Nutrients, Biomass and Primary Productivity of Nannoplankton in Eutrophic Lake Vombsjön, Sweden

Seasonal variations of physical and chemical factors were studied in the eutrophic, usually totally-circulated, Lake Vombsjon in South Sweden, 1970 through 1973. Biomass and primary productivity of nannoplankton (< 20 jm) and of the total phytoplankton community were investigated 1971 through 1973. Nannoplankton biomass, estimated as chlorophyll a, was highest in early spring (3040 mg m-3) and averaged 20 mg m-3 in summer. A 10-fold variation of nannoplankton biomass occurred throughout the year, compared with a 25-fold variation for netplankton biomass. During late summers, when temperature was high and the surface water enriched with nutrients, blue-green algae (netplankton) dominated. Productivity of nannoplankton and of the total phytoplankton community was 3-193, and 8-550 mg C m-2 h-1, respectively. Correlations between biomass and productivity were established. A significant difference in the photosynthetic capacity of nannoplankton, as compared with netplankton, was found. Mean annual productivity of the total phytoplankton community was 525 g C m-2 yr-1, of which about 50%. was photosynthesized by nannoplankton.