AbstractThe aerobic decomposition of freshwater phytoplankton was monitored over a 10 day period to determine rates of production and microbial utilization of total dissolved organic carbon and dissolved carbohydrates. Following molecular weight fractionation of the total dissolved organic and carbohydrate carbon produced, it was found that each component contained a highly labile as well as a partially refractory fraction. Specific decomposition rate constants were determined for both fractions. Molecular weight retention characteristics of the ultrafilter used were also evaluated.