Microbiological investigations in the river Danube: Measuring microbial activities and biomass

Abstract

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.

Remineralization of organic matter and degradation of the organic fraction of suspended solids in the River Danube

“…The predominance of small bacteria (0.24 pm3; Kasimir 1992) and a high flagellate abundance (mean: 4.6 X 103 ml-') in the River Danube support this conclusion. The flagellate abundance found in this study is in good agreement with that reported by Kasimir (1992) (range: 1 to 22 X 103 ml-l); similarly, Carlough & Meyer (1989) found l l X 103 flagellates ml-' in the Ogeechee River. Despite high flagellate numbers commonly occurring in rivers, Fenchel (1986) noted that protists are not important in lotic systems because of high wash-out rates.…”

“…During periods of tant abiotic factors regulating bacterial activity (via generally high remineralizatlon activity, the abunalteration of the amount of suspended and dissolved dance of more refractory compounds led to a lower organic matter), no correlation could be detected bepercentage of DOC being utilized by the bacterial tween BOD rates and discharge (Kasimir 1992). Fluctucommunity and hence to lower oxygen consumption in ations in suspended matter may influence other imporBODs.…”

Spatio-temporal Investigations on the Planktonic Organisms of the Middle Loire (France), During the Low Water Period: Biodiversity and Community Dynamics

“…As observed by Grobois et al (2001), the downstream site remained the most productive zone of this stretch all along the sampling period, owing to the tributaries input. The bacterial density increased up-to downstream as observed in the Meuse (Servais, 1989) and in the Danube (Kasimir, 1992). At 4Ch, the very high numbers of bacteria, certainly supported by the carbon inputs of the tributaries, were in the upper range of the values observed in rivers (Servais,1989;Kasimir, 1992;Hoch et al, 1995;Basu & Pick, 1997;Meybeck et al, 1998).…”

The Prevalence of Freshwater Flocculation in Cold Regions: A Case Study from the Mackenzie River Delta, Northwest Territories, Canada

“…Bacteria often show an affinity for flocs because of their protective support as a beneficial microhabitat and because organic nutrients adsorb onto particulate surfaces and thus represent a nutrient source and colonization site for the bacteria (Paerl, 1975;Goulder, 1976;Logan and Hunt, 1987). While attached bacteria may not always be dominant, the significance of this sediment-bacteria relationship lies in the fact that bacteria associated with particulate surfaces demonstrate greater metabolic activity than free-floating bacteria (Logan and Hunt, 1987;Kasimir, 1992). Liss et al (1996) have demonstrated that it is the bacteria's metabolic production of EPS which is the dominant mechanism controlling floc development, structure, stability, and behaviour.…”

“…Bacteria have been shown to be an integral part of most natural floc structures (Logan and Hunt, 1987;Droppo and Ongley, 1989, 1992Muschenheim et al, 1989;Liss et al, 1996) and were observed to be an important constituent of MRD flocs for the September samples. While often the majority of bacteria are free-floating in freshwater environments (Geesey and Costerton, 1979;Kirchman, 1983), there are reports of environments and conditions where the attached bacteria are dominant (Goulder, 1976;Bell and Albright, 1981;Lind and Lind, 1991).…”