Abstract
Pelagic bacteria (BAC), heterotrophic flagellates (HNF), ciliates (CIL), autotrophic picoplankton (APP), phytoplankton (PHY) and zooplankton (ZOO) were studied for 2 ice-free periods in 7 low-alkalinity alpine lakes of 6 Lake Districts. Another 304 alpine lakes from 10 Lake Districts were sampled once per season (late summer) for BAC, ZOO and chlorophyll (CHL).
BAC abundances (0.02-2.7 mill.per ml) corresponded to values found in other oligotrophic lakes. Exceptionally high values were found in two high-conductivity Lake Districts, Julian Alps and Greenland.
APP abundances were scarce or absent, except of lake Lochnagar in Scotland, with high sodium chloride concentration. Biomass of HNF and CIL usually reached 6 to 30% of BAC biomass, except North Finland with CIL up to 50% of BAC.
PHY biomass varied considerably among lakes and during season. Redundancy analysis proved that more of explained variation in BAC is accounted for physico-chemical parameters than for ZOO and CHL.