Planktonic bacterial biomass and seasonal pattern of the heterotrophic uptake and respiration of glucose and amino acids in the shallow sandpit lake of Cr�teil (Paris Suburb, France)

Abstract

Biomass and activity of planktonic bacteria were investigated during a one year study in a shallow sandpit lake. The shallowness of the lake helped keep the water column homogeneous regarding bacterioplankton. Small free-living bacteria (0.03 µm3 cell−1) dominated the populations throughout the period studied. Bacterial abundances varied from 1 to 11 × 106 cells ml−1. Kinetic parameters (V max, K + S and T) were determined with 14C labelled compounds (glucose and amino acids mixture). V max values were high and averaged 0.056 and 0.050 µgCl−1 h−1 for glucose and amino acids respectively. Maximal V max values were observed in summer at the highest temperatures, but also in early spring. T values were much greater in winter. K + S values were significantly higher for amino acids (3 µg Cl−1) than for glucose (1 µg Cl−1). A low percentage of mineralization (about 25% for both tracers) could be the expression of the high growth efficiency expected when bacteria are growing at the expense of low molecular weight compounds as phytoplankton exudates.