The concentration of Be-10 in detrital quartz (Be-10(qtz)) from river sediments is now widely used to quantify catchment-wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low Be-10(qtz). Major landslide-triggering events can provide large amounts of low-concentration material to rivers in mountain catchments, but changes in river sediment Be-10(qtz) due to such events have not yet been measured directly. Here we examine the impact of widespread landslides triggered by the 2008 Wenchuan earthquake on Be-10(qtz) in sediment samples from the Min Jiang river basin, in Sichuan, China. Landslide deposit material associated with the Wenchuan earthquake has consistently lower Be-10(qtz) than in river sediment prior to the earthquake. River sediment Be-10(qtz) decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence (i.e., with greater than similar to 0.3% of the upstream catchment area affected by landslides), because of input of the Be-10-depleted landslide material, but showed no systematic changes where landslide occurrence was low. Changes in river sediment Be-10(qtz) concentration were largest in small first-order catchments but were still significant in large river basins with areas of 10(4)-10(5) km(2). Spatial and temporal variability in river sediment Be-10(qtz) has important implications for inferring representative denudation rates in tectonically active, landslide-dominated environments, even in large basins. Although the dilution of Be-10(qtz) in river sediment by landslide inputs may complicate interpretation of denudation rates, it also may provide a possible opportunity to track the transport of landslide sediment. The associated uncertainties are large, but in the Wenchuan case, calculations based on Be-10 mixing proportions suggest that river sediment fluxes in the 2-3 years following the earthquake increased by a similar order of magnitude in the 0.25-1 mm and the <0.25 mm size fractions, as determined from Be-10(qtz) mixing calculations and hydrological gauging, respectively. Such information could provide new insight into sediment transfer, with implications for secondary sediment-related hazards and for understanding the removal of mass from mountains.