AME 09:279-288 (1995)  -  DOI: https://doi.org/10.3354/ame009279

To determine the role of microbes in the degradation of organic matter in the River Danube, the biochemical oxygen demand (BOD) was followed over 2 and 5 d from July to December 1993, and the fluctuations of the microbial community were monitored in incubation flasks over the incubation periods of 2 and 5 d from January to December 1993. In the BOD flasks, bacterial abundance increased by up to 63% of the initial abundance during the first 15 h of incubation followed by an increase in flagellates, reaching their maximum about 35 h after starting the incubation. After 60 h, bacterial abundance declined to 15% of the initial density. This rapid fluctuation indicates that the BOD method routinely used to monitor water quality may be inappropriate for measuring the degradability of organic matter since the confined bacterial community is efficiently controlled by flagellates. The role and degradability of the organic coating of suspended solids was evaluated by Alcian blue staining and transmission light microscopy. Degradation experiments revealed that the number of particles decreased by up to 50% during the incubation period indicating rapid microbial utilization of this particulate matter.

River Danube . Large river . Particle . Bacteria . Flagellates . BOD . Seston . Degradation