Interdecadal patterns of total sediment yield from a montane catchment, southern Coast Mountains, British Columbia, Canada

We reconstruct sediment yield for a mountain watershed of western Canada since the mid-twentieth century from studies of annually laminated lake sediments, delta progradation, and solute transfer. Total yield averaged 320±40Mgkm^-2a^-1 and comprised ~35% suspended load, 50% bedload, and 15% dissolved load. Ratios between the individual yield components varied approximately threefold at interannual timescales because of significant variability in the suspended and bedload fractions. Asynchronous flux in suspended and bedload fractions through time arise from differences in sediment availability and transitory sediment storage in the channel. Periods of elevated yield coincide with rapid glacier recession, an extreme rainstorm, and a landslide. Our results indicate that in montane environments, extrapolation from even decade-long monitoring programs may lead to biased projections of long-term yield and delivery mode proportions if variations in sediment supply and catchment response to hydroclimatic and geomorphic controls are not considered.