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Northern Adriatic mesocosm experiment Rovinj 2003: dynamics of organic microparticles studied by the electrochemical technique

Background and Purpose: Mesocosm bloom experiment "Rovinj 2003" was the unique opportunity to evaluate relation and relevance of presently available measurement techniques for monitoring organic microparticles in the northern Adriatic. A more specific goal was to contrast particle formation in low P and high P nutrient enrichments using the advantages offered by electrochemical method. Materials and Methods: A dropping mercury electrode (DME) immersed in seawater sample was used for direct measurement of organic microparticles, which were recorded as single particles and classified through their specific amperometric signals as: -surface-active (vesicle structure), SAP or -gel microparticles (three dimensional network structure), GeP. Results: SAP are the main fraction of electrochemicaly detected particles throughout the bloom experiment.Maximum SAP abundance is 25x10^6 particles per liter in low P nutrient enrichment and is smaller in high P regime. The dynamics of SAP appears to correlate well with that of microphytoplankton. GeP represent a smaller fraction (maximum 30%) of electrochemicaly recorded particles, being more abundant in earlier phases of the bloom. Conclusions: Two distinct classes of microparticles were identified to form during the phytoplankton bloom that differ in their molecular organization rather than in chemical composition. Dynamics of microparticles formation is enhanced in high P enrichment, while the particles are more abundant in low P enrichment.

surface-active particles; gel microparticles; electrochemical detection of microparticles; TEP; phytoplankton bloom; northern Adriatic Sea

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