Seasonal and Interannual Trends of Oceanographic Parameters over 40 Years in the Northern Adriatic Sea in Relation to Nutrient Loadings Using the EMODnet Chemistry Data Portal

: Long-term data series (1971-2015) of hydrological and biogeochemical parameters were analysed in order to assess trends and variability of oceanographic conditions in the northern Adriatic Sea (NAS), a mid-latitude shallow continental shelf strongly impacted by river discharges, human activities and climate changes. Interpolation maps and statistical models were applied to investigate seasonal and spatial variability, as well as decadal trends of temperature, salinity, chlorophyll-a and nutrients. The analysis showed that sea surface temperature increased by +0.36% y-1 over four decades. Annual mean flow of the Po River markedly changed due to the occurrence of periods of persistent drought, whereas the frequency of flow rates higher than 3000 m3 s-1 decreased between 2006 and 2015. Moreover, it was observed a long-term decrease of surface phosphate concentrations in Po River water (-1.34% y-1) and in seawater (in summer -2.56% y-1) coupled, however, to a significant increase of nitrate concentration in seawater (+3.80% y-1) in almost all the seasons. These changes indicated that phytoplankton communities in the NAS have been largely modulated in the last forty years by the evolution of environmental management practices and of the runoff, and that further alteration of this marine environment have to be expected as a consequence of the climate changes.