The relation between bacterial carbon and dissolved humic compounds in oligotrophic lakes

The mean annual biomass of planktonic bacteria showed large variations both within and between lakes. The lowest bacterial biomass was found in acidified lakes (7.8–12.1 μg C · 1−1), and tended to increase with increasing water colour (up to 44.1 μg C · 1−1). The highest recorded bacterial biomass was 138 μg C · 1−1. The mean annual bacterial biomass equalled 23–45% of the algal biomass. Zooplankton biomass was high, compared to algal biomass (40–50%). Multiple regression analysis of 10 variables showed a strong positive correlation between bacterial biomass and humic content (r= 0.74, P < 0.001), while other parameters, except pH, showed no correlation. The observation thus strongly supports the role of humic compounds in aquatic secondary production.