THE RELATIONSHIP BETWEEN BACTERIAL ABUNDANCE AND CONCENTRATION OF PLANKTONIC CHLOROPHYLL IN FRESH-WATER LAKES

The relationship between the total bacterial abundance (N-b) and the c oncentration of planktonic chlorophyll a (CHL) was analyzed in six lak es in southern Karelia, 16 lakes on the Karelian Isthmus, and two smal l lakes in the Luzhskii raion of Leningrad oblast, one of which was us ed as a hatchery for whitefish and carp, N-b values varied from 0.67 t o 14 million cells/ml, and CHL values, from 0.33 to 200 mu g/l. Such v ariability was accounted for by intra-and interseasonal fluctuations a nd by the different trophic states of the lakes. Based on aggregate da ta (n = 163), the relationship between N-b and CHL could be approximat ed by the equation N-b = 1.552 CHL0.275. The exponent in this equation is reliably less than 1. This means that the number of bacterial cell s per unit phytoplankton mass increases with a decrease in the chlorop hyll a (i.e., with the change in the trophic state of the lakes from e utrophic to oligotrophic). This regularity, also noted by other resear chers in the lakes of Japan, Canada, the United States, and New Zealan d, has not yet been convincingly explained. A hypothesis is proposed i mplying that, with the change in the trophic conditions in the reservo irs from eutrophic to oligotrophic, the role of heterotrophic microorg anisms in the transformation of organic matter produced by phytoplankt on increases.