Distribution of surface-active substances in the northern Adriatic Sea

Spatial distribution and seasonal variability of surfactant activity (SA) of seawater were studied in the northern Adriatic Sea and compared to the temperature and salinity patterns in the 2-year period from February 1998 to January 2000, based on monthly surveys. Surface-active substances (SAS) were determined with alternating current voltammetry (in-phase mode) using o-nitrophenol as an electrochemical probe. A general characteristic of the SA seasonal variability for the northern Adriatic is the sinusoidal change of SA within the period of 1 year; similar behaviour was observed for the seasonal variations of temperature. Maximum SA values appeared during the summer period, while minimum SA values were measured in winter, during the period of well-mixed water layers and lower phytoplankton production. In May and October, the highest SA values were obtained in the upper seawater layer, which was ascribed to the influence of high inflow of nutrient-rich Po River freshwater. Riverine inputs indirectly favour autochthonous production processes, which result in increased concentration of organic matter (OM), particularly surface-active substances.