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

Abstract

Abstract. Glaciated high-alpine areas are fundamentally altered by climate change, with well-known implications for hydrology, e.g., due to glacier retreat, longer snow-free periods, and more frequent and intense summer rainstorms. While knowledge on how these hydrological changes will propagate to suspended sediment dynamics is still scarce, it is needed to inform mitigation and adaptation strategies. To understand the processes and source areas most relevant to sediment dynamics, we analyzed discharge and sediment dynamics in high temporal resolution as well as their patterns on several 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 suspended sediment concentrations are available for up to 15 years (2006–2020). The catchments of the gauges in Vent, Sölden and Tumpen range from 100 to almost 800 km2 with 10 % to 30 % glacier cover and span an elevation range of 930 to 3772 m a.s.l. We analyzed discharge and suspended sediment yields (SSY), their distribution in space, their seasonality and spatial differences therein, and the relative importance of short-term events. We complemented our analysis by linking the observations to satellite-based snow cover maps, glacier inventories, mass balances and precipitation data. Our results indicate that the areas above 2500 m a.s.l., characterized by glacier tongues and the most recently deglaciated areas, are crucial for sediment generation in all sub-catchments. This notion is supported by the synchronous spring onset of sediment export at the three gauges, which coincides with snowmelt above 2500 m but lags behind spring discharge onsets. This points at a limitation of suspended sediment supply as long as the areas above 2500 m are snow-covered. The positive correlation of annual SSY with glacier cover (among catchments) and glacier mass balances (within a catchment) further supports the importance of the glacier-dominated areas. The analysis of short-term events showed that summer precipitation events were associated with peak sediment concentrations and yields but on average accounted for only 21 % of the annual SSY in the headwaters. These results indicate that under current conditions, thermally induced sediment export (through snow and glacier melt) is dominant in the study area. Our results extend the scientific knowledge on current hydro-sedimentological conditions in glaciated high-alpine areas and provide a baseline for studies on projected future changes in hydro-sedimentological system dynamics.

Reconstructing five decades of sediment export from two glaciated high-alpine catchments in Tyrol, Austria, using nonparametric regression

“…Suspended sediment concentrations at the gauge in Vent showed to be the highest in an Austria-wide comparison (Lalk et al, 2014) and annual suspended sediment yields are about 1500 t/km² on average (Schmidt et al, 2022b).…”

“…However, the equipment is reinstalled early enough to capture the spring rise in concentrations, and winter sediment transport can be considered negligible (Schmidt et al, 2022b). At gauge Vernagt, water is diverted into a measuring chamber (Bergmann and Reinwarth, 1977), where turbidity can be recorded while avoiding damage to the equipment by large rocks in the main channel.…”

“…Our results suggest that in the Rofental, the step-like increase in sSSY reconstructed by our models is linked to the onset of increased ice melt as well, as we will discuss in section 6.3. (Kormann et al, 2016;Weber and Prasch, 2016;Schmieder et al, 2018;Schmidt et al, 2022b). This is also reflected in the mass balance time series of the Hintereisferner and Vernagtferner, which are almost exclusively negative after 1980, with very negative summer mass balances in 1982and 1983.…”

“…The catchment is drained by the river Rofenache, which flows into the Ötztaler Ache, one of the largest tributaries to the river Inn. The hydrological regime (glacial to nival) shows a pronounced seasonality as most of the discharge is fed by snow and glacier melt and about 89 % of the discharge in Vent occurs from April to September (Schmidt et al, 2022b;Hanzer et al, 2018).…”

A Generic Relation Between Turbidity, Suspended Particulate Matter Concentration, and Sediment Characteristics

“…Suspended particulate matter (SPM) flux estimates are pivotal for monitoring the land surface geomorphological evolution, as suspended load sediment transport dominates bedload sediment transport in many rivers and deltas. An accurate estimation of the material exported by rivers allows to evaluate sediment transport to the oceans, continental erosion and organic carbon cycling (Galy et al., 2015; Hoffmann et al., 2020; Horan et al., 2019; Schmidt et al., 2022), leading to a better understanding of the long‐term factors that influence the Earth's surface amid and beyond the influence of human interventions (Baronas et al., 2020; France‐Lanord & Derry, 1997; Hilton et al., 2018; Maher & Chamberlain, 2014; Owens et al., 2005; Wang & Xu, 2018). These human interventions, such as damming, river channelization and deepening of estuaries, alter natural SPM fluxes and sediment dispersal, sometimes result in water quality deterioration (De Jonge et al., 2014; Dyer, 1989; Grangeon et al., 2014; Maren et al., 2015; Sun et al., 2020; van Ledden, 2003).…”