Examination of a freshwater surface microlayer for diel changes in the bacterioneuston

The surface microlayer of a small freshwater pond was sampled every 6–8 hours on four occasions (April, July, September, and November) to examine changes in total and respiring bacterioneuston for diel cycles and comparing them to similar measurements of the bacterioplankton. Dissolved organic carbon (DOC), dissolved reactive phosphorous (DRP) and ammonia nitrogen (NH₃-N) were also measured. Both the mean numbers and enrichments of the two bacterial parameters in the surface microlayer samples showed seasonal differences, but in general, no significant difference (P > 0.05, ANOVA) in the mean numbers of total and respiring bacterioneuston were observed over diel periods except in November. The converse was true for the bacterioplankton. The presence of a visually thick surface film contributed to the results. The mean numbers of bacterioneuston and their enrichments were not correlated to any of the physical/chemical parameters measured.