Empirical factors for converting 3H thymidine incorporation into bacterial production were determined from samples taken in a mesotrophic lake. Twenty five diluted water cultures were conducted at "in situ" temperature (4-22° C) from April 1987 to February 1989. The conversion factors varied through the year ; the average conversion factor was 6.29 × 109 cells (2-10.7) per nanomole of thymidine incorporated into cold TCA precipitate and 7.18 × 109 cells (3.47-10.7) nmol-1 , when corrected for the increase in cell biomass which occured during the incubations. The validity of these factors, higher than the theoretical conversion factors values, is discussed considering the diluted water culture conditions and the data analysis methods.

Stygoelaphoidella stygia n. sp. est décrite d'une grotte dans les Vasilijovska Mountains du Nord de la Bulgarie et d'une petite rivière dans la grotte du village de Lipnitza - District de Sofia - en Bulgarie occidentale.

Zooplankton samples collected at low and high water in 14 and 21 stations respectively along some 900 km of the Orinoco and its Delta, revealed the presence of 100 rotifer and 48 cladoceran taxa. Of these, only 13 rotifer and 8 cladoceran species were frequent and numerically important, mainly Keratella americana, Lecane proiecta, Ploesoma lenticulare, Polyarthra vulgaris, Bosmina tubicen, Bosminopsis deitersi, Diaphanosoma birgei and Moina minuta. Nauplii were dominant among the copepods. At low water, rotifers were by far the most abundant group (mean 49 org./l ) followed by cladocerans (mean 2.8 org/l) and copepods (1.5 org/l). At high water, rotifer densities declined to a mean of 3,5 org/l, followed by copepods (mean 3.4 org/l) and cladocerans (1.2 org/l). Mean zooplankton densities at low water were eight times higher than at high water. At low water, longitudinal zooplankton densities seemed to be influenced by tributary river waters. At high water, densities were generally low up to the Delta where a longitudinal increase was observed. A high proportion of egg carrying cladocerans, particularly B. tubicen, B. deitersi and M. minuta, were observed at low water along the sampling sites, suggesting an ability of the species for growth and reproduction in the river.

The authors present a list of aquatic Enchytraeidae for the streams of Southern England. They examine the distribution of the species.

Une espèce nouvelle, Baetis albinatii nov. sp., est décrite (imago mâle et larve au dernier stade) à partir de matériel récolté en Corse. Elle appartient au groupe muticus et est très voisine de B. navasi Müller-Liebenau, 1974.

Le développement larvaire des 4 espèces de Plécoptères Capnia ? arensi Zhiltzova, Brachyptera galeata Koponen, Protonemura libanocypria Zwick et Isoperla libanica Aubert est étudié. Ces espèces colonisent un ruisseau temporaire du Liban. C. ? arensi est une espèce hivernale, B. galeata et P. libanocypria sont printanières, I. libanica est printanière tardive.

Deux espèces de Simulies appartenant au groupe de Simulium monticola (Friederichs) sont décrites d'après du matériel récolté dans des ruisseaux froids de haute altitude dans le Haut Atlas central. Simulium atlasicum est connue dans une seule station, à 2 100 m d'altitude. Simulium berberum a été récoltée dans cinq stations entre 2 300 et 3 200 m d'altitude.

Le catalogue des Chironomidés des Alpes françaises et des basses régions avoisinantes, c'est-à-dire de la portion du territoire français située au sud et à l'est du Rhône (Camargue comprise), est établi à partir des travaux antérieurs. L'aire couverte se présente comme une interpénétration complexe d'une partie de la zone 4 (Alpes au-dessus de 1 000 m d'altitude) et d'une partie de la zone 13 (basses régions occidentales au-dessous de 1 000 m d'altitude) de la Limnofauna Europaea d'Illies(1978).On a recensé au total 335 espèces, dont 13 nouvelles pour la zone 4 et 123 nouvelles pour la zone 13. En France, le total des espèces de Chironomidés connues des Pyrénées, du Massif Central, des Alpes et des basses régions situées approximativement au sud de la Loire et du Rhône s'élève actuellement à 496.

Species composition, distribution and biomass of benthic macrophyte communities have been studied in a high mountain, oligotrophic, softwater lake from the Central Pyrenees. Isoetids (Isoetes lacustris L., Isoetes setacea Lam., Subularia aquatica L. and Eleocharis acicularis (L.) Roemer & Schultes) are the dominant macrophytes in areas over 2-3 meters in depth. Natopotamids (Sparganium angustifolium Michx.) are restricted to shallow waters. Algae (Nitella gracilis (Smith) Agardh) only predominate in deep waters. Three main communities have been distinguished : the Sparganium angustifolium community (160 g dwt m-2), the Isoetes lacustris community (120-460 g dwt m-2) and the Nitella gracilis community (11 g dwt m-2). Biomass differences between shallow and deep water Isoetes populations have been attributed to ice-scour stress. Neither irradiance nor slope can explain the lower boundaries observed in the distribution of vascular plants ; sediment features may be responsible for them. Mean lake macrophyte biomass amounts to 140 g dwt m-2 (20 g C -2), a very high value if compared with boreal lakes with similar limnological characteristics.