Biological utilisation of the major nutrients in the western coastal waters of the north Adriatic Sea

The availability and distribution of the dissolved inorganic and organic fractions of nitrogen (DIN and DON) and phosphorus (DIP and DOP) are extremely variable in the north-western Adriatic Sea. Freshwater inputs, mainly from the PO River, and biological processes significantly affect the nutrient behaviour in this region. The purpose of this contribution is to describe these processes by the comparison of the dissolved nitrogen and phosphorus distributions to computed estimates of their biological production or consumption in the marine environment. The variations of dissolved nitrogen were mainly due to freshwater inputs of DIN, especially in winter (up to 18 a high marine release of DON was observed in summer (up to +22 pmol-N•dm-3 compared to the contribution of advection). The DIP concentrations were generally lower than 0.06 DOP values ranged from 0.01 to 0.1 pmol-P•dm -3 . The evident inverse relationship between DIP and DOP behaviours indicated that the phosphorus availability in the coastal zone is mainly regulated by recycling processes rather than by terrestrial inputs.