## 1 Peculiarity of the Northern Adriatic Sea  
The Northern Adriatic Sea is particularly vulnerable to nutrient pollution due to its unique characteristics, including shallow depths, limited water exchange, and the influence of river discharges. The Northern Adriatic Sea (Figure 1), covering an area of 19,000 km\({}^{2}\) with an average depth of 35 m, receives freshwater input from numerous rivers and streams, including the Po River (1500 m\({}^{3}\) s\({}^{-1}\), [1]), which contributes more than 50% of the external nutrient input [2, 3, 4]. The Adriatic's salinity is lower than that of the Mediterranean because the Adriatic collects one-third of the freshwater flowing into the Mediterranean Sea [5].  
The Po watershed is very large (75,000 km\({}^{2}\), [1]) and includes highly developed Italian regions with a resident population of 16 million people [6, 7]. This area is intensively cultivated with heavy use of natural and artificial fertilizers [8]. Being one of the most densely populated and agriculturally productive areas in Europe [9], the Po Valley significantly influences the nitrogen (N) and phosphorus (P) input to the Northern Adriatic Sea, affecting the productivity and trophic dynamics of the whole Mediterranean basin [10, 11, 12, 13]. When these N and P inputs enter the sea, they fuel the growth of phytoplankton and macroalgae. However, when present in excessive amounts, they can lead to eutrophication. This process in the Adriatic Sea is significantly influenced by seasonal circulation patterns [14, 15, 16]. In winter, the anticlockwise superficial and deeper circulation along the western coasts (Figure 2) brings in nutrient-rich waters from the Po River [17, 18, 19, 5] and other rivers originating in the Apennines [20, 21, 22, 23]. These colder and less saline waters flow close to the Italian coast throughout the water column.  
In contrast, during the summer season, the hydrodynamic conditions change, resulting in weaker currents and a series of clockwise and anticlockwise gyres, as well as strong water column stratification, with colder waters from the previous winter near the bottom [12; 24; 25; 26; 27; 28; 29]. As a result, nutrient concentrations in the surface waters increase, creating favorable conditions for the growth of phytoplankton and macroalgae. Following the cyclonic circulation, the waters of the Mediterranean Sea flow into the Adriatic Sea from the eastern side of the Strait of Otranto while on the western side, they flow from the Adriatic to the Mediterranean Sea [30; 31; 32; 33; 34].  
Figure 1: Map of the Mediterranean Sea with details of the Northern Adriatic and the hydrographic basin of the Po Valley (bottom left corner: Lat. 43.324050 N, Lon. 6.547654 E; top right corner: Lat. 46.537197 N, Lon. 16.027382 E; Source: Google Maps).  
Figure 2: Trends of the daily Po River discharge (m\({}^{3}\) s\({}^{-1}\)) from 1970 to 2022, with the significant long-term linear regression. Data from the Pontelagoscuro station available through the Regional Open Data Portal [[https://simc.arpae.it/dext3r/](https://simc.arpae.it/dext3r/)]([https://simc.arpae.it/dext3r/](https://simc.arpae.it/dext3r/)) (accessed on 1 July 2023), provided by the Agenzia Regionale per la Protezione dell’Ambiente of the Emilia Romagna Region (ARPAE-ER).  
We used long-term data from the Northern Adriatic Sea, in conjunction with a comprehensive literature review, to illustrate the impact of anthropic factors during this post-industrial century on the future state of the continental shelf. Moreover, our investigation aims to assess the responses of aquatic ecosystems to the persistent impacts of climate change.