Importanza e distribuzione spazio-temporale delle frazioni organiche disciolte dell'azoto e fosforo nel bacino del nord Adriatico

The effects of continental inputs and biological processes acting on dissolved inorganic (DIN and DIP) and organic (DON and DOP) nitrogen and phosphorus are discussed in the North-western Adriatic Sea. The allocthonous contributions of DIN are evidenced, particularly in winter, in the mixed layer (up to 18 ?mol-N·dm-3) while the other fractions of nitrogen and phosphorous show behaviours which depend more on the biological activity in the marine environment. The presented. data evidence the importance of DON and DOP which can constitute, in this basin, up to 93% and 96% of the available nitrogen and phosphorus, respectively. Moreover, the phosphorus deficiency, when compared to nitrogen, has been evidenced not only in the inorganic fraction (DIN/DIP ratios from 25 up to 3000) but also in the organic fraction (DON/DOP ratios from 50 up to 1500). At last, spatial and seasonal trends of these parameters suggest the uncoupling between these nutrients and indicate a faster recycling of phosphorus with respect to nitrogen through the biological compartments of the ecosystem.