AME 11:31-41 (1996)  -  doi:10.3354/ame011031

We examined the horizontal variability of bacterioplankon growth dynamics in the western part of Lake Constance, Germany, including its northwestern fjord-like arm, Lake Überlingen. From May until September 1993, we measured depth profiles of bacterioplankton abundance and production as well as temperature and chlorophyll at 7 stations on the same day or on 2 consecutive days. In addition, we examined the horizontal distribution of bacterioplankton growth with a higher areal resolution in Lake Überlingen in August 1993 and May 1994 by collecting samples from the upper 20 m at 10 stations on 4 occasions. In August 1994 we also measured these growth dynamics in 1 km² in the center of Lake Überlingen by sampling 9 stations. The results show that the variability of bacterioplankton production was more pronounced than that of abundance and that the variability was always greatest in the upper 10 m. Total horizontal variability of bacterioplankton production ranged from <2- to 8-fold but in most cases remained <3-fold. Greatest variabilities always occurred at the transitions between different seasonal phases such as the phytoplankton spring bloom and clear-water phase or clear-water phase and phytoplankton summer bloom. On the basis of the coefficient of variation of the horizontal mean of production rates (standard error/mean) variability in the total study area and in Lake Überlingen was greater than that in 1 km² in the center of Lake Überlingen, which was still greater than the within-sample variation. The seasonal dynamics of bacterioplankton growth were fairly similar at all 7 stations and 3- to 6-fold higher than the horizontal variability. We did not find any systematic horizontal patterns of bacterioplankton growth dynamics and there were no clear correlations to horizontal patterns of chlorophyll or temperature.

Bacterioplankton growth · Horizontal variability · Large lakes