Spatial and temporal variations of bacterioplankton in a high-mountain reservoir in the Colombian Andes

Abstract

The contribution of bacterioplankton (BP) to the planktonic food web, as well as environmental and biological factors involved in its control remains unexplored in tropical high mountain environments. In a tropical high-mountain aquatic system of Colombian, Neusa reservoir, the spatial and temporal dynamics of abundance, biovolume and biomass of BP were evaluated in relation to environmental variability and density of autotrophic nanoplankton (NA) and heterotrophic nanoflagellates (NFH). There was no clear association between BP dynamics and nutrients. However, this relationship appeared to be indirect through stimulation of NA production during periods of increased mixing and rainfall. The highest BP abundances and biomasses were detected in the littoral station in consistency with low numbers of NFH and potential organic inputs derived from macrophytes. The total cellular carbon and average cell biovolume of BP were weakly correlated with the dynamics of NFH, which was attributed to the predominance of phosphorus-limiting conditions and potential removal of NFH and BP by larger zooplankton fractions (> 20 ?m). Approximately, 60% of the total prokaryotic biomass was provided by small sizes (<0.18 ?m3). The data suggest that the distribution of cell biovolume could be the result of the synergistic effect between nutrient limitation and selective grazing. BP dynamics in the Neusa reservoir indicates the existence of a slightly fluctuating carbon reservoir and an inefficient carbon transfer through the microbial loop to higher
trophic levels.