949]). The above study compares the zooplancton of this lake in the years 1902/03 when it was yet oligotrophic with its plancton in the year 1943 during the investigations in the lake become eutrophic and finally in the year 1951 when it had again grown sound after five seasons of estival acration.      

Etude hydrobiologique du lac de Bret

Sans résumé La publication de cette étude a bénéficié d'une subvention du Fonds national suisse pour la recherche scientifique.—Voir cette Revue Vol. XVI, fasc. 2, 1954, études de MM.P. Mercier etS. Gay et deM. Ch. Linder.     

Les macrophytes du lac de Bienne

The study of the qualitative and quantitative distribution of macrophytic vegetation of Bienne lake is realized with the help of colour aerial photographies and verifications on the field. This distribution is discussed in relation to the trophic level of the lake and compared with that of the Geneva lake and Morat lake.     

Recherches hydrobiologiques au lac de barrage de Barberine (Valais)

Sans résumé Avec 2 illustrations     

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.      

Evolution de l'état sanitaire de la baie d'Auvernier (lac de Neuchâtel) de 1962 à 1973

The evolution of the trophic state of a part of the Lake of Neuchâtel was investigated by means of a study of 4 parameters (temperature, dissolved oxygen, total phosphorus and nitrates) in the waters of the Auvernier Bay (fig. 1). Each year is composed of a stratification period (June to November) and a circulation period (December to May) (fig. 2). Notwithstanding the heavy consumption of oxygen in the metalimnion during the stratification period, the waters are sufficiently abundant in dissolved oxygen (fig. 3). As a matter of fact, over the 12-year period studied, no decrease in the oxygen content was observed at any depth (fig. 4). On the other hand, the quantities of nutrients were enriched in nitrates (30%) and phosphorus (230%) (fig. 5–8). The Auvernier Bay may be thought to have evolved from an oligotrophic state in 1963 to an eutrophic state in 1972 if we consider only these latter two criteria.     

Les hyaloclastites de la rive nord du lac Kivu (Congo)

Geological environment and origin of the palagonitised tuff volcanoes of the Kivu. Petrographical features (lapilli, palagonitisation, gangue). Their magmatic minerals and xenoliths.     

Le complexe filonien de Fuerteventura (Iles Canaries)

Two sectors in the island have been distinguished which depend on the intensity of the penetration of the dyke swarm: the central-western sector, where the proportion of dykes in relation to the host rocks is — in some cases — more than 90% and all the rest of the island, where the dykes are in less proportion. In the central-western sector the predominant direction varies from N-10^o-E to N-20^o-E, whilst in the rest of the island a clear constant direction does not exist, although there are some directional trends more or less well defined. Most dykes are of basaltic composition, but there are also salic dykes (trachytic and phonolitic) and camptonites. The dykes from the western sector have suffered intense transformation processes (albitization and amphibolization), so that it is frequent to find dykes that do not preserve practically any one of their primary minerals. As the albitization process also affects the host rocks and has a regional development; we can speak of a regional metamorphism equivalent in its intensity to the Green Schist. Three main generations of dykes have been established: 1st) those of an approximately N-S direction, forming the older generation, constituted by multiple injections, 2nd) those genetically related to the Basaltic Series I, 3rd) those of salic composition, closely related with the syenitic-trachytic intrusions.     

La végétation macrophytique d'un lac hautement eutrophe du Plateau suisse: Le Baldegger See

The study of the qualitative and quantitative distribution of the Baldeggersee macrophytic vegetation is undertaken in 1980 with the help of colour aerial photographies and verification on the field. The comparison with old data allows then a short survey of the macrophytic evolution in relation to the eutrophication.      

Le teneur de l'air en petits et gros ions radioactifs

Résumé En assimilant à des petits ions les atomes RaA provenant de la désintégration du Radon présent dans l'air, on évalue par le calcul la fraction de ces particules fixées sur les poussières et les noyaux de condensation, ainsi que leur durée de fixation.Pour vérifier ces considérations, on compte les petits et gros ions radioactifs par la méthode deZeleny, en maintenant l'électrode axiale des tubes sous tension négative, les autres particules sont fixées par captation électrostatique ou avec un filtre papier et les activités des différents échantillons sont étudiées par comptage . On trouve une concentration de l'air en petits ions RaA de 1.5·10^–4 atome par cm³. Connaissant la teneur de l'air en Radon, et en admettant que l'équilibre radioactif est atteint entre le Radon et le Radium A qui en provient, on obtient par différence les concentrations de RaA fixée sur les autres particules.

---

Summary The proportion and free life time of RaA atoms arising from the radioactivity of atmospheric radon, and catched by dust particles, large ions and condensation nuclei, is evaluated, with assumption that these atoms are identical to the ordinary small ions.Experimental verification of the calculation are made by catching small and large ions withZeleny tubes, axial electrode being negatively charged. Other particles being catched with electrical precipitation and filter paper, activities of different samples are measured by counting. 1.5·10^–4 per cm³ small ions RaA concentration is found. Knowing the air radon value concentration, and with the assumption of radioactive equilibrium only between radon and RaA in free air, it is possible to evaluate the concentration of RaA catched by other particles.

     

Croissance et reproduction de l'omble-chevalier,Salvelinus alpinus (L.), dans le lac de Neuchâtel (Suisse)

The arctic char (Salvelinus alpinus) which has disappeared from Lake Neuchatel near 1963, has been reintroduced into this lake since 1979. In this study, growth and reproduction of char have been analyzed 4 years after reintroduction. Age determination based on scales were more reliable then those based on otoliths. Growth rate decreased from the cohort born in 1979 to the cohort born in 1982. Nevertheless growth of char in Lake Neuchatel is fast compared to other char populations. About 33% of the males were sexually mature in the second year of life. At this age, no females, and in the third year of life, only 18% of the females were mature. Most fish of both sex were mature at an age of 4 years. A high correlation was found for data taken from other authors between fecundity and length of char. The data from Lake Neuchatel char (this study) fit very well with this general relation.      

Premier complément à l'inventaire de la biocénose planctonique du lac Léman

New phytoplanktonic and zooplanktonic species have been observed for the first time in Lake Geneva (Lac Léman); moreover, the presence of some Rotatoria and Entomostraca has been confirmed in the lake biocenosis.      

Concentrations en PCB et DDT des sédiments superficiels de la rive suisse du lac Léman

The PCB concentrations of sediments can be considered as high and risk to produce a long-term contamination of the lake ecosystem. The shoreline near Lausanne area is the most polluted. Those results show that pollution by DDT is decreasing.