The aim of the work is the investigation of the biogeochemical factors influencing the oxygen dynamics of the Baltic Sea. During the investigation of these factors the dependency of a variable C:N:P ratio on PO4 for the parametrization in cyanobacteria was proposed. The parametrization of additional oxygen consumption due to oxidation of reduced forms of sulfur, Mn and Fe was stated. The possible parametrization of spring N-fixation was suggested.