Suspended sediment and discharge dynamics in a glaciated alpine environment: identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria

[摘要] Glaciated high-alpine areas are fundamentally altered byclimate change, with well-known implications for hydrology, e.g., due toglacier retreat, longer snow-free periods, and more frequent and intensesummer rainstorms. While knowledge on how these hydrological changes willpropagate to suspended sediment dynamics is still scarce, it is needed toinform mitigation and adaptation strategies. To understand the processes andsource areas most relevant to sediment dynamics, we analyzed discharge andsediment dynamics in high temporal resolution as well as their patterns onseveral spatial scales, which to date few studies have done. We used a nested catchment setup in the Upper Ötztal in Tyrol, Austria,where high-resolution (15 min) time series of discharge and suspendedsediment concentrations are available for up to 15 years (2006–2020). Thecatchments of the gauges in Vent, Sölden and Tumpen range from 100 toalmost 800 km 2 with 10 % to 30 % glacier cover and span anelevation range of 930 to 3772 m a.s.l. We analyzed discharge and suspendedsediment yields (SSY), their distribution in space, their seasonality andspatial differences therein, and the relative importance of short-termevents. We complemented our analysis by linking the observations tosatellite-based snow cover maps, glacier inventories, mass balances andprecipitation data. Our results indicate that the areas above 2500 m a.s.l., characterized byglacier tongues and the most recently deglaciated areas, are crucial forsediment generation in all sub-catchments. This notion is supported by thesynchronous spring onset of sediment export at the three gauges, whichcoincides with snowmelt above 2500 m but lags behind spring dischargeonsets. This points at a limitation of suspended sediment supply as long asthe areas above 2500 m are snow-covered. The positive correlation of annualSSY with glacier cover (among catchments) and glacier mass balances (within acatchment) further supports the importance of the glacier-dominated areas.The analysis of short-term events showed that summer precipitation eventswere associated with peak sediment concentrations and yields but on averageaccounted for only 21 % of the annual SSY in the headwaters. Theseresults indicate that under current conditions, thermally induced sedimentexport (through snow and glacier melt) is dominant in the study area. Our results extend the scientific knowledge on currenthydro-sedimentological conditions in glaciated high-alpine areas and providea baseline for studies on projected future changes in hydro-sedimentologicalsystem dynamics.

[学科分类] 土壤学