THE CARBON BALANCE OF PHYTOPLANKTON PRODUCTION AND LOSS PROCESSES BASED ON IN-SITU MEASUREMENTS IN A SHALLOW LAKE

The balance of phytoplankton biomass was studied during spring and early summer 1986 and 1987 in Lake Muggelsee, a eutrophic polymictic lake. It is assessed as the result of biomass changes, gross primary production (C-14-method) and physiological or internal and ecological or external losses. Biomass changes, primary production, grazing, dark carbon losses and exudation were estimated from in situ measurements. The remaining light carbon losses and net sedimentation were calculated from the phytoplankton balance of the lake. On average the physiological losses of algae ranged between 80.5 of primary production in 1986 and 72 % in 1987. Dark carbon losses by respiration ranged between 15 and 20 %, and grazing losses between 24.5 and 21.9 % of gross primary production in 1986 and 1987, respectively. The remaining 16.6 and 23.6 % of primary production which were lost in 1986 and 1987, respectively, are mainly attributed to sedimentation.