SUSPENDED SEDIMENT DYNAMICS IN THE MORTERATSCH PRO-GLACIAL ZONE, BERNINA ALPS, SWITZERLAND © The authors 2008 Journal compilation © 2008 Swedish Society for Anthropology and Geography 299 SUSPENDED SEDIMENT DYNAMICS IN THE MORTERATSCH PRO-GLACIAL ZONE, BERNINA ALPS, SWITZERLAND BY TIM STOTT 1 , ANNE-MARIE NUTTALL 2 , NICK EDEN 3 , KATIE SMITH 4 AND DARREN MAXWELL 4 1 Physical Geography and Outdoor Education, Liverpool John Moores University, UK 2 Geoscience, School of Biological and Earth Sciences, Liverpool John Moores University, UK 3 School of the Built Environment, Liverpool John Moores University, UK 4 School of Biological and Earth Sciences, Liverpool John Moores University, UK Stott, T. A., Nuttall, A., Eden, N., Smith, K. and Maxwell, D., 2008: Suspended sediment dynamics in the Morteratsch pro-glacial zone, Bernina Alps, Switzerland. Geogr. Ann., 90 A (4): 299–313. ABSTRACT. Suspended sediment concentration (SSC) in the Ova da Morteratsch, Switzerland, meas- ured during July 2007 was closely associated with discharge (Q) and showed statistically significant re- lationships at the p < 0.001 level at the proximal and distal ends of the 600 m pro-glacial zone. SSC pre- dicted from 10-minute turbidity records gives a much more detailed insight into SSC fluctuations and identified SSC peaks which do not coincide with discharge peaks. Net (proximal – distal) 10-minute suspended sediment loads (SSL) are predominantly positive (i.e. suspended sediment is being stored in the reach) for most of the 7–19 July 2007 record. Net (proximal – distal) SSLs correlate closely with dis- charge for the first part of the record (7–13 July) but from 14 to 19 July suspended sediment exhaustion is in evidence and discrete phases of negative net SSL (i.e. sediment flushing) are likely for up to six hours on three separate days which coincide with phases of high discharge and exhaustion of the gla- cial suspended sediment sources. Analysis of Q at the Berninabach–Pontresina gauging station (5 km downstream) for the past five years revealed that maximum monthly discharges capable of generat- ing sediment flushing events occur in an average of four months each year. The study emphasises the rapid change in suspended sediment transport and yields with distance from the glacier snout and high- lights the importance of measurements as close to the glacier snout as possible if data are to be repre- sentative of the glaciated land up-valley. A better un- derstanding of the processes of sediment exchange and the colonisation and stabilisation of sediment stores by vegetation in such pro-glacial zones is es- sential if we are to improve predictions of the im- pacts of climate change on river sediment dynamics and the subsequent effects on aquatic ecology. Key words: suspended sediment load, Alpine, pro-glacial, global warming Introduction and aims Most studies of glacier mass balance conducted over recent decades have reported widespread contraction in glacier area and volume (e.g. Østrem et al. 1967; Hoelzle et al. 2003). Reported changes in runoff timing and yield in glacier-fed rivers respond to rising trends in global mean tem- perature and changes in precipitation timing and amount (Moore and Demuth 2001; Pelto 1996). However, few data are available to gauge the im- plications of these changes on sediment fluxes from glaciers to rivers. This study aims to improve our understanding of sediment transfers in pro- glacial environments. The Inter-governmental Panel on Climate Change (IPCC 2001; 2007) has indicated that the average global surface air temperature increased by 0.6 ± 0.2°C since the late 19th century and is projected to increase by 1.4–5.8°C over the period 1990–2100. The impact of global warming on wa- ter resources has been receiving attention from hy- drologists in recent years (Hansen and Lebedeff 1987; Singh and Kumar 1997; Oerlemans et al. 1998; Jones 1999; Singh and Bengtsson 2005) who have modelled increased evaporation rates from snow-fed basins and increased melt from glacierised basins. Suspended sediment transfer from mountains to lowland regions is sensitive to changes in river flows (Phillips 1991; Stott and Grove 2001), in turn controlled by precipitation (snowfall) and temperature. The unusually warm summer of 2003 in the Ecrins Massif, SE France, caused suspended sed- iment loads to be three or four times greater than the cooler 2004 and 2005 seasons in the Torrent du Glacier Noir (Stott and Mount 2007a, b). In many mountainous regions of the world glacial reces-