ANAEROBIC PROCESSES IN CYANOBACTERIAL AGGREGATES IN AERATED SURFACE WATERS

• The coupling of aerobic and anaerobic processes in cyanobacterial aggregates was investigated. Major pathways of the nitrogen cycle (N2 fixation, nitrification, denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA)) were measured via the isotope pairing technique in individual cyanobacterial colonies (Nodularia spumigena) collected in the Baltic Sea. Oxygen and N2O fluxes were measured with microsensors. High rates of dark respiration in Nodularia aggregates reached the limit set by O2-diffusion from the surrounding water to Nodularia colonies creating anoxic microzones within aggregates. The release of NH4+ deriving from N2 fixation supplied the microbial community with dissolve inorganic nitrogen (DIN), and we proofed the potential of nitrification, denitrification and DNRA in anoxic aggregates. Hence, mm-large aggregates of cyanobacteria and attached bacteria are not just sites of N2 fixation but also meet the physical/chemical constraints (oxic–anoxia interface, DIN, OM) for coupled aerobic and anaerobic processes to occur in fully aerated waters. These results may also apply for other particulate material (marine snow) in marine and freshwater systems which would be of major significance for the global nitrogen cycle.

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NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

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