Abstract
This study presents the vertical distribution of phosphorus fractions in three postglacial mid-forest humic lakes: oligohumic, mesohumic, and polyhumic. Total phosphorus concentrations were similar in these humic lakes (mean 76 μg 1-1 P). The greatest share of phosphorus was in mineral fractions, while a lesser share was in organic, especially soluble, fractions. Concentrations of mineral forms (phosphates and polyphosphates) were the lowest at the time of maximum development of phytoplankton, especially of bacterioplankton near the bottom of the oligohumic lake. An exceptionally high participation of soluble polyphosphates was found in the polyhumic lake near the surface.