Spatial and seasonal distribution of particulate phosphorus in coastal and offshore waters of the middle Adriatic Sea

The seasonal and spatial distributions of particulate phosphorus (PP) in the water column of the coastal area and open sea of the middle Adriatic Sea area were investigated for the first time. The relationship between PP and two other important forms of phosphorus (dissolved inorganic phosphorus (DIP), and organic phosphorus (P-ORG)), and the relationship between PP and other nutrients (nitrogen and silicon salts) and oceanographic parameters (temperature, salinity, oxygen saturation, chlorophyll a) from the water column were also examined. PP concentrations ranged from 0.007 μmol dm-3 in the open sea near Palagruža archipelago to 0.589 μmol dm-3 in the Krka River estuary. In the coastal area, PP concentrations were highest in autumn and lowest in winter. The vertical distribution of PP concentrations in the water column of the coastal area were highest in the surface layer during most of the year due to input of PP by freshwater inflows. In the open sea area, there were no significant seasonal or vertical differences in the distribution of PP concentrations in thewater column. Seasonal analysis of the total phosphorus pool (PP, DIP and P-ORG) in the water column indicated that PP and P-ORG concentrations were higher in the coastal area compared to the open sea, while DIP concentrations were comparable.The results further demonstrate that PP can be an important fraction of the total phosphorus pool. A significant positive correlation was found between PP and chlorophyll a, indicating that PP was mainly of biological origin, and with nutrient salts of nitrogen and silicon, while a negative correlation was found with salinity. Sezonska i prostorna raspodjela partikularnog fosfora (PP) istraživana je u vodenom stupcu obalnog i otvorenog mora srednjeg Jadrana po prvi put. Istražen je i odnos PP-a s drugim važnim oblicima fosfora (otopljeni anorganski fosfor (DIP) i organski fosfor (P-ORG)), kao i odnos između PP-a i ostalih nutrijenata (soli dušika i silicija) ioceanografskih parametara (temperatura, salinitet, zasićenost kisikom, klorofil a) iz vodenog stupca. Koncentracije PP-a su bile u rasponu od 0.007 μmol dm-3 na otvorenom moru kod otočja Palagruže do 0.589 μmol dm-3 u estuariju rijeke Krke. Uobalnom području srednjeg Jadrana najviše koncentracije PP izmjerene su tijekom jeseni, a najniže tijekom zime. Vertikalna raspodjela koncentracija PP-a u vodenom stupcu obalnog područja pokazala je najviše vrijednosti u površinskom sloju tijekomvećeg dijela godine,