Effects of variations in po river discharge on physical water characteristics and chlorophyll-a levels in the gulf of manfredonia

Abstract Rivers remarkably contribute to the transfer of fresh water and nutrients between land and marine ecosystems, underscoring their essential ecological role. The Po River contributes approximately one-third of the total freshwater discharge into the Adriatic Sea. Despite its importance, there is a lack of information regarding the impact of Po River discharge on the physical and biological characteristics of specific regions within the Adriatic Sea, such as the Gulf of Manfredonia. By using ocean model results and satellite data for 2014, 2015, 2016, and 2017, this study attempts to assess how Po River discharge fluctuations affect the Gulf’s physical properties and chlorophyll-a concentrations. We demonstrate here that river discharge, physical characteristics, and chlorophyll-a interact in complex ways within the Gulf of Manfredonia. The Gulf's temperature (correlation coefficient r = −0.33) and salinity (r = −0.38) are inversely correlated with Po River discharge, whereas sea level (r = 0.59) and vertical velocity (r = 0.54) are directly correlated to the discharge. In the Gulf, a seasonal anticyclonic eddy exhibits varying strength and shape throughout the summer and autumn, influenced by the fluctuation in Po River discharge. In December 2014, chlorophyll-a concentrations increased remarkably (over 10 mg m −3 ) following a remarkable rise in Po River discharges. However, there is a one-month time lag between the discharge increase and the subsequent rise in chlorophyll-a levels in the gulf.