HETEROTROPHIC BACTERIAL PRODUCTION AND ITS DEPENDENCE ON AUTOTROPHIC PRODUCTION IN A HYPERTROPHIC AFRICAN RESERVOIR

Incorporation of [methyl-3H]thymidine (TdR) into bacterial DNA in Hartbeespoort Dam, South Africa was measured over 16 mo and at nine depths. Bacterial numbers at the surface ranged between 2.45-and 32.20 × 106 cells.mL-1 (mean 8.83 × 106 mL-1) while bacterial production varied between 1.0-251 pmol TdR.L-1.h-1 (0.01-1.9 mg C.m-3.h-1). At the bottom, production ranged between 0-26.7 pmol TdR.L-1.h-1 (0-0.2 mg C.m-3.h-1). At the surface, bacterial production was dominantly correlated to chlorophyll a (6.6-6530 mg.m-3) and phaeopigments (0.9-378 mg.m-3) followed by primary production (26.6-8886 mg C.m-3.h-1). Below 5 m, water temperature and bacterial numbers were the dominant correlates. Bacterial production for the water column averaged 2% of daily, areal primary production. The low bacterial production compared with primary production, together with the small size of the bacteria, suggest substrate supply was a major limiting factor of bacterial growth. -from Authors