Interdecadal patterns of total sediment yield from a montane catchment, southern Coast Mountains, British Columbia, Canada Erik Schiefer a, ⁎, Marwan A. Hassan b , Brian Menounos c , Channa P. Pelpola d , Olav Slaymaker b a Department of Geography, Planning & Recreation, Northern Arizona University, Box 15016, Flagstaff, AZ 86011, USA b Department of Geography, University of British Columbia, 1984 West Mall, Vancouver, BC, Canada V6T1Z2 c Natural Resources and Environmental Studies Institute and Geography Program, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N4Z9 d Stantec Consulting Ltd., 4370 Dominion Street, Burnaby, BC, Canada V5G4L7 abstract article info Article history: Received 24 September 2009 Received in revised form 3 January 2010 Accepted 4 January 2010 Available online 11 January 2010 Keywords: Sediment yield Suspended load Bedload Dissolved load Coast Mountains British Columbia 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 ± 40 Mg km -2 a -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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Sediment yield, defined as the total outflow of sediment from a catchment per unit time, integrates the intensity and pattern of catchment denudation and sediment delivery over time. Three components of sediment flux in rivers—the suspended load, bedload, and dissolved load—together represent the total fluvial delivery from a drainage basin. Mountain streams supply a disproportionate sediment load to continental margins, yet they are underrepresented in global monitoring programs (Milliman and Syvitski, 1992). Reconstructions of total yield are of interest for montane catchments because both the amount and the mode of sediment transport may be sensitive to land use and climate change (Slaymaker and Owens, 2004). Most sediment yield data are derived from either suspended or dissolved river loads and rarely are all three components measured simultaneously (Walling and Fang, 2003; Meybeck and Vörösmarty, 2005). Short-term bias also impedes most monitoring programs, which limits their potential to infer long-term change in rates of sediment transfer (Caine, 2004). Accurate estimation of sediment yield from montane catchments is further complicated because transport formulae are notoriously unreliable and operational challenges impede conven- tional monitoring (Gomez and Church, 1989; Meybeck et al., 2003). Because of these limitations, ratios between river load components are commonly assumed to be constant over time, often with little empirical or theoretical support. In some cases, long-term yield records can be recovered from depositional systems, such as lakes and deltas (Duck and McManus, 1994; Loso et al., 2004; Pratt-Sitaula et al., 2007), which can address some of the limitations that face conventional monitoring programs. In this paper, we examine the interannual variability of sediment yield for Fitzsimmons Creek, a mountain stream of western Canada, since the mid-twentieth century. We derive suspended, bedload, and dissolved load fractions of yield (respectively) from studies of lake sedimentation, delta progradation, and solute monitoring. The integration of these data presents a unique opportunity to assess the long-term dynamics of total fluvial load for the catchment. Our integrated yield record is related to hydroclimatic trends and geomorphic events to examine how these factors affect the quantity and mode of sediment delivery through time. 2. Study area and methods 2.1. General setting Fitzsimmons Creek, the primary inflow to oligotrophic Green Lake, drains 95 km 2 of the south Coast Mountains near the resort town of Whistler, British Columbia, Canada (Fig. 1). Bedrock geology is typical of the Coast Plutonic Complex, consisting of granodiorite to quartz Geomorphology 118 (2010) 207–212 ⁎ Corresponding author. Tel.: +1 928 523 6535; fax: +1 928 523 2275. E-mail address: Erik.Schiefer@nau.edu (E. Schiefer). 0169-555X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2010.01.001 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph