No abstract

Human noroviruses (NoV) were quantified and characterized in an 18 month survey conducted along the Llobregat river catchment in Spain. Sample types included freshwater, untreated and treated wastewater and drinking water. High NoV genome copy numbers were reported, reaching up to 10(6)  l(-1) and 10(9)  l(-1) in freshwater and raw sewage respectively. In both types of samples, GII NoV genome copies outnumbered those of GI, although without significance. All samples of semi-treated and treated drinking water were negative for NoV. A clear seasonality of NoV occurrence was observed both in river water and sewage samples, with significantly higher genome copy numbers in the cold than in the warm months period. Mean NoV log reduction rates after biological treatment of sewage were 2.2 and 3.1 for GI and GII respectively. A total of 77 NoV strains isolated in the Llobregat river catchment could be phylogenetically characterized, 44 belonging to GI and 33 to GII. The most prevalent genotype was GI.4, followed by GII.4 and GII.21. Several variants of the pandemic GII.4 strain were detected in the environment, corroborating their circulation among the population.

Bacterial numbers, biomass and production estimates were performed in the impound ment of Altenworth (Austrian part of the Danube) and in a longitudinal profile of the Danube between stream kilometers 16 and 1934. For production estimates, two approaches were compared. The frequency of dividing cells (FDC) approach gave higher estimates compared with the thymidine incorporation approach. The two approaches showed no parallel results, FDC seems to reflect past activities of allochthonous bacteria in their indigenous biotopes. Bacterial numbers and biomass were in the range of other big rivers and showed an increase from upstream to downstream. This trend is disturbed during HQ-situations, however. The discharge has the greatest impact on the system and superimposes other influences. A large part of the bacteria originate from soil biotopes. In spite of the long generation times (up to 5 days), bacterial production is high enough to allow the production of a considerable part of the existing bacterial biomass within the Danube. Particle-bound bacteria represent a high percentage (up to 43%) of the entire bacterial count. A high percentage of the bacteria is extremely small. Heterotrophic nanoflagellates are present in such numbers in the Danube that they probably exert pressure on the bacterial population.

After a high water event of the River Danube in April 1994, bacterial cell numbers were determined in newly formed deposits in a backwater near Hainburg (Lower Austria) within a time course of 140 days. This data set shows that expressing bacterial numbers per fresh sediment volume, per sediment dry mass, or per pore-water fluid volume, respectively, yield significantly different results and ecological conlusions. These findings refer particularly to intra-study and time-course comparisons as presented in our case. Bacterial cell numbers expressed per gram sediment dry mass revealed statistically significant differences between the beginning and the end of the study, whereas expressed per cm 3 of fresh sediment or fluid volume of sediment pore water, no statistical difference could be detected. It is argued that these differences were caused by physical sediment compaction and mineralisation processes over the considered time-course. Such mechanisms may simulate biological activity if some basic sediment parameters are neglected and thus standardisation has to be done with caution for the particular situation being observed.

No abstract