Excretion of Organic Matter during an Experimental Phytoplankton Bloom Followed Using o-Nitrophenol as an Electrochemical Probe*

Extracellular excretion of the surface active organic matter during a nutrient enriched phytoplankton culture growth was studied using o-nitrophenol (ONP) as an electrochemical probe. Changes in the hydrophilic and hydrophobic acid fractions, as compared to the unfractionated seawater sample, were followed during the twelve days of the experiment. Diatoms were the dominant phytoplankton species growing during the experiment. It was observed that the enrichment of natural seawater by nutrients caused increased concentrations of both polysaccharides and proteins, in dissolved and particulate phases. At the end of the experiment, polysaccharides were the dominant adsorbable organic matter on the mercury electrode according to the changes of the electrochemical characteristics of the ONP probe. The excreted polysaccharides were weakly acidic. Their estimated concentration was equivalent to 1.2 mg dm¿3 as neutral dextran T-500 or 3 mg dm¿3 as weakly acidic hyaluronic acid.