The abundances of the different compartments of the microbial loop (i.e., viruses, heterotrophic bacteria, heterotrophic nanoflagellates, and pigmented nanoflagellates), total (TPP) and excreted (EPP) primary production, bacterial production (BP), viral lytic activity (LA), and bacterivory by nanoflagellates (FG) were measured on June 15 and 16, 1998, in a moderate-altitude oligomesotrophic lake (Lac Pavin, France), at 5 and 10 m depths. At both depths, losses of the bacterial community by viral lysis (LA5 m = 1.7 x 106 cells.1-1.h-1, LA10 m = 2.0 x 106 cells.1-1.h-1) were, on average, lower than those due to the grazing activity of flagellates (FG5 m = 10.3 x 106 cells.1-1.h-1 , FG10 m = 8.4 x 106 cells.1-1.h-1). A carbon budget exercise indicated that, for the sampling period and depths, 17.8 % of C from TPP (= 38.1 % of EPP) was used by bacteria. On the other hand, 52.7 % of BP (= 2.15 % of TPP) was grazed by nanoflagellates, while 11.0 % of BP (= 0.45 % of TPP) was lysed by viruses.

The morphology and ecology of a†new species of the cyanophyte/cyanobacterial genus Aphanizomenon Morren ex Bornet etFlahault, A. slovenicum Rekar et Hindák, are described from Lake Bled, NW Slovenia. The species produced a heavy waterbloom in May - December 1997 but disappeared during 1998. Macroscopic flakes of bundles of trichomes similar to A. flos-aquae (L.) Ralfs ex Bornet et Flahault formed in a layer between 10 - 20 m depth. They differed from A. flos-aquae by shorter and narrow short cylindrical to barrel-shaped cells, and by trichomes that sometimes consisted of morphologically different cell sections. Maximum abundance was found in August : 655 trichomes.m1-1. Heterocytes were occasionally present and akinetes have been observed only in laboratory cultures. The main characteristics of the investigated cultures of A. slovenicum and A.flos-aquae isolated from a fishpond at Ledava (NE Slovenia) are given.

Les variations verticales et saisonnières de l'activité de la phosphatase alcaline (APA) des communautés microplanctoniques ont été étudiées dans le lac réservoir mésotrophe Allai El Fassi, situé sur l'oued Sebou. Les échantillons ont été collectés à différentes profondeurs au point le plus profond du lac, de mars à décembre 1998. Les résultats montrent que l'APA totale est exclusivementassociée à la fraction de taille 0,22-100 μm dont les valeurs moyennes sont comprises entre 0,107 et 1,780 mmol PNP1-1 h-1 . La fraction dissoute (< 0,22 μm) ne présente aucune activité liée à cette enzyme. Au niveau des couches superficielles,plus de 60 % de l'APA totale sont corrélés à la fraction de taille 0,22-0,65 μm à majorité bactérienne. Cependant, avec la profondeur,l'APA est plutôt associée à la fraction de taille 0,65-100 μm à dominance phytoplanctonique (> 58 % de l'APA totale).Cette activité liée aux algues est significativement corrélée avec la densité phytoplanctonique et avec les concentrations de lachlorophylle a. L'absence de corrélation significative entre l'APA et les teneurs en phosphore total et orthophosphates suggèreune indépendance entre l'APA et les orthophosphates.

The epiphytic diatom communities living on two macroalgae, Chara vulgaris L. and Cladophora glomerata Kütz.) and oneangiosperm Potamogeton densus L., were collected in the Mediterranean river Durance. Each macrophyte species was studied on the basis of three plant replicates, each of which cut into three segments. Although considerable heterogeneity was observed in density of the epiphytic populations between the plant species studied as regards, the composition of these algal populations showed a conspicuous degree of homogeneity within each macrophytic species. These observations were corroborated by the coefficients of variation calculated on the main diatoms and by the non parametric Friedman tests.The qualitative homogeneity of epiphyton on Potamogeton densus foliage made it possible to map the spatial repartition of the main groups of diatoms growing on the upper side of leaves.These data support the hypothesis that the epiphytic algae occupy specific microhabitat niches on their host plants according to a non stochastic pattern of distribution.

Flavodoxin and ferredoxin can be used as molecular markers for determination of biolimitation of iron in phytoplankton. TwoELISA tests have been used for determination of flavodoxin and ferredoxin respectively in samples from three endorheiclagoons.

Concentrations of a wide range of chemical variables were determined in 206 water samples taken between May 1996 and May 1998 from a set of 25 natural lakes in the French Massif Central. From each lake 6 to 9 samples were collected. Mean and standard deviation of total alkalinity, conductivity, pH, concentrations in K+ , Mg2+ , Ca2+ , Na+ , Cl-, SO2 4 , total phosphorus, nitrate-nitrogen, dissolved silica, chlorophyll a, and water colour were calculated for each lake. These results are briefly compared with those obtained in an earlier study in which chemical analyses were carried out on a reduced set of lakes from the same region. In most lakes and for most elements, concentrations observed in the present study were similar to those observed previously. The seasonal variations of the elements which are most strongly influenced by biological processes were also investigated. Using hierarchical cluster analysis three main lake groups were distinguished : i) alkaline lakes, ii) deep lakes with lowalkalinity and iii) shallow lakes with low alkalinity. The major patterns of variation in the data set were also investigated using principal components analysis (PCA), which confirms that total alkalinity and maximum water depth are the main environmental gradients in this set of lakes. In conclusion, the potential of this data-set for building diatom-based transfer functions to reconstruct past limnological conditions is discussed.

Les modèles biologiques constituent un élément fondamental de la méthode des microhabitats pour l'évaluation de la capacité d'accueil potentielle des cours d'eau vis-à-vis des organismes aquatiques. Avec l'importance croissante de la problématique «habitat» dans les études d'impact est apparue la nécessité de disposer d'outils informatiques performants pour la réalisation des calculs complexes et fastidieux qui en découlent. ProCURVE est un logiciel entièrement dédié à la construction de courbes depreferenda et de profils écologiques pour les organismes aquatiques. Il élabore ces modèles biologiques en accompagnant l'utilisateur dans une démarche analytique logique et rigoureuse. Le logiciel permet une gestion aisée des données. La souplesse de la base de données relationnelles lui confère de nombreuses possibilités d'analyses linéaires ou transversales. Son ouverture surles bases de données externes permet d'envisager le traitement de données déjà disponibles dans la bibliographie. Les variables écologiques utilisées communément sont fournies par défaut mais l'utilisateur a la possibilité de les configurer selon ses besoins. Les résultats générés sont visualisés directement. Ils peuvent être sauvegardés sous forme graphique ou exportés au format des principaux tableurs pour un traitement complémentaire.

Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju, a potentially toxic bloom forming cyanobacteria(Nostocales), was recorded in the River Seine in August 2001. The cyanobacterium was previously observed in some French ponds but this is the first report of this reputedly tropical species in a river in France.