Submodels of a Brackish Water Environment.

Microbial biomass production rates were determined in the brackish water of Kiel Fjord (Western Baltic Sea). The calculated rates are based on the actual uptake data of 14C-U-labelled carbohydrates (ribose, glucose, fructose and galactose). The relation to data obtained from uptake of HC-labelled phytoplankton exudates is discussed. The average microbial biomass production varied from 0.018 to 5.81 μg C I1 h-1. This represents an average of 15 % of the primary production over an annual cycle. A comparison with other data concerning microbial biomass production indicates that glucose may be used as a model to calculate fluxes of dissolved organic matter in this ecosystem. The amount of produced particulate matter by microheterotrophes is discussed with regard to higher trophic levels.