| Citation |
Stott T., Leggat M., Owens P., Forrester B., Déry S. and Menounos, B (2016) Suspended sediment dynamics in the proglacial zone of the rapidly retreating Castle Creek Glacier, British Columbia, Canada. In A. Beylich, J. Dixon, & Z. Zwoli_ski (eds.), Source-to-Sink Fluxes in Undisturbed Cold Environments, pp. 293–312. Cambridge: Cambridge University Press. DOI:10.1017/CBO9781107705791.023 |
| Abstract/Description or Keywords |
Climate change is affecting our use of water-related resources (IPCC, 2007; Pike et al., 2008; Piao et al., 2010; Jacob et al., 2012; Mernild et al., 2012a). Diminishing snowpacks and receding glaciers (Singh and Kumar, 1997; Demmer and Mooers, 2005; Mernild et al., 2012b, 2013a, 2013b) directly affect water resources, including melt and evaporation in snow and glacier-fed drainage basins (Singh and Bengtsson, 2005); flow regime for fish; soil moisture and aquifer recharge; groundwater reserves; and reservoir levels and water supplies to communities (BCMOE, 2002, 2007). Recent warming has caused most mountain glaciers on Earth to retreat (Reichert et al., 2002; Zhang et al., 2011; Mernild et al., 2013b). In British Columbia (BC), Canada, glaciers cover about 3% (ca. 29,000 km2) of the landmass (Moore et al., 2009). The majority of glaciers in BC are recording appreciable area and volume losses (Schiefer et al., 2007; Bolch et al., 2010; Tennant et al., 2012), which are associated with changes in discharge and the timing of peak flows in many rivers in BC and northern Canada (Déry and Wood, 2005; Déry et al., 2009; Moore et al., 2009). The rapid retreat of mountain glaciers exposes fresh glacial debris that forms an important but poorly understood sediment source to downstream river systems. For example, in the proglacial zone of the Bas Glacier d'Arolla, southern Switzerland, Warburton (1990) reported that proglacial sediment sources contributed 23% to the total basin sediment yield. The overwhelming proportion of the proglacial sediment (95%) was eroded from the valley sandur during a brief period of meltwater flooding between July 15 and 18, 1987. The sediment budget suggested that four basic process subsets could be distinguished: (1) channel processes, (2) valley sandur (channel margin) processes, (3) hillslope processes, and (4) slopewash. Large magnitude, infrequent flood events were the dominant control on the release of sediment from proglacial storage. Building on this, Porter et al. (2010) have suggested that enhanced delivery of water-saturated, ice-marginal sediments to the glacier surface is a response to glacier thinning that has the potential to increase both levels of sediment transfer through the glacier hydrological system and total basin sediment yields. Hodgkins et al. (2003) found that the Finsterwalderbreen proglacial zone, Svalbard, served as both a source and sink for sediment during different periods of the melt season, where the majority of sediment evacuation occurred during periods of high flow and sediment storage varied from year to year. Orwin and Smart (2004) used a network of nine turbidimeters in the Small River Glacier basin, British Columbia, and found that the proglacial area was the source for up to 80% of the total suspended sediment yield transferred from the basin for the 2000 melt season. The unusually warm summer of 2003 in the Ecrins Massif, SE France, caused suspended sediment loads to be three to four times greater than the cooler than- average 2004 and 2005 ablation seasons in the Torrent du Glacier Noir (Stott and Mount, 2007a, 2007b, 2007c). In the Morteratsch proglacial zone, Switzerland, Stott et al. (2008) reported a clear decline in suspended sediment transport rates between a station 50 m from the glacier snout and another 600 m away across the proglacial zone. In both the Ecrins and Morteratsch studies, however, short but discrete phases 313 of suspended sediment “flushing” were observed when the net output from the poglacial zone exceeded the net input. These “flushing” phases were normally associated with summer rainstorms and melt-induced high flows. The preceding review illustrates that proglacial zones can act as both a sink and a source of sediment, which varies both spatially and temporally in response to changes in glacier dynamics (e.g., melt) and hydroclimatic conditions (e.g., rain events). Given these varied findings, a better understanding of the processes of sediment exchange (sources, fluxes, and storage) in proglacial zones could improve predictive modeling of river sediment dynamics and how these dynamics affect downstream aquatic ecology and water resources (Milner et al., 2009; Moore et al., 2009; Owen et al., 2009). This chapter draws together and compares data on sediment fluxes gathered in two melt seasons, 2008 and 2011, in the Castle Creek Glacier proglacial zone, BC, to examine the relative importance of snow/ice melt events and summer rainfall events on the suspended sediment dynamics at three locations within the proglacial zone. Specific research objectives were: 1) How do suspended sediment concentrations and fluxes compare between the two field seasons given the difference in hydroclimatic conditions? 2) Is the proglacial zone a net source or sink of suspended sediment? |
