Benthic prokaryotic diversity in Po River delta lagoons (North Adriatic Sea) is shaped by riverine freshwater inputs

The Adriatic Sea hosts several highly productive lagoons that serve as critical habitats for many aquatic organisms, but also as key connectivity sites with the adjacent coastal sea. This study investigates the benthic prokaryotic diversity and community composition in the seven main lagoons of the Po River delta (Northern Adriatic Sea, Italy). We aimed to explore whether each lagoon hosts different microbial assemblages and how riverine inputs and anthropogenic pollutants affect community structure Our findings revealed significant differences in the diversity and composition of benthic prokaryotic communities across the lagoons, as well as a substantial variability within individual lagoons. The significance of freshwater taxa to the overall communities was higher in stations where higher river inputs were expected. Feces- and sewage-associated bacteria were found at multiple locations, highlighting the occurrence of anthropogenic contaminants. However, their abundance, did not correlate with the abundance of freshwater taxa, suggesting that they are not only influenced by riverine waters. Multivariate statistical analysis indicated that various factors, such as sediment grain size, nutrient, Al, Fe contents and concentration of inorganic pollutants (As, Hg, Ni, Pb, Zn) significantly contribute to the assembly mechanisms of prokaryotic communities in these lagoons. Our results imply that riverine freshwater inputs and human activities jointly shape the microbial composition of these lagoons, which is consistent with their close connection to the Adriatic Sea. Furthermore, they may facilitate the spread of potentially pathogenic bacteria to the adjacent coastal waters, potentially impacting water quality and recreational activities.