Rivers beneath the surface: how riverine inputs shape sedimentation in a large peri-alpine lake

Climate change is increasing the frequency of floods, droughts, and storms, yet how these events shape sedimentation, water quality, and biogeochemical cycling in large lakes remains poorly understood. Riverine inflows play a central role, as their intrusion depth and intensity govern vertical and horizontal transport of suspended matter, nutrients, and minerals. To explore these dynamics, we measured vertical fluxes of total particulate mass, organic and inorganic carbon, nitrogen, phosphorus, and minerals from 2020 to 2024 in Lake Geneva, a large perialpine lake fed by the Rhône River. Sediment traps at multiple depths revealed higher particle fluxes below 30 m, particularly in summer, when dense Rhône interflows intruded at the thermocline. Peak fluxes coincided with high river discharge and suspended sediment loads, with Rhône-derived minerals dominating total fluxes despite contributions from primary production and calcite precipitation. Extreme events strongly influenced particle transport. Flooding in 2021 produced the highest sinking particle fluxes of the study, indicating efficient transport of Rhône material to mid-depth and deep waters. The sedimentation signal during the 100-year return flood in 2024 was weaker, likely reflecting differences in inflow structure and mixing dynamics. Drought conditions in 2022 reduced sediment delivery, interrupted by short pulses from convective storms. In late autumn 2023, windstorms and heavy rainfall triggered shoreline resuspension and lateral transport of fine sediments, producing the second-highest fluxes. These results highlight the Rhône inflow as a key mechanism for mid-depth particle transport and nutrient redistribution. Understanding these processes is essential to predict how climate-driven extremes may alter sedimentation and biogeochemical cycling in large perialpine lakes.