Hydrological and biogeochemical features of the Northern Adriatic Sea in the period 2003-2006

This paper reports on the main biogeochemical properties of the NorthernAdriatic Sea in the period May 2003–November 2006 within the framework ofthe European program INTERREG III Italy-Slovenia. Spatial and temporal distributionsof water density, dissolved oxygen, nutrients (nitrogen, phosphorousand silicon) and chlorophyll a are presented. Multivariate methods such asfuzzy k-means, self-organising maps and cluster analysis were used to identifythe different water masses and to characterise the temporal and spatial variabilityof the main biogeochemical features present in the area. The results confirmthat the Po River outflows and the meteorological forcing factors are the maincomponents triggering the alternation of stratification and mixing of the watercolumn and that strongly affect the trophic state of the basin. In general,oligotrophic conditions dominate, and were more pronounced offshore, butmesotrophy occurred episodically in May 2004 and July 2005, when phytoplanktonblooms were observed concomitant with vertical stability of the watercolumn. A marked interannual variability was also observed, supporting theimportance of maintaining long-term observations of the basin.