Sediment discharge from the proglacial zone of a retreating Alpine glacier

Abstract

It is gene nerally a sumed t at c y assumed that clima e catte change and a d accelle erated g d glaciier me t le er mellt lead to an increase se i in su sus- pended sediment discharge from proglacial zones. This study demonstrates that the connectivity between glaciall se me sediment pro uc on a d dow stre production and downstream se me sediment ? ux uxes durin ring deglacier z rizi ation is sign gni? ca cantlly y reduced ced by the deve opme e devellopmentt o pro of proglacial lake kes. Susp spended a d solut ded and solute se ment sediment ? uxes from the proglacial zone of the re rettreating Ob Obersu bac kees sulzbachkees glacier acier,, Hohe he Taue uern, Austria, were qu were quanti? ed within a 2 mon a 20 months mon or monittor- ing p g period from J nu om January 1 t 2 y 1st 2010 to Sept ptember 2 r 28th 2011.. T e l nd The landsys sttem is in? uenced by a progllacia acial l lak ake ((~ ~ 95 × 103 m2 and an ??2 × 10 m3)) t at h mp s se ment out ut f om ~ ??? 2 × 1 6 that hampers sediment output from ~ 18.7 km2 of the s e sttudy a y area.. S sp Suspende ded sediment concentra on se ment conc attiions (SSC)) a d solut conc and solute concentra on attiions (SOC)) me measured dow stre downstream of the pr e proglacial lake ke were i were in the r e range o e of 71.3 to 702.3 mg/l (/l (? SS ???C ??200 mg/ /ll)) a d 3 and 3.58 to 8.33 mg/l (/l (? 5 56 mg 5.56. mg/l) respec vel ecttiively and b d both are con idered e considered t to be l low ow. It cou d b shown b could be shown by sys sttema c up- a d dow stre attiic up- and downstream sampl sampling tha tat tt he proglacial lake reduced SSCs by 88 – 95 %. However, the lake prevented considerable decrease of SSCs at very l low d sc ve ow discharge a d t mpor e and temporally extende nded the de vee delivery of higher SSCs when the e l lake ke’s susp suspended se ment ded sediment budge wasett was elevated ed by ex e extternal forc rcing (e..g rag. rain fa fall induced ced hills sllope sediment supply). In these s ese siituations ns the he l lake c ke changed f om a s d from a sink to a mpor a t temporal sou source.. I It is assumed t at b d lo sumed that bed load was ne s negligiible for the du ble for the duration on of this s sttudy b y because t e pre ause the presentt d y b d lo day bed load transport s st sport system is interrup d a d supply l uptted and supply limited. A A t total sediment discharge o se ment d sc e of 18170 ± 1 4 t t0 ± 194 t to 18399 ± 212 t w s c c 399 ± 212 t was callcula atted de depend g on t e c c nding on the callcula on me attiion method used.. S sp Suspended lo ded load accounted for 9 % a d ~ d for 98% and ~ 77 % o % of the solut e solute l lo oad probab probablly or originat ated from c om chemicical weathering.. T mpor weathe Temporally,, t e m or the majjority of se ment w s e sediment was exported in the ab e abllation se on seasons ( % S L a d 8 ons (94 % SSL and 88 % SOL).. T e o The overalll m ss e mass exported cor corresponds tnds to an ave average a nue annual sp speci? c se ment y c sediment yield d i in the r e range o e of 45145 ?????5 /k 5 t/k t m2/a to 457?????5 /k 457 5 t/k t m2/a. T e resul s i . The resultts indicate tha t e Ob su at tt he Obersulzbachke kees pro proglacial zone zone i is a sup a sup- plly limited s std system with resp respectt t to both bed o p y l d lo l ad and suspd suspended se ment lo ded sediment load.. I It is expected tha t e numb at tt he number of proglacial lakes will rise within the Alps following accelerated glacial retreat. Hence, sediment delivery from glacial valleys will most likely be signi? cantly a alltered i in hn t the near fu ur futture, leadiin ng to changes i in n sed ment dimi ? ux of Alpine s pine sttreams w s with impacts on h s on hydrolo ology, river e olo y a d r se ver ecology and reservo r moiir managementment.