prvi kongres hrvatskih znanstvenika iz domovine i inozemstva - HATZ

PRVI KONGRES HRVATSKIH ZNANSTVENIKA IZ DOMOVINE I INOZEMSTVAZagreb - Vukovar, 15. - 19. studenog 2004.P - 28RECENT CHANGES OF THE OCEANOGRAPHIC CONDITIONS ANDEUTROPHICATION DEGREE IN THE NORTHERN ADRIATIC SEADjakovac, Tamara; Degobbis, Danilo; Precali, Robert; Smodlaka, NenadRuñer Bošković Institute, Zagreb, CroatiaSignificant seasonal and long-term fluctuations of oceanographic, chemical and biologicalproperties in the northern Adriatic were observed in the period 1972-1992 due to variable(primarily climatic) and anthoropogenic factors. In fact, the shallow northern Adriaticpelagic ecosystem is very sensitive to changes of the nutrient load, primarily due to thePo River contribution that accounts for about 75% of the total nutrient inputs in the region.Data related to oceanographic parameters (temperature, salinity and dissolved oxygen),nutrients and chlorophyll a were collected approximately monthly in the period 1993-2000at 5 stations at the Rovinj-Po Delta profile. These data, as well as the Po River flow rates,were analysed and compared to the previously observed long-term changes for periodssince 1972. It was established that in the nineties significant changes in the hydrologicalregime of the Po River occurred, characterized by frequently higher flow rates in Octoberand November compared to previous periods. As a consequence, nutrient andchlorophyll a concentrations were maximal in autumn, while the spring values were lowerthan in the seventies and eighties. Changes in concentrations of nitrate and orthosilicatein the surface layers was primarily related to the distribution of freshned waters, while fororthophosphate, ammonia and nitrite different biological processes have played a moreimportant role (assimilation, regeneration and nitrification). Eutrophication degreeappeared to be higher in the period 1993-2000 than in the late eighties, when significantdecreases of orthophosphate concentrations in the Po River occcurred, but still lowerthan in the early eighties. Interestingly, in previous periods, near anoxia events appearedmore frequently than in the period 1993-2000. The main reason is that the higher nutrientload by the Po River in the autumn has minor effect on the ecosystem than in the springbecause of the vertical and horizontal exchanges of the water masses. Excessivelyproduced organic matter is therefore less likely to accumulate near bottom and lessoxygen is consumed for the remineralization processes.Presented on:Scientific and policy challenges towards an effective management of the marineenvironment - emphasis on the Black Sea and the Mediterranean regionsVarna, Bulgaria; 12-18.10.2003.Principal Investigator : Dr.sc. Danilo DegobbisProject No. 009811130