Sediment discharge from the proglacial zone of a retreating Alpine glacier
Geilhausen, Martin; Morche, David; Otto, Jan-Christoph; Schrott, Lothar
published: Jul 1, 2013
ArtNo. ESP023105702003, Price: 29.00 €
It is generally assumed that climate change and accelerated glacier melt lead to an increase in suspended sediment discharge from proglacial zones. This study demonstrates that the connectivity between glacial sediment production and downstream sediment fluxes during deglacierization is significantly reduced by the development of proglacial lakes. Suspended and solute sediment fluxes from the proglacial zone of the retreating Obersulzbachkees glacier, Hohe Tauern, Austria, were quantified within a 20 months monitoring period from January 1st 2010 to September 28th 2011. The landsystem is influenced by a proglacial lake (∼95 × 103 m2 and >2 × 106 m3) that hampers sediment output from ∼ 18.7 km2 of the study area. Suspended sediment concentrations (SSC) and solute concentrations (SOC) measured downstream of the proglacial lake were in the range of 71.3 to 702.3 mg/l (∅ SSC<200 mg/l) and 3.58 to 8.33 mg/l (∅ 5.56 mg/l) respectively and both are considered to be low. it could be shown by systematic up- and downstream sampling that the proglacial lake reduced sscs by 88-95%. however, the lake prevented considerable decrease of sscs at very low discharge and temporally extended the delivery of higher sscs when the lake's suspended sediment budget was elevated by external forcing (e.g. rain fall induced hillslope sediment supply). in these situations the lake changed from a sink to a temporal source. it is assumed that bed load was negligible for the duration of this study because the present day bed load transport system is interrupted and supply limited. a total sediment discharge of 18170 ±194 t to 18399 ±212 t was calculated depending on the calculation method used. suspended load accounted for 98% and ∼77 % of the solute load probably originated from chemical weathering. temporally, the majority of sediment was exported in the ablation seasons (94 % ssl and 88 % sol). the overall mass exported corresponds to an average annual specific sediment yield in the range of 451±5 t/km2/a to 457±5t/km2/a. The results indicate that the Obersulzbachkees proglacial zone is a supply limited system with respect to both bed load and suspended sediment load. It is expected that the number of proglacial lakes will rise within the Alps following accelerated glacial retreat. Hence, sediment delivery from glacial valleys will most likely be significantly altered in the near future, leading to changes in sediment flux of Alpine streams with impacts on hydrology, river ecology and reservoir management.