Diel changes in numbers and activities of bacterioplankton in a reservoir in relation to algal production

Abstract

The changes in bacterial numbers, relative growth rates, and glucose uptake kinetics were studied in the surface layer of a reservoir during several 24‐h observation periods at intervals of 3 or 6 h, and once a day at intervals of 4 or 6 weeks from April through October. Microscopic and plate counts did not show any diel periodicity. All the other measures had regular diel patterns and the range of diel variation increased with increasing algal production. The diurnal average relative growth rates, Kt + Sn values, and turnover times were distinctly higher than the nocturnal ones and there were also characteristic diel changes in glucose uptake kinetics during the periods of algal activity. The diel changes in bacterial net uptake rate of algal extracellular products in autumn samples were twice as high as the maximum glucose uptake rate. Only for microscopic counts and maximum glucose net uptake rates were the diel variations significantly lower than the seasonal variation. For other parameters, the diel and seasonal variations were similar.