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

Climate change is increasing the frequency and intensity of floods, droughts, and storms, yet their effects on sedimentation and biogeochemical cycling in large lakes remain poorly constrained. Riverine inflows play a central role by controlling the vertical and horizontal transport of suspended matter through density-driven intrusions. Here, we quantify sediment flux dynamics over 5 years, using sediment traps and high-frequency environmental observations in Lake Geneva, a large peri-alpine lake influenced by the Rhône River. Fluxes of total mass, organic matter, calcite, and minerals reveal higher particle export below 30 m than at 10 m, particularly in summer when interflows intrude at the thermocline. Peak fluxes coincided with high river discharge, with minerals fractions dominating total export. Extreme events emerge as the primary driver of variability, producing distinct sedimentation responses. Floods produced the highest particle fluxes and promoted efficient transport to depth, whereas drought conditions strongly reduced sediment supply, with short-lived storm-driven pulses. In contrast, wind-driven storms drove sediment inputs through resuspension and redistribution. These results demonstrate that the interaction between fluvial inputs, stratification, and hydrodynamics governs sediment export in large, river-influenced lakes worldwide. This study provides a transferable framework for predicting sediment responses to hydroclimatic extremes in such systems.