engleski

Variability of surface active organic material in the northern Adriatic

Sorption properties of naturally present surface active substances (SAS) on the XAD-8 resin and their adsorption behaviour at the mercury electrode surface have been investigated during the development of mixed plankton assemblages collected in the area of the Gulf of Trieste and incubated in early summer of 1994 and early spring of 1995 and 1996. Daily variations of SAS in mixed cultures were studied, including fractionation of the complex mixture of SAS into hydrophobic neutral, hydrophobic acid and hydrophilic compounds at different growth phases of phytoplankton communities. During the developemnt of microflagellates, quantitative and qualitative compositions of SAS have not been changed significantly. The concentrations of SAS were rather high (0.225-0.250 mg/l eq. Triton-X-100), and showed oscillations with an increasing trend in the last two days of the experiment. The distributions of different groups of SAS in the initial seawater sample and in the sample, which was taken in a later exponential growth phase, were similar, i.e. the highest surfactant activity was found in hydrophobic neutral fractions (44.1% and 44.6%, respectively), while hydrophobic acid and hydrophilic SAS contributed in a less extent. Similar distributions of SAS were found in the monoculture plankton media of Prorocentrum micans and Emiliania huxley. The distribution of different groups of SAS in the mixed culture and in monoculture media of diatoms were quite different of flagellates and strongly dependent on the physiological conditions of the plankton species. In general, initially low concentration of SAS (=0.06 mg/l eq. Triton-X-100) increased during the plankton developemnt (up to 0.41 mg/l), while the contribution of hydrophobic neutral components changed from 0 at the beginning to 42.3% after 9 days of the experiment. It was also shown that in the stationary phase, along with the appearance of degradation products, the hydrophobic neutralcomponents were reduced again, while the concentration of hydrophylic organic substances increased, contributing with 63% of total SAS. The adsorption characteristics of hydrophilic organic material were similar to those of the mucilage sample, analysed during the extreme diatoms bloom in the northern Adriatic Sea in 1989.

Surface active substances; hydrophobic and hydrophilic compounds

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