Sedimentary characteristics of fluvial deposits from the Serio River, northern Italy: implications for recent channel evolution

This study investigates fluvial sediments from the Serio River in the southern Alps of northern Italy to evaluate how source lithology, sediment transport, depositional processes, and anthropogenic modification influence sediment characteristics and recent channel evolution. Grain size, sand composition, and geochemical analyses from mountain valley and piedmont plain depositional contexts pronounced spatial and vertical variations in sediment properties. The Serio River, which is heavily regulated, exhibits strong spatial and vertical variability in sediment properties, with heterogeneous grain-size distributions and sediment compositions. Channel bank profiles record a transition from older, coarser, lithic-rich sediments at depth, to younger, finer, more carbonate-rich deposits near the surface, reflecting channel incision, lateral migration, and overbank deposition. Geochemical and petrographic evidence further demonstrates that downstream sediment composition is controlled by source lithology, hydraulic sorting, and sediment mixing. Weathering indices indicate increasing chemical alteration associated with longer sediment residence times in floodplain and channel bank deposits. These results show that downstream fining, increasing carbonate content, and vertical transitions from lithic-rich basal gravels to finer carbonate-rich overbank deposits record the combined effects of channel incision, sediment sorting, and river regulation.