Bacterial population dynamics, production, and heterotrophic activity in a recently formed reservoir

Seasonal and spatial fluctuations in abundance, biomass production, and potential heterotrophic activity (i.e.,C-14-glucose uptake) of bacterioplankton assemblages in a 1-year-old reservoir (the Sep Reservoir, Puy-de-Dome, France) were examined concurrently with water temperature, phytoplankton chlorophyll a concentration, and primary production (PP). Based on the values observed for these biological variables, the Sep Reservoir was considered to have evolved to an oligo-mesotrophic state. Spatiotemporal variations of bacterial variables were a consequence of the seasonal evolution of the reservoir coupled with the resource availability. Multivariate regression analyses suggest that about 14 and 26% of the variance in bacterial standing stock and activity may be explained by the physical environment (i.e., temperature) and a resource availability index (chlorophyll a concentration or primary production), respectively. A carbon budget indicated that 4-126% (mean = 20%) of the ambient PP may be channeled through the microbial loop via bacterial biomass production. Heterotrophic bacterial production in the Sep Reservoir may therefore, on occasion, represent a significant source of carbon for higher order consumers.