Recent dynamics of bacterioplankton in Lake Ladoga

New data are presented on the dynamics of total bacterioplankton numbers (BN) and dark CO2-fixation (DCF) in 1989–1993. During this period, both BN and DCF have been much higher than in the preceding years. Summer averages of DCF and BN for the period 1985–1988 were 0.49 ug C l–1 d–1 and 0.54 x 106 cells ml–1, and for 1989–1993 they were 2.4 µg C l–1 d–1 and 1.02 x 106 cells ml–1, respectively. The summer 1992 averages of BN, 2.26 x 106 cells ml–1 in epilimnion and 1.16 x 106 cells ml–1 in hypolimnion are the highest values recorded since the beginning of bacterioplankton investigations in Lake Ladoga in 1977. The increase of DCF and BN has been accompanied with a considerable decrease (from 9 down to 6.3–8.3 mg l–1) of total organic carbon levels in Lake Ladoga.