*2.1. Study Area*

The Po River is the most important Italian river, with a drainage basin of 71,000 km2, 44% of which is devoted to agricultural activities, and more than 15 million people. The mean flow discharge is characterized by two major flooding periods, due to snowmelt in the spring and rainfall in the autumn [24]. The Po River outflow of water and sediments is mostly constrained along the western coast of the Adriatic Sea, driven southward by the general circulation of the basin [25,26].

The Sacca di Goro Lagoon is a shallow (average depth 1.5 m) water embayment (27 km2) of the Po River Delta facing the northern Adriatic Sea from the Italian counterpart (Figure 1). This lagoon is characterized by strong daily variations of salinity and nutrient concentrations due to a microtidal regime (with a maximum amplitude < 1.0 m) and freshwater inputs from the Po River, and saline water input from the adjacent northern Adriatic Sea. The Sacca di Goro Lagoon, being one of the most economically relevant clam farming sites in Europe, whilst at the same time being threatened by dystrophic events [27–29], has largely been investigated in terms of the biogeochemistry [15,30,31], ecophysiology of blooming macroalgae [32], meio- and macrofauna communities [33–35], and ecosystem functions [36,37].

**Figure 1.** Sampling area: (**A**) the Po River basin, flowing into the North Adriatic sea, Central Mediterranean and (**B**) location of the sampling stations along the Po River basin, the Goro Lagoon, and at sea.

Due to the large inputs from the Po river (which alone accounts for ca. 50% of the terrigenous flux into the whole basin), the sediments of the north western Adriatic are characterized by a strong accumulation of organic loads [9,38–42], which have, for years, triggered hypoxic crises [43–45]. Indeed, the NW Adriatic Sea, which is the most productive basin of the entire Mediterranean Sea, has experienced huge and long-lasting anthropogenic environmental alterations in the last 50 years. Such changes have led to severe consequences for the whole ecosystem functioning, which have ultimately manifested as red tides, mucilage formation, and strong eutrophication along the entire Italian coastline of the basin [46,47].
