Abiotic formation of particles from extracellular organic carbon released by phytoplankton.

(14)C-labeled extracellular organic carbon (EOC) released by the phytoplankton in a Danish Estuary was shown immediately to form particles (>0.2μm) when the products were added to a natural water sample. About 14%-20% of the added activity could be recovered as particles. Any bacterial assimilation of the extracellular products was thus masked. The abiotic origin of the particulate EOC was verified, and it was shown that the particle formation was due to some factors present in the estuarine water with a nominal diameter >0.2μm. Precaution must be taken to avoid misinterpretations in studies concerning carbon flow from algae to bacteria.